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11

Managing CoverCrops Profitably

Handbook Series Book 9Published by the Sustainable Agriculture Network, Beltsville, MD

A publication of the Sustainable Agriculture Network withfunding by the Sustainable Agriculture Research and Education

Program of CSREES, U.S. Department of Agriculture

THIRD EDITION

SUSTAINABLEAGRICULTURE NETWORK

This book was published in 2007 by the SustainableAgriculture Network (SAN) under cooperative agreementswith the Cooperative State Research, Education, andExtension Service,USDA, the University of Maryland and theUniversity of Vermont.

Every effort has been made to make this book as accurate aspossible and to educate the reader.This text is only a guide,however, and should be used in conjunction with other infor-mation sources on farm management.No single cover cropmanagement strategy will be appropriate and effective for allconditions.The editor/authors and publisher disclaim any lia-bility, loss or risk, personal or otherwise,which is incurred asa consequence, directly or indirectly, of the use and applica-tion of any of the contents of this book.

Mention, visual representation or inferred reference of aproduct, service,manufacturer or organization in this publi-cation does not imply endorsement by the USDA, the SAREprogram or the authors. Exclusion does not imply a negativeevaluation.

SARE works to increase knowledge about—and help farmersand ranchers adopt—practices that are profitable, environ-mentally sound and good for communities. For more informa-tion about SARE grant opportunities and informationalresources, go to www.sare.org. SAN is the national outreacharm of SARE. For more information, contact:

Sustainable Agriculture Network10300 Baltimore Ave.Bldg. 046 BARC-WESTBeltsville,MD 20705-2350(301) 504-5236; (301) 504-5207 (fax)[email protected]

To order copies of this book, ($19.00 plus $5.95 s/h)contact (301) 374-9696, [email protected], or order online atwww.sare.org.

Project manager and editor:Andy ClarkGraphic design and layout:Diane BuricInterior illustrations:Marianne Sarrantonio and Elayne SearsCopy editing:Andy ClarkProofreading:Aneeqa ChowdhuryIndexing:Claire BrannenPrinting:United Book Press, Inc.

Library of Congress Cataloging-in-Publication Data

Managing cover crops profitably / project manager andeditor, Andy Clark.—3rd ed.

p.cm. -- (SustainableAgriculture Network handbook series ;bk.9)

“A publication of the Sustainable Agriculture Networkwith funding by the Sustainable Agriculture Research andEducation Program of CSREES,U.S.Department ofAgriculture.”

Includes bibliographical references and index.ISBN 978-1-888626-12-4 (pbk.)1. Cover crops—United States—Handbooks,manuals, etc.

I. Clark, Andy. II. Sustainable Agriculture Network. III. Series.

SB284.3.U6M36 2007631.5'82—dc22

2007024273

Cover photos (clockwise from top left):Annual ryegrass overseeded into kale is already providingcover crop benefits before cash crop harvest. Photo byVern Grubinger,Univ. of VT.

Jeff Moyer, farm manager for The Rodale Institute, kills a hairyvetch cover crop with a newly designed, front-mountedroller while a no-till planter drops seed corn behind thetractor. Photo by Matthew Ryan for the Rodale Institute.

“Purple Bounty”hairy vetch, an early-maturing,winter hardyvariety for the Northeast,was developed by Dr.Tom Devine,USDA-ARS in collaboration withThe Rodale Institute,Pennsylvania State University and Cornell UniversityAgricultural Experiment Stations. Photo by Greg Bowman,NewFarm.org.

Guihua Chen, a Univ. of MD graduate student, studies theability of forage radish to alleviate soil compaction. Photo byRayWeil, Univ. of MD.

Red clover, frostseeded into winter wheat, is well establishedjust prior to wheat harvest. Photo by Steve Deming,MSU Kellogg Biological Station.

Back cover photo: Sorghum-sudangrass increased irrigatedpotato yield and tuber quality in Colorado,whether it washarvested for hay or incorporated prior to potato planting.Photo by Jorge A.Delgado,USDA-ARS.

Printed in the United States of America on recycled paper.

FOREWORD 3

Cover crops slow erosion, improve soil,smother weeds, enhance nutrient andmoisture availability, help control many

pests and bring a host of other benefits to yourfarm. At the same time, they can reduce costs,increase profits and even create new sources ofincome. You’ll reap dividends on your cover cropinvestments for years,because their benefits accu-mulate over the long term.

Increasing energy costs will have a profoundeffect on farm economics in coming years.As wego to press, it is impossible to predict how fastenergy costs will increase, but since cover cropeconomics are rooted in nitrogen dynamics (howmuch N you save or produce with cover crops),fuel costs (the cost of N and trips across the field)and commodity prices, energy prices will certain-ly impact the economics of cover crop use.

Economic comparisons in the 2nd edition werebased on the old economy of two-dollar corn,twenty-cent nitrogen and cheap gas. Some studiesshowed that cover crops become more profitableas the price of nitrogen increases. We retainedsome of these excellent studies because data fromnew studies is not yet available.What we do knowis that cover crops can help you to increase yields,save on nitrogen costs,reduce trips across the fieldand also reap many additional agronomic benefits.

There is a cover crop to fit just about everyfarming situation.The purpose of this book is tohelp you find which ones are right for you.

Farmers around the country are increasinglylooking at the long-term contributions of covercrops to their whole farm system. Some of themost successful are those who have seen the ben-efits and are committed to making cover cropswork for them.They are re-tooling their croppingsystems to better fit cover crop growth patterns,rather than squeezing cover crops into their exist-ing system, time permitting.

This 3rd edition of Managing Cover CropsProfitably aims to capture farmer and otherresearch results from the past ten years.We verifiedthe information from the 2nd edition, added new

results and updated farmer profiles and researchdata throughout.We also added two new chapters.Brassicas and Mustards (p. 81) lays out the

current theory and management of cover crops inthe BRASSICACEAE family. Brassica cover crops arethought to play a role in management of nema-todes, weeds and disease by releasing chemicalcompounds from decomposing residue. Resultsare promising but inconsistent. Try brassicas onsmall plots and consult local expertise for addi-tional information.Managing Cover Crops in Conservation

Tillage Systems (p.44) addresses the managementcomplexities of reduced tillage systems. If you arealready using cover crops, the chapter will helpyou reduce tillage. If you are already using con-servation tillage, it shows you how to add or bet-ter manage cover crops. Cover crops andconservation tillage team up to reduce energy useon your farm and that means more profits.

We have tried to include enough informationfor you to select and use cover crops appropriateto your operation.We recommend that you defineyour reasons for growing a cover crop—the sec-tion, Selecting the Best Cover Crops for YourFarm (p. 12) can help with this—and take asmuch care in selecting and managing cover cropsas you would a cash crop.

Regional and site-specific factors can complicatecover crop management. No book can adequatelyaddress all the variables that make up a crop pro-duction system.Before planting a cover crop, learnas much as you can from this book and talk to oth-ers who are experienced with that cover crop.

We hope that this updated and expanded edi-tion of Managing Cover Crops Profitably willlead to the successful use of cover crops on awider scale as we continue to increase the sus-tainability of our farming systems.

Andy Clark, CoordinatorSustainable Agriculture Network (SAN)June, 2007

FOREWORD

4 MANAGING COVER CROPS PROFITABLY

MANAGING COVER CROPS PROFITABLYTHIRD EDITION

Foreword . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 5How to Use this Book . . . . . . . . . . . . . . . . . . . . 7Benefits of Cover Crops . . . . . . . . . . . . . . . . . . 9Selecting the Best Cover Crops

forYour Farm. . . . . . . . . . . . . . . . . . . . . . . . 12Building Soil Fertility andTilth

with Cover Crops . . . . . . . . . . . . . . . . . . . . 16• Cover Crops Can StabilizeYour Soil . . . . 19• How Much N? . . . . . . . . . . . . . . . . . . . . . . 22

Managing Pests with Cover Crops . . . . . . . . . 25• Georgia Cotton, Peanut FarmersUse Cover Crops to Control Pests . . . . . . 26

• Select Covers that Balance Pests,Problems of Farm . . . . . . . . . . . . . . . . . . . 30

Crop Rotations with Cover Crops. . . . . . . . . . 34• Full-Year Covers Tackle ToughWeeds . . . 38• StartWhereYou Are . . . . . . . . . . . . . . . . . 41

Managing Cover Crops in ConservationTillage Systems. . . . . . . . . . . . . . . . . . . . . . . 44• After 25Years, ImprovementsKeep Coming . . . . . . . . . . . . . . . . . . . . . . . 52

Introduction to Charts. . . . . . . . . . . . . . . . . . . 62Chart 1: Top Regional Cover Crop Species . . 66Chart 2: Performance and Roles. . . . . . . . . . . 67Chart 3A: Cultural Traits . . . . . . . . . . . . . . . . . 69Chart 3B: Planting . . . . . . . . . . . . . . . . . . . . . . 70Chart 4A: Potential Advantages. . . . . . . . . . . . 71Chart 4B: Potential Disadvantages.. . . . . . . . . 72

COVER CROP SPECIESOverview of Nonlegume Cover Crops . . . 73Annual Ryegrass. . . . . . . . . . . . . . . . . . . . . . . . 74Barley . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77Brassicas and Mustards . . . . . . . . . . . . . . . . . . 81• Mustard Mix Manages Nematodes inPotato/Wheat System . . . . . . . . . . . . . . . . 86

Buckwheat . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90Oats . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93• Oats, Rye Feed Soil inCorn/Bean Rotation. . . . . . . . . . . . . . . . . 96

Rye . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98• Cereal Rye: Cover CropWorkhorse . . . . 102• Rye SmothersWeeds Before Soybeans . 104

Sorghum Sudangrass Hybrids . . . . . . . . . . . . 106• Summer Covers Relieve Compaction . . 110

WinterWheat. . . . . . . . . . . . . . . . . . . . . . . . . 111•Wheat Boosts Income andSoil Protection . . . . . . . . . . . . . . . . . . . . . 113

•Wheat Offers High-VolumeWeed Control Too . . . . . . . . . . . . . . . . . . 114

Overview of Legume Cover Crops . . . . . 116Cover Crop Mixtures ExpandPossibilities . . . . . . . . . . . . . . . . . . . . . . . 117

Berseem Clover . . . . . . . . . . . . . . . . . . . . . . . 118• Nodulation:Match Inoculant toMaximize N . . . . . . . . . . . . . . . . . . . . . . . 122

Cowpeas . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125• Cowpeas Provide Elegant Solutionto Awkward Niche . . . . . . . . . . . . . . . . . 128

Crimson Clover . . . . . . . . . . . . . . . . . . . . . . . 130Field Peas . . . . . . . . . . . . . . . . . . . . . . . . . . . 135• Peas Do Double Duty for KansasFarmer . . . . . . . . . . . . . . . . . . . . . . . . . . . 140

Hairy Vetch. . . . . . . . . . . . . . . . . . . . . . . . . . . 142• Cover Crop Roller Design HoldsPromise for No-Tillers. . . . . . . . . . . . . . . 146

•Vetch Beats Plastic . . . . . . . . . . . . . . . . . . 150Medics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152• Jess Counts on GEORGE for N andFeed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153

• Southern Spotted Bur Medic offersReseeding Persistence . . . . . . . . . . . . . . . 154

ACKNOWLEDGMENTS 5

This 3rd edition could not have been written without the help of many cover crop experts. It isbased in large part on the content of the 2nd edition, researched and written by Greg Bowman,Craig Cramer and Christopher Shirley.The following people reviewed the 2nd edition, suggested

revisions and updates and contributed new content.

Aref Abdul-Baki, retired,USDA-ARSWesley Adams, Ladonia,TXKenneth A.Albrecht,Univ. ofWisconsinJess Alger, Stanford,MTRobert G. Bailey,USDA Forest ServiceKipling Balkcom,USDA-ARSRonnie Barentine,Univ. of GeorgiaPhil Bauer,USDA-ARSR. Louis Baumhardt,USDA-ARSRich and Nancy Bennett,Napoleon,OHValerie Berton, SARERobert Blackshaw,Agriculture andAgri-Food CanadaGreg Bowman,NewFarmRick Boydston,USDA-ARSLois Braun,Univ. of MinnesotaEric B. Brennan,USDA-ARSPat Carr,North Dakota State Univ.Max Carter,Douglas,GA

Guihua Chen,Univ. of MarylandAneeqa Chowdhury, SAREHal Collins,USDA-ARSCraig Cramer,Cornell Univ.Nancy Creamer,North Carolina State Univ.William S.Curran, The Pennsylvania State Univ.Seth Dabney,USDA-ARSBryan Davis,Grinnell, IAJorge Delgado,USDA-ARSJuan Carlos Diaz-Perez,Univ. of GeorgiaRichard Dick,Ohio State Univ.SjoerdW.Duiker, The Pennsylvania State Univ.GeraldW.Evers, Texas A&M Univ.Rick Exner, Iowa State Univ. ExtensionRichard Fasching,NRCSJim French, Partridge,KSEric Gallandt,Univ. of MaineHelen Garst, SARE

ACKNOWLEDGMENTS

Red Clover . . . . . . . . . . . . . . . . . . . . . . . . . . . 159Subterranean Clovers . . . . . . . . . . . . . . . . . . 164Sweetclovers . . . . . . . . . . . . . . . . . . . . . . . . . 171• Sweetclover: Good Grazing, GreatGreen Manure. . . . . . . . . . . . . . . . . . . . . 174

White Clover . . . . . . . . . . . . . . . . . . . . . . . . . 179• Clovers Build Soil, BlueberryProduction . . . . . . . . . . . . . . . . . . . . . . . . 182

WoollypodVetch . . . . . . . . . . . . . . . . . . . . . . 185

APPENDICESA.Testing Cover Crops onYour Farm . . . . . . 189B.Up-and-Coming Cover Crops. . . . . . . . . . . 191C. Seed Suppliers . . . . . . . . . . . . . . . . . . . . . . 195D. Farming Organizations with

Cover Crop Expertise . . . . . . . . . . . . . . . . 200E. Regional Experts . . . . . . . . . . . . . . . . . . . . 202F.Citations Bibliography . . . . . . . . . . . . . . . . 280G.Resources from the Sustainable

Agriculture Network . . . . . . . . . . . . . . . . . 230H.Reader Response Form . . . . . . . . . . . . . . . 232

INDEX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 233


INTRODUCTION

Conservation tillage is defined as a system thatleaves enough crop residue on the soil surfaceafter planting to provide 30% soil cover, theamount needed to reduce erosion below toler-ance levels (SSSA). Today, however, most conser-vation tillage practitioners aim for greater soilcover because of additional benefits of cropresidue.Cover crops are critical to producing thisresidue and have the potential to maximize con-servation tillage benefits.

Benefits of conservation tillage systems include:• reduced soil erosion• decreased labor and energy inputs• increased availability of water for crop production• improved soil quality

Cover crops further benefit conservation tillagesystems by:• producing crop residues that increase soil

organic matter and help control weeds• improving soil structure and increasing infiltration• protecting the soil surface and dissipating rain-

drop energy• reducing the velocity of water moving over

the soil surface• anchoring soil and adding carbon deep in the

soil profile (via roots)

Conservation tillage has been adopted on moreand more acres since the 1970’s thanks toimprovements in equipment, herbicides andother technologies. Several long-term, incremen-tal benefits of conservation tillage have emerged.The most important benefits have been attributedto the accumulation of organic matter at the soilsurface.

This accumulation of surface organic matterresults in:• increased aggregate stability,which helps to

increase soil water infiltration and resist erosion• improved nutrient cycling and water quality,

due to keeping nutrients in the field• increased biological activity,which improves

nutrient cycling and can influence diseasesand pests

Additional benefits from conservation tillage sys-tems compared to intensive or conventionaltillage systems (89) include:• Reduced labor and time—one or two trips to

prepare land and plant compared to three ormore reduces labor and fuel costs by 50% ormore.

• Reduced machinery wear—fewer trips meanfewer repairs.

• Increased wildlife—crop residues provideshelter and food for wildlife, such as gamebirds and small animals,which can result inadditional farm revenue.

• Improved air quality—by reducing winderosion (amount of dust in the air), fossil fuelemissions from tractors (fewer trips) andrelease of carbon dioxide into the atmosphere(tillage stimulates the release of carbon fromorganic matter).

In an Iowa study comparing no-till and conven-tional tillage in a corn>soybean>wheat/cloverrotation, corn and soybean yields were lower inno-till plots the first year.With yearly applicationof composted swine manure, however, yield ofboth corn and soybean were the same for bothsystems beginning in year two of the study.Wheatyields were not affected by tillage, but increasedwith compost application (385).

MANAGING COVER CROPS IN CONSERVATIONTILLAGE SYSTEMSby Kipling Balkcom, Harry Schomberg,Wayne Reeves and Andy Clarkwith Louis Baumhardt, Hal Collins, Jorge Delgado, Sjoerd Duiker, Tom Kaspar and Jeffrey Mitchell

MANAGING COVER CROPS IN CONSERVATION TILLAGE SYSTEMS 45

Cover crop contributions toconservation tillage systemsBiomass. Conservation tillage systems dependon having crop residues on the soil surface formost of the year. Cover crops help provide theadditional biomass needed to meet this year-round requirement. A typical high residue covercrop should contain at least 4000 lb. biomass/A.

In low-fertility soils, you can increase biomassproduction of grass cover crops with the additionof a small amount of N fertilizer. Cover cropsgrown in soils with higher levels of organic mat-ter, or following a legume summer crop like soy-bean, may not need additional N fertilizer.Remember, minimal cover crop residue or bio-mass translates into minimal benefits.Soil improvement. Cover crop biomass is a

source of organic matter that stimulates soil bio-logical activity.Soil organic matter and cover cropresidues improve soil physical properties, result-ing in:• greater water infiltration, due to direct effects

of the residue coverage or to changes in soilstructure

• greater soil aggregation or tilth, resulting inbetter nutrient and moisture management

• less surface sealing, because residue interceptsrain drops, reducing the dispersal of clay parti-cles during a rainfall or irrigation event

• greater soil porosity, due to the macroporesthat are formed as roots die and decompose

Improvements in soil physical properties dependon soil type, crops grown and residue manage-ment system, as well as temperature and rainfall.Regardless of soil type, however, tillage will veryquickly negate cover crop benefits associatedwith increased soil organic matter. Simply put,tillage breaks down organic matter much fasterthan no-till.

Improvements in soil physical properties dueto cover crops have been documented widely inconservation tillage systems (25,52,106,114,115,119, 238, 318, 419).Erosion control. Cover crops and conserva-

tion tillage combine to reduce soil erosion andwind erosion (26, 115, 119, 223, 267).

In Kentucky,on a Maury silt loam soil with a 5%slope, soil loss was 8 tons/A for conventionallytilled corn with the corn residue and cover cropturned under in the spring. In contrast, for no-tillage corn with 3 tons/A of corn residue remain-ing on the soil surface,soil loss was 1 ton/Awithout a cover crop and0.9 tons/A with a wintercover crop (91,151).

In Missouri, on aMexico series silt loamsoil with a claypan,inclusion of a rye orwheat cover crop reduced soil loss in no-tillagesilage corn from 9.8 to 0.4 tons/A/year (437).Rotation effects. Crop rotation provides

numerous benefits to any cropping system. It iscritical to reducing the incidence of diseases andpests,and is also credited with improving nutrientuse and reducing weeds.Cover crops increase thecomplexity and intensity of crop rotations, effec-tively increasing crop rotation benefits. Note,however, as addressed throughout this book, thatcover crops can adversely affect other crops inthe rotation.

Cover crop management inconservation tillage systemsNutrient management. Nitrogen and phospho-rus are the two macronutrients most likely to belost from cropping systems. Cover crops helpreduce losses of these nutrients by:• increasing infiltration—thus reducing surface

runoff and erosion• taking up nutrients—or acting as a ‘catch crop’• using water for cover crop growth during

peak leaching season (late fall through earlyspring)—reducing the amount of water avail-able to leach nutrients

Grasses and brassicas are better than legumes atreducing N leaching (106, 234, 265). Cereal rye isvery effective at reducing N leaching because it iscold tolerant, has rapid growth, and produces alarge quantity of biomass (111). Winter annualweeds do not effectively reduce N losses.

Tillage breaks

down organic

matter much

faster than no-till.


Cover crops may reduce the efficiency of N fer-tilizer in no-till systems,depending on the methodof application. Surface applications of urea-con-taining fertilizers to soils with large amounts ofcover crop residues can result in large losses ofammonia N.When applied to the soil surface,ureaand urea-ammonium nitrate (UAN) solutionsvolatilize more than ammonium nitrate and sub-sequently lose more N to the atmosphere.

Injecting urea-containing fertilizers into the soileliminates volatilization losses. Banding urea-con-taining fertilizers also reduces volatilization lossesbecause banding minimizes fertilizer and residuecontact,while increasing fertilizer and soil contact.Nitrogen dynamics with nonlegume cover

crops. Differences between nonlegumes andlegume cover crops are mostly related to nitrogenmanagement. Legumes fix N while nonlegumescan only use N already in the soil. Legumeresidues usually contain more total N that is morereadily available to subsequent crops.

The addition of fresh crop residues stimulatesgrowth of soil microbes and increases microbialdemand for nutrients, particularly N. Micro-organisms use C, N and other nutrients as a foodsource in order to break down the residues. If theamount of N in the residues is too low, themicroorganisms use soil N instead, reducing Navailability to the cash crop. This is called Nimmobilization. If the amount of N in theresidues is greater than microbial demand, N isreleased and N availability for plant growth isincreased, a process called N mineralization.

Small grain and other grass cover crops usuallyresult in an initial, if not persistent, immobilizationof N during the cash crop season.The N contentof small grain cover crop residues varies greatly,but generally ranges from 20 to 50 lb./A for theaboveground biomass and 8 to 20 lb./A in theroots.The N contribution from small grain covercrops depends on N availability during the covercrop growing period, the total amount of biomassproduced and the growth stage when the cover isterminated.

The carbon to nitrogen ratio (C:N ratio) ofcover crop residue is a good indicator of whetherimmobilization or mineralization will occur.

Values exceeding 30 parts carbon to one partnitrogen (C:N ratio of 30:1) are generally expect-ed to immobilize N during the early stages of thedecomposition process. For more informationabout C:N ratios and cover crop nutrient dynam-ics, see Building Soil Fertility and Tilth withCover Crops (pp. 16).

The C:N ratio of small grain residues is mostlydependent on time of termination. Early termina-tion of grass cover crops results in a narrower C:Nratio, typical of young plant tissue. If killed tooearly, this narrower C:N ratio results in rapiddecomposition of a smaller amount of residue,reducing ground coverage.

Because of the need for residue in conservationtillage systems, small grain cover crops are oftenallowed to grow as long as possible.Terminationdate depends on crop rotation and climate.Whensmall grain cover crops are killed at flowering, theC:N ratio is usually greater than 30:1.

In Pennsylvania, delaying rye termination datefrom early to late boot stage increased averageabove-ground dry matter accumulation from 1200to 3700 lb./A with no negative effect on cornyield (118).

In Alabama, rye, black oat and wheat covercrops were terminated at different growth stageswith a roller or roller-herbicide combinations.Biomass production was about 2.0 – 2.6 tons/A atthe flag leaf stage and corresponding C:N ratioaveraged 25:1, regardless of cover crop species.

At flowering,biomass averaged 4.2,3.8, and 3.3tons/A for black oat, rye and wheat, respectively,and the C:N ratio for all covers was 36:1.Killing atsoft dough stage did not increase biomass pro-duction for any of the covers,but did increase theC:N ratios, which would increase N immobiliza-tion (13).

The wide C:N ratio of small grain residues mustbe taken into account for best N management.Nitrogen fertilizer rates for cash crops may needto be increased 25 to 30 lb./A following a highresidue cereal cover crop.

In N-limited soils, early-season growth of thecash crop is usually enhanced if this N is appliedas starter fertilizer.Although yield increases fromstarter N applications are dependent on rainfall


and crop, they occur frequently enough to justifythe practice. Starter fertilizer promotes morerapid canopy development, which reduces weedcompetition and can offset the negative effects ofcool, wet soils often experienced with conserva-tion tillage systems. Ideally, starter fertilizersshould be placed near the seeding row in a 2 X 2band, i.e. 2 inches to the side and 2 inches belowthe seed.Legumes add N. Legume cover crops obtain

nitrogen from the atmosphere through a symbiot-ic relationship with nitrogen fixing bacteria.TheN content of legume cover crops and the amountof N available to subsequent crops is affected by:• Legume species and adaptation to soil and

climatic conditions• residual soil N• planting date• termination date

Cover crop management affects the N content oflegume cover crops and the contribution of N tothe following cash crop. Early establishment oflegume cover crops results in greater biomassproduction and N production.The nitrogen con-tent of legume cover crops is optimized at theflowering stage. Legumes can contribute from 15to 200 lb. N/A to the subsequent crop, with typi-cal values of 50 to 100 lb./A.

In North Carolina,delaying the kill date of crim-son clover 2 weeks beyond 50% bloom,and hairyvetch 2 weeks beyond 25% bloom increased thebiomass of clover by 41% and vetch by 61%.Corresponding increases in N content were 23%for clover and 41% for vetch (427). In Maryland,hairy vetch fixed about 2 lb. N/acre/day fromApril 10 to May 5, resulting in an additional 60 lb.N/A in aboveground biomass (82, 83, 86).

The C:N ratio of mature legume residues variesfrom 25:l to 9:1 and is typically well below 20:1,the guideline threshold where rapid mineraliza-tion of the N in the residue occurs. Residueson the soil surface decompose more slowlythan those incorporated in conventional tillagesystems.Consequently, in conservation tillage sys-tems, legume-residue N may not be readily avail-able during the early part of the growing season.

Due to the initial lag in availability of N fromlegume cover crop residues, any additional fertil-izer N should be applied to cash crops at plantingin conservation-tillage winter annual legume sys-tems. Splitting N applications to corn grown inthese systems, as is generally recommended forconventional-tilled corn grown without legumecover crops, is not necessary (347).Grass-legume mixtures. Mixtures of grass

and legume cover crops provide the same bene-fits to conservation tillage but often mitigate thenitrogen immobilization of pure grass covercrops. The grass component scavenges residualnitrogen effectively, while the legume adds fixednitrogen that is more readily available to the cashcrop (86, 343, 344, 345).

The C:N ratio of grass-legume mixtures is usu-ally intermediate to that of pure stands. In severalstudies in Maryland, the C:N ratio of mixtures ofhairy vetch and rye never exceeded 25:1; the C:Nratio of pure rye ranged from 30:1 to 66:1 acrossseveral spring kill dates (81, 83, 84, 85, 86).Water availability. Cover crops use soil water

while they are growing.This can negatively affectcash crop yields.Once killed, however, cover cropresidues may increase water availability by increas-ing infiltration and reducing evaporation losses.

Short-term soil water depletion at planting mayor may not be offset by soil water conservationlater in the growing season.This is dependent onrainfall distribution in relation to crop develop-ment. A rainfall event following cover crop termi-nation enables soil surface water recharge,whichusually provides adequate soil moisture in humidregions to facilitate cash crop planting. Time oftermination becomes more critical as the proba-bility of precipitation decreases (423).

Cover crops increase water availability by:• decreasing evaporation due to a mulching

effect• increasing infiltration of rainfall by decreasing

runoff velocity• increasing organic matter,which increases

water-holding capacity• improving soil structure and consequently

increasing root interception of soil water


• protecting the soil surface from raindropimpact, thus reducing development of a sur-face seal or crust,which can greatly reduceinfiltration

InAlabama,cover crop residue left on the soil sur-face reduced runoff and increased infiltration by50 to 800% compared to removing or incorporat-ing the residues (418,419). In Georgia, infiltrationrates were 100% greater even after removal ofcrop residues for a Cecil sandy loam when grainsorghum was no-till planted into crimson clovercompared to a tilled seedbed without a covercrop (52).

In Maryland, pure and mixed stands of hairyvetch and rye did not deplete soil water oradversely affect corn yield. Rather, the additionalresidue from cover crops killed in early May con-served soil moisture and contributed to greatercorn yield (84, 85).

In Kentucky, surface evaporation from May toSeptember was five times less under no-till(which leaves a surface mulch) than with con-ventional tillage. Because less water was lost toevaporation, more water was available for thecrop (91).

Cover crop use in dryland systems is oftenlimited by moisture availability. A literaturereview of dryland cover crop studies on the GreatPlains concluded that use of cover crops on dry-land cropping systems of the Great Plainsreduced yields of subsequent crops. However, insemi-aridTexas,5 tons/A of wheat straw increasedavailable soil water by 73% and more than dou-bled grain sorghum yields from 26 to 59bushels/A (423).

The risk for early-season soil water depletion bycover crops is the same regardless of the tillagesystem.However, the full potential of cover cropsto increase infiltration and conserve soil watercan only be achieved in a conservation systemwhere cover crop residues are left on the surface.Conservation tillage increased water use efficien-cy compared to a traditional wheat>fallow systemwith tillage (319, 135).

One way to reduce the risk of early-season soilwater depletion by cover crops is to desiccate thecover some time prior to planting the cash crop.

For example, yield reductions due to early-seasondepletion of soil water can be reduced by killingthe cover crop 2 to 3 weeks before planting thecash crop (428, 290, 348).Depending on your sit-uation, you could extend this window to termi-nate cover crops in conservation systems from 4to 6 weeks prior to planting the cash crop.

Cover crops can sometimes be used to depletesoil water on poorly drained soils,allowing an ear-lier planting date for the cash crop, but the prac-tical advantage of this practice is not certain.Soil temperature. Cover crop residues keep

the soil cooler, reduce daily fluctuations of soiltemperature, and reduce soil temperature maxi-mums and minimums. The cooler soil tempera-tures, which benefit the cash crop throughoutthe summer, can delay spring planting comparedto a system without a cover crop.

Spring soil temperature is particularly impor-tant in cover crop/conservation tillage systems.Where possible, plant your cash crop accordingto soil temperature rather than the calendar.Follow local recommendations about the appro-priate soil temperature for your cash crop. Asnoted below, the use of row cleaners will allowfaster soil warmup.

The harmful effects of planting when the soiltemperature is too low were demonstrated inColorado for conservation tillage with continuouscorn (but not cover crops).Low soil temperaturescontributed to reduced corn yields over 5 years(171, 172).Insects and diseases. Conservation tillage sys-

tems alter pest dynamics, due in large part toresidues left on the soil surface. Conservationtillage systems with surface residues create amore diverse plant/soil ecosystem than conven-tional tillage systems (137, 185, 416).

Cover crops may harbor insects, diseases, andnematodes that could be harmful to the cashcrop. Before planting a cover crop, be sure toinvestigate specific pest/crop interactions thatmay become a problem (100). Understandingthese interactions and the conditions that favorthem helps you make good management deci-sions. For example:• Cereal rye, orchardgrass and crimson clover

may attract armyworms.


• Clover root curculio, a common pest of redclover, can attack alfalfa.

• Chickweed can attract black cutworm orslugs.

• Johnsongrass is a host to maize dwarf mosaicvirus (MDMV),which also infects corn.

Conversely, cover crops can be used in conserva-tion tillage systems to attract beneficial insects.One approach is to allow a live strip of covercrops to remain between crop rows to serve ashabitat and a food source until the main crop isestablished. This approach resulted in one lessinsecticide application in conservation-tilled cot-ton compared to conventional cotton in SouthGeorgia (368, 416).

For more information about cover crops andbeneficial insects, see Manage Insects on YourFarm: A Guide to Ecological Strategies (409,http://www.sare.org/publications/insect.htm).

Cover crop residues have been shown toreduce the incidence of several diseases in manydifferent cash crop systems by reducing splashdispersal of pathogens. Small grain cover crops inconservation tillage have also been shown toreduce peanut yield losses from Tomato SpottedWilt Virus (TSWV), with greater residue amountsresulting in lower incidence of TSWV. Thisbenefit was directly related to less incidence ofdamage from thrips, the vector of TSWV (49).

Some cover crops can serve as an overwinter-ing host for nematodes and may thus increase theseverity of nematode damage. This may be agreater concern where crops are not rotated, likecontinuous cotton in some areas of the South.Onthe other hand, cover crops such as brassicas canreduce nematode populations (48, 231, 283, 284,285, 353, 430).

On a Maryland sandy soil, winterkilled forageradish increased bacteria-eating nematodes, ryeand rapeseed increased the proportion of fungalfeeding nematodes,while nematode communitieswithout cover crops were intermediate. TheEnrichment Index, which indicates a greaterabundance of opportunistic bacteria–eatingnematodes, was 23% higher in soils that hadbrassica cover crops than the unweeded controlplots.These samples, taken in November, June (a

month after springcover crop kill), andAugust (under corn),suggest that the covercrops, living or dead,increased bacterialactivity and may haveenhanced nitrogencycling through the food web (432).

The need for sound crop rotation is greater inconservation systems than in conventional sys-tems. Cover crops should be a key component ofany conservation rotation system. With the vastnumber of potential combinations of crops,covercrops, and diseases, consult local experts toensure that you manage cover crops in conserva-tion tillage systems to minimize the potential forpest problems.Weed management. Cover crops affect

weeds and weed management in conservationtillage systems in several ways:• Cover crops compete with weeds for light,

water and nutrients.• Cover crop residue can suppress weed seed

germination; the more residue the better.• Grass cover crops (high C:N ratio) usually pro-

vide longer-lasting residue than legumes.• Some cover crops release weed-suppressing

allelopathic compounds.• Conservation tillage does not continually turn

up new weed seeds for germination.• Cover crops can become weeds.

Some legume, cereal and brassica cover cropsrelease allelopathic compounds that can reduceweed populations and/or suppress weed growth(39, 45, 176, 177, 178, 336, 359, 410, 422).Unfortunately, these same allelopathic com-pounds can also stunt and/or kill cash cropseedlings,particularly cotton (24) and some smallseeded vegetable crops. Allowing time betweenthe termination date and the cash crop plantingdate reduces the risk to cash crops because thesechemicals leach out of the cover crop residue andare decomposed by soil microorganisms.

Cereal rye is known to release phenolic andbenzoic acids that can inhibit weed seed germi-nation and development. InArkansas, the concen-

Consult local

experts to minimize

the potential for

pest problems


tration of these allelopathic chemicals varied 100-fold among ten varieties of rye in the boot stage,with the cultivar BONEL having the greatest con-centration and PASTAR the least. Factoring in theyield of each cultivar with the concentration andactivity of the inhibitors, BONEL,MATON and ELBON

were considered the best rye cultivars for allelo-pathic use (66).

Conservation tillage and the allelopathic effectsof cover crop residue can both contribute to thesuppression of weeds in these systems (452). InAlabama, a conservation tillage system using ryeor black oat cover crops eliminated the need forpost-emergence herbicides in soybean and cotton(335, 349). Including rye or black oat increasedyields of non-transgenic cotton in 2 of 3 years,com-pared to conservation tillage without a cover crop.

Economics of cover cropestablishment and useUsing cover crops in any tillage system usuallycosts more time and money than not using covercrops. Depending on your particular system, youmay or may not be repaid for your investmentover the short term. If you are already using covercrops but are considering switching to conserva-tion tillage, the economics are similar to usingcover crops in conventional tillage systems, butthe benefits may be expressed more in the con-servation system (51).

Factors affecting the economics of cover cropuse include:• the cash crop grown• the cover crop selected• time and method of establishment• method of termination• the cash value applied to the environment, soil

productivity and soil protection benefitsderived from the cover crop.

• the cost of nitrogen fertilizer and the fertilizervalue of the cover crop

• the cost of fuel

The economic picture is most affected by seedcosts,energy costs and nitrogen fertility dynamicsin cover crop systems.Cover crop seed costs varyconsiderably from year to year and from region toregion, but historically, legume cover crops cost

about twice as much to establish as small graincovers. The increased cost of the legume covercrop seed can be offset by the value of N thatlegumes can replace.

Depending on your system, legume covercrops can replace 45 to 100 lb. N/A. On theother hand, a rye cover crop terminated at a latestage of growth might require 20-30 lb. moreN/A due to N immobilization by the wide C:Nratio rye residue. Thus, the difference in costbetween a rye cover crop and a legume covercrop would be offset by the value of 65 to 125lb. N/A. At a price of $0.45/lb. N, this would beworth $29 to $56/A.

Cover crop establishment inconservation tillage systemsThe major challenges to cover crop adoption inboth tilled and conservation tillage systemsinclude seeding time and method,killing time andmethod, and cover crop residue management toensure good stands of the cash crop.Success withcover crops requires adequate attention to each.Plant cover crops on time. In order to maxi-

mize benefits—or to work at all—cover crops needto be planted early, sometimes before the summercrop is harvested.Timely planting results in:• good root establishment and topgrowth

before the crops go dormant• reduced chance of winter kill• more biomass production compared to later

planting dates• greater uptake of residual soil N

Timely fall planting is particularly importantbefore early vegetables or corn. Corn is typicallyplanted early in the spring,which forces an earlycover crop termination date. A late planted covercrop that must be terminated early will not pro-duce sufficient biomass to provide adequate soilprotection and enhance soil quality.Planting methods. Cover crops in conserva-

tion tillage systems are usually planted with a drillor broadcast on the soil surface, but several alter-nate methods can be used.Good soil-seed contactis required for germination and emergence. Mostsmall seeded legumes require shallow seed place-ment (1/4 inch),while larger seeded legumes and


small grains are generally planted up to 1.5 inch-es deep (see CHARTS, p. 62).Conservation tillage drills can handle residue

and provide uniform seeding depth and adequateseed-soil contact, even with small seeded covercrops. In some situations, preplant tillage can beused to control weeds and disrupt insect and dis-ease life cycles.Broadcast seeding requires an increase in the

seeding rate compared to other methods (seeCHARTS, p. 62). Broadcasting is often the leastsuccessful seeding method. Small-seeded speciessuch as clovers tend to establish better by broad-casting than larger seed species. A drop-type orcyclone-type seeder can be used on small acreageand provides a uniform distribution of seed.Conventional drills work adequately in some con-servation tillage systems—depending on theamount of residue—and may be more successfulthan broadcast seeding.

On larger areas, aerial seeding by fixed-wingaircraft or helicopter in late summer during cropdie-down can be effective. As the leaves of thesummer crop drop off, they aid germination bycovering the seed, retaining moisture and pro-tecting the soil.

In colder climates, frost-seeding can be usedfor some cover crop species (see individualcover crop chapters in this book). Seed is broad-cast during late fall or early spring when theground has been“honeycombed”by freezing andthawing. The seed falls into the soil cracks andgerminates when the temperature rises in thespring.

Some legumes can be managed to reseed thefollowing year. This reduces economic risks andseeding costs. Reseeding systems generallydepend on well-planned rotations such as thatreported in Alabama (311),where crimson cloverwas followed with strip-tilled soybean plantedlate enough to let the clover reseed. Corn wasgrown the next year in the reseeded clover. In thissystem,the cover crop is planted every other yearrather than annually.Grain sorghum can be plant-ed late enough in the South to allow crimsonclover to reseed in a conservation-tillage system.

The introduction of legume cover crops thatbloom and set seed earlier also improves their util-

ity for reseeding inconservation-tillage sys-tems. Auburn Universityin cooperation withUSDA-NRCS has releasedseveral legume covercrops that flower early,including AU ROBIN

and AU SUNRISE crimsonclover, and AU EARLY

COVER hairy vetch (288). Leaving 25 to 50% of therow area alive when desiccating the cover cropallows reseeding without reducing corn grainyields. However, the strips of live cover crop maycompete with the cash crop for water, a potentialproblem during a spring drought.

Spring management of cover cropsin conservation tillage systemsKill date. Timing of cover crop terminationaffects soil temperature, soil moisture, nutrientcycling, tillage and planting operations, and theeffects of allelopathic compounds on the subse-quent cash crop. Because of the many factorsinvolved, decisions about when to kill the covercrop must be site- and situation-specific.

There are a number of pros and cons of killinga cover crop early vs. late. Early killing:• allows time to replenish soil water• increases the rate of soil warming• reduces phytotoxic effects of residues on cash

crops• reduces survival of disease inoculum• speeds decomposition of residues, decreasing

potential interference with planter operation• increases N mineralization from lower C:N

ratio cover crops

Advantages for later kill include:• more residue available for soil and water con-

servation• better weed control from allelopathic com-

pounds and mulch affect• greater N contribution from legumes• better potential for reseeding of the cover

crop

Decisions about

when to kill the

cover crop must

be site- and

situation-specific.


Talk to 10 no-tillers and you’ll probably hear 10different viewpoints on why it pays to quit dis-turbing and start building the soil.At SheridanFarms,we’ve got our list, too.We are able to bet-ter time planting, weed control and other pro-duction chores. And we’ve got the potentialfor sediment and nutrient runoff into SaginawBay on Lake Huron under control.

Like a lot of no-tillers would testify, however,these changes didn’t come quickly,nor withoutsome reluctance and skepticism along the way.In our first years of no-tilling, starting in 1982,we did just about everything wrong and had anabsolute train wreck.We overcame a few hur-dles early on, started adding more no-till acresand were 100% continuous no-till by 1990.

Cover Crop SuccessWe started working with cover crops about 20years ago.We deal with about a dozen differentsoil types, 80 percent of which are clay loam.And much of our land is poorly drained, low-organic-matter lake bed soils.

Cereal rye has been a good cover crop yearin and year out for this mixture of soils.We likethe AROOSTOCK variety from Maine because itprovides fast fall and spring growth and itssmaller seed size makes it more economical toplant.

In late August, we fly rye into standing cornand also into soybeans if we’re coming backwith soybeans the following year. We learnedthat rye is easier to burn down when it’s morethan 2 feet tall than when it has grown only afoot or less.

The rye crop also helps us effectively managesoil moisture. If it looks like we’re going to geta dry spring,we burn down rye with Roundup

After 25 Years, Improvements Keep ComingBy Pat Sheridan, Sheridan Farms, Fairgrove, Mich as interviewed by Ron Ross for the No-Till Farmer

as soon as we can; but if it’s wet,we let the ryegrow to suck up excess moisture. We can bevery wet in the spring, but Michigan alsoreceives less rain during the growing seasonthan any other Great Lakes state, on average.Moisture management is critical to us.

We’ve seen less whitemold in no-tilled soy-beans wherever we haveheavy residue.We’ve hadyears with zero whitemold when our conven-tional till neighborsfaced a costly problem.It’s become a simpleequation: the heavier theresidue mat, the lesswhite mold.

Deep-Rooted CropsWe’re looking for a covercrop that will help establish a more diverserotation, so we can always follow a broadleafcrop behind a grass crop and vice-versa.Oilseedradish is beginning to show real promise. It hasabout the same tremendous appetite for nitro-gen as wheat, and it develops a very deep rootmass. It’s an excellent nutrient scavenger.

This combination enables the cover crop tocapture maximum nitrogen from deep in thesoil profile to feed the following corn crop.Noone has ever proven to me that we need nutri-ents down deep. It sounds good to have a plantfood layer at 16 to 18 inches, but I much preferthe nitrogen and other nutrients near the sur-face where the crop can use them.

Deep-rooted cover crops like oilseed radishcan help reverse the traditional theory of nitro-

An open mind

welcomes a lot

of ideas that,

with a little

tweaking, can

deliver even

more success

to your fields.


gen stratification. Nitrogen allowed to concen-trate deep in the soil scares us because it ismore likely to leach into the tile lines and reachLake Huron.

We’ve also tried wheat, hairy vetch, crimsonclover and a dry bean and soybean mix forcover crops, and we’ll keep experimenting.Recently, I traded oilseed radish seed to Kansasno-tillers Red and David Sutherland forAustrianwinter pea seed.The Sutherlands have reportedgood moisture retention and nitrogen fixationwith the peas.We like what we’ve seen with thepeas, as well.

Less Nitrogen, More CornWe partly credit the cover crop program withsharply reducing our fertilizer bills. In fact, thefirst time I hit a 200-bushel corn yield, I did itwith only 140 to 150 pounds of nitrogen peracre, or about 0.7 to 0.8 pounds of nitrogenper bushel. As anyone who has been growingcorn knows, the typical nitrogen recommenda-tion has been about a pound-plus per bushel.Oversupplying nitrogen has absolutely novalue. I think the whole nutrient cycle conceptis intriguing; no-till in conjunction with covercrops really makes it work.

Organic Matter BoostWhen we started no-tilling, we had heard sto-ries from farmers and others that we couldexpect to see increased organic matter contentin our soils after a few years. But some soilexperts cautioned that this likely wouldn’t hap-pen. Fortunately, we’ve triggered significanthumus development during the past 20 years,with organic matter increasing from about 0.5to as much as 2.5 percent. This is a real bonusin addition to all the other benefits from no-till-ing, and we expect to see even more improve-ment as we include more cover crops in ourrotation.

What Works At Home?Our county is part of the Saginaw Bay water-shed, the largest in the state with more than8,700 square miles. Everything we do as farm-ers can affect the water quality of the bay, andwe’re very conscious of that.

A group of about 150 farmers from threecounties formed the Innovative Farmers ofMichigan in 1994. Our objectives have been toreduce the amount of sediment entering thebay and change our farming practices toreduce nutrient and pesticide runoff. Wedon’t want our soils in the bay. After a 3-yearstudy, financed with an EPA 319 grant in 1996,we came up with some pretty dramatic results.We found that conservation tillage does notreduce yields; in fact we saw significant yieldincreases in corn.

Also, reduced tillage increases the soil’scapacity to supply nitrogen and phosphorus toa growing crop. Water-holding capacity andwater infiltration rates were higher on no-tillfields.We reduced the potential for soil erosionfrom water by up to 70 percent and from windby up to 60 percent, compared to conventionaltillage.At the end of the project, we were get-ting a lot better handle on what no-till systemswork best in our three-county area.

At Sheridan Farms, we’ll keep looking formore diversity and hope to get back to a four-or five-crop continuous no-till system.The mostvaluable lesson we learned is there is no uni-versal truth or no-till game plan that will applyfor everyone. Eventually, we adapted a no-tillsystem that fits our particular soil types, crops,climate, long-range goals and farming style.

—Adapted with permission from “The No-TillFarmer,”May 2006. www.no-tillfarmer.com


As a general rule, cover crops,particularly cereals,need to be terminated 2-3 weeks ahead of planti-ng to allow plant material to dry out and becomebrittle. Dry brittle cover crop residue allowstillage and planting equipment to cut through theresidue more easily, as opposed to semi-dry covercrop residue. Semi-dry residue is tough and hardto cut, which can result in considerable draggingof the residue as implements traverse the field.

Allelopathic compounds can be a greater prob-lem with crop establishment when fresh residuesbecome trapped in the seed furrow, a conditionknown as “hairpinning.” Hairpinning can be aproblem even for residues that have been on thesurface for a number of weeks if planting in themorning when residues are still moist from pre-cipitation or dew.Hairpinning can reduce seed tosoil contact and cash crop stands.

You can sometimes plant the cash crop directlyinto standing (live) cover crop, then kill the covercrop.This allows more time for cover crop growthand biomass production, and usually side-steps theproblem of planting into tough cover crop residue.However, planting into standing green residue canincrease the risk of allelopathic chemicals affectingsensitive cash crop seedlings,and can make it diffi-cult to align rows when planting.

Killing methodsMany kill methods have been developed and test-ed. Some are described below. Be sure to checkwith Extension or other farmers for recommend-ed methods for your area and crop system.Killing with an herbicide. Killing cover

crops with a non-selective herbicide is the stan-dard method used by conservation tillage grow-ers.They favor this option because they can covermany acres quickly and herbicides are relativelycheap. Herbicides can be applied at any time orgrowth stage to terminate the cover crop.Killing with a roller-crimper. Cover crops

can be killed using a mechanical roller (oftencalled a roller-crimper).The roller kills the covercrop by breaking (crimping) the stems. Thecrimping action aids in cover crop desiccation.

The cover crop is rolled down parallel to thedirection of planting to form a dense mat on thesoil surface, facilitating planter operation and aid-

ing in early season weed control.When using aroller alone for cover crop termination, bestresults are obtained when rolling is delayed untilflowering stage or later.

Roller-crimpers work best with tall-growing covercrops. Small weeds are not killed by rolling. Weedsuppression by the mat of rolled cover crop residuedepends on cover crop,weed species and height,andthe density (thickness) of the cover crop mat.

Rollers can be front- or rear-mounted.They usu-ally consist of a round drum with equally spacedblunt blades around the drum. Blunt blades areused to crimp the cover crop.This is preferable tosharp blades that would cut the cover crop anddislodge residue that might interfere with seedsoil contact at planting.

The roller-crimper is a viable way to kill covercrops without using herbicides. It also helps pre-vent planter problems that can occur when tall-growing cover crops lodge in many differentdirections after chemical termination

InAlabama, a mechanical roller was used to killblack oat, rye and wheat cover crops.The rollercombined with glyphosate at one-half the recom-mended rate was as effective as using glyphosateat the full recommended rate to kill all covercrops.The key was to use the roller at flowering.Herbicides can be eliminated if the roller opera-tion occurs at the soft dough stage or later,a goodoption for organic growers (13).

▼Precaution: Applying non-selective herbicidesat reduced rates could lead to weed resistance.The half rate of herbicide may not completelyeradicate the weed,increasing the chance that theweed will produce seed. Under these circum-stances, such seeds are more likely to be resistantto the herbicide. Therefore, it is safer to com-pletely eliminate the use of the non-selectiveherbicide with a roller or use the non-selectiveherbicide at the labeled rate,with or without theroller.

Growers and researchers are addressing severalbarriers to the use of rollers:• Operation speed was hampered by vibration.

Using curved blades on the roller drum allevi-ates this problem.


• Most rollers are 8 rows or smaller, but growershave built wider rollers that can be folded fortransportation.

• Rolling and planting can be done in one oper-ation by using a front-mounted roller and rear-mounted drill, saving time and energy.

For more information about cover crop rollers,see ATTRA (11) and Cover Crop Roller DesignHolds Promise for No-Tillers, p. 146.Mowing/chopping. Mowing and chopping

are quick methods to manage large amounts ofcover crop residue by cutting it into smallerpieces.An alternative to the use of herbicides, it ismore energy intensive.

In humid climates, mowed residues breakdown faster,negating some of the residue benefitsof conservation tillage. In drier climates, covercrop residues do not decompose as fast,but windand water may cause residue to accumulate inlow areas or remove it from the field altogether.

Cutting residue into smaller pieces mayadversely affect the performance of tillage andplanting equipment because coulters designed tocut through residue may instead push smallresidue pieces into the soil.Use“row cleaners”or“trash whippers” to prevent this problem.Living mulch. Living mulches are cover crops

that co-exist with the cash crop during the grow-ing season and continue to grow after the crop isharvested. Living mulches do not need to bereseeded each year (182). They can be chosenand managed to minimize competition with themain cash crop yet maximize competition withweeds. The living mulch can be an annual orperennial plant established each year, or it can bean existing perennial grass or legume stand intowhich a crop is planted.

Living mulch systems are dependent on adequatemoisture for the cash crop.They can be viable forvineyards, orchards, agronomic crops, such as corn,soybean, and small grains, and many vegetables.Legumes are often used because they fix nitrogen,aportion of which will be available for the compan-ion crop. If excess nitrogen is a problem, livingmulches (especially grasses) can serve as a sink to tieup some of this excess nitrogen and hold it until thenext growing season.

In conservation tillage systems,livingmulches canimprove nitrogen budgets, provide weed and ero-sion control, and may contribute to pest manage-ment and help mitigate environmental problems.

Living mulch systems are feasible in Midwestalfalfa-corn rotations (386). Use in corn-soybeanrotations was also feasible but more challengingbecause soybean is more susceptible to competi-tion from the living mulch. With adequate sup-pression, living mulches can be managed tominimize competition with corn with little or noreduction in yield.The system requires close mon-itoring and careful control of competitionbetween the living mulch and grain crop to main-tain crop yields.Cash crop establishment. Cash crop estab-

lishment can be complicated by the use of covercrops in conservation-tillage systems.Cover cropscan reduce cotton,corn and soybean stands if notmanaged well.Possible causes of stand reductionsinclude:• poor seed-soil contact due to residue interfer-

ence with planter operations• soil water depletion• wet soils due to residue cover• cold soils due to residue cover• allelopathic effects of cover crop residues• increased levels of soilborne pathogens• increased predation by insects and other pests• free ammonia (in the case of legume covers)

To prevent stand problems following cover crops:• Check for good seed-soil contact and seed

placement, particularly seeding depth.• Be sure that coulters are cutting through

cover crop residue rather than pushing it intothe soil along with the seed.

• Desiccate the cover crop at least 2 to 3 weeksbefore planting the cash crop.

• Monitor the emerging crop for early seasoninsect problems such as cutworms.

Small seeded crops like vegetables and cotton areespecially susceptible to stand reductions follow-ing cover crops.Winter annual legumes may causemore problems due to allelopathic effects and/orincreased populations of plant pathogens.


Residue management systems that leave covercrop residue on the surface can reduce the risk ofstand problems provided the residue does notinterfere with planter operation.

Good seed placement is more challengingwhere residues remain on the soil surface.However, improvements in no-till planter designhave helped. Equipment that removes cropresidue from the immediate seeding area can helpto reduce stand losses (see equipment discussion,below).

Surface residues reduce soil temperature. Therelative influence of this temperature reductionon crop growth is greater in northern areas of acrop’s adapted zone.Removal of residue from thezone of seed placement will increase soil temper-ature in the seed zone and also decrease theamount of residue that comes in contact with theseed. This will result in better seed-soil contactand less allelopathic effects from residue to thedeveloping seedling.No-till planters. The key to successful no-till

cash crop establishment in cover crop residues isadequate seed to soil contact at a desired seedingdepth. No-till planters are heavier than conven-tional planters.The additional weight allows theplanter to maintain desired seeding depth inrough soil conditions and prevents the planterfrom floating across the soil surface and creatinguneven seed placement. Individual planter rowunits are typically equipped with heavy-dutydown-pressure springs that allow the operator toapply down pressure in uneven soil conditions tomaintain depth control.

Row cleaners are designed to operate in heavycover crop residue. Manufacturers have devel-oped different types of row cleaners that can bematched to various planters.All row cleaners aredesigned to sweep residue away from the open-ing disks of the planter units. Removing thisresidue reduces the chance of pushing residueinto the seed furrow (hairpinning).

All row cleaners can be adjusted to match spe-cific field conditions. Row cleaners should beadjusted to move residue but not soil. If too muchsoil is disturbed in the row, the soil will dry outand can crust over,which will hinder emergence.In addition, disturbed soil can promote weed

emergence in the row creating unnecessary com-petition between weeds and the cash crop.

Spoked closing wheels improve establishmentin poorly drained or fine-textured soils. On thesesoils, traditional cast-iron or smooth rubber clos-ing wheels can result in soil crusting.Spoked clos-ing wheels crumble the seed trench closed foradequate seed to soil contact, but leave the soilloose and friable for plant emergence.

Additional planter attachments to ensure ade-quate seed to soil contact in rough soil conditionsinclude V-slice inserts and seed firmers. V-sliceinserts clean the seed trench created by the open-ing disks. Seed firmers press the seed into the soilat the bottom of the seed trench.Strip-tillage equipment. Strip-tillage equip-

ment is designed to manage residue and performsome non-inversion tillage in the row. In theSouth, strip-tillage refers to in-row subsoiling (14-16 inches deep) to reduce compaction,with min-imal disturbance of residue on the soil surface. Inthe Midwest, zone-tillage typically refers to shal-low tillage within the row designed to removeresidue and enhance soil warming in the seedzone.

Regardless of manufacturer, strip tillage imple-ments typically consist of a coulter that runsahead of a shank,followed by such attachments asadditional coulters, rolling baskets, drag chains, orpress wheels. Depending on conditions, theseattachments are used alone or in various combi-nations to achieve different degrees of tillage.

When strip-tilling in cover crop residue, thecoulter should be positioned as far forward of theshank as possible and centered on the shank.Thisallows the coulter to operate in firm soil enablingit to cut residue ahead of the shank.By cutting theresidue ahead of the shank, the residue can flowthrough the shanks more easily and not wrap upor drag behind the implement.

Fine-textured soils sometimes stick to theshank and may accumulate there, disturbing toomuch soil and making the slit too wide.This canimpede planter operations and is referred to as“blowout.” Plastic shields that fit over the shankhelp prevent blowout. Another way to reduceblowout is to install splitter points on the subsoilshanks. The splitter points look like shark fins


that attach vertically upright to the tips of theshank points.They fracture the soil at the bottomof the trench, preventing soil upheaval to the soilsurface.The soil fracture created is analogous tostress cracks in concrete.

Row cleaners can be used on cool, poorlydrained soils to enable faster soil-warming inspring.This may allow earlier planting and helpsensure optimal plant emergence conditions.Available for most strip-tillage implements, rowcleaners function much like row cleaners forplanters, sweeping cover crop residue away fromthe row. Adjustments for strip tillage row cleanersare not as flexible as those on planters.Vegetable establishment. Adoption of no-

tillage systems for transplanted vegetable cropswas limited by equipment and stand establish-ment problems. This problem was overcome inthe 1990’s with the development of the Subsur-face Tiller-Transplanter (287). The SST-T is a“hybrid,” combining subsurface soil loosening toalleviate soil compaction and effective setting oftransplants, in one operation with minimumdisturbance of surface residues or surface soil.

The spring-loaded soil-loosening component ofthe subsurface tiller tills a narrow strip of soilahead of the double disk shoe of the transplanter.The double-disk shoe moves through the residueand the tilled strip with relatively little resistance.In addition, the planter can be equipped with fer-tilizer and pesticide applicators to reduce thenumber of trips required for a planting operation.

Regional Roundup: Cover Crop Usein Conservation Tillage Systems

Midwest—Tom KasparSoils. Soils of the Midwest contain high levels oforganic matter compared to other regions.Research has yet to confirm if cover crops canincrease soil organic matter contents beyond cur-rent levels.The possibility of using corn stover as abioenergy source would leave the soil unprotectedand much more vulnerable to degradation, butcover crops could offset any detrimental effectsassociated with corn stover removal. The degreeto which cover crops could protect the soil follow-ing corn stover removal has not been investigated.

Farm systems. Midwest farms are large, aver-aging 350 acres. Cover crops and conservationtillage are most common in corn and soybean sys-tems, with or without livestock. Cover crops arealso commonly used in vegetable systems.Cover crop species. Rye and other small

grains are the primary cover crops used in theMidwest. Legume cover crop include red clover,hairy vetch and sweetclovers.Cover crop benefits. Advantages of cover

crops in the Midwest include reducing erosion,anchoring residues in no-till systems, suppressingwinter annual weeds and nutrient management.The ability of cover crops to scavenge nitrates isparticularly beneficial in the Midwest, where themajority of United States corn is produced,because the high N requirement of corn increas-es the potential for nitrate loss.Drawbacks. Cover crops have reduced corn

(but not soybean) yields when they are terminat-ed at planting. Earlier termination helps reducethis problem, but residue benefits are reduced.The potential biomass production is complicatedby the already short,cold cover crop growing sea-son between harvest and planting of corn andsoybean crops. Cash crop planting and harvestcoincide with cover crop kill and planting dates.Management. Cover crops need to be planted

at the same time farmers are harvesting corn andsoybean to ensure adequate biomass production.Producers would benefit from alternative covercrop establishment methods, such as overseedingbefore harvest, seeding at weed cultivation withdelayed emergence, or frost seeding after harvest.Environmental payments or incentives may enticegrowers to try alternative practices.

Northeast—Sjoerd DuikerCover crops are becoming an integral part of cropproduction in the Northeast. This is due in largepart to the increasing adoption of no-tillage sys-tems, because cover crops can be managed moreeasily than with tillage, while cover crop residuesin no-till systems lead to multiple benefits.Soils. There are many soil types in the

Northeast, including soils developed in glacialdeposits or from melt water lakes; sedimentarysoils formed from the sedimentary rocks sand-


stone, shale and limestone; Piedmont soils, rem-nants of a coastal mountain range with complexgeology,characterized by a gently to strongly undu-lating landscape;and coastal plain soils,developedin unconsolidated material deposited by rivers andthe ocean,often sandy with a shallow water table.

Soil and nutrient management in the region aimto address soil erosion, clay subsoils, fragipans,shallow water tables and the nutrient enrichmentcaused by the high density of animal production.Farm systems. Farms in the Northeast are

diverse, tend to be small, and include cash grain,perennial forage, dairy, hog, poultry, fruit and veg-etable operations. Nutrient management regula-tions in some states encourage the use of covercrops and conservation tillage practices, particu-larly for the application of manure. Farmer orga-nizations such as the Pennsylvania No-TillAllianceactively promote cover crops for their soil-improving benefits, while government programssuch as the 2006 Maryland cover crop subsidy of$30-$50 per acre led to a dramatic increase incover crop acreage.Cover crop species. Cover crop options and

niches are as diverse as the farming systems in theregion.Rye,wheat, oats and ryegrass are the mostcommon grass cover crops; hairy vetch, crimsonclover and Austrian winter pea are importantlegumes; buckwheat finds a place in many veg-etable systems and brassica crops such as forageradish are increasingly being tested and used inthe region.Cover crop benefits. Cover crops are planted

for erosion control, soil improvement, moistureconservation, forage and nutrient management,particularly the nitrogen and phosphorus fromintensive animal agriculture. Cover crops can fitinto many different niches in the region, particu-larly fruit and vegetable systems (1,2,3,4).Recentwork with forage radish (Raphanus sativus L.)suggests that its large taproot can penetrate deepsoil layers and alleviate compaction (446).Drawbacks. Barriers to the adoption of cover

crops include the time and cost of establishmentand management, water use, and, for some sys-tems, the length of the growing season.Management. Farmers and other researchers

fit cover crops into many different niches using:

• timely seeding, overseeding into standingcrops, or interseeding, including some use ofliving mulches

• various termination methods, including mow-ing or rolling standing cover crops

• manipulation of cover crop kill and cash cropplanting dates to maximize cover crop benefits

Southeast—Kipling BalkcomHigh-residue cover crops are essential to the suc-cess of conservation systems in the Southeast.Soils. Soils in the Southeast are highly weath-

ered, acidic, and often susceptible to erosion dueto their low organic matter content. Decades ofconventional tillage practices have exacerbatedtheir poor physical and chemical condition.Farm systems. Southeast farms raise various

combinations of cotton, soybeans, corn, peanutsand small grains. Some include livestock, haveaccess to irrigation or raise fruit and vegetables.Cover crop species. Rye, wheat, oats, hairy

vetch and crimson clover are the cover cropmainstays for grain and oil crop systems.Cover crop benefits. Cover crop biomass is

needed on the weathered soils of the Southeast toadd organic matter and improve soil physical,chemical, and biological properties. Cover cropresidues reduce soil erosion and runoff, increaseinfiltration and conserve soil moisture, particularlybeneficial in dry years or on drought-prone soils.Drawbacks. Major concerns are:

• water management• integration of different cover crop species into

southeastern crop production• reduced effectiveness of pre-emergence herbi-

cides in high-residue systems

Producers are also concerned about residue inter-ference with efficient equipment operation, ade-quate soil moisture at planting, and standestablishment problems. In addition, some are notwilling to commit to the additional managementlevel or perceived costs.Management. Producers like the idea of

reducing trips across the field,which reduces fueland labor costs and saves time.Significant increas-es in the use of cover crops and conservationtillage systems in the Southeast have paralleled


the adoption of new genetic varieties of corn,soy-bean and cotton that are herbicide resistant orhave incorporated genes for improved insectresistance.These genetic changes reduced someof the challenges associated with weed and insectmanagement,making the conservation tillage sys-tems easier to manage.The relatively longer grow-ing season usually allows ample time to plantcover crops after cash crops.

Northern Plains—Jorge DelgadoRainfall and moisture availability are the major fac-tors affecting the use of cover crops in conserva-tion tillage systems.Soils. Soils of the Northern Great Plains are

exposed to high wind conditions with enoughforce to move soil particles off site in minimumtillage conditions where soil cover is low. Cropsystems do not, in general, leave substantialresidue on the soil surface, due in part to lowannual rainfall in non-irrigated systems.Farm systems. Farms in the Northern Plains

tend to be large and can be divided into irrigatedand non-irrigated systems.Crops rotations includepotato, safflower, dry bean, sunflower, canola,crambe, flax, soybean, dry pea,wheat and barley.Cover crop species. Rye, field pea (Austrian

winter pea, trapper spring pea), sweetclover andsorghum-sudangrass are commonly grown.Cover crop benefits. Cover crop residues

improve water retention, helping to increase soilwater content and yields. Cover crops reduce winderosion and nutrient loss, and increase soil carbon.High crop residue and winter cover crops alsosequester carbon and nitrogen and increase the avail-ability of other macro- and micronutrients (7,113).Drawbacks. Rainfall amount, the availability of

irrigation and water use by cover crops are criti-cal considerations for the region.Cool,wet springweather is exacerbated by cover crop residuesthat delay soil-warming. Cover crops and conser-vation tillage often reduce cash crop yields, evenin irrigated systems (171, 172).Management. Management is key to increas-

ing nutrient use efficiencies and reduce nutrientlosses to the environment (112, 113, 114, 371).Management is also the key to increasing wateruse efficiency.

Southern Plains —Louis BaumhardtConservation tillage was first introduced for soilerosion control on the Great Plains. It followedinversion tillage that incorporated crop residueand degraded the soil’s natural cohesiveness andaggregation. Combined with the 1930’s dry andwindy conditions, this intensive tillage producedcatastrophic wind erosion known historically asthe “Dust Bowl” (26). Use of conservation tillagepractices for much of the Southern Great Plainsseems to lag behind other regions, but may beunderestimated, in part, because insufficientresidue is produced in dryland areas to qualify asconservation tillage acres.Soils. Soils of the Southern Great Plains were

formed from a range of materials including, forexample, an almost flat aeolian mantle in thenorth (Texas High Plains and western Kansas) andreworked Permian sediments of theTexas RollingPlains extending towards western Oklahoma.These soils have varied mineralogy, are frequentlycalcareous, and generally have poor structure andlow organic matter content (37). All SouthernGreat Plains soils are managed for wind erosioncontrol and water conservation.Farm systems. Farm systems on the Southern

Great Plains vary with irrigation.They are largerand more diverse as irrigation declines to distrib-ute risk and meet production requirements.Principal crops include cotton,corn,peanut,grainsorghum, soybean, and sunflower. Grain and for-age crops support the regional cattle industry.

Wheat-sorghum-fallow is a common rotationand permits cattle grazing on wheat forage andsorghum stubble (27). This and similar rotationsmay include additional years of sorghum or awheat green fallow before cotton.Cover crop species. Water governs cover

crop species selection, but wheat, rye, and oatsare most common.Wheat is commonly grown forgrain or forage and as a green fallow cropbetween annual cotton crops (29).Cover crop benefits. Cover crop residue

helps meet the 30% cover requirement for con-servation tillage, helps control wind erosion inlow residue crops, and provides other water infil-tration and storage benefits.


Drawbacks. Cover crop use in the regiondepends on precipitation or the availability andeconomy of irrigation to produce residue. Somecrops such as cotton produce insufficient residuefor soil cover, but establishing cover crops com-petes for water needed by the subsequent cottoncrop (28). Grazing crop residues and cover cropsalso limits the amount of crop residue left on thesoil surface and must be balanced against thevalue of the forage.Management. Southern Great Plains produc-

ers often use cover crops to control wind erosionin annual crops like cotton that produce insuffi-cient cover to protect the soil. During years withlimited precipitation, cover crops compete forwater resources needed to establish primary cashcrops (28). Nevertheless, producers wishing togrow cotton on soils subject to wind erosion havesuccessfully introduced residue producing wintercereal crops with minimum irrigation input.

Conservation tillage increases storage of pre-cipitation in the soil through increased infiltrationand reduced evaporation. This additional watersupplements growing season precipitation andirrigation to meet crop water needs on the semi-arid Southern Great Plains.

Pacific Northwest —Hal CollinsUnder dryland conservation tillage systems in thePacific Northwest (PNW), winter precipitationand limited water availability are major factorsaffecting the use of cover crops.With irrigation,heavy crop residues from previous grain cropscan negatively impact cover crop stand establish-ment. Annual precipitation in agricultural regionsof the PNW ranges from 15 to 76 cm, due to oro-graphic effects of the Cascade and Blue MountainRanges that strongly influence total precipitationand distribution patterns in Washington, Oregonand Idaho.Soils. Soils of the PNW have developed from

aeolian and flood deposits originating from vol-canic activity and the last continental glaciations(~12,000 years BP) under shrub-steppe vegeta-tion. Soils that developed on wind blown loessaldeposits are typically silt loams with moderate tostrong structure and soil organic C contents rang-

ing from 1-2%. Soils developing on the flooddeposits of Glacial Lakes’Missoula and Bonnevillein the Columbia Basin ofWashington,Oregon andIdaho are predominately sands to silt loams withweak soil structure and low soil organic C (<1%).Cultivated soils of the region are exposed tosevere soil erosion from water and snow melt inthe higher precipitation zones and due to highwind conditions in low rainfall areas (ColumbiaBasin).Farm systems. Farms in the dryland and irri-

gated regions of the PNW tend to be large(2,000+ acres on average). Dryland regions arecommonly cropped to wheat, barely, canola, oats,grass seed and dry peas. Crop rotations under irri-gation are diverse, vegetable based rotations thatinclude potato, onion, carrots, field corn, sweetcorn, fresh beans and peas, sugar beets, mint,canola, mustards, safflower, dry pea, grass seed,alfalfa,wheat and barley.Cover crop species. Field pea (Austrian

winter pea), sweetclover, hairy vetch, sudangrass,small grains (wheat, triticale) and a variety ofbrassica species are used in the region.Cover crop benefits. Cover crop residues

improve water retention, infiltration and storage,soil structure, soil carbon reserves, microbialactivity and crop yields.Cover crop residues havebeen shown to reduce water and wind erosionand nutrient loss from leaching and overland flowof sediments. High crop residues and the use ofwinter cover crops under irrigation sequester car-bon and nitrogen and increase the availability ofother macro and micronutrients. Cover cropresidues can meet or exceed the 30% coverrequirement for conservation tillage in low rain-fed areas.Drawbacks. Rainfall amount and distribution,

the availability of irrigation and water use by covercrops are critical considerations for the drylandregions. Heavy residues under irrigation inhibitstand establishment.Cool,wet spring weather exac-erbated by cover crop residues delay soil warmingand seedling emergence of cash crops. Absenteeland owners combined with the diversity of crop-ping under irrigation of high value vegetable crop-ping has limited adoption of conservation tillage


and cover crop use. Cover crops and conservationtillage can reduce economic benefits and cropyields under some situations.Management. Management of cover crops is

complex and differs in dryland and irrigated sys-tems. Cover crops are managed to reduce nutri-ent losses, increase nutrient use efficiencies andreduce severity of soil pathogens (88, 111, 115,430).Management is also key to increasing wateruse efficiency and can affect protein content ofsmall grains.

California —Jeffrey MitchellDespite the many benefits of cover cropping andconservation tillage, adoption by row crop pro-ducers in California has been limited.Cover cropsare used on less than 5% of California’s annualcrop acreage and conservation tillage practicesare used on less than 2% of annual cropland.Soils. A wide range of soil types are used for

agricultural production in California. Cover cropsand conservation tillage are used predominantlyon finer-textured clay loams or loam soils. Morerecently, conservation tillage is increasingly usedin dairy forage production systems on coarser soiltypes.Farm systems. Most cover crop use in con-

servation tillage systems in California has been forprocessing and fresh market commercial tomatoproduction systems (187). Research is underwayevaluating cover crops in CT corn and cotton sys-tems (281).Cover crop species. In tomato systems, the

most successful and manageable cover crops aremixtures of triticale, rye and pea.Vetches are usedfor field corn.Cover crop benefits. California farmers use

cover crops to reduce intercrop tillage, suppresswinter weeds, reduce pathogen buildup and man-age nutrients.Drawbacks. Producers are most concerned

about cooler temperatures above and belowmulch, slower maturing crops, cover cropregrowth and specialized management required.In-season weed management options may be lim-ited in conservation tillage systems.Management. Cover crops are normally

grown from mid-October to mid-March in

California’s Central Valley. Aboveground biomassproduction can reach 11,000 lb. of abovegrounddry matter/A without irrigation (279, 280).The cover crops are mowed or chopped inMarch using ground-driven stalk choppers, ormerely allowed to collapse following herbicideapplication.

Tomatoes can be no-till transplanted directlyinto the mulch or transplanted following a strip-till pass using either narrow PTO-driven rotarymulchers or ground-driven strip-till implementsmodified for tomato beds (250). Because of inad-equate weed control by the cover crop mulchitself,high residue cultivators that effectively slicethrough residues while cultivating weeds are nec-essary for in-season weed control.

Field corn has also been successfully directseeded into flail mowed vetch cover crops in theSacramento Valley. Corn yield is similar to “greenmanure”systems in which winter cover crops areincorporated.

SUMMARY AND RECOMMENDATIONS

Cover crops benefit conservation tillage systemsby:• decreasing soil erosion• providing crop residues to increase soil

organic matter• improving soil structure and increasing

infiltration• increasing availability of water for crop

production• improving soil quality• aiding in early season weed control• breaking disease cycles

To enhance the beneficial effects of cover crops:• Plant in a timely fashion.• Consider additional N fertilizer for small grain

covers only if residual N is low.• Terminate covers 2-3 weeks ahead of antici-

pated planting date to allow soil moisturerecharge and reduce problems associated withallelopathy, pests, and planter operation.

• Take advantage of equipment modificationsdesigned for tillage and/or planter operationsin heavy residue.

Managing Cover Crops Profitably Third EdiTion...editor, Andy Clark.—3rd ed. p. cm. --...

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Transcript of Managing Cover Crops Profitably Third EdiTion...editor, Andy Clark.—3rd ed. p. cm. --...