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EXTENSION

Agriculture and Natural Resources Family and Consumer Sciences 4-H Youth Development Community and Economic Development

COOPERATIVE EXTENSION SERVICE UNIVERSITY OF KENTUCKY COLLEGE OF AGRICULTURE, LEXINGTON, KY, 40546

AGR-203

Landscapes with little or no topsoil canmake it difficult to produce a garden,lawn, or other plants. opsoil, dark incolor compared to the underlying soil, isthe part of a soil that is most biologicallyactive, nutrient rich, and easily managed.It also is usually more easily worked thanunderlying soil, supplies most of theplants water and nutrients, and is gener-ally best for plant growth.

Subsoil generally contains moreclay and is usually more acidic than the

topsoil. Soils with high amounts of clayare generally sticky, cloddy, generallyhard to work, and wetter (water may notinfiltrate them quickly). Clayey soils willhold appreciable amounts of water, butthey hold it tightly, so that plants cannotreadily use as much of it as they would ina more loamy or silty topsoil. Te reasonto amend clay soils is to improve structure (you cannot easily change

the texture) infiltration/drainage plant-available water supply workability

All these improvements will reducethe tendency of clayey soils to form clods.

Soil Texture and Structure Soil texture and structure are twodifferent soil properties, both often mis-understood. Soil texture is the relativeproportions of sand, silt, and clay sepa-rates in the soil (Figure 1). Soil separatesare defined according to their size, withclay being the smallest separate (less than0.002 mm), sand being the largest (2 to0.05 mm), and silt in between (0.05 to0.002 mm). exture is hard to manipulateand rarely helps. An acre of soil to a depthof about 7 inches weighs about 2 mil lionlb, so changing textural percentage by 1%for one separate would require 20,000lb of material (1% of 2 million lb). Even

Improving the Productivity ofLandscapes with Little or No TopsoilEdwin L. Ritchey, Plant and Soil Sciences

clay

clayloam

silty clayloam

sandy

clay

sandy clayloam

loam

silt loamsandy loamloamysand

silt

102030405060708090100

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siltyclay

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For example, a soil containing 30% sand,60% silt, and 10% clay is classified as a siltloam.

Figure 1. Soil texture triangle.To determine a soils texture,

determine the percentages of sand, silt, andclay. The soil separates will sum to 100%. Forof least two of those percentages, go to theside of the triangle for a least two of the sepa-rates and follow the gray line for the percent-age point to where the lines converge.

if this change were feasible, you wouldlikely not be able to see any benefit. Forexample, adding sand to a clayey soilslightly reduces proportions of clay andsilt but does not measurably changeinfiltration or the tendency of clayey soilto form clods. Adding sand also would

slightly lower plant-available water, sincesand does not hold as much water as clay.

Soil structure is the arrangement ofthe primary soil particles (sand, silt, andclay) into aggregates, or peds. It affectssoil porosity. Soil structure is influencedby soil fauna, roots, til lage, compost, ma-

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nure, and cover crops. Structure is whatusually needs to be modified to improveproductivity where there is little or notopsoil.

o increase productivity of lawns,gardens, and landscape plants in topsoil-deficient areas, here are some options forimproving soil structure and other soil

properties:

Soil Sampling andSoil Testing

Before amending soil, take a represen-tative soil sample of the area as well asany topsoil you might plan to place overit. Te soil should be sampled to a depthof 6 to 7 inches in about a dozen placesusing a soil probe, auger, or spade (Figure2). Te sample should be hand crushedand well mixed, then submitted to thelocal county extension office or a privatesoil testing laboratory.

A sample submitted to your localextension office will be sent it to the UKRegulatory Services soil laboratory foranalysis. Te cost for the test will varydepending on the extent of analysisrequested. Results will be returned inone to two weeks and will provide infor-mation about nutrient availability andrecommendations for lime and nutrientadditions. est results typically indicatehow much phosphorus (P), potassium

(K), (calcium (Ca), magnesium (Mg), andzinc (Zn) are available in the soil and thedegree of soil acidity/alkalinity (soil pH).Tere is no soil test for nitrogen (N), sonitrogen recommendations are basedon the crop or plants to be grown andwhether the crop/plants are establishedor a new planting. For an additionalfee, soil organic matter (OM) contentcan also be determined using the samesample. For more information regardingsoil sampling, see the UK CooperativeExtension Publication Taking Soil Test

Samples(AGR-16), online at http://www.ca.uky.edu/agc/pubs/agr/agr16/agr16.pdf.

Replacing Topsoil If topsoil has been removed during sitepreparation and is still on the property,move it back to the lawn and garden area.Another option is to purchase/obtaintopsoil, though buying it may be costly.

When purchasing/obtainingtopsoil, make sure that thematerial is of high quality: freeof trash (bottles, cans, plas-tic, etc.), rocks, constructiondebris, and problem weeds.Be aware that Kentucky hasno legal definition of topsoil.

Sometimes the material beingsold as topsoil is actually lesssuitable for a lawn or gardenthan subsoil at the site. Adver-tising does not make any givenmaterial topsoil. Some materi-als removed from the top layerof another soil might not besuitable as topsoil because thesoil from the other area wasdisturbed previously and itstopsoil removed or eroded.

High-quality topsoil should

be dark brown to reddishbrown in color, not cloddy,and without excessive amounts of clayor sand. ypically, Kentucky topsoilcontains 2% to 4% organic matter. Any-thing below 1.5% organic matter is onlymarginally suitable as topsoil. Off-sitetopsoil should be tested, preferably beforepurchase, for levels of available nutrientsand content of organic matter, which isan indication of its quality.

Ideally, 6 inches of topsoil would beadded, but any topsoil addition, even if

less than 6 inches, would be beneficial.Before adding topsoil, check your site forcompaction with a tiling rod or penetrom-eter. If you suspect your site is compacted,your county extension agent can help youchoose the best option to improve it. Deepsoil disturbance may be necessary. Tebest option is to add and then incorporatethe first 2 inches of topsoil into the exist-ing soil to prevent abrupt changes in soiltexture, then add and incorporate the re-maining topsoil. With a lawn, one optionis to spread layers of new topsoil over theexisting grass, keeping those layers thin toavoid killing the lawn. Grass completelycovered by soil will be smothered anddie. Multiple thin topsoil applications overtime will slowly increase the yards topsoildepth. Its critical to spread added topsoilevenly to keep the yard from becomingtoo rough. Rake to smooth added soil ifan uneven spread occurs.

Another option is to add the desiredamount of topsoil to the existing lawn inone application, smothering the lawn andthen reseeding. Use this method whenyou want a new gra ss lawn as well astopsoil. Replacing topsoil is usually moreexpensive than improving it. For smallareas, such as garden plots and homelots, replacement may be an economi-cally feasible choice, but it becomes costprohibitive for large acreages or farms.

Building Topsoil Another option is to build topsoil,which will take several years but canbe accomplished with diligence andpatience. o build topsoil, the currentsoil surface needs to be amended with or-ganic materials. Tese materials includemanures as well as composts made fromleaves, yard clippings, and kitchen wasteswithout the meat scraps that attract pests.For more information on composting,

consult University of Kentucky Coopera-tive Extension Publication Home Com-posting: A Guide to Managing Yard Waste(HO-75), found online at http://www.ca.uky.edu/agc/pubs/ho/ho75/ho75.pdf.

Plant material generated in the gar-den or lawn should also be returned tothe soil. Be careful, however. Diseaseand insect buildup can occur when youreturn plant material to a garden if the

Figure 2. A soil auger (left), spade (center), or probemay be used to sample soils. If you are using a spade,the sample should be trimmed with a knife, as shown.

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newly planted crops are similar to whatwas there before. Rotate crop families tominimize this potential. Tese organicmaterials can be surface applied. Teydont have to be incorporated, but mixingthem into the soil is preferable becauseit will combine them and acceleratedecomposition and formation of soil

organic matter. Te incorporation willalso dilute added fresh manures, whichwill reduce odors, dilute manure salts,and encourage death of pathogens. Stabi-lized or composted manure is sometimespreferred to fresh manure. If youre usingfresh manure in a vegetable garden, it isbest to apply it 120 days before harvesting.

For lawns, topsoil can be built byreturning grass clippings and addingcomposts made from manure, yardwaste, and other organic materials. Add-ing fresh manure is not recommended in

residential settings because of odor andpathogen concerns. Wood ash can also beadded to gardens and lawns to raise soilnutrient (Ca, Mg, K) levels and neutralizesoil acidity (by raising soil pH), but woodash does not increase soil organic matter.Generally, the more organic material youcan add and incorporate into the soil thebetter, but there are limits. A good rule isto apply no more than about a half-inch oforganic material into the top 5 inches ofsoil. If too much material high in carbon(leaves, straw, or grass clippings) is added,

theres a greater chance that nitrogen willbe immobilized and you will have to addmore nitrogen to help the residue breakdown.

Careful use of fertilizer can also helpbuild topsoil and generally improve soilquality. Properly fertilized plants donthave nutrient deficiencies, grow better,and produce more of the biomass that im-proves soil structure and quality when itsreturned to the soil. A soil test will showwhat nutrients your soil needs and pro-

vide recommended application rates soyou will be better able to choose the bestfertilizer source. For example, if the soilhas an adequate supply of phosphorus,a nitrogen source such as urea (46-0-0)would be preferred over DAP (18-46-0)since DAP contains unneeded phospho-rus. Oftentimes, fertilizer products aresold as complete fertilizers containingnitrogen, phosphorus, and potassium butwith a low analysis (nutrient concentra-tion in percent N , P2O5, and K2O, suchas 5-5-5, 5-10-15, and 10-10-10). Gener-

ally, the lower the products fertilizeranalysis, the higher the unit price ($/lb)of the desired nutrients. Purchase of suchproducts makes more likely the additionof nutrients not required for optimalplant growth.

If specific fertilizer products are notreadily available, add the amount of prod-uct that delivers the amount of nutrientmost needed by the plants to be grown.Be aware that soil concentrations of othernutrients will likely increase with time, sothat at some point only nitrogen fertilizer

will be required based on plant need;other nutrients wont be needed. Prod-ucts containing only nitrogen shouldbe available at fertilizer retailers, and if

used appropriately, their use will lowertotal fertilizer costs. For more informa-tion regarding fertilizer application rates,consultFertilizer Calculations.

Cover Crops, GreenManures, and Mulch Another way to increase soil organic

matter is to use cover crops and greenmanure. Cover crops are planted duringthe off season to protect the soil fromerosion. When the cover crop is killedand incorporated into the soil, it becomesa green manure that helps maintain orincrease soil organic matter. Decayingroots leave behind soil pores for futureaeration, water infiltration, and rootpenetration by new plants. Wheat iscommonly used as a cover crop, but itshould be incorporated (killed) in earlyApril before its size becomes unmanage-able. Legume cover crops like crimsonclover or winter pea will also supplythe soil with additional nitrogen. Cropssuch as mustard greens and turnips areedible cover crops that also have deeptap roots that can penetrate moderatelycompacted soil and improve water infil-tration. Te main goal of cover croppingis to keep the soil covered with livingvegetation throughout the year.

During the growing season, mulchcan be added between plant rows in the

garden to help reduce weed pressure andwater lost through evaporation and alsoto lessen potential soil erosion. Mulchescan either be organic (plant-based)

Fertilizer Calculations

On the fertilizer label, nutrients concentra-tions are expressed in percent (%) lb of N-P2O5-K2O/100 lb of fertilizer. For example, afertilizer with an analysis of 5-5-5 contains5 lb of N, 5 lb of P2O5, and 5 lb of K2O ineach 100 lb of fertilizer. Ammonium nitrate

(34-0-0) contains 34 lb of N/100 lb of fertil-izer, or about 7 times more fertilizer/100 lbthan 5-5-5. That means it would take about the amount of 34-0-0 fertilizer to providethe same amount of N as 100 lb of 5-5-5, orabout 15 lb.

For homeowners, nutrient recommenda-tions in soil tests are often expressed in lbof nutrient/1,000 ft2of lawn or garden area,but may be reported in lb of nutrients/acre.Recommendations in lb/acre can be con-

verted to lb/100 ft2or lb/1,000 ft2(or anyother area you choose). One acre equals43,560 ft2. The recommendation conver-sion can be made by simply cross multiply-ing and then solving for the desired rate forthe desired area, as follows:

50 lb N per acre = x

=

= 1.15 lb N per 1,000 ft2

50 lb N

43,560 ft2

? lb N

1,000 ft2

50 x 1,000

43,560

Based on this calculation, we need 1.15lb of N for every 1,000 ft2of area to befertilized, but the 1.15 refers to lb of actualN, not lb of fertilizer. To determine theamount of needed fertilizer, the fertilizer

analysis must be known and, by law, thatwill be reported somewhere on the label.Using the 5-5-5 fertilizer to provide theneeded 1.15 lb N/1,000 ft2, we know the5-5-5 contains 5 lb of N/100 lb of fertil-izer. Using the conversion shown belowwe determine that 23 lb of 5-5-5 will beneeded for each 1,000 ft2of area to be

fertilized. Only 3.4 lb of 34-0-0 would beneeded/1,000 ft2.

(1.15 lb N) x (100 lb 5-5-5)

5 lb N= 23 lb 5-5-5

(1.15 lb N) x (100 lb 34-0-0)

34 lb N

and

= 3.4 lb 34-0-0

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Educational programs of Kentucky Cooperative Extension serve all people regardless of race, color, age, sex, religion, disability, or national origin. Issued in furtherance of Coop-erative Extension work, Acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture, M. Scott Smith, Director of Cooperative Extension Programs, Uni-versity of Kentucky College of Agriculture, Lexington, and Kentucky State University, Frankfort. Copyright 2011 for materials developed by University of Kentucky CooperativeExtension. This publication may be reproduced in portions or its entirety for educational or nonprofit purposes only. Permitted users shall give credit to the author(s) and includethis copyright notice. Publications are also available on the World Wide Web at ww w.ca.uky.edu.

Issued 8-2011

products such as straw, grass clippings,or shredded paper or a synthetic productsuch as plastic. Plant-based mulches areusually preferred over synthetic productsdue to cost, nutrient value, and ease ofdisposal (they can be incorporated asadditional organic matter before plant-ing a cover crop). hey also are more

environmentally friendly. Either type ofproduct will work, however.

In summary, many home-site soilsare not ideally suited for gardens, lawns,or other plants and need improvement,which usually takes time and diligence.You reap what you sow with the homegarden or lawn. Yields or productivitymight be lower initially but will increaseover time, especially if improvements are

made with care and best managementpractices are followed.

For more information on home gar-dening and lawn care consult Univer-sity of Kentucky Cooperative ExtensionpublicationsImproving Yard and GardenCare (IP-62) at http://www.ca.uky.edu/agc/pubs/ip/ip62/ip62.pdf and Homeand Vegetable Gardening in Kentucky(ID-128) at http://www.ca.uky.edu/agc/

pubs/id/id128/id128.pdf.

http://www.ca.uky.edu/agc/pubs/ip/ip62/ip62.pdfhttp://www.ca.uky.edu/agc/pubs/ip/ip62/ip62.pdfhttp://www.ca.uky.edu/agc/pubs/id/id128/id128.pdfhttp://www.ca.uky.edu/agc/pubs/id/id128/id128.pdfhttp://www.ca.uky.edu/agc/pubs/id/id128/id128.pdfhttp://www.ca.uky.edu/agc/pubs/id/id128/id128.pdfhttp://www.ca.uky.edu/agc/pubs/ip/ip62/ip62.pdfhttp://www.ca.uky.edu/agc/pubs/ip/ip62/ip62.pdf