Assessing and Supplying Fertilizer Needs Under Organic Systems

M. Elena Garcia, ProfessorHorticulture Dept.

University of Arkansas

Conventional vs. Organic Plant Nutrition

Fundamental principles the same, whatever the production system used:Conventional systems: Relies on targeted short-term solutions

ReactiveApplication of soluble fertilizers

Plant Nutrition in Organic Systems

Organic systems: Long-term solutions and ecological approach

Preventive not reactiveWork within natural systems and cyclesMaintain or increase long-term soil fertilityUse renewable resources as much as possibleManagement of soil organic matter (OM)Rotation design for nutrient cycling

Organic Fertilizers

Naturally occurring materials of biological or mineral origin and are low in nutrient concentration or solubility or have both propertiesMay be altered physically in processing for agricultural use, but chemical processing does not usually occur

(Baker, 2010)

Advantages and Disadvantages of Organic Fertilizers

Advantages

Mild, non-caustic materials Slow release makes them available for longer time If high OM content = improvements in soil physical properties Sources of many essential elements Recycling of materials

DisadvantagesLow concentration of nutrients = large application Slow release may not supply plant’s immediate needsConcentration may be too low to supply plant’s needsExpense

Conventional vs. Organic Plant Fertilizers

Difference between organic and synthetic fertilizers:

Not in the kind of nutrients supplied but, Rate of release

Generally: Organic fertilizers release nutrients slowly and in response to environmental factors such as soil moisture and temperature

Organic Regulations

Organic regulations require growers to rely on the use of manures, cover crops, crop rotations, and the use of untreated products

Organic Horticulture Systems

IntensiveHigh dependency on imported nutrientsCrops have high demand for major and minor nutrientsUsually several crops within one growing seasonCrop rotation difficult in perennial systemsSoli fertility maintenance major concern

The Fertility Equation: SoilThe ability of the soil to supply nutrients needed for plant growth.

Recognize: physical, biological, and chemical components

these are interrelated.

Soil Quality

Capacity of a soil to function within ecosystem boundaries to:Sustain biological activityMaintain environmental quality Promote “plant health” It is not a soil propertySoil health = soil quality

Soil Health

Physical Chemical

Biological

Overlapping of the physical, chemical, and biological properties

• General picture of soil’s capacity to support plant growth without degradation… sustainability

Ability of Soils to Supply Nutrients

Soil textureSoil chemistrySoil moistureSoil tilth Soil aeration

Soil Organic Matter (SOM)

Organic matter will prevent deterioration of the physical properties of the soil by serving as an energy source (i.e. food) for microorganisms which promote stable aggregation of the soil particles.Essential nutrients are obtained by plants as organic matter decomposes

Using Organic Amendments to Improve Fertility

Organic amendments increase OM content in soil

OM increases CEC, increasing nutrient storage capabilities

OM supplies plant nutrients

OM improves buffering capacity (stabilizes pH)

OM promotes/aides beneficial microbial populations

Types of Organic Amendments:– Animal Manure– Cover Crops– Crop residues– Yard debris– Biosolids

Plant Available N

Knowing total amounts of N-P-K does not tell how much is available

Manure: total N is ~ 25-40%Available N in compost is < 10% (stabilized from)

Plant Available Nitrogen (PAN) from Amendments ( Gale et al)PAN (%)

Amendment C:N NH4-N (g kg-1 Field Lab

Dry broiler litter 9 6.3 41 45

Composted dry broiler litter

9 7.3 38 45

Composted chicken litter

8 5.6 47 25

Yard-trimmings 13 3.0 19 25

Composted yard trimmings

17 0.7 3 5

Bio-Gro pelleted fish byproduct

5 1.1 77 57

Feather meal 4 2.0 99 74

On-farm compost 15 0.1 6 4

Composted rabbit manure

27 0.1 -6 -7

SOM, pH and Buffering Capacity

SOM has ability to moderate major changes in pH

Soil pH is determined by amount of positively charged H ions (H+) in the soil solution

OM buffers the soilMaking H+ more constant Taking and releasing H+

Pre-Plant Preparations Soil analysis must!!Adjust pH prior to planting.

Difficult to change pH after establishment.Addition soil amendments prior to planting.

Generally, fruits crops do not respond P applications after establishment.

Cover Crops

• Grasses or legumes grown in pure or mixed stands

• Planted after harvest of primary crop, as a fallow crop, or interplanted with primary crop

• Can be incorporated into soil or left on surface as residue

• Sometimes referred to as green manure, catch crop, or living mulch depending on purpose

• Benefits:– Reduced soil erosion– Improve soil structure– Suppress of weeds,

insects, and diseases– Enhance soil fertility

• Increases OM content• Retention of nutrients • Prevention of

leaching losses• Increases N content• Greater diversity of

soil microbes

Crop Residue

• Portion of plant remaining after harvest left on soil surface

• Widely used method of maintaining OM

• May be partially incorporating at planting time

• Can harbor disease and insect pests– May be avoided by: crop

rotation, removing residue to compost it, or proper timing of incorporation

• Benefits:– Increases OM

content– Increases soil

aggregation– Prevents soil

crusting and erosion– Improves water

infiltration rates– Provides nutrients

Mulches

Helps keep soil cool in summerHelps retain soil moistureAdds organic matter, helps in nutritionImproves soil structureHelps reduce weed pressureIncreases soil water holding capacity

Tillage Effects on Fertility

• Purpose:– Prepare seedbed– Control weeds– Break up traffic pans &

soil compaction– Incorporate crop residue

• Tillage and cultivation practices should be implemented that maintain or improve soil health and minimize soil erosion.

• Negative effects of conventional tillage on fertility:– Destroys soil organic

matter– Decreases diversity

and populations of soil microbes and earthworms

– Decreases water infiltration rates

– Increases compaction

Effect of pH and Element Availability in Mineral Soils

organicgarden.org.uk/?page_id=2387

Nutrient Budgets

Commonly used to evaluate the effects of nutrient management on farm and field sustainabilityAre the outcome of a simple accounting process that tracks inputs and outputs to a given, defined system over a fixed period of timeUseful when accounting for renewable resources in production and processing as a way to avoid pollution and waste.

The Nutrition Equation

Balancing Act

Soil

Plant needs

The Fertility Equation: Plant Demand

Plant healthAbility of root system to absorb nutrients

Soil typepHSoil water content

Ability of plant to utilize nutrients

Physiological stageCrop loadWeed control

Essential Elements

16 elements are classified as essential for all cropsTwo criteria are used to establish the essentiality

If the plant fails to grow and complete its life cycle without this elementConstituent of a necessary metabolite b

Law of the Minimum

Justus von Liebig, generally credited as the "father of the fertilizer industry", formulated the law of the minimum: if one crop nutrient is missing or deficient, plant growth will be poor, even if the other elements are abundant.

Essential Elements

From air Carbon: CO2

Hydrogen: H2OOxygen: H2O and O2

Plant Needs for Growth and Development

MacronutrientsNitrogen: NH4

+,NO3-

Phosphorus: H2PO4-, HPO4

2-

Potassium: K+

Calcium: Ca++

Magnesium: Mg++

Sulfur: SO42-

Plant Needs

Micronutrients:Iron, Zinc, Manganese, Copper, Boron, Molybdenum, Chlorine, Silicon, Sodium, Cobalt, Vanadium essential to some plants

Role of Mineral Nutrients

Mineral nutrients affect crop quality and yield

DirectIndirectN excess over stimulates growth:

Fruit often softer, does not store as wellShading causes loss of color in fruit

Flow of Nutrients into Plant

Simplistic viewXylem transports water and mineral nutrients from roots to the rest of the treePhloem transports leaf-assimilated compounds through the stems to roots

Mature leaf

Fruit

Roots

xyle

m

Phlo

em

Nutrient Movement from Soil to Plant

Mobile vs. immobile elements

Ionic Form

Soil Mobility Plant Mobility

N NH4+NO3-

ImmobileMobile

ImmobileMobile

P H2PHO4- -Immobile ImmobileK K+ -Immobile MobileS SO4- Mobile MobileCa Ca+ Immobile -- ImmobileMg Mg++ Immobile MobileB H3BO3 Mobile --ImmobileZn Zn++ --Immobile ImmobileCu Cu++ --Immobile ImmobileMn Mn++ --Immobile ImmobileMo MoO4- Immobile Immobile

Monitoring Mineral Nutrition

Knowledge of:Site/soil characteristics and chemistryPlot design requirementsPlant physiological stagesFertilizer inputsCultural practicesTissue analysisObservation and judgment

Nutrient Status Limitations

CropRootstockVarietySoil depthRoot distributionSoil water statusTemperature Crop loadSoil pestsSoil Chemistry / nutrient availability

Nitrogen Utilization

Tagliavini, et al. 2000

Phosphorous Utilization

Tagliavini, et al. 2000

Interactions

N: Too much = Poor fruit qualityToo much N may create nutrition imbalancesN deficiencies common in organic orchards during establishment years

K: Pre-planting applicationsDepletion commonAdding K without Mg can create Mg deficiencies

P: Pre-plant application very importantToo much P can create Zn and Cu deficiencies

Diagnosing Nutritional StatusSoil analyses: Tell what is in the soil– pH, OM

Limitations: Sampling

TimeDepth

Foliar analyses: Tell what is actually in the plantLimitations:

SamplingTimeCondition of sample

Soil vs. Foliar Analyses

Many studies show poor correlation between soil tests and leaf analyses in orchards

Deep rooted Accumulation of nutrients through out the year

IMPORTANT TO DO BOTH ON A REGULAR BASIS!

Ground vs. Foliar Application

The most efficient way to apply nitrogen, phosphorus, potassium, and magnesium is by ground application. Foliar applications of these elements should be viewed as temporary or emergency solutions only. Boron, zinc, copper, and manganese can be added by either foliar or ground application. The foliar method is usually preferred because very small amounts are applied per acre.

Sources for Organic Fertilizers

Sources of Organic Fertilizers, and amendmentshttp://attra.ncat.org/attra-pub/orgfert.php

How to convert an inorganic fertilizer recommendation into an organic one

http://pubs.caes.uga.edu/caespubs/pubs/PDF/C853.pdf

crops_generic.pdfhttp://www.omri.org/

Acknowledgements

This presentation address general organic production practices. It is to be to use in planning and conducting organic horticulture trainings. The presentation is part of project funded by a Southern SARE PDP titled “Building Organic Agriculture Extension Training Capacity in the Southeast”Project Collaborators• Elena Garcia, University of Arkansas CES

Heather Friedrich, University of ArkansasObadiah Njue, University of Arkansas at Pine BluffJeanine Davis, North Carolina State UniversityGeoff Zehnder, Clemson UniversityCharles Mitchell, Auburn UniversityRufina Ward, Alabama A&M UniversityKen Ward, Alabama A&M UniversityKaren Wynne, Alabama Sustainable Agriculture Network