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Chemical Soil Health for Organic Production Charles Mitchell, Auburn University Alisha Rupple, University of Arkansas Heather Friedrich, University of.

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Presentation on theme: "Chemical Soil Health for Organic Production Charles Mitchell, Auburn University Alisha Rupple, University of Arkansas Heather Friedrich, University of."— Presentation transcript:

1 Chemical Soil Health for Organic Production Charles Mitchell, Auburn University Alisha Rupple, University of Arkansas Heather Friedrich, University of Arkansas

2 Surface mineral layer of the earth that is mixed with organic matter (living and non-living) that serves as a growing media for land plants Combination of biological, physical, and chemical processes, particular to regions and climates What is soil?

3 Agriculture / growing plants

4 50% Pore Space 25% Water-filled 25% Air-filled 45% Mineral Material 5% Organic Matter Three Main Soil Components


6 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)

7 Physical Chemical Biological

8 Proportion of sand, silt, and clay particles The ideal texture depends on which crop will be grown. Potatoes grow best in a sandy soil while rice grows best in clay soil. Sand: good drainage, ease of cultivation, dries easily, nutrients lost to leaching Clay: good water-holding capacity, high CEC, holds nutrients, easily compacted, poor drainage Texture CLAY <0.002mm 0 1mm2mm3mm 4mm5mm SAND mm mm SILT Soil Particle Sizes

9 Soil Texture Triangle

10  Arrangement of soil particles into stabilized aggregates  Affected by texture and organic matter content Soil Structure Soil aggregates  Soil organisms break down organic residues, producing glomalin that stabilizes aggregates  Ideal=granular or crumb


12 Resist wind and water erosion Maintain low bulk density Increased pore space Benefits of Good Structure Ease of cultivation Allows root penetration Increased water storage Better water percolation Increased aeration



15 Physical Chemical Biological

16 Cation Exchange: the replacement of one adsorbed cation by another cation free in solution CEC: quantity of exchangeable cation sites per unit weight dry soil Dependent on structure, texture, and organic matter content Greatly influences nutrient availability and retention Cation Exchange Capacity (CEC)

17 CEC in Various Soil Types

18 Exchangeable Ca 2+, Mg 2+, and K + major source of plant Ca 2+, Mg 2+, and K + Amount of lime needed to raise pH dependent on CEC (>CEC = > lime) Cation exchange sites hold Ca 2+, Mg 2+, K +, NH 4 +, and Na + ions and reduce leaching Cation exchange sites adsorb many metals (Cd 2+, Zn 2+,, Ni 2+,, Pb 2+, )that might be present in waste water. CEC and Soil Management

19 -log [H + ]; measure of acidity/alkalinity of soil Soils under field conditions vary from : range for most crops Strongly acidic soils- Al 3+ and Mn 2+ at toxic level; microbial activity reduced; Ca 2+, Mg 2+, and K + limited; fungi favored Strongly alkaline soils- Fe 2+, Zn 2+, Cu 2+, Mn 2+, and P limited; salinity toxicity pH

20 pH Effects on Nutrient Availability

21 Physical Chemical Biological

22 Ranges from 1-5% in most soils Living fraction: roots, microorganisms, soil fauna Alkaline soil favors bacteria Acidic soil favors fungi, mites, collembola Neutral soil favors earthworms, termites Non-living fraction: surface litter, dead roots, microbial metabolites, humus Greatest concentration in the top 6 inches Soil Organic Matter

23 Components of Soil OM

24 Improve soil structure by ingesting organic matter and soil and excreting stable aggregates Aerate and stir soil, which improves water infiltration and root penetration Earthworms Generally live in top 2m of soil Unfavorable conditions include: sandy, salty, arid, or acid soils; temperature extremes; presence of mice, mites, moles, and millipedes; tillage.

25 Decompose OM Mineralize and recycle nutrients Fix nitrogen Detoxify pollutants Maintain soil structure Able to suppress plant pests Parasitize and damage plants Soil Microbes USDA-NRCS Soil Biology Primer

26 Soil bacterial colonization of POM (Active C fraction of SOM) ** ** Microbes are concentrated on/near POM rather than distributed homogenously in soil ** Haynes, Adv. Agron. 85: Important to maintain actively decomposing organic material in soils

27 Decomposition of plant residue to stable soil humus Plants and Animals Decomposable Organic Residues Heterotrophic Biomass Soil Humus (50-80% of OM) Soil Surface Biologically resistant organics Microbial products Nutrients

28 Stabilizes particles together as aggregates, esp. in sandy and clay soils Decreases bulk density, providing resistance to compaction and improved porosity Improves water infiltration and retention Able to retain 20x its weight in water Improves friability, allowing for better root penetration Effect of OM on Physical Properties

29 Increases CEC Increases nutrient retention Forms stable, chelated complexes with Fe 3+, Mn 2+, Zn 2+, Cu 2+, and other cations Effect of OM on Biological Properties Provides C source and energy for soil microbes Improves microbial population and diversity Diverse, active microbial population less likely to support spread of plant pathogens Effect of OM on Chemical Properties

30 Proper use of tillage Conventionally thought necessary for weed control, to incorporate OM, and allow root growth Damages structure, lowers OM content and overall soil productivity Decreasing tillage improves soil quality and fertility No-till practices may initially decrease yields and increase fertility needs Management of Soil OM

31 Proper management of OM is a major factor in sustainable production Maintain constant inputs of organic materials to replace loses from harvest/decomposition Encourage biodiversity of plant species Management of Soil OM Bob Kremer, USDA ARS

32 Use cover crops Incorporate crop residues Avoid pests/diseases by crop rotation, proper timing of incorporation, or compost residue away from field Management of Soil OM

33 33 Maintenance of vegetative residues through cover cropping, refuge areas, buffer strips, etc not only restores organic matter but also provides habitats for natural insect predators of weed seeds Osage County, MO ‘Micro-insect’ larva attacking Amaranthus (i.e., pigweed) seed

34 Integrate livestock Distribution of OM over landscape Grazing stimulates root growth and subsequent release of C into rhizosphere soil Add animal manures Simultaneously add OM and nutrients Problems with containing/storing /transporting/applying large quantities Management of Soil OM Better for small, integrated farms Nitrogen losses through ammonification

35 Compost Size allows for uniform distribution Optimal C:N ratio Free from weed seeds (if composted correctly) Can suppress soil diseases Vermicompost- compost produced through action of worms, esp. good for small farms, gardens Eisenia foetida (red worm)- known for composting ability Management of Soil OM

36 Temperature Most effective bacteria thrive at 70°-100°F 90°-140°F- rapid decomposition >140°F- most weed seeds and pathogens killed; bacterial activity significantly decreased Aerobic conditions Require O 2 levels >5% Allows for most rapid and effective decomposition Regular mixing/turning enhances aeration Moisture content of 40-60% Excess moisture causes nutrient leaching, odor, slowed decomposition “squeeze test”- damp to the touch, with a few drops of liquid extracted with tightly squeezed Compost


38 MaterialC:N Ratio Vegetable wastes10-12:1 Coffee grounds20:1 Grass clippings12-25:1 Cow manure20:1 Horse manure25:1 Poultry litter13-18:1 Leaves30-80:1 Corn stalks60:1 Bark40-100:1 Paper :1 Wood chips & sawdust :1 Microorganisms require C for energy and N for protein Require N in a C:N ratio of 8:1 Net N mineralization- C:N ratio <20:1 Stable- C:N ratio 20-30:1 Net N immobilization- C:N ratio >30:1 Blending different materials may be necessary to obtain optimum C:N ratio C:N Ratios- important issue in composting

39 5000 lbs of wheat straw, 37%C and 0.5% N Microbes assimilate 35% of C Microbes C:N ratio is 8:1 5000lbs wheat straw X 0.37 (37% C) 1850 lbs C in straw X 0.35 (35% assimilated) lbs C assimilated lbs C = 8 = 81 lbs N (x) Lbs N 1 needed x 5000lbs= 25 lbs N in straw 81 lbs N needed- 25lbs N in straw= 56 lb N deficit 56 lbs N immobilized from soil Will N be mineralized or immobilized?

40 Good soil tilth Sufficient depth Sufficient, but not excess, supply of nutrients Small population of plant pathogens and pests Good soil drainage Large population of beneficial organisms Low weed pressure Free of chemicals and toxins that may harm the crop Resistant to degradation Resilience when unfavorable conditions occur Characteristics of a Healthy Soil

41 IndicatorBest time to testHealthy Condition Earthworm presenceWith moist soil (spring/fall) >10 worms/ft3; many castings in tilled clods Color of OMWhen soil is moistTopsoil distinctly darker than subsoil Presence of plant residues AnytimeResidue on most of soil surface Conditions of plant rootsLate spring or during rapid growth Roots extensively branched, white, extended into subsoil Degree of subsurface compaction Before tillage or after harvest A stiff wire goes in easily to 2x plow depth Soil tilth or friabilityWhen soil is moistSoil crumbles easily Signs of erosionAfter heavy rainfallNo gullies, runoff from field clear Water holding capacityAfter rainfall during growing season Soil holds moisture at least a week w/o signs of drought stress Water infiltrationAfter rainfallNo ponding or runoff; soil surface does not remain excessively wet pHSame time each yearNear neutral and appropriate for crop Nutrient holding capacitySame time each yearN, P, and K increasing or stable, but not into “high” zone Indicators of Soil Health

42 Organic Soil Fertility NCAT-ATTRA Sustainable Soil Management, pub/ pub/soilmgmt.html Soil Management: National Organic Program Regulations, Cornell Soil Health Building Soils for Better Crops, 3rd Edition SARE Resources

43 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 Arkansas Obadiah Njue, University of Arkansas at Pine Bluff Jeanine Davis, North Carolina State University Geoff Zehnder, Clemson University Charles Mitchell, Auburn University Rufina Ward, Alabama A&M University Ken Ward, Alabama A&M University Karen Wynne, Alabama Sustainable Agriculture Network Elena Garcia Heather Friedrich Obadiah Njue Jeanine Davis Geoff Zehnder Charles Mitchell Rufina Ward Ken Ward Karen Wynne

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