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Using Soil Fertility Practices to Solve Problems on Your Farm Laurie Drinkwater Cornell University NOFA-VT, January 19, 2010 Soil ecology: Plant-microbe interactions Break-out session Management strategies and tools for problem solving Soil fertility has consequences at multiple levels Animal & human health Crop health, yield, food quality Arthropod community (herbivores, predators, parasitoids) Plant community (weeds) Soil management: Nutrient availability, SOM dynamics, microbial community (pathogens, competitors, symbionts, decomposers), the soil physical environment Challenges to organic nutrient management Nutrient release: Complex living and environmental processes We can only estimate the capacity of soils to provide nutrients Don’t know the amount of nutrients being added (soil amendments, N-fixation) Uncertain about the proportion of nutrients that will be released from these residues o Biological processes & dynamic soil traits Organic matter additions Increase soil life & diversity Decomposition Nutrients release Plant growth Biological processes & dynamic soil traits Organic matter additions Increase soil life & diversity Disease suppression Pore structure improved Decomposition Aggregation Humus formation Improved tilth Plant growth Nutrient release Rhizosphere = Plant-soil interface F = fungal hyphae RH = root hair M = mucigel Dense bacterial colonization Rhizosphere The rhizosphere Plant Microbes Soil o How do plants influence soil microbial community composition? Soil from a 50-year corn field + Legume and grasses commonly used as cover crops; crops grown in rotation with corn. ƒ ∆ ∆ ƒ ∆ ƒ ∆ ƒ Greenhouse-grown replacement plants in corn-soil. Corn (∆) and no plant (ƒ) treatments were used to determine the baseline microbial community. Soil microbial diversity after six weeks 200 Microbial diversity index 180 160 140 120 100 80 60 40 20 Maul and Drinkwater, 2010 So pl an t no Tr iti c al e t he a W yb ea n (d o) lfa al fa w he at bu ck s gr as Ry e It al ia n ve tc h So yb ea n co (m o. rn ) 0 Series3 Unique species Present in Corn and other plants Series2 Common in all samples (common soil microbe) Series1 Plant microbial interactions and soil fertility 1. Plants influence soil microbial community composition in a very short time frame. Decomposition ORGANIC RESIDUE HEAT CO2 PRIMARY DECOMPOSERS bacteria fungi mineralization assimilation humification HUMUS NUTRIENT RELEASE (NH4+, PO4=, SO4=) Plants and SOM decomposition soybean tripled SOM decomposition rates. soil-derived CO2 (g C pot-1 ) Wheat doubled and 12 10 6 219% 4 2 0 Cheng, W., SSSA 2002. 308% 8 100% Roots and mineralization of SOM Nitrogen cycling is TEN times greater in the rhizosphere compared to bulk soil. (Firestone, 2004) Food web in the rhizosphere: Plays a key role in delivering plant nutrients N P Ni, Pi C Ni, Pi Bacteria, fungi N o P C,N,P Grazer C,N,P Predator Clarholm, 1985; Ingham et al., 1985; Ferris, 1998, Chen and Ferris, 1999. Swarm of protozoa grazing on red fluorescent bacteria Bringhurst et al. (2001) PNAS Plant microbial interactions and soil fertility 1. Plants influence soil microbial community composition in a very short time frame. 2. Plants stimulate microbes to breakdown organic matter and release nutrients like nitrogen. 3. Grazers in the rhizosphere play a key role in releasing these nutrients to the plant. o Soil from conventional and organic plots after 18 years of management CNV ORG Aggregate Formation and Stabilization Incorporation of plant residues & roots (POM) Colonization & microbial growth Aggregate formation: trapping of POM Loss of aggregate stability Biodegradation: decline of microbial activity Modified after P. Puget-1997 Roots secrete carbon: Exudates Sugars, amino acids, enzymes o Rhizosphere microbes also secrete sticky compounds and promote aggregate formation adjacent to roots increasing drought tolerance. Rhizosphere and aggregation: lupin and wheat. Crop Aggregate stability (MWD, mm) Microbial biomass C (ug g-1) Fungal hyphae (m g-1) Active bacteria (no. x 109) Lupin Wheat 0.49 0.30 320 300 1224 310 8.1 5.8 Haynes and Beare, Soil Biol. Biochem. 29:1647-1653, 1997. 100 Fate of vetch C Free POM 75 % Root-derived C Shoot-derived C 50 25 Loss of C in particulate organic matter fraction occurs within one growing season 0 60 AT T0 about 50% of root-derived C is present as O-POM & C loss from this pool proceeds at a slower rate Occluded POM 50 40 % 30 20 10 0 Puget and Drinkwater 2001 May 12 1997 Oct 7 1997 May 18 Oct 28 1998 1998 Plant microbial interactions and soil fertility 1. Plants influence soil microbial community composition in a very short time frame. 2. Plants stimulate microbes to breakdown organic matter and release nutrients like nitrogen. 3. Grazers in the rhizosphere play a key role in releasing these nutrients to the plant. 4. Cover crops, and legumes in particular, promote aggregate formation and improve soil tilth. • Soil ecology: New understanding of plantmicrobe interactions • Break-out session – Is there a fertility-related problem or challenge you are currently facing? – Do you have an example of a soil fertility management practice/strategy that is working well on your farm? • Management strategies and tools for problem solving o • Soil ecology: New understanding of plantmicrobe interactions • Break-out session – Is there a fertility-related problem or challenge you are currently facing? – Do you have an example of a soil fertility management practice/strategy that is working well on your farm? • Management strategies and tools for problem solving o Biological community: plant growth, size and composition of soil community Nutrient cycling: N, P, S Soil organic matter Hydrology Soil structural properties: aggregation, water holding capacity, water infiltration SOIL ORGANIC MATTER CONTINUUM Easily decomposed Resistant to decomposition ORGANIC MATTER CONTINUUM Easily decomposed green manure compost Resistant to decomposition Soil Organic Matter Fractions ORGANIC RESIDUES Living Active SOM Recently dead Dead but protected Very dead (Passive) Optimizing biological N fixation Why legumes in organic systems? Legume cover crops are the primary source of new N Build SOM and improve soil health Contribute to active cycling of N and P in soil Promote aggregate formation Legumes can access P that is stored in soil and transfer it into active SOM for subsequent cash crops Nitrogen fixation is regulated by a complex set of factors Environmental Biological –Plant, microbe species –Symbiosis –Community (+ and –) –Plant-microbe-soil interactions http://www.csuchico.edu/bccer/Ecosystem Environmental factors that impact N fixation Climate and soil fertility Nitrogen availability impacts N fixation rates Phosphorus is also important. P limitation can reduce growth of N fixing plants Micronutrients are also important--Molybdenum (Mo) and cobalt (Co) are involved in biological N2-fixation pH--N fixation is inhibited in acid soils Soil aeration: N fixation is energy intensive, high oxygen demand N fixation decreases as soil N fertility increases Fixed N Soil N pool Compost N additions o Nitrogen fixation The response of N fixation to soil fertility varies, depending on availability of P and N P, other nutrients no longer limiting P, other nutrients are limiting N availability increases, N fixation is inhibited Increasing soil fertility lb N/ac from soil (for rye) or air (for vetch) Fields with greater soil fertility had reduced N fixation 120 2 low N fields 2 high N fields 80 40 v. low vetch Biomass, NDFA estimated 0 rye vetch vetch alone, alone, in mix, N from N from N from soil air air rye vetch vetch alone, alone, in mix, N from N from N from soil air air high available soil nitrogen rye vetch vetch alone, alone, in mix, N from N from N from soil air air rye vetch vetch alone, alone, in mix, N from N from N from soil air air low soil available nitrogen How do non-legumes impact N fixation? Fixed N N fix Soil nitrogen Competition for soil nutrients. How do non-legumes impact N fixation? Fixed N N fix Soil nitrogen N fixation rates on NE organic farms are greater in mixes Proportion of N coming from nitrogen fixation in monocultures versus mixes for Field Pea and Vetch on Northeast Organic Farm fields 100% 80% 60% 40% 20% 1 2 3 4 5 6 7 8 13 rye/vetch fields 9 10 11 12 mix alone mix alone mix alone mix alone mix alone mix alone mix alone mix alone mix alone mix alone mix alone mix alone alone mix 0% 13 Cowpea fixed more N when intercropped w/Japanese millet % N from fixation Total N fixed (lbs/ac) Cowpea 39 37 Cowpea + Japanese millet 72 59 Cowpea + SorgumSudan 56 26 Cover crop species Forage soybean could not compete with either grass species % N from fixation Total N fixed (lbs/ac) Forage soybean 67 88 Forage soybean + Japanese millet 82 28 Forage soybean + SorgumSudan 90 35 Cover crop species Optimizing use of legumes •Need to balance compost additions to avoid suppressing N fixation •Legumes are a great complement to compost •Mixes showed less variation across farms– good strategy •Challenging to balance weed suppression and N fixation Keep track additions and removals Tools for quick estimates of green manure nitrogen inputs Relationship between Biomass Index (% cover x height) and total N uptake for Red Clover biomass 250 200 R2 = 0.62 150 N in aboveground biomass (kg/ha) 100 50 0 0 500 1000 1500 2000 Biomass index (% cover x height cm) 2500 3000 Compost pile sampling protocol Biological processes & dynamic soil traits Organic matter additions Increase soil life & diversity Disease suppression Pore structure improved Decomposition Aggregation Humus formation Improved tilth Plant growth Nutrient release Thank-you Acknowledgements Lab group: Ann Piombino, Jennifer Gardner, Meagan Schipanski, Steven Vanek, Christina Tonitto, Julie Grossman, Burtie van Zyl, Megan Gregory, many, many field and lab assistants. We thank the many farmers who contributed to this research. Funding: USDAOrganic Program, NRI/Managed Ecosystems, NE SARE