Cover Crops and Biofuels

Implications for Soil Characteristics and Plant Development

Deanna Boardman October 21, 20091Outline IntroductionOverview of residue removal for biofuelsEffect on Soil CharacteristicsEffect on plant developmentWhat cover crops can add to an agricultural system with residue removedConclusion

2IntroductionCurrent pace of nonrenewable fuel consumptionRenewable energy sourcesPlant biomassAgricultural biomassesTraditional principle crops vs. energy cropsGrain vs. residuesCorn residue is the single largest source of cellulosic agricultural biomass in America (Reddy & Yang, 2005)3IntroductionResidue removal affects soil characteristics and subsequent crop developmentDegree of change is dependent on the incorporation of other agricultural practicesprimary crop rotationresidue removal rateincorporation of cover cropnitrogen rates applied to principle crop4How can cover crops affect soil characteristic changes associated with residue removal? 5Soil Characteristics Affected by Residue RemovalResidue management influences soil quality and crop productivityStages of decompositionCycle interruption32 year study by Bianca et al. (2008) focused on residue management and tillage, drew two major conclusions:Tillage results in more dramatic changes to soil properties than harvesting of residues Stover harvest is feasible under a no-till practice. 6ErosionProvides protective barrierPrevent direct sunlight, affects temperature and moistureReduce wind velocity near surfaceIntercept impact of rainfall Reduces transport of water and soil from field, increasing infiltrationRunoff results in loss of nutrients

7Soil MoistureMost important factor essential to plant growth is water Evaporation and runoff primary mechanisms of water lossPonding will result in further infiltrationBianca et al. (2008) showed in a long term no till study, soils with complete residue removal had 8% less available water content than residue remaining.

8Soil CrustingCrusting results from the impact of raindropsRearrangement of particles into open soil spaces Low porosity for water to infiltrate Restricted seedling emergence and plant growth9Organic MatterImportant for: soil structurewater permeability microbial activityNutrient source traditionally recycled and utilized Approximated two-thirds corn residue can be removed without causing harmful results on organic matter content32 year study of soils with 100% residue removal had only 8% less organic matter

10Bulk DensityMass per unit volume for the soilResidue naturally degrades and incorporates into the soilSoil gradually increases in bulk density with residue removalA study found complete removal resulted in 6-13% greater densityDenser soils create challenges to root expansion and reduces pore space11Effects on Plant DevelopmentHow does soil changes affect principle crop development? Emergence and other growth phasesChlorophyllStalk stabilityChemical composition100% residue removal resulted in a 23% residue biomass reductionGrain yield decreased by 21%12Cover Crops Biomass compensation for residue removedCan help to minimize the soil changes associated with corn residue removalLegumes vs. non-legumesN fixation vs. catchAdds mulch for soil coverage

13Cover Crops - Organic MatterDecrease bulk densityImproves soil structureAggregatedLow densityHigh porosityEnhances biological activity and transmittance of water, gases, and nutrients

Cover Crops Nutrient SourceOrganic nutrients mineralize relatively quickly Replaces N fertilizer neededAs much as 2/3 N needed in cornRelease depends on C:N ratioRedistribute nutrients to surface to become plant available

15Cover Crops Soil CoverageIncreases infiltration and soil moisture contentReduces evaporation and run-offIntercept rainfallReduce wind velocityPrevent direct sunlightReduces crustingCover Crops Soil Coverage Reduces soil temperature, up to 10o C Depends on reflectivity and massBeneficial during heat stressUnfavorable during cool spring, can result in irregular/delayed emergence and lower populationsPoor coverage of soil and seed-soil contact

Cover Crops Misc. BenefitsPest cycles can be disruptedChemical N reduces pH, cover crops do notSuppress weedsProtect water qualityConclusionResidue removal influences soil characteristics and plant developmentImportant to evaluate management practices to minimize the effects of removalTransformations due to revolutionizing agricultural practices are inevitable19