WSU Tree Fruit Research & Extension Center

Organic & Integrated Tree Fruit Production

Sunday, April 22, 2018

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10225. Rasmussen, P.E. and H.P. Collins. 1991. Long-term impacts of tillage, fertilizer, and crop residue on soil organic matter in temperate semi-arid regions.. Advances Agronomy 45:93-134.
Organic matter is an important soil component in semi-arid regions. Virgin grassland soils lose organic matter rapidly upon first cultivation, with the greatest decline in the first 10-20 years. A new equilibrium is usually established after 50-60 years. Long-term experiments or paired comparisons are needed to evaluate change in organic matter due to managment. Organic matter loss is greater with increasing frequency of fallow and intensity of tillage. Conservation tillage generally increases organic matter, and results from studies worldwide are presented. N fertilizer generally leads to higher organic matter, since it boosts biomass production. About 18% of the applied N at Pendleton was incorporated into the organic fraction in a wheat-fallow system. Amount of crop residue influences organic matter levels far more than type of residue. Organic matter increases linearly with increasing residue additions. Semi-arid soils can sequester from 10-25% of the C added. Many agricultural soils are not receiving sufficient C additions to prevent continued organic matter loss under current management.

10235. Collins, H.P., P.E. Rasmussen, and C.L. Douglas Jr.. 1992. Crop rotation and residue management effects on soil carbon and microbial dynamics.. Soil Sci. Soc. Amer. J. 56:in press.
Total soil and microbial biomass C and N contents were significantly greater in annual crop than wheat-fallow rotations, except when manure was applied. Microbial biomass C in annual crop and wheat-fallow rotations averaged 50 and 25%, repsectively, of that in grass pasture. Residue management significantly influenced the level of microbial biomass C; for example, burning residues reduced microbial biomass to 57% of that in plots receiving manure. Both microbial counts and microbial biomass were higher in early spring than other seasons. Annual cropping significantly reduced declines in soil organic matter and microbial biomass.

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