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6583. USDA Soil Conservation Service. 1974. Soil conditioning rating indices for major irrigated and non-irrigated crops grown in the Western U.S.. Conservation Agronomy Technical Note No. 27.
This document presents a rating system to judge how various cropping systems affect soil condition over time. It assigns numerical values to various practices and totals them over a rotational sequence, with either a +, -, or neutral outcome. It is not a method for determining erosion. The concepts presented are helpful in assessing "soil quality" for cropping systems, both irrigated and dryland.
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.