Influence of management practices on soil organic matter, microbial biomass and cotton yield in Alabama's “Old Rotation”

摘要

The “Old Rotation” cotton experiment was designed to aid farm managers in implementing rotation schemes that not only increase yield, but also improve soil quality. Six different crop rotation treatments were imposed since 1896. Rotations were: IA, cotton (Gossypium hirsutumL.) grown every year without a winter legume and without N fertilization; IB, cotton grown every year with a winter legume and without N fertilization; IC, cotton grown every year without a winter legume and with 134 kg N as NH4NO3ha-1year-1; IIA, 2-year cotton-corn (Zea maysL.) rotation with a winter legume and without N fertilization; IIB, 2-year cotton-corn rotation with a winter legume and with 134 kg N ha-1year-1as NH4NO3; and III, 3-year cotton-corn- alternating soybean Glycine max(L.) Merr. or rye (Secale cerealeL.) rotation with a winter legume and with 134 g N as NH4NO3ha-1year-1. Crimson clover (Trifolium incarnatumL.) was the winter legume cover crop. The 2-year cotton-corn rotation with a winter legume and with 134 kg N ha-1year-1(IIB) and the 3-year cotton-corn soybean/rye rotation with a winter legume and with 134 kg N ha-1year-1(III) had higher amounts of soil organic matter, soil microbial biomass C and crop yield than the other four treatments. The cotton grown every year without a winter legume or N fertilizer (IA) had a lower amount of soil organic matter, soil microbial biomass C and N and cotton seed yield than all other rotations. In 1988 and 1992 cotton seed and legume yield were correlated in positive, curvilinear relationships with soil organic matter (r2ranged from 0.72 to 0.87). In most months, soil microbial biomass C and N was lower in the cotton grown every year without winter legumes or fertilizer (IA) than the other five rotations. In 1994, microbial biomass C and the Cmic:Corgratio correlated in positive, curvilinear relationships with seed cotton yield (r2=0.87 and 0.98, respectively). After 99 years of management the “Old Rotation” cotton experiment indicates that winter legumes increase amounts of both C and N in soil, which ultimately contribute to higher cotton yields. Microbial biomass C and the Cmic:Corgratio are poor predictors of annual crop yield but may be an accurate indicator of soil health and a good predictor of long-term cro