Crop Rotation and Residue Management Effects on Soil Carbon and Microbial Dynamics

TLDR

Microbial dynamics are key to developing management strategies that can reverse declining soil organic matter and fertility. The study aimed to assess how crop rotation, residue management, and nitrogen fertilization affect microbial biomass carbon and nitrogen and microbial group populations in long‑term winter wheat plots. Using 58‑year plots, the authors compared wheat‑fallow treatments (straw incorporated with or without N, straw burned, or straw plus manure) and annual‑crop treatments (continuous wheat, wheat‑pea rotation, or continuous grass pasture) while measuring microbial biomass C and N and microbial group counts. Annual cropping produced higher soil and microbial biomass C and N than wheat‑fallow, except when manure was applied; residue burning lowered microbial biomass to 57% of manure plots, microbial C and N comprised 4.3–2.2% and 5.3.

Abstract

Abstract Understanding microbial dynamics is important in the development of new management strategies to reverse declining organic‐matter content and fertility of agricultural soils. To determine the effects of crop rotation, crop residue management, and N fertilization, we measured changes in microbial biomass C and N and populations of several soil microbial groups in long‐term (58‐yr) plots under different winter wheat ( Triticum aestivum L.) crop rotations. Wheat‐fallow treatments included: wheat straw incorporated (5 Mg ha −1 ), no N fertilization; wheat straw incorporated, 90 kg N ha −1 ; wheat straw fall burned, no N fertilization; and wheat straw incorporated, 11 Mg barnyard manure ha −1 . Annual‐crop treatments were: continuous wheat, straw incorporated, 90 kg N ha −1 ; wheat‐pea ( Pisum sativum L.) rotation (25 yr), wheat and pea straw incorporated, 90 kg N ha −1 applied to wheat; and continuous grass pasture. 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%, respectively, 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 barnyard manure. Microbial C represented 4.3, 2.8, and 2.2% and microbial N 5.3, 4.9, and 3.3% of total soil C and N under grass pasture, annual cropping, and wheat‐fallow, respectively. Both microbial counts and microbial biomass were higher in early spring than other seasons. Annual cropping significantly reduced declines in soil organic matter and soil microbial biomass.