Influence of Straw Incorporation Rates on Soil Stoichiometry, Microbial Biomass, and Enzymatic Activities in Dryland Wheat Fields of the Loess Plateau, Gansu

Understanding how straw incorporation affects soil stoichiometry and biochemical processes is essential for improving soil fertility in dryland wheat systems on the Loess Plateau. We quantified effects of four wheat straw return rates [0 (W0), 3500 (W1), 7000 (W2), and 14,000 kg ha−1 (W3)] on C-N-P stoichiometry, microbial biomass, active carbon fractions, and enzyme activities in a randomized block experiment in Dingxi, Gansu. Composite soil samples from 0–10, 10–20, and 20–30 cm were analyzed for soil organic carbon (SOC); total nitrogen (TN); total phosphorus (TP); microbial biomass C, N, and P; dissolved, particulate, and readily oxidizable organic C; and sucrase, urease, alkaline phosphatase, and catalase activities. Increasing straw input significantly increased SOC, TN, and TP across all depths, with W3 increasing them by up to 42, 33, and 24% relative to W0, respectively. Under W3, microbial biomass C and N more than doubled, and labile C fractions and enzyme activities increased by 35–80% compared with W0. Straw return also modified soil and microbial C:N:P stoichiometry, decreasing microbial C:N and C:N:P and increasing N:P, suggesting alleviated N limitation. Overall, moderate-to-high straw incorporation improved soil fertility and functioning, supporting straw return as a sustainable management practice for Loess Plateau drylands.