[Effects of Straw Return and Planting Density on Soil-microbe-plant Leaf Carbon to Nitrogen Ratio and Homoeostasis]

The aim of this study was to investigate the effects of the interaction between straw return to the field and planting density on the soil, microorganisms, carbon-nitrogen stoichiometric characteristics of maize leaves, and internal stability. This study provides a reference basis for formulating reasonable farmland management measures in the Ningxia Yellow River Irrigation Area. Since 2016, a field positioning experiment has been conducted at the Wanghong base in Yongning County, Ningxia Academy of Agricultural and Forestry Sciences, using a spilt-plot experimental design. The main plot consists of straw returning modes, including no straw return (H0) and complete straw crushing and deep plowing return (H1). The subplot is planting density, which includes: 67 500 plants·hm^-2 (D1), 82 500 plants·hm^-2 (D2), and 97 500 plants·hm^-2 (D3). In 2022 and 2023, the ecological stoichiometric characteristics of soil, microorganisms, and corn leaves, as well as the stoichiometric homeostasis index (H), were explored. The results indicate that H1 significantly increased the soil microbial biomass carbon, nitrogen, and carbon-nitrogen ratio 47.51%, 31.98%, and 10.71% compared to those of H0, respectively. The soil microbial biomass carbon, microbial biomass carbon-nitrogen ratio, and leaf organic carbon in D1 were increased by 20.17%-37.50%, 10.21%-12.26%, and 7.83%-18.25% compared to those of D2 and D3, respectively. Among them, compared with that of H0D3, H1D1 significantly increased the soil organic carbon, total nitrogen, microbial biomass nitrogen, and microbial biomass carbon-nitrogen ratio by 25.83%, 18.78%, 61.05%, and 25.04%, respectively. The results of the internal stability model fitting showed that the leaves were most sensitive to the input of exogenous nutrients. The straw return model helped enhance the internal stability of carbon and nitrogen in the leaves, and under D1 density, the internal stability of carbon in the leaves was stronger. Principal component analysis revealed the comprehensive score ranking for each treatment: H1D1 > H0D1 > H1D2 > H0D2 > H1D3 > HOD3. Comprehensive analysis showed that the combination of the straw return model and planting density of 67 500 plants·hm^-2 in the irrigation area of Ningxia could effectively improve the ecological stoichiometry and internal stability of farmland soil, microorganisms, and maize leaves.