Effects of straw addition on rice yield, soil carbon, nitrogen, and microbial community

Abstract: Crop straw has been widely applied to the field for soil fertility in recent years. Renewable resources can be fully utilized to improve the ecological environment of farmland for the sustainable development of agriculture. Taking a yellow-gluten paddy field as the research object, this study aims to explore the effects of straw addition on the soil carbon, nitrogen contents, and microbiological characteristics. A pot experiment was conducted with five treatments, i.e. CK -control without straw and biochar, ST-straw addition, SB1-straw addition with composting agent No.1, SB2-straw addition with composting agent No.2, and SC-straw biochar. Some parameters were determined, including the rice yield, soil total carbon, total nitrogen, humus component content, extracellular enzyme activity, and phospholipid fatty acid content (PLFA). Specifically, an elemental analyzer was used to measure the soil's total carbon and total nitrogen. A total organic carbon (TOC) analyzer was selected for the soil humus components. The detection kit was used to measure the activities of soil enzymes, including the leucine aminopeptidase, β-glucosidase, peroxidase, and β-cellobiohydrolase. A phospholipid fatty acid (PLFA) was used to assess the soil microbial community structures. Lipid extraction and PLFA analyses were then performed on the modified Bligh-Dyer. The results showed that the ST, SB1, and SB2 increased the rice yields (P<0.05), compared with the CK. Among them, the rice yield of SB2 increased by 55.73%, while, the ST, SB1, SB2, and SC also increased the total carbon, total nitrogen, humus component contents, and the ratio of humic acids to fulvic acids (HA/FA). However, the ST, SB1, and SB2 decreased the ratio of C/N. The soil total carbon of SC, the total nitrogen of SB2, the humus component content, and the ratio of HA/FA of SB1 increased by 31.36%, 40%, 50.01%, and 20.00%, respectively, compared with the CK. Moreover, the activities of leucine aminopeptidase, β-glucosidase, peroxidase, and β-cellobiohydrolase of SB2 enhanced by 42.38%, 69.87%, 31.99%, and 51.29%, respectively, while the bacterial, fungal, and total PLFA of SB1 and SB2 increased by 86.49% ~ 401.59%, similar to the ST, SC, SB1, and SB2 (P <0.05). In addition, the ST, SC, SB1, and SB2 significantly increased the ratio of fungal PLFA /bacterial PLFA (by 80.95% in SB1 and SB2), whereas, reduced the ratio of Gram-positive and Gram-negative bacterial PLFA (by 51.28% in SB1 and SB2), compared with the CK. It infers that the straw combined with composting agent treatment can be widely expected to improve the soil nutrient supply and ecological buffer capacity. A principal component analysis showed that the treatments of ST, SB1, SB2, and SC clustered together, totally different from CK. In summary, the straw addition can be utilized to increase the rice yield, the contents of total carbon, total nitrogen, humus acid, and soil activities of leucine aminopeptidase, β-glucosidase, peroxidase, and β-cellobiohydrolase, further to improve the soil microbial community structure, and finally to enhance the soil nutrient supply and ecological buffer capacity in the field.