Effects Of Returning Maize Straw To Field On CO₂ Efflux, Carbon And Nitrogen Fraction In Farmland Black Soil

The decomposition of crop residues is a major determinant for carbon balance and nutrient cycling in agroecosystem. It’s of great significance for soil carbon sequestration and nutrient management research to ascertain the decomposition characteristics of straw in soil and its influencing factors. To investigate the effects of different parts maize straw chemistry(C/N and lignin concentration) and soil texture on CO2 efflux and microbial biomass in black soil, we did an incubation experiment with controlled conditions of temperature and water content. Furthermore, a field mesocosm experiment had been conducted to study the decomposition of maize straws derive from two conventional varieties(Xianyu335 and Liangyu99) under different returning ways(located in soil surface and incorporated in soil) and its effects on CO2 efflux, carbon and nitrogen fraction in farmland black soil.Result of incubation experiment shown: Different maize straw parts have various C: N ratio and lignin content, and their decomposed rate is different either. The higher C: N ratio or lignin content in roots and upper stem caused lower decomposed rate with lower CO2 efflux, priming effect value and microbial biomass in maize straw-amended soil than its lower stem and leaves. The differences in straw decomposition and CO2 emission with the addition of residues to soils were primarily ascribe to the different lignin/N ratio in the different maize parts. Except for leaves, CO2 emission rate, CO2 efflux and priming effect value were significantly higher in clay loam soil amended with maize straw than sandy loam soil. It’s indicated that clay protection is not the main reason for the different decomposition rate of maize straw in clay loam and sandy loam soil, while soil nutrients like available nitrogen concentration is the limiting factor for maize straw decomposition. The augmenter of microbial biomass in sandy loam soil was greater than that in clay loam soil, but the total dissolved nitrogen was lower. The maize residues added into the sandy loam soil texture could enhance carbon sequestration, microbial biomass and nitrogen holding ability relative to clay loam soil.Result of field mesocosm experiment shown: Conventional breeding had a significance influence on maize straw chemistry, and in turn had an effect in residue decomposition and carbon sequestration. Compared with Liangyu99, Xianyu335 straw have higher C: N ratio, aryl-C content, and lesser alkyl-C, carbonyl-C tends to decompose more slowly, and caused higher straw residual rate, and also increased more carbon storage in soil. Hence, maize breeding or selection appears to be an effective method to increase soil carbon storage, when straw returned to field. Stalk returning approaches had significant effects on soil water and thermal conditions, straw decomposition, soil carbon and nitrogen fraction. Compared with incorporated in soil, maize straw located in soil surface tends to decompose more slowly with higher straw residual rate, C: N ration and lower nitrogen content. Straw mulching also stimulated original soil organic carbon decomposition, and therefore influence carbon and nitrogen fraction of black soil. The soil organic carbon, total nitrogen, microbial biomass carbon and total dissolved nitrogen concentration were higher in soil with straw mulching than soil incorporated with straw. Regardless the undecomposed residues located in soil surface are likely to underestimate the effect of no tillage on carbon sequestration in black soil. So, it’s need to reappraisal the effects of conservation tillage, especially no tillage, on carbon sequestration in black soil based on the amount of undecomposed residues and soil organic carbon storage.