Effect of returning straw added with straw-decomposing inoculants on soil melioration in low-yielding yellow clayey soil

【Objectives】The yellow clayey soil is a less developed paddy soil. A field experiment was carried out to investigate the melioration effect of returning straw added with straw-decomposing inoculants in low-yielding yellow clayey soil. 【Methods】 Three kinds of treatments were established: single chemical fertilizer as control, chemical fertilizer + returning wheat straw, rice straw or rape straw, and these straw returning + straw-decomposing inoculants. Crop yields, soil physical-chemical properties, proportion variation of defacement sizes of soil aggregates, the composition and combining form of soil humus were investigated in double cropping rice in Jingmen City, Hubei Province.【Results】 Both the early and late rice yields were increased with returning straw + straw-decomposing inoculants, with the highest increase of 1423.2 kg/hm2, equaling to 23.5%. Compare with returning straw only, the rice grain yields with the returning straw+ straw-decomposing inoculants was increased by 653.8 kg/hm2, or by 9.6%. In comparison to control, late rice grain yields with rape straw returning + straw-decomposing inoculants were significantly increased. The contents of soil organic matter, total N, alkali-hydrolysable N, available P, available K and the cation exchange capacity with treatment of returning straw + straw-decomposing inoculants were higher than those with the treatment of returning single straw only, but the effect in soil bulk density was opposite. Compared to CK, the percentage of soil dry-aggregates 5 mm with straw returning were increased by 3.78%-8.62%, those 0.25 mm were also increased, but those 0.25 mm were decreased. In addition, the treatment of straw returning increased the content of water soluble substance, humic acid, fulvic acid, humin and extracted humic substances in soil. The ratio of humic acid versus fulvic acid in the straw returning treatments with addition of straw-decomposing inoculants were lower than in the treatments without addition. Compared with CK, the contents of loosely, firmly, tightly combined humus and the total combined humus in the straw returning treatments were all increased, and the contents of loosely combined humus are higher relative to those of firmly and tightly combined humus, and the percentage content was over 60%.【Conclusion】 Straw returning plus straw-decomposing inoculants is effective in rice yield increases and amelioration of the tested soil. Except the soil bulk density, all the tested items are enhanced more with the treatments of straw returning plus inoculants than with straw returning only. Therefore, the addition of straw-decomposing inoculants is recommended in the low yield clayey soils for the high efficiency of straw returning practice.