Effects Of Returning Organic Materials To Field And Site-specific Nitrogen Management On Grain Yield And Quality In Rice

Returning crops straw to field is one of valid and important approaches to utilizing crops straw in agricultural production. However, there had been few researches on the effects of maize straws returning on soil nutrition and grain yield in rice field. and how to manage nutrient application under the condition of maize straw returning has not yet been clear. A long term fixed field experiment was conducted to investigate the effects of returning maize straw and organic materials made of maize straw (black carbon, compost, biogas residue) to field and site-specific nitrogen management (SSNM) on grain yield and quality in rice and their physiological mechanisms. The main results during three years were as follows:1. Returning organic materials to field had obvious effects on soil nutrition and organic matter content, and the effects varied with types of organic materials. In comparison with the control (CK, without organic materials returning), returning maize straw, compost and biogas residue to field increased to different extent for the contents of total nitrogen, total phosphorus, total potassium and organic matter before transplanting and after harvest. The effects of returning of maize straw and compost were higher than returning those of biogas residue and black carbon.2. Effects of returning diverse organic materials to field and SSNM were different on grain yield. Returning maize straw, compost and biogas residue to field significantly increased grain yield under the condition of no nitrogen (N) applied, when compared with CK (without organic materials returning), and their average yields for three years were increased by27.6%,16.7%and25.3%respectively, while returning black carbon to field decreased yield by an average of6.3%for three years. Uuder SSNM, the N rates of returning maize straw, compost and biogas residue to field were decreased by31.0%,12.7%and16.9%averagely for3years, respectively, when compared with CK, but the grain yields were increased by10.3%,13.5%and11.1%. Recovery efficiency and partial factor productivity of N fertilizer were also increased. N rate must be increased for the treatment of returning black carbon to field for achieving similar or higher yield. Under the condition of SSNM, the increase of leaf area index (LAI), grain-leaf ratio, dry matter accumulation, remobilized non-structural carbohydrate, high photosynthetic rate, and high activities of enzymes involved in nitrogen metabolism (nitrate reductase, glutamate syntheses and glutamine synthetase) and membrane lipid peroxidation enzyme (peroxidase and catalase) and low malondialdehyde content of the flag leaf after heading of returning maize straw, compost and biogas residue to field contributed greatly to the high grain yields of these treatments.3. Under the conditions of no N application or SSNM, returning maize straw, compost and biogas residue to field increased head rice rate, decreased chalk kernel percentage, chalk size and chalkiness, leading to the improvement of milling quality and appearance quality. These four treatments also increased protein content and breakdown value and decreased setback value in rice flour, and they also increased the comprehensive eating indices. These results indicated that returning these organic materials to field could improve nutrition quality and eating quality. The impact of improvement was that compost returning> maize straw returning> biogas residue returning> black carbon returning. The above four returning organic materials to field had no significant effects on cooking quality (amylose content and gel consistence). In addition, under the condition of returning organic materials, SSNM was beneficial to improve milling quality, appearance quality, tasting quality and protein content in rice.