Effects Of Full Rice Straw Returning On Formation Of Grain Yield, Quality And Soil Nutrient In Yangfumai 5

This study was carried out from 2012 to 2015 on the Experimental Farm of key Laboratory of Crop Genetics and Physiology of Jiangsu Province in Yangzhou University. Using Yangfumai 5 as the wheat variety, the influences of full rice straw returning lasting for different years on soil nutrients, grain yield and quality, and the physiological and biochemical characteristics of flag leaves of wheat plants were studied to explore the appropriate nitrogen application ratio for achieving high grain yield and quality. This study was of importance for providing theoretical basis and technical support for the realization of high-yielding, efficient, low carbon, and environment-friendly wheat production under the conditions of full rice straw returning. The main results are as follows:1. The grain yield in the treatments of full rice straw returning lasting for 1-3 years was lower than the treatments of no straw returning. The main reason for lower yield was that there were less panicles per unit area(P< 0.01) and less grains per spike in the treatments of full rice straw returning, although 1000-grain-weight was slightly increased but inadequate to compensate for the decrease in the number of spike and grain. Compared with the treatment of no straw returning, rice straw returning lasting for 4 and 5 years slightly increased grain yield, with unnoticeable increase in spike number, grain number per ear, and 1000-grain-weight. Rice straw returning increased the contents of starch and protein. The content of wet gluten was higher in the treatments of full rice straw returning lasting for 4 and 5 years as compared with the treatment of no straw returning. However, the content of wet gluten was decreased by full rice straw returning for 1-3 years. The sedimentation readings were lowered by full rice straw returning. The contents of protein and wet gluten were kept at 13% and 30%, respectively, which were in line with the requirements of the grains of medium gluten wheat.2. Nitrogen fixation at the early stage of rice straw degradation mainly occurred from emergence to re-greening, during which the shortage of soil available nitrogen resulted in nitrogen deficiency in wheat seedlings. The release of nitrogen through straw degradation began at jointing stage (around mid-March) and became prosperous at booting. Full rice straw returning lasting for two consecutive years increased the contents of total nitrogen, organic matter, available nitrogen, phosphorus, and potassium in the plough horizon of cultivated land. The activities of urease and invertase were also increased in the plough horizon by full rice straw returning. These indicated that the soil physiochemical characteristics and fertility were improved by continuous full rice straw returning.3. Full rice straw returning had different effects on the numbers of tiller and stem, LAI, and biomass accumulation of wheat plants at different growth stages. Full rice straw returning reduced the number of tiller and stem at the stages of over-wintering, jointing, and booting, result in lowered final number of tiller and stem as compared with no straw returning. LAIs at over-wintering and jointing were lower in all the treatments of full rice returning. LAI and biomass amount were higher in the treatments of full rice returning lasting for 4 and 5 years. These indicated that LAI and biomass amount were highly dependent on the utilization of nutrients through straw degradation. Under the conditions of this study, the grain yield of Yangfumai 5 was higher than 8000 kg/hm2, LAI ranged between 6.5 and 7.5, and dry biomass accumulation after anthesis was higher than 5800 kg/hm2, occupying more than 80% of dry grain yield.4. Full rice straw returning decreased the content of chlorophyll, net photosynthetic rate, and the activities of SOD, POD, and CAT in flag leaves of wheat plants. However, the content of MDA was reduced by full rice straw returning. The proportion of nitrogen application ratio of 5:1:2:2 (the ratio of nitrogen applied before sowing, at tillering stage, jointing stage, and booting stage) significantly increased the activities of the leaf anti-oxidative system, promoted the accumulation and translocation of photosynthates, increased the efficiency of grain filling and 1000-grain-weight.5. The effects of full rice straw returning on the absorption and accumulation of nitrogen, phosphorus, and potassium in wheat plants were studied. The absorption and accumulation were closely related to the number of year of full rice straw returning. Compared with the treatment of no straw returning, full rice straw returning lasting for 1-3 years reduced the absorption and accumulation of nitrogen in wheat plants from over-wintering to maturity. Full rice straw returning lasting for 4 and 5 years reduced the absorption and accumulation of nitrogen in wheat plants during over-wintering as compared with the treatment of no straw returning, but no difference was observed in the absorption and accumulation of nitrogen between straw treatments from jointing to maturity. Similar trends were observed on the effects of straw returning on the absorption and accumulation of phosphorus. Full rice straw returning was beneficial to the absorption and accumulation of potassium in wheat plants at early growth stages. At late growth stages, the absorption and accumulation of potassium in wheat plants was negatively affected by full rice straw returning. In this study, the nitrogen application ratio of 5:1:2:2 (the ratio of N amount applied before sowing, at tillering stage, jointing stage and booting stage) was highly beneficial to the absorption and accumulation of nitrogen, phosphorus, and potassium in wheat plants.6. For Yangfumai 5 grown under full rice straw returning conditions, the planting density of 225×104 plantS·hm-2, the application amount of nitrogen, phosphorus, and potassium at 240,90, and 150 kg·hm-2, and nitrogen application ratio of 5:1:2:2 produced the best effects on wheat production.