Effects Of Combined Astragalus L. And Rice Straw Incorporation With Reduced Inorganic Nitrogen And Potassium Fertilizer Application On Double-rice Yield And Soil Properties

In order to explore the effect of combined Astragalus L. and rice straw incorporation with reduced inorganic nitrogen and potassium application on double-rice yield and their fertilizer value, a field experiment was carried out in 2013 and 2014 to investigate the effect of combined Astragalus L. and rice straw incorporation with reduced inorganic nitrogen and potassium application on rice growth and development, nutrient uptake and utilization, soil propertiesin a double rice cropping system, and to clarify the relationship between rice growth and soil properties under combined Astragalus L. And rice straw incorporation with reduced nitrogen and potassium applications, Furthermore, the reasonable rate of chemical fertilizers under combined Astragalus L. and rice straw incorporation was determined.The main results were as follows:1. Effects of combined Astragalus L. and rice straw incorporation with reduced nitrogen and potassium applicationon rice growthTwo-year results showed that, compared to conventional fertilization(NPK), reducing 20% of N and K fertilizer application under combined Astragalus L. and rice straw incorporation(G+S-20%) increased the number of grains per panicle and the seed-setting rate, and improved the yield of early rice; it also improved the number of grains per panicle andthe seed-setting rate in late rice but reduced effective panicle number without significant effects on late rice yield. Reducing 40% of N and K fertilizer applications under combined Astragalus L. and rice straw incorporation(G+S-40%) reduced the number of effective panicles in both early and late rice, and had no significant effect on early rice yield, whereas late rice yield was less than that under NPK.Compared with NPK, G+S-20% was increase the total number of tillers and leaf area index, promoted the accumulation of dry matter, increased output rate, conversion rate and contribution rate, and enhanced the photosynthetic potential of early rice, but had no significant effect on late rice. However, leaf area index, accumulation of dry matter, and photosynthetic potential showed a declining trend under G+S-40% in both early and late rice.The net photosynthetic rate, SPAD value of leaf under combined Astragalus L. and rice straw incorporation without reduction in nitrogen and potassium fertilizer rates(GM+RS) were the highest, G+S-20% and NPK secondly, G+S-40 % minimum at the whole growth period of early rice, with the NPK treatment highest before panicle differentiation stage, but lower than GM+RS and G+S-20% after the heading stage in late rice.Combined Astragalus L. and rice straw incorporation was beneficial to increase the canopy temperature depression after heading, G+S-20% was significantly higher than NPK in early rice, but had no marked effects in late rice.2. Effects of combined Astragalus L. and rice straw incorporation with reduced nitrogen and potassium application on nutrient uptake of riceCompared with the NPK, G+S-20% increased the to uptake nitrogen, phosphorus, and potassium; but nitrogen, phosphorus, and potassium uptake under G+S-40% in early rice showed a decreasing trend in late rice. Combined Astragalus L. and rice straw incorporation significantly improved agronomic and nutrient use efficiency of nitrogen in both early and late rice. The nitrogen harvest index, recovery and physiological efficiency were not different among various treatments. The needed amount of N per 100-kg grains was in the following order: GM+RS>NPK>G+S-20%, G+S-40%, and that of P2O5 and K2 O showing G+S-20% and G+S-40% significantly higher than NPK in early rice, whereas no significant trends were observed in late rice.3. Effects of combined Astragalus L. and rice straw incorporation on with reduced nitrogen and potassium application on soil propertiesCombined Astragalus L. and rice straw incorporation was beneficial to improve soil physical properties. After 4 cropping seasons, combined Astragalus L. and rice straw incorporation significantly reduced soil bulk density, increased maximum water holding capacity, capillary water capacity, the total porosity, capillary porosity, and aeration porosity.Compared with the NPK,G+S-20% was beneficial to increase soil nutrient content, especially improving the content of soil available phosphorous and potassium; but G+S-40% showed a decreasing trend in soil available nutrient.Combined Astragalus L. and rice straw incorporation enhanced the activity of soilenzymes. Compared with the NPK, G+S-20% significantly promoted the activity of soilinvertase, cellulose, and acid phosphatases, whereas G+S-40% increased the activity of soil invertase, proteinases,and acid phosphatases, with the activity of cellulose lower than NPK.In conclusion, combined Astragalus L. and rice straw incorporation had a significant role in saving inorganic fertilizers and increasing yield. Although reducing 20% of N and K fertilizer application was also promote rice growth and development, increase the uptake of nitrogen, and improve soil physical, chemical, and biological properties. Thus, reducing 20% of inorganic N and K fertilizers under combined Astragalus L. and rice straw incorporation is appropriate at the site.