Effects Of Soil Fertility And Nitrogen Rates On Grain Quality And Nitrogen Losses In A Double-Rice Cropping System

Improving the yield and quality of double cropping rice is of great significance to ensure food security in China.Improving soil fertility and nitrogen（N）rates are important ways to achieve high yield and grain quality.However,applying a large amount of N causes low N fertilizer use efficiency of rice in China while intensifying the contradiction between rice yield and quality,leading to N losses and environmental pollution.For this reason,previous authors have improved N use efficiency from several perspectives,including N fertilizer dosage,fertilizer type,and application techniques,and elucidated the effects of different soil fertility on rice yield and N fertilizer use efficiency.However,the effects of soil fertility and N rates on double-cropping high-quality rice quality and N losses in in a double-rice cropping system are not well understood.Therefore,in this experiment,four N rates treatments(0,90,150,210 kg·hm^-2,expressed as N₀,N₉₀,N₁₅₀,N₂₁₀,respectively)were set up on low-fertility（F_L）,medium-fertility（F_M）,and high-fertility（F_H）soils with the same parent material（red clay soil developed in the fourth century）to clarify the effects of soil fertility and N rates on grain quality and N losses in a double-rice cropping system,and to provide scientific basis for synergistically improve rice yield and grain quality in the double-rice cropping system,improving N fertilizer use efficiency in red soil double-rice cropping system,and scientific management of N fertilizer.The main results are as follows:（1）Both soil fertility and N rates significantly increased early and late rice yields,and both had significant interactive effects on early and late rice yields.In the early season,N₂₁₀treatment increased yield by 157.7%,156.1%and 74.1%on low,medium and high fertility soils,respectively,compared with no N rates,but the yield differences between N₁₅₀ and N₂₁₀ treatments on different fertility soils were not significant.In the late rice season,yield on low and medium fertility soils increased significantly with increasing N rates.Compared with no N rates,N₂₁₀ treatment increased late rice yield by 76.0%,65.2%and 52.5%on low,medium and high fertility soils,respectively,but yield differences between N₁₅₀ and N₂₁₀ treatments on high fertility soils were not significant.（2）Both soil fertility and N rates significantly improved the milling quality,cooking,eating quality and nutritional quality of early and late rice,and significantly reduced the appearance quality of early and late rice.Soil fertility and N rates had significant interactive effects on head rice percentage,gel consistency and consistency in early and late rice,and no significant interactive effects on chalkiness grain rate amylose content and protein content in early and late rice.In the early season,compared with No N rates,N₂₁₀treatment increased head rice percentage,by 5.8%,6.9%and 8.2%,and gel consistency by 55.0%,31.1%and32.4%on low,medium and high fertility soils,respectively,but the differences in head rice percentage,between N₁₅₀ and N₂₁₀ treatments on low and medium fertility soils were not significant,and N₁₅₀ and N₂₁₀ treatments on medium and high fertility soils were not significant.The differences in gel consistency between N₁₅₀ and N₂₁₀treatments on medium and high fertility soils were not significant.In the late rice season,the head rice percentage on both low and medium fertility soils increased significantly with increasing N rates.Compared with no N rates,the percentage of head rice on low,medium and high fertility soils increased by 11.0%,8.9%and 7.8%,respectively,and the gel consistency increased by 25.7%,24.2%and 11.1%,respectively,for N₂₁₀ treatment,but N₁₅₀ and N₂₁₀ on high fertility soils However,the differences in percentage of head rice between N₁₅₀ and N₂₁₀ on high fertility soils were not significant.The lowest rice consistency were found under F_LN₂₁₀,F_MN₂₁₀,F_HN₉₀ of early rice and F_LN₂₁₀,F_MN₁₅₀,F_HN₁₅₀of late rice treatments.（3）In both early and late rice seasons,the cumulative NH₃ volatilization on high fertility soils was significantly lower than that on medium fertility soils.Soil fertility and N rates had significant interactive effects on both NH₃ volatilization and cumulative NH₃ volatilization during the basal fertilization period of late rice.Compared with no N rates,N₂₁₀ treatment increased basal NH₃volatilization by 12.2,13.7,and 5.2 times and cumulative NH₃volatilization by 6.5,7.0,and 4.3 times on low,medium,and high fertility soils,respectively,but the differences in basal NH₃ volatilization between N₁₅₀ and N₂₁₀ treatments on low and high fertility soils were not significant,and the differences between N₁₅₀ and N₂₁₀ treatments on low fertility soils were not significant.The difference in cumulative NH₃ volatilization between N₁₅₀ and N₂₁₀ treatments on low fertility soils was not significant.The cumulative nitrous oxide（N₂O）emissions were 20.2%and 11.8%lower in the early season and anniversary,respectively,on high fertility soils than on low fertility soils.In contrast,the cumulative N₂O emissions did not differ significantly among soil fertility in the late rice season,and there were no interactive effects of soil fertility and N rates on the cumulative N₂O emissions.In conclusion,compared with no N rates,the application of N fertilizer at 210 or 150kg·hm^-2 for low fertility soil,150 kg·hm^-2 for medium fertility soil and 150 or 90 kg·hm^-2for high fertility soil could improve rice quality while ensuring high and stable yield of double-season high-quality rice,and effectively alleviate the problem of significantly increased NH₃ volatilization in red soil double-rice cropping systems under high N rates.Therefore,improving soil fertility and applying appropriate amount of N rates can improve grain quality and reduce N losses while ensuring good rice yield.