Effects Of Simplified Nitrogen Fertilization On The Yield And Nitrogen Use Efficiency Of Double Cropping Rice In South China

Nitrogen is a most important and responsive nutrient for the growth and development of rice.Nitrogen management plays a key role in grain yield and quality and nitrogen use efficiency of rice.Facing problems of labor shortage,high labor cost,and low nitrogen use efficiency in rice production of China,we need to develop a more simplified and efficient nitrogen fertilization to achieve a high and stable yield in rice production.The field experiment was carried out in 2018 and 2019 in Guangzhou.In the late season of2018,eight treatments were established:no applied nitrogen(N0),three-control technology(TC),nitrogen-reduced three-control technology(RTC),and five simplified nitrogen fertilizer managements(SNM1,SNM2,SNM3,SNM4,SNM5).In the early season of 2019,six treatments were included:N0,TC,farmer’s practice(FP),and three simplified nitrogen fertilizer management(SNM2,SNM6,SNM7).The main results and findings are as follows.(1)The grain yields were significantly different among eight nitrogen management treatments in the late season of 2018.SNM2,with a 10%less N input and a reduction of 2in fertilization frequency relative to TC,had a best performance among all simplified nitrogen managements and could still maintain a same high yielding level as that of TC,but the yield components were different among them.Relative to TC,SNM2 had a larger number of grains per unit area or a larger sink size,but had a lower seed setting rate and a smaller grain weight.In the early season of 2019,the yields of SNM2,SNM6 and SNM7were increased by 3.19%,13.08%and 3.91%,respectively,compared to that of FP.Their sink size and biomass were also greater than those of FP.(2)In the late season of 2018,SNM2 had a significantly higher partial factor productivity of nitrogen(PFPN)than TC,but SNM2 was not significantly different with TC in all other indicators of nitrogen use efficiency.Agronomic use efficiency(AE),recovery efficiency(RE)and PFP were significantly and positively correlated with total nitrogen uptake or the amount of nitrogen taken up from heading to maturity.In the early season of2019,RE,AE and PFPN were significantly altered among different nitrogen fertilizer managements.The total nitrogen uptake,RE,AE and PFP_N of SNM2,SNM6 and SNM7were significantly higher than those of FP,but they were not significantly different with TC in all those indicators.AE and PFP were significantly and positively correlated with the amount of nitrogen absorbed from initial panicle differentiation to heading,and physiological use efficiency(PE)was significantly and positively correlated with total nitrogen uptake.The above results indicates that increasing total nitrogen uptake and nitrogen absorption in the middle and late growth stages is conducive to improving nitrogen use efficiency.(3)In the late season of 2018,the brown rice rate and milled rice rate of the SNM2were reduced in comparison to that of TC,but the difference was not significant.The chalky grain rate and chalkiness were significantly reduced,amylose content was increased,and grain shape was improved under SNM2.In the early season of 2019,the brown rice rate of SNM2,SNM6 and SNM7 was reduced,their milled rice rate was increased and their chalky grain rate and chalkiness were reduced in comparison to those of FP.Compared with those of TC,the brown rice rate of SNM2,SNM6 and SNM7 was reduced,the chalky grain rate of SNM2 and SNM7 was reduced,and the milled rice rate of SNM6 and SNM7was increased.(4)Among simplified nitrogen managements,the treatment with basal dressing had a significantly higher grain yield and nitrogen use efficiency than the treatment with topdressing at root recovering stage.The sink size,seed setting rate,grain weight,total dry matter weight,green leaf area index and total nitrogen uptake were all increased relatively under treatment with basal dressing.The treatment with topdressing at remaining leaf age of-2.5 had significantly higher grain yield and nitrogen use efficiency than treatments with topdressing at remaining leaf age of-1.5 or-3.5.The sink size,canopy light transmittance,total dry matter weight and total nitrogen uptake were all increased relatively under treatment with topdressing at remaining leaf age of-2.5.In comparison to the popular cultivation practice of TC in rice in Guangdong province,simplified nitrogen management with“one basal dressing and one topdressing”could still maintain high grain yield and nitrogen use efficiency when the total nitrogen input was the same or was reduced by 10%and fertilization frequency was reduced by 2.Thus it can alleviate labor shortage and has a good prospect in rice production.Topdressing at remaining leaf age of-2.5 is the best time for this simplified nitrogen management.