| Rice feeds about two-thirds of the population in China.High yield and high quality are the most important objectives of rice production.With the promotion of fertilizer-resistant varieties such as super rice,the nitrogen application rate of rice continues to increase,resulting in resource waste and environmental pollution problems.Therefore,the nitrogen application rate of rice needs to be further reduced.In this study,high-quality indica hybrid rice varieties Yixiangyou2115 and Fyou498 were selected as materials.In Guiyang and Meitan,Guizhou,from 2019 to 2020,Three nitrogen reduction rates(30kg/hm2 nitrogen reduction,60 kg/hm2 nitrogen reduction,no nitrogen application,denoted as N-30,N-60,N0)and Four nitrogen reduction methods(balanced nitrogen reduction,base fertilizer nitrogen reduction,tillering fertilizer nitrogen reduction,panicle fertilizer nitrogen reduction,denoted as T1,T2,T3,T4)were set up with local high-yield cultivation nitrogen(CK,180kg/hm2,base fertilizer:tillering fertilizer:panicle fertilizer is 4:3:3)as control,The rice yield and its components,tiller dynamics and spike rate,photosynthetic material production characteristics,nitrogen absorption and utilization characteristics,plant type and stem lodging resistance characteristics and rice quality variation after nitrogen reduction were systematically studied to provide theoretical basis and technical support for reasonable nitrogen reduction of rice.The main research results are as follows:(1)Under different nitrogen reduction rates(N-30,N-60,N0),the rice yields at Guiyang and Meitan ecological sites were 3.09%,9.04%,34.37%and 2.28%,12.19%,37.60%lower than those under high-yield cultivation(CK),respectively.There was no significant difference between N-30 and CK,and the variation rules among varieties were consistent.Under N-30 treatment,the effective panicle number and grain number per panicle decreased by 4.88%and 1.80%,respectively,compared with CK,and the seed setting rate and 1000-grain weight increased by 2.16%and 0.36%,respectively.The seed setting rate and1000-grain weight increased slightly under N-60 treatment,but the effective panicle number and grain number per panicle decreased significantly.The number of tillers,leaf area,SPAD value of flag leaf,dry matter accumulation,photosynthetic potential and population growth rate of rice at each growth stage showed a continuous downward trend after nitrogen reduction.Compared with CK,N-30could maintain a higher leaf area at heading stage,with an average increase of 4.58%in efficient leaf area rate and an increase in grain-leaf ratio.At the same time,the dry matter accumulation rate,ear distribution rate,apparent output rate and apparent conversion rate increased by 4.11%,8.07%,13.82%and 6.89%,respectively.Appropriate nitrogen reduction(N-30)could significantly reduce the drape of high-efficiency leaves,improve the light-receiving posture of rice leaves,and excessive nitrogen reduction(N-60)inhibited leaf growth.Nitrogen accumulation in rice decreased after nitrogen reduction,and nitrogen physiological utilization,partial productivity,agronomy utilization and absorption utilization increased.At the same time,plant height,gravity center height and bending moment decreased continuously,basal internode shortened,culm type index,culm wall thickness,internode plumpness and breaking moment increased obviously,lodging index decreased continuously.With the increase of nitrogen reduction,the brown rice rate,milled rice rate and head milled rice rate of the two rice varieties at two ecological points increased first and then decreased slightly.The chalkiness,chalkiness grain rate and protein content continued to decrease,and the gel consistency,amylose content and taste value continued to increase.Compared with CK,the head rice rate of N-30 treatment increased by 2.27%on average,chalkiness,chalky grain rate and protein content decreased significantly,gel consistency increased significantly,alkali extinction value and taste value increased by 1.91%and 1.55%,respectively.Although the appearance quality and cooking and eating quality indexes of N-60 treatment continued to improve,the head rice rate decreased.Therefore,under high-yield cultivation conditions,appropriate nitrogen reduction(N-30)can improve the comprehensive quality of rice on the basis of maintaining high yield.However,excessive nitrogen reduction(N-60)is conducive to improving the appearance quality and taste quality of rice,but it is not conducive to the improvement of processing quality and causes serious yield reduction.(2)Under the condition of different nitrogen reduction methods,the yield of two rice varieties showed T2(basal nitrogen reduction)>T1(balanced nitrogen reduction)>T4(panicle nitrogen reduction)>T3(tillering nitrogen reduction),which were 6.17%,4.94%,14.14%and 8.77%lower than that of CK,respectively,and there was no significant difference between T1,T2 and CK.Compared with CK,the effective panicle number and seed setting rate of T2 increased by 2.16%and 1.16%on average,and the grain number per panicle and 1000-grain weight decreased slightly.The effective panicle number and grain number per panicle of T1 decreased slightly,and the seed setting rate and 1000-grain weight increased by 2.16%and 0.36%,respectively,with no significant difference.The effective panicles and grains per panicle of T3 decreased significantly.the effective panicle number of T4 decreased by 2.51%,and the grain number per panicle decreased significantly.Compared with CK,T1 and T2 could maintain high leaf area and SPAD value at the filling and seed setting stage.With the increase of grain-leaf ratio,efficient leaf area rate increased by 10.31%and 8.88%,respectively.The dry matter accumulation rate,ear distribution rate,apparent output rate and apparent conversion rate at late growth stage were all increased.The drooping degree of upper three leaves decreased obviously,and the distance between flag leaves and top 2 and top 3 leaves increased in varying degrees.The SPAD value and leaf area index of flag leaf after panicle of T3 and T4 decreased significantly,and the population growth was insufficient.The drooping degree of T3 leaves increased,and the growth of T4 flag leaves was inhibited.Compared with CK,the physiological nitrogen use efficiency,partial productivity,agronomic nitrogen use efficiency and absorption nitrogen use efficiency of T1 and T2 increased,but the nitrogen use efficiency of T3 decreased generally,and most of T4 did not change significantly.Different nitrogen reduction methods improved the lodging resistance of rice.Different nitrogen reduction methods have great influence on rice quality.Compared with CK,the head milled rice rate of T1 treatment was increased,the chalkiness rate,whiteness and protein content were significantly decreased,the gel consistency was significantly increased,alkali value and taste value increased 7.04%and 1.42%respectively.The milled rice rate and gel consistency of T2 treatment increased by 3.06%and 32.25%,respectively,and the alkali digestibility and taste value increased by 1.96%and 0.49%,respectively.T3 has no significant effect on rice quality.The chalkiness and protein content of rice in T4 treatment were significantly decreased,and the gel consistency was significantly increased.The alkali dissipation value and taste value were increased by7.04%and 2.41%,respectively.The cooking and eating quality was the best,but the brown rice rate,milled rice rate and head milled rice rate were mostly significantly decreased.Balanced nitrogen reduction(T1)and base fertilizer nitrogen reduction(T2)can improve the processing quality,appearance quality and cooking and eating quality of rice on the basis of maintaining high yield.Tiller fertilizer nitrogen reduction(T3)leads to a significant reduction in rice yield.Although panicle fertilizer nitrogen reduction(T4)can significantly improve the appearance quality and cooking and eating quality of rice,it is not conducive to stable yield. |
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