Physiological Studies On Coordination Of Yield And Quality Of Japonica Rice Cultivars With Different Nitrogen Efficiency By Nitrogen And Potassium Application

Northeast China is an important commodity grain base in China and the largest japonica rice-producing area.The promotion and cultivation of nitrogen-efficient japonica rice cultivars can help improve and stabilize grain production capacity and efficiency and guarantee national food security.The promotion and cultivation of rice cultivars with different N efficiency can help improve and stabilize China’s grain production capacity and efficiency and ensure national food security.However,they often run counter to the current demand for higher rice taste due to their lower palatability quality.Therefore,how to balance the relationship between yield and quality of rice cultivars with different N efficiency is an urgent problem we need to solve now.In this study,we used a combination of field,tube,and hydroponic experiments to investigate the effects of N and K application on growth characteristics,N and K uptake and utilization,photosynthetic characteristics,grain filling characteristics,yield and quality of rice cultivars with different N efficiency,and to investigate whether it is possible to balance yield and quality by The study investigated whether the contradiction between yield and quality could be balanced by N and K application,and provided a feasible theoretical basis for improving the quality and efficiency of japonica rice in northeast China.The experiment design included（1）a field experiment on the balance of yield and quality of rice cultivars with different N efficiency by applying N and K.SN265（High-NUE rice cultivar）and MF61（Low-NUE rice cultivar）as different N efficiency cultivars,respectively,with three N supply levels of 180,225 and 270 kg hm^-2,three K fertilizer application ratios of 3:7,5:5 and 7:3 for base fertilizer and tiller fertilizer,respectively,and a total K application of 112.5 kg hm^-2.（2）A hydroponic experiment to determine the relative expression of N metabolism and K channel-related genes in seedlings of rice cultivars with different N efficiency by using SN265 and MF61 as test materials,and setting two N concentrations:low N(10 mg L^-1)and high N(80 mg L^-1).In addition,three K ion concentrations,namely low(10 mg L^-1),medium(40 mg L^-1),and high(80 mg L^-1),were set.（3）Light and efficient N application with K application during the panicle stage:SN265 was used as the test material,and K fertilizer was applied at five leaf ages with five K application levels during the panicle stage:39.38,47.81,56.25,64.69 and 73.13 kg hm^-2,and three N application levels during the panicle stage:72,90 and 108 kg hm^-2.The main results of the study were as follows:1.Differences in N and K utilization and yield of rice cultivars with different N efficiency by N and K rationingN and K application significantly affected the growth and development,N and K uptake,and yield of rice cultivars with different N efficiency.The increase in the ratio of N application to K application in the preliminary period of application significantly increased the dry matter mass,population growth rate,leaf area index,and efficient leaf area index of all organs after the booting period of rice cultivars with different N efficiency,maintained high NR and GS enzyme activities in the upper second leaf,and significantly improved K utilization.The pattern of K application rate under N180 and N₂₂₅and the High-NUE rice cultivar was the same as that of the Low-NUE rice cultivar,but the increase of K pre application rate under high N conditions had the opposite effect on the Low-NUE rice cultivar,limiting their growth and development,reducing N and K utilization,decreasing the grains per panicle and lowering the 1000-grain weight,and finally leading to yield reduction,while the effect of increasing N application rate and K pre application rate on enzymes related to N metabolism was less regular.For the High-NUE rice cultivar,the relative expressions of Os AMT1;1,Os AMT1;2,and Os NRT2.1 genes in the root system were significantly up-regulated with the increase of N and K application,and their uptake of ammonium and nitrate N was not inhibited by the increase of N concentration;for the Low-NUE rice cultivar,the relative expressions of Os AMT1;1,Os AMT1;2 and Os AKT1 genes in the root system were significantly up-regulated at high N and K levels.The relative expression of Os AKT1 genes was significantly down-regulated at high N and K levels,indicating that the uptake of ammonium and K ions by the root system was severely affected by high N and K.2.Effects of N and K application on grain-filling and quality traits of rice cultivars with different N efficiency and its correlationCompared with the Low-NUE rice cultivar,the High-NUE rice cultivar had a higher net photosynthetic rate and upper dichotomous Ru BPase activity,which enabled them to maintain higher photosynthetic efficiency during the filling period,laying a good material foundation for grain-filling,and their superior grains had greater starting growth potential,the higher filling rate of superior and inferior grains,longer active filling period,and shorter effective filling time;while the Low-NUE rice cultivar had a higher average filling rate of superior grains in the early filling period with contribution was relatively high for the superior grains and relatively large for the days and contribution of the inferior grains at the late stage of filling.Compared with the High-NUE rice cultivar,the Low-NUE rice cultivar had higher head rice rate,lower amylose content,protein content,chalkiness degree,and chalkiness percentage,more reasonable protein components,relatively higher peak viscosity,breakdown and peak time,relatively lower trough viscosity,setback,and pasting temperature.The taste value of the High-NUE rice cultivar showed a linear decreasing relationship with the increase of N application and the proportion of K pre application,and the taste value of the Low-NUE rice cultivar showed a linear decreasing relationship with the increase of N application;while the trend of the increasing and then decreasing with the increase of K pre application,and the taste value gradually shifted back with the increase of N application.The effect of superior grain grouting on brown rice rate and milled rice rate was positive,while the effect on head rice rate was negative;the effect of superior grain grouting on amylose content was greater,while the effect of inferior grain grouting on protein components was greater.Both superior and inferior grain grouting indexes had effects on taste value,but superior grains had a greater effect on appearance and hardness,while inferior grains had a greater effect on balance.3.Relationship between yield and quality of rice cultivars with different N efficiency balanced by N and K rationingThe High-NUE rice cultivar can increase dry matter weight at tillering stage,reduce group growth rate and net assimilation rate at the tillering stage and spike number,increase the initial growth potential of superior grains,increase the contribution rate at the mid-filling stage and increase the seed-setting rate,increase the growth rate at maximum growth rate to increase 1000-grain weight,increase the average filling rate and the contribution rate of superior grains at the early filling stage,and improve the balance between yield and quality.By increasing the ratio of growth rate to final grain weight at the maximum growth rate,the overall head rice rate and taste value can be improved,and the balance between yield and quality can be achieved;by increasing the proportion of K application rate under low N conditions and decreasing the proportion of K application rate under conventional N conditions,the dry matter weight,group growth rate and net assimilation rate of each part of the tiller-filling stage can be increased to obtain more spikes.Then,the balance between yield and quality was achieved by increasing the filling rate of vulnerable grains and the average filling rate in the middle of the filling period,delaying the time when the growth rate reached the maximum to improve the seed-setting rate,and reducing the contribution of the middle of the filling period to reduce 1000-grain weight.4.Effects of light and efficient N application pattern with precise K application during the panicle stage on rice yield and qualityThe application of K spike fertilizer at the 12th-leaf age significantly increased the number of effective spikes,and increased yield compared with farmers’common fertilizer（CK）,while the application at the 13th-leaf and 14th-leaf age increased the yield and1000-grain weight.The effects on yield tended to increase and then decrease as the amount of N and K applied during the panicle stage increased,with the highest yield at 91.67 kg hm^-2and 55.00 kg hm^-2of N and K applied during the panicle stage,respectively.The application of K spike fertilizer at the 10th-leaf age reduced the amylose and protein content of rice（mainly reduced gluten content）and improved the nutritional quality of rice.Different N and K ratios during the panicle stage had significant effects on the protein components,and early application（before 12th-leaf age）of K spike fertilizer significantly improved the appearance,viscosity,and balance of rice,significantly reduced the hardness,and improved the taste value by 11.08 points compared with CK.With increasing K application(above 47.81 kg hm^-2),the appearance,viscosity,and balance were reduced and the taste value decreased.Taste value tended to decrease significantly with increasing N application.There was no synergistic correlation between yield and quality with the application of K fertilizer to the spike before the 12th-leaf age,but there was a synergistic effect between yield and quality with the application of K fertilizer after the 13th-leaf age,and some indexes reached positive correlation on yield and quality.