Effects Of Potassium Application Rate On Grain Yield,Potassium Absorbtion And Utilization,and Quality Of Rice

Rice（Oryza sativa L.）is a staple food for over half of the world’s population.In recent years,in order to meet the gradually improving quality of life,the demand for high-quality rice has been further expanded,and the production of rice with high quality and high grain yield as the main goal has become a major feature of rice cultivation in the new era.Scientific fertilization is one of the important ways to improve rice yield and optimize rice quality.Potassium（K）is one of the most important elements in the growth process of rice.Adequate K supply is beneficial to promote the growth of rice,increase the accumulation and transport of photosynthate,and provide sufficient material basis for rice grain filling,thus greatly improving its yield.In addition,potassium has the effect of improving the quality of agricultural products,so it is also known as the"quality element".Previous studies have proposed the methods to determine the appropriate amount of K application for rice based on the optimal rice yield or optimal economic yield,characteristics of K uptake in rice,and the recommendation of fertilizer application by region in combination with soil physical and chemical properties.However,with the improvement of living standards,the fertilization technology of coordinating the combination of high quality and high yield and comprehensively considering the sustainable development of the environment is also emerging.It is particularly important to determine the appropriate K fertilizer application rate for coordinating the high quality and high yield of rice.2 years field experiment were conducted in this paper,to study the effects of different K application rates on the yield,the K uptake and utilization,and the quality of rice.In order to provide a theoretical basis for the rational application of K fertilizer in rice production in the new period,a suitable dosage of K fertilizer based on the main rice quality indexes and considering the yield was put forward.The main results are as follows:（1）Potassium fertilizer application increased rice yield by promoting the accumulation and transport of non-structural carbohydrates（NSC）in the vegetative organs in pre-anthesis.Compared with no K application,the rice yield of Xiadao No.1 and Shenliangyou 5814 was increased by 30.7%-88.4%and 14.0%-44.2%,respectively.The four yield components of rice were all affected by the K application rates.Correlation analysis showed that rice yield had the highest correlation coefficient with seed setting rate（R²=0.76）,followed by grain number per panicle and 1000-grain weight.Compared with no K application,the accumulation of NSC in vegetative organs（leaves,stems and sheath）of Xiadao No.1 and Shenliangyou 5814 increased by 18.7%-84.9%and 18.3%-38.8%,respectively,indicating that K application significantly increased the supply capacity of"source"needed for grain filling.On the other hand,potassium fertilizer application promoted the development of vascular bundles,increased the number of large and small vascular bundles in the neck of panicle,and facilitate the transport of NSC stored in vegetative organs（leaves,stems and sheath）to reproductive organs（grains）,thus providing sufficient material basis for grain filling,increasing grain weight,seed set rate and grain yield.（2）Potassium fertilizer application increased the rate of K absorption and shortened the duration of rapid K accumulation.With the advancement of growth process,the uptake of K in the shoot of rice increased gradually,showing a"slow-fast-slow"growth trend.The period from tillering stage to heading stage is the period of rapid K accumulation in rice,during which the proportion of K uptake accounted for 56.7%-76.5%of the maximum K uptake.Compared with no K application,potassium application significantly increased K accumulation and K accumulation rate at each growth stage,delayed the start time of K rapid accumulation by 2.5-9.8 d,and shortened the duration of K rapid accumulation by0.3-9.2 d.Potassium application significantly increased the K content of straw,but it did not affect the K content of grain,so the K absorbed by rice was mainly distributed in straw.With the increase of K fertilizer application rate,the contribution rate of K fertilizer to yield increase,K use efficiency for dry matter production and grain production decreased.In conclusion,K application can increase K uptake,but reduce K use efficiency.In actual rice production,K fertilizer should be used rationally according to the requirement of K in rice.（3）Potassium fertilizer application significantly improved rice milling quality,appearance quality and eating quality.Compared with no K application,the brown rice rate,milled rice rate and head rice rate of Xiadao No.1 and Shenliangyou 5814 increased by1.1%-3.9%and 0.4%-2.7%,0.3-4.4%and 0.8%-4.7%,3.1%-8.5%and 2.0%-3.8%,respectively,and the processing quality of Shenliangyou 5814 was better than that of Xiadao No.1.With the increase of K application,the chalky percentage and chalkiness decreased significantly,while the length and width of head rice increased significantly,and the appearance quality of rice was better.Potassium application significantly decreased the total protein content and gliadin content of Xiadao No.1 and Shenliangyou 5814 white rice,and increased the amylose content,and increased the taste value of rice by 1.9-13.5 and5.1-9.2,respectively,with the increases of 7.3%-22.8%and 2.7%-14.3%,respectively.Potassium application increased the taste value of rice mainly reflected in the appearance and taste of rice.The RVA characteristics of starch were also affected by K application.Compared with no K application,the peak viscosity,breakdown value,and setback value of Xiadao No.1 and setback value of Shenliangyou 5814 were significantly increased,starch gelatinization temperature was significantly decreased,and starch properties were better,which was consistent with the improvement of rice eating quality by K application.（4）Potassium application significantly increased soluble sugar supply,promoted starch accumulation,and decreased caryopsis protein content of caryopsis.The protein content in caryopsis decreased from 7-14 days after anthesis,and then decreased slightly or holded constant.The contents of amylose and total starch increased gradually and then remained stable.Potassium application significantly increased the soluble sugar supply in caryopsis and the activities of three enzymes related to starch synthesis in grains,thus promoting the accumulation of starch synthesis.Correlation analysis showed that the content of protein in caryopsis was significantly negatively correlated with the accumulation of starch during grain filling,and the decrease of the contents corresponded with the increase of starch.Based on milled rice rate,protein content and taste value,combined with rice yield,the optimal K application rates for the combination of high quality and high yield of Xiadao No.1 and Shenliangyou 5814 were determined to be 159-166 kg K₂O hm^-2 and 179-180 kg K₂O hm^-2,respectively.Under the K application rate,the rice yield was 7.35-8.32 t/hm²and 7.28-8.19 t/hm²,the milled rice rate was 60.4%-64.3%and 67.1%-68.1%,the protein content was 7.0%-7.3%and 6.6%-7.0%,and the taste value were 70.1-71.1 and 74.9-76.2,respectively.