Effects Of Controlled Release Nitrogen Fertilizer On Yield,Quality And Starch Property In Rice

Rice is an important food crop,but a large amount of nitrogen fertilizer input is unfavorable to green,high-quality,and high-efficient production of rice.Compared with fast release nitrogen fertilizer（FRF）,controlled-release nitrogen fertilizer（CRF）has slow nutrient release with long fertilizer efficiency period,which can meet nitrogen requirements without multiple application of fertilizer,which benefit for the simplified and green cultivation of rice.In this study,Yongyou 2640（YY 2640）and Jinxiangyu 1（JXY 1）were used as materials.Seven nitrogen fertilizer treatments were set up,including nitrogen blank zone（T1）,conventional FRF（T2）,conventional CRF（T3）,FRF reduction（T4）,CRF reduction（T5）,CRF+single-application of FRF（T6）,and CRF +phased application of FRF（T7）.The nitrogen application rates for T2 and T3 were 270 kg N hm^-2,and T4-T7 were nitrogen reduction treatments(240 kg N hm^-2).The effects of different nitrogen fertilizer treatments on rice yield and its components,agronomic traits,carbon and nitrogen metabolism,rice quality,starch properties and structure were studied,in order to provide practical and theoretical basis for rice cultivation.The main results are as follows:1.Compared to the nitrogen blank zone,other nitrogen fertilizer treatments significantly increased rice yield,with the CRF+single-application of FRF（T6）showing the highest increase,followed by the CRPF+phased application of FRF（T7）.In 2021,the yield of YY 2640 in T6 and T7 treatments was 12.50 t hm^-2 and 12.40 t hm^-2,respectively,while the yield of JXY 1 was 9.76 t hm^-2 and 9.68 t hm^-2,respectively.All of them were significantly higher than the control of conventional FRF,and the results of 2022 were consistent with 2021.Under the same rate,the yield of YY 2640 in the CRF treatments（T3,T5-T7）was increased by 1.77%～12.95%,while the yield of JXY 1 was increased by 2.08%～10.40%.In terms of yield components,compared to the T2 treatment,the total spikelet number for YY 2640 and JXY 1 significantly increased by 5.14%～13.64%and 7.24%～14.92%under all CRF fertilizer treatments,respectively.The total spikelet number with substantial increasing led to a decrease in filled-grains rate and 1000-grain weight,but the decrease was much lower than the increase in total spikelet number.In summary,the application of CRF can increase the total spikelet number of the rice with a high filled-grains rate and 1000-grain weight,and still achieve high yield under reducing nitrogen application.2.The number of tillers in the CRF treatments（T3,T5～T7）were far lower than that in conventional FRF treatment from middle tillering stage to heading stage,but it was basically the same at maturity stage.It meant that CRF treatment had a higher spike rate.The spike rate of YY 2640 was increased by 10.95%～13.02%compared to the conventional FRF treatment,while that of JXY 1 was increased by 8.72%～11.02%.Starting from the panicle initiation stage,the CRF treatment has higher leaf area index and dry matter accumulation compared to the conventional FRF treatment with the same nitrogen rate.Among them,the leaf area index was best under the CRF+single-application of FRF treatment,while the dry matter accumulation was best under the conventional CRF treatment.Both reducing nitrogen input and applying CRF had the effect of improving nitrogen fertilizer utilization efficiency of rice.Compared to the conventional FRF treatment,the nitrogen uptake in the CRF treatment was significantly increased,and the nitrogen agronomic efficiency,recovery efficiency and partial factor productivity of nitrogen were increased,while the nitrogen physiological efficiency,internal nitrogen use efficiency and nitrogen harvest index were decreased.Compared to the nitrogen blank zone,other nitrogen fertilizer treatments reduced the accumulation of non-structural carbohydrates in stems,leaves,and panicles,and was more significant under high nitrogen application rates.3.The input of nitrogen fertilizer improved the processing quality of rice,and the brown rice rate,milled rice rate,and head milled rice rate of each nitrogen fertilizer treatment were significantly increased compared to the nitrogen blank zone.The processing quality of CRF treatments was basically equivalent to that of FRF treatments.The appearance quality deteriorated with the input of nitrogen fertilizer,but the appearance quality of CRF treatments was better than that of FRF treatments under the same nitrogen application rate.Compared with the nitrogen blank zone,other nitrogen fertilizer treatment significantly increased the protein content in milled rice,significantly reduced the amylose content and gel consistency.In terms of eating quality,the hardness and adheiveness of cooked rice texture significantly increased after nitrogen application,while the taste value significantly decreased.It is worth noting that the CRF+single-application of FRF（T6）resulted in a lighter deterioration of taste value,and the hardness and adheiveness of cooked rice were closer to those in the nitrogen blank zone.Nitrogen application reduced the content of amylose,amylopectin,and total starch,increased the relative crystallinity and surface ordered structure content of starch(1045/1022 cm^-1),and the variation of FRF was larger than that of CRF.Compared with conventional FRF treatments,CRF treatments had a higher pasting viscosity,lower pasting temperature,and starch gelatinization enthalpy,and performs better under reduced nitrogen treatment.To sum up,the application of CRF could improve the leaf area index,promote accumulation of dry matter and nitrogen,make the number of tillers more reasonable,help the tillers to form panicles,increase the number of spikelet,maintain a high filled-grains rate.Therefore,the yield increased when compared nitrogen reduction treatments to conventional FRF treatments.In the CRF treatmentss,CRF+single-application of FRF treatment could promote the nitrogen uptake of rice plant,improve nitrogen fertilizer utilization efficiency,improve the processing quality and starch functional properties,reduce the degradation of appearance and eating quality,and obtein high-yield,high-efficiency,and high-quality,achieving simplified and green cultivation of rice.