Effects Of Controlled Release Urea On Yield,Nitrogen Loss And Nitrogen Use Efficiency For Double-cropping Rice System

Double-cropping rice area in Southern China is the main rice production area in China.Double-cropping rice production increases the multiple cropping index and alleviates the high yield pressure and risk faced by single cropping rice.The annual output of the early and late rice seasons is far greater than the single cropping rice.It has made significant contributions to China's food security.However,due to the fact that traditional double-cropping rice production requires multiple fertilizations,its labor intensity,high production costs,time-consuming and labor-intensive,and low economic benefits,affecting the farmers' cultivation of double-cropping rice enthusiasm,resulting a continuous decline in the area of double-cropping rice.In order to obtain high yields,farmers often use large amounts of nitrogen(N)fertilizer.Excessive N fertilizer not only increases the cost of rice production,reduces N use efficiency,but also causes waste of resources and serious nitrogen loss,thus causing damage to the atmosphere and water environment.The development of slow/controlled release fertilizer has effectively solved the problem of low N use efficiency and serious N loss in rice production.In this study,field experiments were conducted in Wuxue city,Hubei Province from 2013 to 2016 to study the effects of controlled release urea(CRU)on yield,N loss and N use efficiency for double-cropping rice,and to clarify the N uptake pattern of double-cropping rice and the nutrient characteristics of three CRU fertilizers,screening suitable CRU fertilizers for double-cropping rice in Central China,clarifying the mechanism of CRU on increasing yield,improving N use efficiency and reducing N loss,and determining the appropriate dosage of CRU and the best mixing ratio with conventional urea.The main results are listed as follows:(1)The controlled release N properties of CRU should be designed based on the N uptake pattern of rice.The N uptake pattern of double-cropping rice were analyzed to be a ?S? pattern,and the rapid growth period of N uptake of double-cropping rice were 27-59 d and 9-50 d,respectively;the duration of the rapid growth period was 30-31 d for early rice and 36-41 d for late rice,respectively;The maximum N uptake rate was 42-43 d for early rice and 27-30 d for late rice,respectively.Three CRU fertilizers developed based on N uptake pattern of double-cropping rice.The initial nutrient release rates of nitrogen nutrients for three CRU fertilizers did not exceed 15%;The nutrient cumulative release rates at 28 days did not exceed 80%;The time of nutrient cumulative release rates reached 80% were 56 d,42d and 42 d,which is consistent with China's slow release fertilizer production standard.The nutrient release characteristics of three CRU fertilizers in 25? water and paddy soil were similar.However,nutrient release rates of CRU-1 and CRU-2 in the paddy soil were slower than that of in 25? water.The nutrient release rate of CRU-3 in the paddy soil was faster and its release period was shorter than measured in 25? water.The nutrient release of CRU-1 and CRU-2 in the paddy field was well matched with the N uptake pattern of double-cropping rice.(2)CRU could effectively increase the yield,N uptake and N use efficiency,and reduce NH3 volatilization and N runoff loss.CRU-1 and CRU-2 significantly reduced NH3 volatilization(23 to 62%)and N surface runoff losses(8 to 58%)compared with Urea.Application of CRU reduced NH4+-N concentration and p H of surface water and N losses through surface runoff.The CRU produced similar(-3 to 4%)or higher(5 to 16%)rice grain yields and increased NUE(3 to 34%)and N uptake(3 to 55%)compared with U.The highest grain yield among the N fertilization treatments was observed with CRU-2 treatment in both years.CRU treatments resulted in 0.1%-34.0% higher grain N uptake,-0.5%-65.2% higher straw N uptake,2.6%-33.3% higher total N uptake,2.7-30.2 percentage point higher N use efficiency,14.3%-65.0% lower NH3 volatilization and 6.8%-26.9% N runoff loss than that of U treatment.(3)Studying the fate and recovery efficiency of CRU in paddy soil using 15 N tracer technique,the results showed that CRU increased grain yield by 4.3%,increased 15 N accumulation by 13.3%,improved 15 N use efficiency by 13.2%,increased N from fertilizer by 13.3% and Ndff by 12.4%,increased soil 15 N residual rate by 9.9%,improved total 15 N recovery efficiency by 11.4%,and reduced 15 N loss by 6.2% compared with basal application of urea.N from soil is more than 70% during rice growth period.The residual amount of fertilizer nitrogen in soil decreased significantly with the increase of soil depth.After harvest,fertilizer 15 N mainly remained in the 0-20 cm soil layer,accounting for 78% of the total residue.The second is 20-40 cm and 40-60 cm soil layer,and the fertilizer 15 N residue in the two soil layers is similar,accounting for about 19% of the total residue.Below 60 cm soil layer,there is still a trace amount of fertilizer 15 N residue,accounting for less than 4% of the total residue.(4)Within the rate of 165 kg N/hm2 for CRU,the grain yield,effective panicles and spikelets per panicle of double-cropping rice increased with the increase of CRU rate,exceeding this level,these values did not increase significantly,and even decreased.The N concentration and N uptake of double-cropping rice plants showed an increasing trend with the increase of CRU rate.Although the N use efficiency increased,the ratio of N accumulation in rice straw was also increased,and it was easy to cause leggy and late-maturing.NH3 volatilization loss in the double-cropping rice system increased with the increase of CRU rate,and the NH3 volatilization loss was higher in late rice than in early rice.The recommended rates of CRU for double-cropping rice were 153 and 150 kg N/hm2,respectively.(5)Mixing a certain ratio of CRU could increase grain yield,N use efficiency and reduce fertilizer costs and improve economic benefits.Compared with U treatment,the grain yield for CRU treatments increased by 12.0%-19.1% in early rice and 3.0%-7.5% in late rice.With the increase of the mixing ratio of CRU,the grain yield increased.The highest grain yield among the N fertilization treatments was observed with single basal application of CRU treatment in early rice and 60%CRU(Mix-3)treatment in late rice.Considering the agronomic effect,mixing 60%-80% CRU can meet the N demand of rice in the rainy season or year,and mixing 20%-40% CRU can meet the N demand of rice in dry season or year.Considering the economic benefits,mixing 20%-40% CRU can be obtained better economic benefits.