The optimum economic nitrogen rate of blended controlled-release nitrogen fertilizer for rice in the Chanoyu watershed in the Yangtze River Delta, China

Abstract

IntroductionThe application of controlled-release nitrogen fertilizer (CRN) has become an important production method to achieve high crop yield and ecological safety. However, the rate of urea-blended CRN for rice is usually determined by conventional urea, and the actual rate is still unclear.MethodsA five-year field experiment was carried out in the Chaohu watershed in the Yangtze River Delta to study rice yield, N fertilizer utilization efficiency (NUE), ammonia (NH3) volatilization and economic benefit under the four urea-blended CRN treatments with a 4:3:3 ratio applied at one time (60, 120, 180, 240 kg/hm2, CRN60, CRN120, CRN180, CRN240), four conventional N fertilizer treatments (N60, N120, N180, N240) and a control without N fertilizer (N0).Results and DiscussionThe results showed that the N released from the blended CRNs could well satisfy the N demand of rice growth. Similar to the conventional N fertilizer treatments, a quadratic equation was used to model the relationship between rice yield and N rate under the blended CRN treatments. The blended CRN treatments increased rice yield by 0.9-8.2% and NUE by 6.9-14.8%, respectively, compared with the conventional N fertilizer treatments at the same N application rate. The increase in NUE in response to applied blended CRN was related to the reduction in NH3 volatilization. Based on the quadratic equation, the five-year average NUE under the blended CRN treatment was 42.0% when rice yield reached the maximum, which was 28.9% higher than that under the conventional N fertilizer treatment. Among all treatments, CRN180 had the highest yield and net benefit in 2019. Considering the yield output, environmental loss, labor and fertilizer costs, the optimum economic N rate under the blended CRN treatment in the Chaohu watershed was 180-214 kg/hm2, compared with 212-278 kg/hm2 under the conventional N fertilizer treatment. The findings suggest that blended CRN improved rice yield, NUE and economic income while decreasing NH3 volatilization and negative environmental outcomes.

Blended controlled-release nitrogen fertilizer increases rice post-anthesis nitrogen accumulation, translocation and nitrogen-use efficiency

“…Two CRNs with the N release periods of 40 and 90 days are abbreviated as CRN1 and CRN2, respectively. The N release characteristics of CRN1 and CRN2 in 25°C water and paddy fields for 42 and 100 days were measured in the 2019 ( Yuan et al., 2023 ).…”

“…It is reported that the average rice N-use efficiency (NUE) is only 39% ( Yu and Shi, 2015 ), which is 33.3-42.9% lower than that of the United States of America and Europe ( Lassaletta et al., 2014 ; Yu et al., 2022 ). Excessive application of N fertilizer not only increases the production cost of rice, but also reduces NUE, and causes environmental problems such as soil acidification and water eutrophication ( Congreves et al., 2021 ; Yuan et al., 2023 ).…”

“…Therefore, the amount of CRNs or blended CRNs with urea applied is mainly determined by the amount of urea applied to rice ( Wang et al., 2018 ; Lyu et al., 2021 ). We conducted a five-year field experiment to derive the application rate of blended CRNs for rice in the Chaohu watershed of the Yangtze River Delta in China ( Yuan et al., 2023 ). The optimum N rate under the blended CRN treatment was determined to be 180-214 kg N ha -1 with one-time application, reducing the N rate by 32-64 kg N ha -1 compared with the conventional N fertilizer treatment.…”

“…The optimum N rate under the blended CRN treatment was determined to be 180-214 kg N ha -1 with one-time application, reducing the N rate by 32-64 kg N ha -1 compared with the conventional N fertilizer treatment. From an environmental perspective, it was elucidated that a significant reduction in ammonia volatilization in rice fields was the crucial cause for the increase in NUE under the blended CRN treatments ( Yuan et al., 2023 ), but empirical evidence in rice agronomy and physiology is still lacking. Moreover, the data from one field site is insufficient to establish the optimal application rate of blended CRNs in the Yangtze River Delta ( Yuan et al., 2023 ; Zhang et al., 2018b ).…”

“…From an environmental perspective, it was elucidated that a significant reduction in ammonia volatilization in rice fields was the crucial cause for the increase in NUE under the blended CRN treatments ( Yuan et al., 2023 ), but empirical evidence in rice agronomy and physiology is still lacking. Moreover, the data from one field site is insufficient to establish the optimal application rate of blended CRNs in the Yangtze River Delta ( Yuan et al., 2023 ; Zhang et al., 2018b ). Therefore, in this study, field experiments were conducted across three locations over two years to compare rice yield, NUE, pre-anthesis and post-anthesis biomass and N accumulation and translocation to grain yield between the blended CRN treatments and the conventional N fertilizer treatments.…”