Controlled release urea combined with normal urea maintains the N balance and improves the environmental and economic benefits in wheat–maize multiple cropping

Abstract

Controlled release urea combined with normal urea (CRUNU) can potentially improve crop yields and reduce the associated environmental risk. However, the effects of CRUNU on farmland environmental benefits and the agroecosystem nitrogen (N) balance have not been evaluated in the winter wheat–summer maize multiple cropping system in northwest China, and few studies have quantified the impacts of CRUNU on N losses with this cropping system based on life cycle assessment. Therefore, we performed a field experiment for two years during 2020–2022 with two types of N fertilizer (normal urea (NU) and CRUNU) and at three N application rates (low: 135 kg N ha^–1, medium: 180 kg N ha^–1, and high: 225 kg N ha^–1) at Caoxinzhuang experimental farm to comprehensively evaluate the effects of CRUNU on the agronomic, N balance, environmental, and economic benefits in winter wheat–summer maize cropping. Compared with NU, CRUNU helped to synchronize the N supply and demand for wheat and maize, and under all three N application rates, the annual average grain yield and grain N uptake increased with CRUNU, as well as reducing the volatilization of NH₃ by 16.69 %, N₂O emissions by 25.16 %, and N losses due to nitrate (NO₃^–) leaching by 44.23–61.65 %, thereby maintaining the total N storage. Considering both the N input and output, CRUNU achieved a lower N surplus than NU and maintained the N balance in the farmland ecosystem. In addition, CRUNU significantly reduced the reactive N losses at the three N application rates to decrease the N footprint (NF) by 25.48–42.85 %, where CRUNU obtained the lowest NF at the medium N application rate. More importantly, the benefits of CRUNU for increasing the grain yield at different N application rates offset the higher agricultural input costs and reduced the environmental costs due to N₂O emissions, NH₃ volatilization, and NO₃^– leaching losses, so the net benefits increased by 23.14–29.25 %. Furthermore, the net benefits under CRUNU did not differ significantly at the medium and high N application rates. Therefore, we recommend CRUNU application at the medium rate as an effective strategy for improving the N balance, environmental effects, and economic benefits in wheat–maize multiple cropping systems