Nitrogen rate is more important than irrigation rate in mitigating nitrogen leaching in flood-irrigated maize: A 6-year lysimeter experiment
Liyao Hou, Xiaotong Liu, Jianhang Luo, Ying Zhao, Xuejun Zhang, Qiuliang Lei, Hongbin Liu, Peng Zou, Zhanjun Liu
Abstract
Excessive nitrogen (N) fertilization and irrigation prevail in irrigated agriculture worldwide. However, little information is available that systematically evaluates grain yield, plant N uptake, residual soil NO 3 − -N (RSN), and N leaching under different irrigation–N regimes in an irrigated maize production system. To address such agronomic and environmental issues, a 6-year in situ lysimeter field trial was conducted in the Hetao Irrigation District of China with five treatments: 1) conventional irrigation (3,900 m 3 /ha) and local farmer fertilizer N rate (490 kg ha −1 ) (CON); 2) conventional irrigation and the recommended fertilizer N rate (420 kg ha −1 ) (RN); 3) deficit irrigation (2,730 m 3 /ha) and the recommended fertilizer N rate (SRN); 4) deficit irrigation and the recommended fertilizer N rate (with ∼ 10 % organic fertilizer N substitution) (SMN); and 5) conventional irrigation and controlled-release N fertilizer (270 kg ha −1 ) (CRF). Maize yield was not significantly different across treatments in 2015–2020. Averaged across years, SMN, SRN, and CRF significantly increased plant N uptake compared with that in CON by 28.84 %, 19.15 %, and 17.53 %, respectively. Residual soil NO 3 − -N at 0–90 cm was ranked as SRN > CON ≈ SMN > RN > CRF, whereas cumulative N in leachate from 2015–2020 (N loss ) in CON was 86.2 % to 187.1 % higher than that in other treatments. The N loss in SRN was equivalent to that in RN and SMN, but N loss in SMN decreased significantly compared with that in RN, indicating additive benefits of deficit irrigation and organic input on reducing N leaching. Structural equation modelling revealed that irrigation had greater effects on plant N uptake than those of fertilization, whereas N rate had a greater total effect on N leaching than that of irrigation. Overall, rampant excessive irrigation and N fertilization by farmers can be substantially reduced while maintaining grain yield and mitigating N leaching loss, with further benefits gained by applying controlled-release N fertilizer and manure in irrigated maize production.