Rice yield, water productivity, and nitrogen use efficiency responses to nitrogen management strategies under supplementary irrigation for rain-fed rice cultivation

Abstract

Rainfall-adapted irrigation (RAI) or supplementary irrigation for rain-fed rice cultivation consumes less amount of irrigation water by harvesting rainfall and thus is vital for sustainable rice (Oryza sativa L.) production in multi-rain areas, including the Jianghan Plain in China. However, nitrogen management strategies influence rice growth and water and nitrogen utilization under RAI remains unclear. Thus, we conducted a two-year (2016 and 2017) field experiment at Jingzhou City, central China to investigate the effects of nitrogen management strategies on grain yield, crop water productivity (CWP), and nitrogen use efficiency (NUE) of rice under conventional flooding irrigation (CF) and RAI. The nitrogen management strategies included local farmers’ nitrogen fertilization (CN), common urea (30% nitrogen) blended with controlled-release nitrogen fertilizer (70% nitrogen) (U+CRF), and optimized nitrogen fertilization (ON), at a nitrogen rate of 180, 180, and 150 kg ha−1, respectively. Compared to the CF condition, RAI down-regulated the numbers of irrigation (−3 in 2016 and −4 in 2017) and reduced the total amount of irrigation water (−41.6% in 2016 and −45.6% in 2017), suggesting that rainfall-adapted irrigation enhanced the rainwater storage capacity and usage. RAI also increased root length, root and shoot biomass, net photosynthetic rate, crop growth rate, nitrogen accumulation, percentage of productive tillers, harvest index, and nitrogen harvest index. The U+CRF and ON increased or maintained these parameters compared with the CN. Compared to the traditional irrigation and nitrogen fertilization pattern (CF interacted with CN), RAI combined with U+CRF or ON enhanced root length and root biomass, and had a relatively high spikelets number per panicle, grains filled percentage, and 1000-grain weight, and thus produced a high grain yield. Moreover, the new treatment reduced amount of irrigation water and improved utilization of nitrogen fertilizer, resulting in a greater CWP and NUE. The enhanced grain yield, CWP, and NUE were associated with the increased root biomass and root length. Therefore, rainfall-adapted irrigation combined with the new nitrogen management (U+CRF or ON) can synergistically increase grain yield and resource use efficiency by improving root growth in rice.