Nitrogen forms and irrigation regimes interact to affect rice yield by regulating the source and sink characteristics

The interaction between nitrogen management and irrigation regimes plays important roles in regulating the rice (Oryza sativa L.) source, sink characteristic, and grain yield. However, if and how nitrogen forms could synergistically interact with irrigation methods in rice remain unclear. Herein, a soil-grown experiment was conducted with three nitrogen forms, namely, ammonium nitrogen (AN), ammonium, nitrate mixed (ANM), and nitrate nitrogen (NN), as well as three irrigation regimes, namely, submerged irrigation (0 kPa), alternate wetting and moderate drying (-20 kPa), and alternate wetting and severe drying (-40 kPa). Results demonstrated that grain yield was the highest in the ammonium nitrate and alternate wetting and moderate drying irrigation. Nitrate nitrogen application decreased grain yield in each irrigation regime. The alternate wetting and moderate drying and ammonium nitrate treatment had higher chlorophyll content, leaf nitrogen content, leaf area index (LAI), photosynthesis rate, and chlorophyll fluorescence, superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), and sucrose-synthase activity and decreased leaf malondialdehyd (MDA) content than the other treatments at mid-tillering, panicle initiation, heading, and maturity stages. By contrast, AN treatment exhibited very small difference between AN and ANM treatment in submerged irrigation. Besides, grain yield was positively correlated with chlorophyll content, leaf nitrogen content, LAI, photosynthesis rate, antioxidant enzymes, and sucrose-synthase activity at main growth stages. Therefore, the adoption of ANM and alternate wetting and moderate drying can synergistically increase grain yield by promoting the leaf-source and grain-sink activity of rice. Results of the present investigation provided new ideas for increasing grain yield by nitrogen forms management in alternate wetting and drying irrigation.