Exploration of water-nitrogen coupling effects in paddy field based on ORYZA (v3) model.

Background: Nitrogen and water are two major factors in rice production. Due to the lack of ample evidence and much uncertainty in field experiments, the coupling effects of water and nitrogen in paddy fields have remained debatable over recent years.

Results: A fine-calibrated ORYZA (v3) model was applied to simulate rice growth and development under different nitrogen (N) rates and irrigation regimes for a double rice-cropping system in South China. We designed a numerical experiment of 504 treatments, consisting of seven nitrogen rates (0-300 kg ha ), eight irrigation thresholds (30-100%, presented as the percentage of saturated soil water content) and nine irrigation quotas (20-100 mm), and each treatment was simulated for 30 years. Yield varied greatly with different water-nitrogen conditions, particularly in the scenario of frequently alternate wetting and drying irrigation and low-N rates. The coupling effects had a negligible influence on water input and water loss, which were found to be sensitive only to the irrigation regime and rainfall distribution. Based on the results, the N fertilizer for early rice growing in the wet season is suggested as 150-200 kg ha , and 200-250 kg ha for late rice growing in the dry season. The irrigating threshold and irrigation quota for early rice are suggested as lower than 70% and 30-40 mm, respectively, and, for late rice, 70-80% and 40-60 mm.

Conclusion: Remarkable water-nitrogen coupling effects were found in the paddy field, and integrative water-nitrogen management strategies were suggested for both early rice and late rice in South China. © 2021 Society of Chemical Industry.