Nitrogen fertilizer reduction in combination with cover for reducing ammonia volatilization and improving nitrogen use efficiency of rice.

BACKGROUND

Excessive nitrogen (N) application rate with low N use efficiency (NUE) caused a considerable amount of N losses, especially ammonia volatilization (AV). Proper N fertilizer reduction (RN) could significantly reduce AV. However, continuous RN led to a nutrient deficiency in the soil and therefore negatively impacted the NUE and rice yield. Paddy , a good green manure, is considered as a promising measure to decrease AV and improve NUE and grain yield of rice. However, there is limited information on the integrated effects of RN and cover on the AV, NUE, and rice yield, especially in the highly fertilized rice-growing systems.

METHODS

The experiment was conducted including eight treatments: the control (without N fertilizer and cover), cover without N fertilizer (A), farmer's N application rate (FN), FN + cover (FNA), 15% RN from FN (RN), RN + cover (RNA). 30% RN from FN (RN), RN + cover (RNA). The integrated effects of N fertilizer reduction and cover on AV, NUE, and rice grain was evaluated.

RESULTS

RNA and RNA substantially reduced total AV by 50.3 and 66.9% compared with FN, respectively, primarily due to the lower surface water ammonia concentrations and pH. RN improved the efficiency of cover on reducing AV, with 4.1-9.9% higher than for FN. Compared with the FN, RNA and RNA enhanced apparent N recovery efficiency (ANRE) by 46.5 and 39.1%, which might be responsible for the lower NH emission and the increased total N uptake / total chemical N applied. Furthermore, RNA and RNA reduced yield-scaled volatilization by 52.3 and 64.3% than for FN, respectively. Thus, combining 15-30% RN with cover may be a way to reduce AV and improve ANRE without decreasing rice grain yield.