Alfalfa green manure amendment improved P use efficiency and reduced P losses from paddy fields

Low phosphorus (P) use efficiency of synthetic P fertilizers leads to soil degradation and environmental problems. Holistic approaches are required to increase crop productivity and enhance P use efficiency. The application of green manure results in multiple benefits for soil–plant systems. In this study, the following treatments were investigated: control (no fertilizer), 36NPK, 72NPK, 27NPK+ broad bean manure, 27NPK+ alfalfa manure, 36NPK+ broad bean manure, 36NPK+ alfalfa manure, 72NPK+ broad bean manure, and 72NPK+ alfalfa manure (27, 36, and 72 corresponds to the application rate of synthetic P fertilizer in kg ha −1 ). Our results showed that grain yields were similar between fertilization treatments, except that the 72NPK+ alfalfa treatment significantly decreased grain yield by 20% compared to the 72NPK treatment. The 27NPK+ alfalfa treatment significantly increased the total P uptake by 19% compared to the 36NPK treatment. The recovery efficiency of P for the 27NPK+ alfalfa and 36NPK+ alfalfa treatments significantly increased by 32% and 12%, respectively, and for the 72NPK+ alfalfa treatment, it decreased by 9% compared to the 72NPK treatment. The rice productivity, P uptake, and P recovery efficiency for the 27NPK+ alfalfa treatment were slightly higher than those with the 27NPK+ broad bean treatment owing to the high P concentration in alfalfa. Potential P losses in the 27NPK+ alfalfa, 36NPK+ alfalfa, 72NPK+ alfalfa, and 72NPK treatments were 1, 10, 43, and 38 kg ha −1 , respectively. In conclusion, an appropriate application rate of synthetic P fertilizer along with alfalfa green manure enhanced the recovery efficiency of P and reduced P losses from paddy fields.