Alternate wetting and drying water management can reduce phosphorus availability under lowland rice cultivation irrespective of nitrogen level

The limited availability of phosphorus (P) in the soil, which is affected by soil moisture, has a significant impact on crop production. However, we still don't fully understand how water management and nitrogen addition affect the availability of phosphorus in paddy soil. An evaluation of the effects of two water management strategies that is continuous flooding (CF) and alternate wetting and drying (AWD) irrigation along with various nitrogenous fertiliser addition rates (equivalent to 0, 100%, 133%, and 166% recommended dose of N addition) on P availability in paddy soil took place over the course of a two-year field experiment. The results showed that water management had a significant influence on ferrous iron, microbial biomass P, and soil available P. However, the addition of nitrogen did not affect the availability of P in the soil. When nitrogen was added at various rates, AWD consistently reduced the amount of soil-available P compared to CF. This was primarily because AWD increased microbial biomass, which immobilized phosphorus and decreased the content of ferrous iron. As a result, the soil's ability to absorb phosphorus increased, leading to a decrease in the amount of phosphorus available. In conclusion, AWD decreases the amount of available P in paddy soil compared to CF.