Transformation, interaction, and bioavailability of nutrients in the fertisphere

This project is being implemented by the Nanjing Institute of Soil Science, Chinese Academy of Science. Results so far have indicated that the movement of P in soil is usually less than 6 cm, and that the P moving distance in grey alluvial soil is shorter than in paddy soil. No significant change occurred in the P moving distance in soil with or without the application of oxalic acid and fertilizer P. However, this application reduced P fixation by soil and increased the moving rates. Further, the release rate and moving distance of coated mono-ammonium phosphate (MAP) in soil increased with the increase in soil temperature. Therefore, when soil temperature increases, coated MAP could increase the P use efficiency during the growing season.

The transformation of P in soil is closely related to P fertilizer type and soil characteristics. Initially, P fertilizers applied to the soil form soluble P. But mono-calcium phosphate (MCP) and MAP can be fixed more easily than di-ammonium phosphate (DAP). In black soil, MAP gets mainly transformed to Al-P and Fe-P, while in grey alluvial soil, it is mainly transformed to Ca₈-P. Similarly, in a paddy soil, MAP is mainly transformed to Fe-P, Ca₂-P, Ca₈-P, and Al-P, thereby, keeping a balance. Flooding leads to the formation of Al-P and Fe-P. On a paddy soil, broadcast P fertilizer would greatly increase the P concentration in groundwater, thereby, increasing the risk of P loss by runoff. Phosphorus fertilization with banding or row placement in fields could greatly reduce P loss.

Fertilizer K application together with ammonium N fertilizers could improve the availability of K fertilizers in the fertisphere of paddy soil. The influence of ammonium on K availability is larger than the influence of K on ammonium availability. Nanjing-11