Effects of long-term fertilization on available P, P composition and phosphatase activities in soil from the Huang-Huai-Hai Plain of China

Combining organic materials with chemical fertilizers is gradually becoming the primary fertilization strategy in China for increasing soil phosphorus (P) concentration; however, the relationships between soil available P, P composition and phosphatase activities in treatments with long-term crop straw or animal manure combined with chemical NPK fertilizers are not fully understood. In this study, a field fertilization experiment was conducted in a light sandy loam soil from the Huang-Huai-Hai Plain of China to determine the variation in soil available P, P composition and phosphatase activities with 23 years of continuous application of maize straw or cattle manure in combination with chemical fertilizers at the depth of 0-20 cm, with special attention paid to their relationships. The experiment was arranged in a randomized block design with three replications for each treatment, including the unfertilized control (CK), chemical nitrogen (N) with phosphorus (P) and potassium (K) (NPK), NPK plus maize straw (NPKS), and NPK plus cattle manure (NPKM). Results indicated that all fertilization treatments significantly increased soil P concentration and crop yields. Among the fertilization treatments, NPKM treatment showed the significantly highest total P and available P concentrations, while no significant difference in either wheat or maize yield between NPK, NPKS and NPKM treatments was found. Compared to the application of chemical NPK fertilizers alone, the NPKS treatment significantly increased soil organic P, pyrophosphate and orthophosphate concentrations, as well as soil phosphatase activities. The increase in orthophosphate concentration under the NPKS treatment may be associated with the hydrolysis of organic P and pyrophosphate catalyzed by acid phosphomonoesterase (AcP), phosphodiesterase (PD) and inorganic pyrophosphatase (IPP), which was conducive to keeping soil available P concentration under NPKS treatment at an appropriate level that could not only satisfy crop P demand but also have no negative impacts on the environment. However, the increase of orthophosphate and available P concentrations under NPKM treatment may be primarily related to the manure P inputs, and although NPKM treatment significantly increased soil inorganic P concentration in comparison to other fertilization treatments, it also increased the risk of P leaching. Overall, from the perspective of P nutrient management, our results suggest that NPKS treatment might be an effective long-term fertilization practice in the light sandy loam soil of Huang-Huai-Hai Plain of China.