Abstract
Aims The objectives of this study were to examine the long-term substitution of mineral phosphorus (P) fertilizers with manure (M) plus nitrogen (N) fertilizers and how they affect the forms of P that occur in soil, soil P distribution, and plant growth.Methods We used a solution of 31P nuclear magnetic resonance (31P-NMR) spectroscopy to study the correlations between long-term fertilization regimes and the forms of P that occur at different soil depths. Then we investigated yield, plant growth, and soil properties.Results A 40-year field experiment showed that the use of M + N fertilizers can significantly improve plant growth and yield. The proportion of organic P in the 20-40 cm soil layer was significantly increased by long-term M fertilization. The concentrations of various forms of P (orthophosphate, pyrophosphate, diesters, monoesters, and total inositol hexakisphosphate, IHP) in topsoil increased significantly with the combination of M with N + P mineral fertilization. The addition of M greatly increased the stereoisomers of IHP (myo-IHP, scyllo-IHP, neo-IHP, and D-chiro-IHP) and the proportion and concentration of corrected diesters. There were no significant differences in the pyrophosphate contents of the 40-60 cm soil layer according to fertilization type and year of fertilization. There were also no significant differences in IHP stereoisomers and diesters according to fertilization year. The P forms that contributed to corn yield were orthophosphate, diester, and IHP. Further, pyrophosphate made no significant contribution to corn growth. Conclusions Over the long-term, pig manure can significantly increase the amount of orthophosphate that is directly absorbed by crops and the amount of IHP stereoisomers that can be used by plants. Orthophosphate and IHP are the two key factors that have a positive effect on plant growth.
Rice growth and yield under twenty years of cropping in a long term fertilizer experiment in central laterites of Kerala
