Exploring phosphorous dynamics within soil aggregate after 17 years long-term manuring in lateritic Inceptisols in rice paddies

Abstract

Understanding phosphorous dynamics can provide valuable insights for sustainable nutrient management and long-term fertilizer experiments are better source for elucidating such mechanism. In this study, eight distinct nutrient management treatments (combination of N, P, K fertilizer along with FYM and lime) were evaluated in an ongoing long-term fertilizer experiment. The experiment investigated the prolonged effects of both balanced and imbalanced fertilizer applications, the combined use of organic manure and inorganic fertilizers, and the application of liming material in a rice-rice cropping system on yield attributes and changes in soil properties. Integrated use of organic manure with NPK fertilizers and lime application (100% NPK + FYM + Lime) positively influenced soil properties and significantly increased yield by 41.4% and P-uptake by 88.4% compared to sole NPK application. The long-term fertilization contributed to significant relative accumulation of CaP fraction (∼240% increase) in 100% NPK + FYM + Lime in comparison to initial CaP fraction. The distribution pattern of inorganic phosphorus fractions varied with following sequence: Fe-P > Red-P > Al-P > Ca-P > Occl-P > Sal-P. Among these fractions, CaP (r = 0.949**), Occl-P (r = 0.884**), and Sal-P (r = 0.866**) were correlated with available P. The mean weight diameter (MWD) exhibited the strongest correlation with Occl-P (r = 0.936**), whereas the geometric mean diameter (GMD) and water stable aggregate (WSA) had the strongest correlation with CaP (0.893** and 0.875**, respectively). The adjusted R² values indicated that the total contribution of all inorganic P fractions accounted for 99.9% of the variability in available P, 80.6 % in P uptakes, and 67.9% in grain yield. This study underscores the critical relationship among soil structure, crop yield, and P availability, emphasizing that macroaggregates play a crucial role in improving soil health and enhancing P retention and availability.