Impact of long-term use of fertilizers on soil phosphorus fractions and its uptake

Abstract

Understanding the dynamics and transformation of soil phosphorus (P) is imperative for formulating sustainable agricultural P management strategies. This study examined the long-term impacts (over 52 cropping cycles) of various fertilization regimes on P dynamics in Inceptisol (Typic Ustochrept) and the associated productivity of the maize-wheat cropping system. The fertilizer treatments involved: T1) control, T2) 50 % NPK, T3) 100 % NPK (120:26.5:25.0 kg ha⁻¹, N:P:K), T4) 100 % NPK, T5) 150 % NPK, and T6) 100 % NPK + farmyard manure (FYM @10,000 kg ha⁻¹), implemented in a randomized block design with three replicates. The source of P was single super phosphate, except T4 (diammonium phosphate). The results highlight a significant accumulation of P under continuous fertilization compared to the control treatment. Olsen P in surface soil under the 100 % NPK + FYM treatment exhibited an increase of 522 % relative to the control and 108 % compared to the 100 % NPK treatment. The accumulation was characterized by varied distributions across inorganic and organic P fractions, which were influenced by the fertilizer applications. A general enhancement in P fractions was observed with fertilization, with levels ranging from a minimum under 50 % NPK to a maximum under 100 % NPK + FYM treatment. The distribution of P fractions followed the order: Ca-P > Al-P > Org-P > Fe-P > Red-P (reductant-soluble phosphate) > Sol-P (soluble P). Regarding the distribution of P fractionation, an incubation study was conducted to assess the effects of organic amendments, specifically paddy straw and FYM, on P fractions at different levels of added P. The findings revealed a pronounced enhancement in P distribution into its labile fractions. The P balance sheet indicated a net positive soil P balance following 52 cropping cycles under varied fertilization except control. Additionally, correlations between soil P fractions and crop yield were calculated. These findings necessitate further investigation to refine P management strategies to optimize the utilization of residual P for sustainable crop production.