Changes in soil phosphorus forms in a long-term cropping system as influenced by fertilization and tillage

Abstract

ABSTRACT Imbalanced use of chemical fertilizers can deteriorate soil quality; however, it can be reversed by organic matter management. Substituting fertilizer N by farmyard manure (FYM) without correcting for extra phosphorus being added could pose an environmental problem. A long-term experiment on rice-lentil cropping system was examined, where N was substituted through FYM without correcting for the P being added. Three fertilizer treatments (100% inorganic, 50% organic and 100% organic fertilization) were superimposed over two tillage treatments (conventional and minimum tillage) in a split plot design in a Typic Haplustepts. P uptake did not correlate to phosphorus application, and partial phosphorus balance (PPB) was positive. Zero PPB was obtained at P application of 11.7 kg ha−1 signifying that all treatments were over-fertilized with respect to phosphorus. Total and available phosphorus increased in response to increase in PPB. Changes in soil phosphorus fractions with depth were compared to control plot and considerable increase in all the P fractions was noticed. P application rate in excess of zero PPB (11.7 kg P ha−1) would increase various soil P fractions, especially soluble P, and could be a reason for concern of P loss to the environment through overland flow or leaching losses to groundwater. Abbreviations: PPB: partial phosphorus balance; FYM: farmyard manure; q: quintal; P: phosphorus; S-P: soluble phosphorus; Al-P: aluminium bound phosphorus; Fe-P: iron bound phosphorus; R-P: reductant soluble phosphorus; Ca-P: Calcium bound phosphorus.