Manganese availability and transformations in soil profiles under different wheat based cropping systems in north-western India

Abstract

We studied the depth-wise distribution of DTPA-Mn and Mn fractions of variable solubility in soils under three different cropping systems viz. rice-wheat (RWCS), maize-wheat (MWCS) and cotton-wheat (CWCS) in Punjab, north-western India. The surface (0-15cm) layer of soils under RWCS had significantly lower (by ~31.8%) DTPA-Mn concentration, compared with MWCS. The surface soils under CWCS had ~18.4% higher DTPA-Mn than the soils under RWCS. The DTPA-Mn increased significantly with increased depth of soils under RWCS, in contrast to a significant decrease in MWCS and CWCS. A sequential extraction of Mn in different fractions of variable solubility revealed that the surface layer of soils under RWCS had significantly lower concentration, while the lower layers had higher concentration. On the other hand, the surface layer of soils under MWCS and CWCS had significantly higher concentration, which decreased with increased soil depth. The Res-Mn fraction comprised the largest proportion (67-70%) of total-Mn in soils under different cropping systems. The (WSEX+SpAD)-Mn fraction were the smallest Mn fraction of high solubility, comprising ~2-3% of total-Mn in soils under different cropping systems. The relative distribution of different fractions followed: OM-Mn ≤ WSEX-Mn ≤SpAD-Mn <AFeOX-Mn <CFeOX -Mn < Ox-Mn <  residual-Mn.