Long-term effect of varying nutrient management practices on the distribution of native iron and manganese in various chemical pools under rice – wheat cropping

Abstract

A long-term experiment under a rice – wheat system was used to investigate the effect of organic manures and chemical fertilizers application on the distribution of Fe and Mn in various soil fractions. The cultivation of rice – wheat continuously for seven years without any fertilization did not deplete the amounts of Fe and Mn in various fractions from their original levels. Application of farmyard manure, press mud and green manure along with chemical fertilizers increased the Fe content by 37.5, 56.3 and 75.0% in water-soluble plus exchangeable fraction, respectively compared to chemical fertilizer only treatment (N150P75K75Zn25). In organically bound Fe fractions, the increases due to corresponding treatments over fertilizer-only treatment were 16.4, 20.7 and 10.3%, respectively. The water-soluble plus exchangeable Mn registered an increase of 84.6, 46.2 and 46.2% with N150P75K75Zn25 + farmyard manure, N150 + press mud and N150P37.5K37.5Zn25 + green manure treatments, respectively, compared to N150P75K75Zn25 treatment. The organically bound Mn fraction was almost 2.6 times greater in organic manures + inorganic fertilizers treatments than fertilizer alone treatment. The amounts of both Fe and Mn in water-soluble plus exchangeable, organically bound and Mn-oxide fractions were significantly higher after rice than after wheat harvest.