Evaluation of Nutrient Index using Manganese as a Measure of Fertility Status of Soils under Different Cropping Systems of Punjab in North-Western India

Abstract

Due to intensive cropping, improper agricultural practices and use of high grade chemical fertilizers, the areas gradually tend to show depletion of macro and micronutrients which has an adverse impact on quality and quantity of crops. Therefore, this study was undertaken in three districts of Punjab (north-western India) with the aim of assessing the fertility status of soils of major cropping systems through nutrient index criteria. A total of 150 surface soil samples were collected from various blocks of three districts of Punjab located in the north-western region of India from major cropping systems viz., rice-wheat (Ludhiana district), maize-wheat (Ropar district) and cotton-wheat (Mansa district). These samples were analyzed for pH, electrical conductivity (EC), soil organic carbon (SOC), cation exchange capacity (CEC), sand, silt, clay, DTPA-extractable manganese (DTPA-Mn) and different Mn fractions of variable solubility. In soils, with DTPA-Mn content (>5.0 mg kg-1 soil), the concentration of water soluble + exchangeable Mn (WSEXMn), specifically adsorbed Mn (SpAD-Mn), oxides bound Mn (OX-Mn), amorphous iron oxide bound Mn (AFeOX-Mn), crystalline iron oxide bound Mn (CFeOX-Mn) and organic matter bound Mn (OM-Mn) fractions was significantly higher as compared to soils with DTPA-Mn content (<3.5 or 3.5-5.0 mg kg-1 soil). Among all the Mn fractions, the residual-Mn (RES-Mn) fraction comprised the largest (65-71%) and OM-Mn fraction comprised the lowest (0.3-0.8%) proportion of total-Mn in all DTPA-Mn categories. Based on fertility ratings, SOC concentration in soils with DTPA-Mn categories (<3.5, 3.5-5.0 or 5.0 mg kg-1 soil) was medium with more than 60% of soil samples falling in the medium (0.40-0.75%) category. The EC in soils with different DTPA-Mn categories (<3.5, 3.5-5.0 or 5.0 mg kg-1 soil) was significantly low with more than 80% of soil samples falling in the low (<0.8 dS m-1) category. Based on the nutrients indices (2.63, 2.47 or 2.37), soil pH status was high in soils with different DTPA-Mn categories (<3.5, 3.5- 5.0 or >5.0 mg kg-1 soil), respectively. The EC was low in all DTPA-Mn categories. Organic carbon status was medium in all soils with different DTPA-Mn categories.