Long-term Nutrient Management Influences the Vertical Distribution of DTPA-Extractable Micronutrients in a Vertisol under Soybean-Wheat Cropping System

Abstract

Long-term nutrient management plays an important role in maintaining soil micronutrient fertility under continuous cropping. The present study evaluated the effect of long-term fertiliser and manure application on the vertical distribution of DTPA-extractable Zn, Cu, Mn and Fe in a Vertisol under a soybean-wheat cropping system during 2024-25 at the AICRP-LTFE experimental farm, JNKVV, Jabalpur, Madhya Pradesh, India. The long-term experiment was initiated in 1972 and comprised nine nutrient-management treatments, including graded NPK levels, nutrient omission treatments, NPK + Zn, NPK + FYM, sulphur-free NPK and an unfertilised control, and was arranged in a randomised block design with three replications. Soil samples were collected after wheat harvest from six depths (0-15, 15-30, 30-45, 45-60, 60-75 and 75-90 cm) and analysed for DTPA-extractable micronutrients. All four micronutrients showed clear treatment- and depth-dependent variation, with concentrations generally declining with increasing soil depth. At 0-15 cm, DTPA-Zn, Cu, Mn and Fe ranged from 0.24-1.03, 0.90-1.83, 10.97-17.11 and 13.61-28.35 mg kg-1, respectively, compared with 0.10-0.46, 0.46-0.84, 3.78-8.87 and 4.37-9.13 mg kg-1 at 75-90 cm. The 100% NPK + Zn treatment recorded the highest Zn concentration, whereas 100% NPK + FYM maintained the highest Cu, Mn and Fe concentrations across the soil profile. The 150% NPK treatment also maintained high Mn and Fe and was at par with NPK + FYM at 60-75 cm. In contrast, the control consistently recorded the lowest concentrations. The results demonstrate that balanced fertilisation, particularly when integrated with FYM, is effective in sustaining micronutrient fertility and improving the vertical distribution of extractable micronutrients in long-term soybean-wheat cultivation on Vertisol.