Diethylenetriaminepentaacetic Acid-Extractable Micronutrients Status in Soil under a Rice-Wheat System and Their Relationship with Soil Properties in Different Agroclimatic Zones of Indo-Gangetic Plains of India

Available micronutrient status of zinc, copper, manganese, and iron (Zn, Cu, Mn, and Fe) in surface soil samples under a rice-wheat system collected from farmers' fields in 40 districts representing different agroclimatic zones of the Indo-Gangetic Plain (IGP) were determined. The selection of farmers, villages, blocks, and districts within an agroclimatic zone was made on the basis of a multistage statistical approach. In Trans-Gangetic Plains, the diethylenetriaminepentaacetic acid (DTPA)-extractable Zn ranged from 0.11 to 5.08, Cu ranged from 0.22 to 4.72, Mn ranged from 2.9 to 101.2, and Fe ranged from 1.05 to 97.9mgkg-1. In the Upper Gangetic Plains, the DTPA-extractable Zn ranged from 0.04 to 2.53, Cu ranged from 0.06 to 4.32, Mn ranged from 11.1 to 421.0, and Fe ranged from 3.48 to 90.2mgkg-1. In the Middle Gangetic Plains, the DTPA-extractable Zn ranged from 0.17 to 8.60, Cu ranged from 0.09 to 7.80, Mn ranged from 3.0 to 155.1, and Fe ranged from 9.22 to 256.7mgkg-1. In the Lower Gangetic Plains, the DTPA-extractable Zn ranged from 0.04 to 3.46, Cu ranged from 0.21 to 4.38, Mn ranged from 9.54 to 252.2, and Fe ranged from 3.60 to 182.5mgkg-1. The intensively cultivated Trans-Gangetic transect representing the midplain and Siwalik had more available micronutrients than the arid plain. Midplain and arid plain showed 17 to 20% of soil samples were low to medium in Zn and 5 and 8% were low in Fe. In the Upper Gangetic Plains, only 25% samples were deficient in Zn, especially in central and southwest plains. In the Middle Gangetic Plains, 20 to 30% of samples were deficient in Zn, and very few samples were deficient in other micronutrients. In the Lower Gangetic Plains, a majority of the samples were medium to high in micronutrients except in Barind and Rarh Plains where 30% of samples were deficient in Zn. In the Lower Gangetic Plains, the available micronutrients were plentiful. Available micronutrients increased with increase in organic C content and decreased with increase in sand content, pH, and calcium carbonate. These soils are alluvial in nature, and there was no definite pattern of micronutrient distribution with depth in the profile. However, there was more accumulation in the Ap horizon than in the B horizon.