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MICRONUTRIENT STATUS OF INDIAN SOILS

The amount and distribution of available micronutrient in soils are determined by
several factors such as geochemical composition, soil type, soil horizon, soil age, intrinsic
properties of the soils, input of trace elements, available macronutrients and their interactions
with micronutrients, and vegetation (Fageria et al, 2002, Alloway 2008, Shukla et al 2016,
Shukla and Tiwari 2016). The low level of available micronutrients and their rampant
deficiencies in Indian soils are attributed to above reasons, in addition to intensification of
agriculture without adequate replenishment of micronutrients to soils through fertilization.
Furthermore, loss of micronutrients through leaching, liming of soils, decreased use of
manures and increased use of high analysis fertilizers devoid of micronutrients as impurities
have contributed to accelerated exhaustion of available micronutrients in soils.
Total soil micronutrient content is a complex function of parent material and
pedogenic processes. Their content, distribution, and availability vary widely among soils
within and across regions because parent materials differ widely in micronutrient content
owing to variable modes of deposition and transport and weathering regimes.
In spite of the relatively high total concentrations of micronutrients in soils of India,
micronutrient deficiencies have been frequently reported in different crops grown on these
soils due to low levels of available micronutrients in soils (Behera and Shukla, 2014, and
Shukla et al 2014, Shukla and Tiwari, 2016). Availability can be defined as the quantity of a
soil nutrient that is accessible to plant roots during the growing season. Since plant roots
absorb micronutrients directly from the soil solution, the total pool of soil micronutrients
remotely relevant. Based on the critical limits followed in different states of India, the
micronutrient deficiency status has been assessed in different soils during 2013-2018. The
analysis of more than 2.0 lakhs soil samples during this period revealed widespread
micronutrient deficiency in soils. On average, 6, 30 and 31% area are acute deficient,
deficient and latent deficient in sulphur across the country (Figure 2.1). The deficiency of Zn
has been reported in 2, 28 and 23% area under acute deficient, deficient and latent deficient
category respectively. The area under acute deficient, deficient and latent deficient category
are 1, 7 and 8% for Fe, 1, 2 and 5% for Mn and 0.5, 1.5 and 5% for Cu respectively.
Although acute B deficiency is in 2% area of the country, the area under deficient (21%) and
latent deficient (25%) category is high.
The available Zn, Fe, Mn, Cu and B in different soils varied widely (Table 2.1). The
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available Zn concentration varied from traces to 45.4 mg kg in different soil types. The
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mean values of available Zn varied from 0.40 mg kg (desert soils-lithosolic) to 2.4 mg kg -1
(glacier and eternal snow and sub-montane soils). The per cent samples deficient in available
Zn were highest in desert soils-lithosolic (86.3%) followed by skeletal soils (63.2%), desert
soils-rhegosolic (54.0%), medium black soils (39.4%), mixed red and black soils (36.2%) and
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so on. The values of available Fe in different soils varied from 0.01 to 964 mg kg . The
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highest mean value of 69.8 mg kg was recorded in laterite soils whereas the lowest value of
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7.0 mg kg was recorded in desert soils-rhegosolic.