Page 15 - index

The per cent samples deficient in available Fe followed the order: desert soils-
lithosolic > desert soils-rhegosolic > grey brown soils > old alluvial soils > calcareous
sierozemic soils > skeletal soils > medium black soils and so on. Available Mn in different
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soils ranged between 0.01 and 445 mg kg . The lowest and the highest mean value of
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available Mn were recorded in desert soils-lithosolic (4.70 mg kg ) and deltaic alluvium
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(32.6 mg kg ) respectively. Like available Zn and Fe, the highest per cent samples deficient
in available Mn were in desert soils-lithosolic (37.8%). Different soils had traces to 136 mg
-1
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kg of available Cu, and the mean values of available Cu varied from 0.40 to 3.90 mg kg .
The per cent samples deficient in available Cu were higher in desert soils followed by old
alluvial soils, calcareous sierozemic soils and so on. Available B concentration ranged from
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0.01 to 170 mg kg with mean values spanning from 0.54 mg kg (sub-montane soils) to
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12.9 mg kg (deltaic alluvium). Higher extent of B deficiency was recorded in grey brown
soils (46.3%), sub-montane soils (33.7%), desert soils-rhegosolic (24.7%), calcareous alluvial
soils (24.4%) and red sandy soils (22.8%). On the other hand, skeletal soils, desert soils-
lithosolic and old alluvial soils exhibited lower magnitude of deficiency. Such a wide
variation in the available micronutrient concentrations in different soils is due to variation in
soil parent material, prevailing climatic conditions and soil management practices (Shukla et

al., 2016).
Mapping soil micronutrient status
Maps illustrating the geographic distribution of soil micronutrient availability are necessary
to understand the level of micronutrient deficiency/toxicity and their judicious management
for improvement of agriculture and livestock production, improvements in diet quality, and
animal/human health. For assessing micronutrient deficiency or toxicity areas, a variety of
methods have been used to derive qualitative and quantitative maps illustrating plant-
available micronutrient content in soils at various scales. Earlier, micronutrient mapping was
performed using nutrient index (NI) for whole area considering number of samples falling in
low, medium and high categories, which was often misleading. For example, out of the 100
soil samples analysed for a district, if 20, 25 and 55 numbers of samples fall in low, medium
and high category respectively, gives high (2.35) NI value. Later on, maps prepared based on
per cent sample deficient (PSD) basis at district level were useful in estimating the extent of
deficiency across the country. These maps were used in understanding the extent of
deficiency however, it did give any idea about area really deficient in particular nutrients.
Hence, precise prescriptions based on nutrient variability in a block or village was not
possible as these maps did not reflect variation in soil micronutrient status within the
districts. The present GIS based digitized maps of micronutrient status are highly useful in
understanding the nature and extent of micronutrient problems, besides formulating
strategies to alleviate their deficiency and help policy makers and industry to produce and
distribute the right kind of micronutrient fertilizers in based on area spread deficiency.
These maps are also helpful in mitigating micronutrient deficiencies through site- specific
variable rate application of micronutrients controlled by prescription maps. These maps
were useful for the policy makers and fertilizer industry in distribution of fertilizers. Further,
the maps also provide quantitative support for decision and policy making to promote
balanced and prudent micronutrient management and precision agriculture.