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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
               soils  ranged  between  0.01  and  445  mg  kg .  The  lowest  and  the  highest  mean  value  of
               available  Mn  were  recorded  in  desert  soils-lithosolic  (4.70  mg  kg )  and  deltaic  alluvium
               (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
               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
               0.01 to 170 mg kg  with mean values spanning from 0.54 mg kg  (sub-montane soils) to
               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.
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