Page 13 - index
P. 13


                       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
               available  Zn  concentration  varied  from  traces  to  45.4  mg  kg   in  different  soil  types.  The
               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
               so on. The values of available Fe in  different  soils varied from  0.01 to  964 mg kg . The
               highest mean value of 69.8 mg kg  was recorded in laterite soils whereas the lowest value of
               7.0 mg kg  was recorded in desert soils-rhegosolic.
   8   9   10   11   12   13   14   15   16   17   18