Study on Manganese Distribution and Availability in South Gujarat Soils

Nine profiles from the fields growing different and continuous crops were collected from heavy rainfall area of Sow h Gujarat to assess Mn staus, its distribution in profiles, factors affecting its availability and its supplying power. The average values for water soluble + exchangeable, easily reducible, active and total Mn were 8.5, 692.7, 701.2 and 1573.5 ppm respectively. The level of different fractions of Mn showed a very wide variation among the soils under dfferent crops. There was, in general, accumulation of water soluble + exchangeable Mn in surface layers, of active Mn in midlayers and cj total Mn in surface layers or midlayers. Organic ma'ter and clay contents of soils govern the distribution patterns ofwater soluble + exchangeable Mn and active Mn respectively.

Among the soil characteristics, organic matter showed significant positive and pH negative relationship with water soluble + exchangeable Mn, -whereas the levels of easily reducible and active Mn showed highly significant positive relationship with clay. The total Mn content of soils did not show any consistent relationship with any of the soil characteristics.

Among all the cropping patterns, grasses exerted a pronounced effect on status, distribution and supplying power of Mn. This may be due to easily decomposible organic matter and excellent aggregation. The cultural and management practices also affect the levels of different fractions of Mn. Wide variation in the ratio of active to total Mn suggests the variation in the nature of oxides of Mn present in soils.

No chemical extractant tested in the present investigation showed significant correlation with Mn extracted by paddy test plant (Neubauer technique). However, among the chemical extractanis tested, 0.7N H₃PO₄ is considered as the best extractant for these soils.

The soils of this zone are rich in potentially available (active) Mn having very good Mn supplying power and very good store of total Mn.