FORMS AND DISTRIBUTION OF PHOSPHORUS AS INFLUENCED BY VARIOUS LAND USE SYSTEMS OF A MICRO-WATERSHED IN NORTHERN TRANSITION ZONE OF KARNATAKASabyasachi Majumdar, P.L. Patil and C.R. Patil
An investigation was undertaken during 2013-14 in northern transition zone of Karnataka to study the forms and distribution of phosphorus and their correlation with different soil properties under different land use systems of Singhanhalli-Bogur micro-watershed. Three land use systems [agriculture (paddy land and non paddy land), forest and horticulture] were selected for the study. From each land use system, fifteen surface (0-20 cm) soil samples were collected randomly and analyzed for different phosphorus fractions by modified method of Chang and Jackson (1957) as outlined by Peterson and Corey (1966). The experimental data obtained was subjected to statistical analysis and testing of significance was done by SPSS 16.0 version. The average percentage of inorganic P fractions in surface soils followed the order; Reductant Soluble-P > Fe-P > Al-P > Ca-P > Occluded-P > Saloid-P (paddy land), Ca-P > Reductant Soluble- P > Al-P > Occluded-P > Fe-P >Saloid-P (non-paddy land), Reductant Soluble-P > Al-P > Fe-P > Ca-P > Occluded-P > Saloid-P (horticulture land), and Reductant Soluble-P > Al-P > Occluded-P > Fe-P > Ca-P >Saloid-P (forest land). The per cent contribution of saloid-P to the total P in surface samples varied from 0.27 per cent (forest land use) to 0.82 per cent (non-paddy land use). The higher Fe-P content in surface soils of paddy land, horticulture and forest land use might be attributed to the presence of more organic carbon which provides organic acids which leads to solubilization of iron to ferrous form along with phosphates resulting in precipitation of ferrous phosphate. The contribution of Reductant Soluble-P to total P was observed the highest under forest land use system. However, the ratio of Occluded-P to total P in different soil under different land use system varied within a narrow limit of 4.20 to 9.25 per cent. The high Ca-P content of surface soils under non-paddy land use could be attributed to high CaCO3-content. Soil pH had negative and significant correlation with Al-P in almost all the land uses. Ca-P and occluded- P showed a significant positive correlation with organic carbon in all the land use systems.
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