SULPHUR RETENTION AND RELEASE AS INFLUENCED BY SOIL TYPE AND MANAGEMENT PRACTICES IN THE AGROCLIMATIC ZONES OF JAMMU REGION

Soil samples from thirty profiles (depth wise) from cultivable areas representing three agroclimatic zones viz. sub-tropical, intermediate and temperate zones were studied for sulphate retention and release. Besides, a field experiment was conducted at Research Farm, Faculty of Agriculture, Chatha to study the response of sulphur on oilseed crop and its residual effect on the succeeding rice crop. In the current study, it was found that the amount of total sulphur content in soils varied between 65 to 882 mg kg"' and it decreased with increasing depth. Mean contents of total S in temperate, intermediate and sub-tropical zone was 848, 601 and 371 mg kg"' in surface layers and 671, 439 and 272 mg kg" in sub-surface layers. Organic S was the dominant fraction constituting 65, 50 and 41 per cent of total S in temperate, intermediate and sub-tropical zones, respectively with a range of 31 to 592 mg kg"' in the soils of different agro-climatic zones and followed distribution pattern as that of organic carbon. Sulphate S constituted the lowest component of in-organic S. the amount being 2.4 to 51.1 mg kg"' constituting on an average 5.3, 5.2 and 2.8 per cent of total S in subtropical, intermediate and temperate zone soils, respectively. Non-sulphate S ranged from 28 to 361 mg kg"' in all the profiles studied and was second largest fraction of total S after the organic S. Water soluble S varied from 9.2 to 66.5 mg kg"' and this fraction on an average constituted 6.5 per cent of total sulphur. Adsorbed S in all the soils varied between 23.0 and 98.0 mg kg"' showing an increasing trend down the profile. Consequently, order of abundance of S content in soils studied was : Total S > Organic S > Non-sulphate > Adsorbed S > Water soluble S > Sulphate S. Total S had a significant and positive association with organic carbon content and soil pH in all the three agro-climatic zones, whereas, it exhibited a positive relationship with silt and clay content in intermediate and sub-tropical zones. Multiple regression analysis indicated significant influence of organic carbon on total S. Organic, sulphate and water soluble S fractions were significantly and positively correlated with organic carbon in all the three zones. Non-sulphate S had a significant and positive association with pH and organic carbon but negatively correlated with exchangeable aluminium. All the forms of S were positively and significantly correlated with each other except adsorbed S and from these studies it is evident that different forms of S are dependent upon soil characteristics and a relationship exists among themselves. Sulphate adsorption by soils of three agro-climatic zones of Jammu region, irrespective of the treatments increased with rise in concentration of added sulphate solution, the magnitude of its increase however varied between soils and concentrations. In sub-tropical zone maximum adsorption of sulphate was noticed in Samba soils (296.2 mg kg"') while lowest adsorption was noticed in Lakhanpur soils (100 mg kg"') at 300 mg L"' of sulphate added. In intermediate zone soils, maximum sulphate was adsorbed in Rakhsansu soils. Temperate zone soils recorded sulphate adsorption of 87.5 to 437.5 mg kg"' at different concentrations of sulphate added. Adsorption isotherms indicated that adsorption of sulphate increased with increasing concentration and the percentage of adsorbed sulphate decreased from 70.0 to 6.6, 77.0 to 13.4 and 70.0 to 25.8 per cent in subtropical, intermediate and temperate zone soils, respectively. Langmuir adsorption maxima (b), bonding energy (k) and maximum buffering capacity of these soils varied from 11 I.I to 556.0 mg kg"',0.009 to 0.058 L mg"' and 2.36 to 19.34 L kg"', respectively. Sulphate adsorption maxima and maximum buffering capacity had significant negative relationship with pH and significant positive relationship with exchangeable aluminium and free iron oxides. Bonding energy was positively associated with clay content. Freundlich K value varied from 11.26 to 61.10 mg kg"' in all the three zones and showed a positive and significant relationship with clay content. However. Freundlich l/n varied from 0.256 to 0.596 for soils of three zones. The amounts of sulphate extracted by KH2PO4 varied considerably with the levels of sulphur and increased with increasing amounts of sulphate sorbed. Amount of S desorbed varied from 62.4 to 84.4 per cent of the sorbed sulphur. Field studies conducted to find out the direct and residual response of sulphur indicated that up to 30 kg S ha"' applied through gypsum, increased yield of mustard (variety Varuna) by only 21.3 per cent over control. Although the residual effect of S on rice yield was non-significant, the grain yield of rice increased by 5.32 per cent. Student Major Advisor