Patgiri, Dilip KumarGogoi, Manjurima2024-09-232024-09-232023https://krishikosh.egranth.ac.in/handle/1/5810214821The present investigation was carried out for assessment of soil physico-chemical and biological properties, distribution of different forms of soil carbon and contribution of different forms of soil carbon on soil aggregation under different fodder crop based system. Soil samples were collected from twenty three crop situations of three locations of Jorhat and Golaghat districts of Assam including virgin soils. Samples were collected as bulk soil samples, large core samples and mini core samples from 0–20, 20-40, 40-60, 60-80 and 80-100 cm soil depth from each plot under fodder crop and virgin soil. It was observed that soil physico- chemical and microbiological properties were greatly improved by continuous cultivation of fodder crops. The pH of soils under fodder crops down the depth were higher than those in virgin soils making these soils less acidic in reaction. Continuous cultivation of fodder crops increased the per cent organic carbon content of soil and it is high in case of napier than other fodder crops. Available nitrogen, phosphorus, potassium, calcium and magnesium contents increased due to continuous cultivation of fodder crops and continuous cultivation of napier grass as well as setaria showed high range of these nutrients than other fodder crops. Continuous cultivation of fodder crops increased hydraulic conductivity of soils and six years continuous cultivation of napier showed highest range of hydraulic conductivity of 0.119 cm sec-1 to 0.001 cm sec-1 with a mean value of 0.028 cm sec-1. Bulk density decreased due to continuous cultivation of fodder crops and continuous cultivation of setaria for six years showed lowest bulk density ranged from 0.93 Mg m-3 to 1.05 Mg m-3 with a mean value of 1.00 Mg m-3. Per cent available water content increased due to continuous cultivation of fodder crops and fourteen years continuous cultivation of napier showed highest range of available water content of 13.37% to 6.79% with a mean of 10.59%. Continuous cultivation of napier, setaria and congosignal showed higher soil aggregation and mean weight diameter than other fodder crops and virgin soil. The microbial biomass carbon, phosphomonoesterase activity and dehydrogenase activity of fodder crops was much higher than the virgin soils. The highest microbial biomass carbon range was found in case of fourteen years continuous cultivation of napier (769.3 μgm gm-1 to 96.6 μgm gm-1 with a mean of 388.3 μgm gm-1). Six years continuous cultivation of maize showed highest phosphomonoesterase activity (336.5 μgmgm-1hr-1 to 210.1 μgmgm-1hr-1 with a mean of 249.0 μgmgm-1hr-1) and five years continuous cultivation of hybrid napier showed highest dehydrogenase activity (22.94 μgmgm-1hr-1to 5.69 μgmgm-1hr-1with a mean of 15.82 μgmgm-1hr-1). The highest total organic carbon content wasfound in case of continuous cultivation of napier followed by continuous cultivation of setaria and it was higher in 20-40 cm layer of soil than in 0-20 cm layer. Six years continuous cultivation of napier showed highest range of soil carbon stock of 37.01 t ha-1 to 24.64 t ha-1 with a mean of 31.46 t ha-1. The oxidisable organic carbon decreased with the increase in soil depth down the profile anddue to high vegetative growth, continuous cultivation of napier or hybrid napier showed high oxidisable organic carbon in soils. Highest hot water extractable organic carbon was found in continuous cultivation of hybrid napier followed by setaria. The highest cold water extractable organic carbon content was found in six years continuous cultivation of cowpea. The highest range ofhumic acid and fulvic acid were found in continuous cultivation of napierfollowed by continuous cultivation of setaria.The very labile carbon and labile carbon also decreased down the profile with increase in soil depth and continuous cultivation of napier as well as setaria showed higher values than other fodder crops and virgin soils. Fourteen years continuous cultivation of napier showed highest very labile carbon (0.94% to 0.27% with a mean of 0.58%) and labile carbon (0.87% to 0.20% with a mean of 0.50%).The highest range of less labile carbon was found in six years continuous cultivation of napier (0.29% to 0.47% with a mean of 0.39%) which was high in lower soil depths than upper 0-20 cm soil layer. The non labile pool of carbon first increased and later decreased down the profile with increase in soil depth in both fodder crops and virgin soils. Significant positive correlation was observed for labile carbon with very labile carbon; cold water extractable organic carbon with hot water extractable organic carbon; humic acid with very labile carbon, labile carbon and hot water extractable organic carbon; fulvic acid with very labile carbon, labile carbon ,hot water extractable organic carbon, cold water extractable organic carbon and humic acid; microbial biomass carbon with labile carbon, hot water extractable organic carbon, humic acid and fulvic acid; phosphomonoesterase activity with hot water extractable carbon, humic acid, fulvic acid and microbial biomass carbon; dehydrogenase activity with hot water extractable organic carbon, humic acid, fulvic acid and microbial biomass carbon; mean weight diameter with hot water extractable organic carbon, humic acid and fulvic acid.Less labile carbon and non labile carbon showed negative correlation with almost all the parameters. Aggregation was higher in macroaggregates than microaggregates and in upper layers of soil mainly 0-20 cm and 20-40 cm soil layers. Growing of napier grass and also setaria, seemed to have greater influence on soil aggregation as compared to other crops. Different forms of aggregate associated soil organic carbons were higher in fodder crops than virgin soils and aggregate associated total organic carbon, oxidisable organic carbon (%), hot water extractable organic carbon, cold water extractable organic carbon, humic acid and fulvic acid, very labile carbon and labile carbon of soils were higher in 0.25 mm to 1.00 mm size range of aggregates in case of both fodder crops and virgin soils. Very labile carbon and labile carbon content were higher in 0.5 mm to 0.10 mm size range than 0.25 mm size range. The aggregates in the size range of 0.50 and 0.25 mm contained higher humic acid as compared to the other size ranges.The aggregate associated less labile carbon per cent were higher in case of macroaggregates. The non labile carbon was higher in 20-40 cm soil depth and in 5.00 mm, 2.00 mm and 0.10 mm size range of aggregates than 0.25 mm to 1.00 mm size range. It is seen that continuous cultivation of napier showed highest percentage of aggregate associated different forms of soil carbon.EnglishThesis