Tension infiltration for estimating pore distribution of alfisols under different land management systems

A field infiltration study was undertaken to evaluate near-surface pore characteristics under long-term land management systems in the semi-arid tropical Alfisols of India. Double ring and tension infiltrometer methods using tension equivalent to 3, 6 and 15 cm of water column were applied to soil under four land use systems; viz. cultivated field, under sorghum (Sorghum bicolor (L.)-castor [Ricinus communis (L.)] in two years rotation for last ten years; grassland, under Cenchrus ciliaris (L.) since 1991; forest soil, under subabul (Leucaena leucocephala) plantation since 1991; and an undisturbed bare soil within a micro-watershed. Ponded infiltration rates under forest, grassland and bare soil were 5.8, 2.2 and 1.4 times more than in cultivated field. At tension of 3 and 6 cm of water, maximum infiltration was found in the forest soil followed by grassland, cultivated field and bare soil and at l5-cm water tension, the trend was: grassland followed by forest soil, cultivated field and bare soil. The relatively large contribution of water flow in forest and grassland was probably due to combination of root chemicals, invertebrated burrows and the structural development of soil matrix materials. Lower bulk density, higher mean weight diameter of aggregates and higher organic carbon content were recorded in the forest and grassland soil compared to those of cultivated and undisturbed bare soils. Though number of macropores (diameter > 0.1 cm) were very less in all the soils except forest soil, nevertheless, nearly 77.5, 77.1, 72.5 and 64.5% of the saturated flux occurred in forest soil, bare soil, grassland, and in cultivated field, respectively through these macropores.