ORGANIC MATTER DYNAMICS IN SOILS OF TWO DIFFERENT CROPPING PATTERNS OF GANGES ALLUVIUM

Organic matter releases nutrients in a plant-available form upon decomposition. In order to maintain this nutrient cycling system, the rate of organic matter addition from crop residues, manure and any other sources must equal the rate of decomposition, and take into account the rate of uptake by plants and losses by leaching and erosion. The labile carbon fraction has been shown to be an indicator of key soil chemical and physical properties. For example, this fraction has been shown to be the primary factor controlling aggregate breakdown in Ferrosols (non-cracking red clays), measured by the percentage of aggregates measuring less than 0.125 mm in the surface crust after simulated rain in the laboratory (Bell et al., 1999). The resistant or stable fraction of soil organic matter contributes mainly to nutrient holding capacity (cation exchange capacity [CEC]) and soil colour. This fraction of organic matter decomposes very slowly. Therefore, it has less influence on soil fertility than the active organic fraction. So, the relationship between soil organic carbon and soil aggregate in different size is needed to understand for the management of soil. Under Barbati/Aus/Jute/Vegetable cropping pattern, the (%) SOC in the aggregate size ranges from 0.25-0.05 mm is high and >0.05 mm is low but the NSI value of this cropping pattern was low and in case of Sugarcane-jute/Vegetable cropping pattern the (%) SOC in the aggregate size >2 mm is high and >0.05 mm is low but the NSI value of this cropping pattern is slightly high.

The study area was located in Dumuria of Khulna. Soils from two different land use patterns were taken for study. The land use patterns were Barbati/Aus/Jute/ Vegetables and Sugarcane-Jute/Vegetable.

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