A Study of carbofuran adsorption and leaching in three soil series of Jaffna Peninsula

Carbofuran is a widely used nematicide and insecticide in Jaffna peninsula. Carbofuran is relativelymobile in soil and has the potential to contaminate groundwater. This study examined the adsorptionand leaching potential of carbofuran in three soil series of Jaffna Peninsula. Four replicate soil samplesfrom Chankanai, Inuvil, and Navatkuli series were used for the adsorption study. To study the leaching, a pot experiment was carried out with four replicates in complete randomized design (CRD). Each soil was treated with carbofuran at the departmental rate. Leachate was collected in the 1st, 2nd, and 3rd week and amount of carbofuran was analyzed. The percentages of adsorption were 37.6, 19.2 and 5.6 in Chankanai, Inuvil and, Navatkuli series respectively. Highest percentage of organic matter content (1.71%) may be the reason for the highest adsorption of Chankanai soil. This soil has 17% clay content.Navatkuli series soil had lowest percentage of organic matter content (0.62%) as well as lower percentage of clay content (8%). Highest carbofuran leaching of 400?g was observed in Navatkuli series. Inuvil and Chankanai soils recorded 244 and 225 ?g respectively. Lowest leaching of Chankanai soil can be explained by highest adsorption of this soil. Likewise, highest leaching of Navatkuli soil can be explained by lowest adsorption. Study indicates that risk of ground water pollution by carbofuran is highest inNavatkuli serie

Organic carbon fractions, aggregate stability, and available nutrients in soil and their interrelationships in tropical cropping systems : a case study

Tropical agricultural soils have been claimed as a source of carbon. As agricultural systems in the tropics are highly diverse, it is useful to study soil organic C (SOC) of different agricultural systems. We quantified the SOC fractions, available nutrients, and aggregate stability in eight different tropical agricultural systems, including annual crops under different management scenarios, such as organic, inorganic, and combined fertilizer applications. Annual crops treated with organic fertilizer only (A–OF), inorganic fertilizer only (A–IF), both organic and inorganic fertilizers (A–O/IF), perennial crops (PC), home gardens (HG), and abandoned home gardens (AHG) in Eutrustox soils and annual crops with organic fertilizer only (A–OFS) and uncultivated land on Quartzipsamments soil (USR) were studied. The links between SOC fractions, available nutrients, and aggregate stability in these soils were analyzed. Regression models were fitted for SOC fractions and available nutrients. Our results indicated that the different land use types exhibited significant variations in organic carbon fractions, aggregate stability, and available nutrients in soils. The available macro and micronutrients, except for nitrogen, showed a significant positive correlation with either total organic C (TOC) or carbon fractions indicating the synergy between them. The differences in soil C stocks clearly reflected the differences in litter fall and soil disturbance, as indicated by the highest C stocks in AHG. The dry weight of collected litter showed that AHG accumulated the highest litter content (97.38 g/m2) compared to the lowest (37.63 g/m2) in A–I/F. Organic matter addition to soil also increased the C stocks, even in annual crops. Aggregate stability showed a positive correlation with C fractions. The regression models developed in this study can be used to predict available nutrients by measuring TOC or C fractions in similar land use types in the tropics. This study confirmed that tropical agricultural systems that include annual crops have potential for storing and maintaining C in soils, if appropriately managed. The beneficial influence of SOC on available nutrients and aggregate stability could be a driving force to increase carbon stock in tropical agricultural systems