LAUSR

Optimizing the utilization of agroindustrial organic waste such as palm oil mill effluent (POME) can prevent environment pollution and soil nutrient cycling can be a valuable alternative to improve soil quality. The objective of this study was to evaluate the changes of soil organic fractions and nutrients after application of treated  palm oil mill effluent. The treatments consisted of control and effluent application at rates of 5, 10, 15 and 20 ton ha -1 . The treatments were arranged in a completely randomized design with three replications.  Application of effluent significantly increased total organic C, labile organic C, humic acid C, pH, total N, available P, and exchangeable K.  A significant reduction of exchangeable Al also occurred with effluent application. The increases of total organic C and labile organic were found with the application of 20 t ha -1 of effluent, but the increase was not significant compared to the effluent application at rates of 10 and 15 t ha -1 . Sensitivity indexes of total organic C, labile organic C and humic acid C following effluent application were 24-66%, 103-197% and 95-114% respectively in which labile organic C showed the highest sensitivity index.   Total organic C, labile organic C and humic acid were positively correlated with increasing rates of effluent application. Labile organic C revealed the strongest relationship (R 2 =0.91) with effluent application compared to total organic C (R 2 =0.88) and humic acid (R 2 =0.67). A significant increase of total N was only found by the effluent application at rate of 20 t ha -1 . Significant increases in available P and exchangeable K occurred at rate of 10, 15 and 20 t ha -1 . It can be concluded that the increase in soil organic carbon  levels was related to the amount of organic (effluent) input added to the soil. In addition, the application of treated effluent can improve soil pH and nutrient availability.