Abstract
A field experiment was conducted to evaluate the effects of directly, residually, and cumulatively applied mixed sludge generated by the soft-drink industry on rice and wheat yields, soil fertility, grain heavy-metal uptake, depthwise distribution of micronutrients and heavy-metals after 3 years of application. Crop (rice/wheat) yield (grain/straw) increased significantly with direct sludge application at 10.0 t ha−1 year−1, either alone or jointly with fertilizers, over the absolute control. Interestingly, the effects of sludge application on crop (rice/wheat) yield either applied directly at 10.0 t ha−1 year−1, residually at 30.0 t ha−1 year−1, and/or cumulatively at 15.0 t ha−1 were nonsignificant. Direct sludge application at 5.0/10.0 t ha−1 year−1 resulted in significant increase in heavy-metal uptake over the absolute control. The micronutrient/heavy-metal contents in surface soil were significantly greater with sludge application than those in subsurface layers. The results thus show that sludge application results in significant improvement in yield and soil fertility.