Residual and accumulative effects of sewage sludge on bioavailability of some macronutrients in basil (Ocimum basilicum L.) medicinal plant

To study the residual and accumulative effects of sewage sludge on bioavailability of some macronutrients in basil (Ocimum basilicum L.) medicinal plant an experiment was arranged in split plot based randomized complete block design with three replications. The main plots included fertilizers at six levels including control; recommended chemical fertilizer; sewage sludge as the rate of 20 and 40 Mg ha-1 both enriched and non-enriched with 50% chemical fertilizer. The sob plots were considered one (2006), two (2006-2007), three (2006-2008) and four (2006-2009) consecutive application periods of different fertilizers. Results showed that interaction of sewage sludge and application period (residual and accumulative effect) significantly affected the macronutrients accumulation in basil leaves. Orthogonal comparisons also showed that effects of sewage sludge application on P, N and K content in leaves was significantly higher than chemical fertilizers. The accumulative effects of 40 Mg ha-1sewage sludge both enriched and non-enriched with 50% chemical fertilizer after three consecutive years improved the leaves nitrogen content by 72%. Similarly residual effect of sewage sludge 20 Mg ha-1 enriched and non-enriched with 50% chemical fertilizer for one year increased the P content of leaves by 83%. In addition results derived from the regression diagram showed a strong linear relationship between the amount of nitrogen, phosphorus and potassium absorption with basil dry matter yield.