Sewage Sludge as Nitrogen Source for Irrigated Silage Sorghum

Abstract

Field experiment was conducted in clay loam soil in Van, located in the eastern part of Turkey, to study sewage sludge and ammonium sulphate as nitrogen sources for sorghum. Silage and dry matter yield, plant height, stem, leaf and particle ratio, plant nitrogen content, total N uptake, leaf nutrient and heavy metal content, soil DTPA-extractable nutrient and heavy metal content were quantified. The experimental design was a randomized complete block with four replications. Two rates of ammonium sulphate (50, 100 kg ha(-1)) and three rates of sewage sludge (5.95, 11.90 and 23.80 Mg ha(-1)) were applied to plots. Sorghum plant was irrigated once a week until soil water content reached to field capacity. Silage and dry matter yield, plant height and total N uptake increased with application of chemical N fertilizer and sewage sludge as compared to control. The yield results revealed that, 100 kg ha(-1) nitrogen rate and 23.80 Mg ha(-1) sewage sludge rate caused to produce almost the same amount of silage and dry matter yield. Leaf N, P, Ca, Mg, Fe and Mn content of sorghum increased with application of N fertilizer and sewage sludge. Mentioned nutrients in leaf were found pretty similar with application of 100 kg ha(-1) N rate and 23.80 Mg ha(-1) sludge rate. Besides, Potassium content of sorghum leaf was not affected by either treatment. Leaf Zn content increased with application of N fertilizer and sewage sludge and it reached the highest level at 23.80 Mg ha(-1) sludge rate. Leaf Cu content increased only with application of sewage sludge. Also, Fe, Zn, Cu and Ni contents in experiment soil increased with application of sewage sludge and their levels reached to the highest at 23.80 Mg ha(-1) sludge rate. None of heavy metal reached toxic level either in plant or in soil. Results indicated that sewage sludge, produced in Van region, could be used as a fertilizer nitrogen source for sorghum, without risks associated with toxic heavy metals.