Change in cotton plant quality in response to application of anaerobically digested sewage sludge

Treated municipal sewage sludge (TSS) was applied to the cotton plant at rates of 10, 20 and 30 t/ha per year. Seed cotton yield (71.4%), lint yield (67.7%) and cottonseed yield (74.1%) were increased significantly when sludge was applied at a rate of 30 t/ha (TSS3). The effects of TSS applications on seed yield, lint yield and cottonseed yield were listed as TSS3 > TSS2 > CF > TSS1 > C according to the applications. The increasing TSS levels had a positive effect and increased the total N concentration compared to the control. The highest N value was observed in TSS3 plots, while the lowest value was recorded in control (C) plots. The highest P value was found in control (C) at 0.80% and in 10 t/ha (TSS1) at 0.80%, while the lowest value was found in the TSS2 application (0.70%). The K concentration of cottonseed increased with the increasing TSS rates, from 1.56% in control plots to 2.20% in 20 t/ha application (TSS2). Corresponding to the TSS levels, the calcium of plant tissues was determined by a range of 0.12–0.13%. The treatments of TSS and mineral fertilizer had similar effects on the Mg content of cottonseed, which was in the range of 0.38–0.43%. Na content in plant tissue increased with increasing dose of sludge application compared to control soils. Increasing doses of TSS had no significant effect on the concentrations of iron (Fe), copper (Cu), zinc (Zn), manganese (Mn) and boron (B) in cottonseed. The order of the elements with respect to their amounts in cottonseed was as follows: Fe > Zn > Na > B > Mn > Cu. The concentrations of non-essential elements (Ni, Cd, Cr, Pb, Hg and As) in cottonseed were below the permissible limits.