Effect of sewage sludge and synthetic fertilizer on pH, available N and P in pasture soils in semi-arid area, Turkey
Activated sewage sludge from the aerobically-digested treatment and synthetic fertilizer were used to determine total N, available P and pH in different soil depth of pasture in semi arid ecological condition, in Van, Turkey. The study was carried out in a completely randomized block. Four treatment of sewage sludge, one treatment of synthetic fertilizer and no treatment as a control were used in two consecutive years. Soil samples were collected from surface soil (0 to 20 cm) and subsoil (20 to 40 cm) 11 months after SS (sewage sludge) and TSP (triple super phosphate) application and 7 months after AN application for both years. By using sewage sludge and synthetic fertilizers treatments, surface and subsoil pH decreased. The decreases of pH in SF and control plots in both soil depths in 2008 were attributed to root biomass. Although, sewage sludge contains less amount of nitrogen than synthetic fertilizer does, it enabled nitrogen detection in both soil depths for a longer time and in a higher amount. While an increase in the amount of nitrogen in surface soil and subsoil was determined in 2007, a decrease in these was determined in 2008 in both depths. Amount of subsoil available phosphorus increased more by sewage sludge applications. However, amount of surface soil available phosphorus increased more by sewage sludge applications in 2007, while it increased more by synthetic fertilizer application in 2008. The lowest pH value, highest amounts of total N and available P was obtained by higher doses of sewage sludge. However, when long time applications and mineralization process were considered, sewage sludge’s dose of 2.5 ton/ha-1 ya-1 can be said to provide more beneficial results than the synthetic fertilization’s highest dose which is suggested for pastures and meadows.
Key words: Sewage sludge, synthetic fertilizer, pH, N, P, available duration.