Evaluation of sewage sludge compost quality through maturity index and biomass yield of Italian ryegrass (Lolium multiflorum L.)

Abstract

Sewage sludge as raw material and Composts was collected from composting plant “Chugoku Yuki” in Okayama prefecture, Japan to evaluate Compost quality at 8, and 50 days in process. Compost quality was assessed by analyzing of chemical properties: pH, total carbon, total nitrogen, C/N ratio, available nitrogen, total phosphorus, available phosphorus and P fractions. A pot experiment was conducted to investigate the effects of four Compost application rates (1, 2, 4 and 6 tons ha-1) on biomass yields and nitrogen – phosphorus uptake efficiency by Italian Ryegrass. Control treatments included without and with chemical fertilizers supplying equal amounts of N + P2O5. The results showed that Compost reached to degrees of stability and maturity after 50 days of composting. Composts contain high levels of nitrogen and phosphorus, heavy metals contents meet the acceptable standards. Total biomass yields significantly increased with increasing application rates following Mitscherlich’s asymptote regression model, by which the maximum yields were estimated to decrease in following order: Compost 50 days > Chemical fertilizer > Compost 8 days. Nitrogen uptake efficiency by ryegrass were similar between two above Composts, while those of Phosphorus was higher at Compost 50 days.