Determination of Application Effects of Sewage Sludge on Growth, Soil Properties, and N Uptake in Komatsuna by using the Indirect15N Isotope Method

Abstract: By using the indirect 15nitrogen (N) method, the application effects of sewage sludge (SS) on growth indices, yield, and nutrient uptake in Komatsuna (Brassica campestris var. perviridis) grown in a low fertility soil were investigated and compared with those of chemical fertilizer (CF) and no‐fertilizer (NF) treatments. The N‐use efficiencies of CF and SS were 19.7% and 12.1%, respectively, of the applied N. Therefore, the relative efficiency of the sewage sludge to chemical fertilizer was 61.5%. In comparison to NF and CF, the application of SS apparently increased the soil microbial activity, which was evaluated by measuring hydrolysis of fluorescein diacetate. After cultivation, the electrical conductivity (EC) of CF soil (0.175 dS m−1) was significantly higher than those of NF (0.067 dS m−1) and SS soils (0.057 dS m−1). The concentrations of phosphorus (P), calcium (Ca), and magnesium (Mg) in SS leaves were significantly higher than those in CF leaves; however, the concentration of potassium (K) was significantly lower in SS than in CF.