Efficacy of bokashi-composting methods and quality assessment of organic fertilizers on spinach (Spinacia oleracea L.)

Abstract

Raw materials of corn stalk and Japanese watercress at four volumetric ratios of 4:1, 3:1, 2:1, 1:2 were composted for 40 days using compost (PP compost) and bokashi (PP bokashi) methods. The quality of organic fertilizer products as solid (RComp) and liquid (LComp & LBoka) was analyzed for physico-chemical properties and initially evaluated for spinach (Spinacia oleracea L.) in a pot study. The single-factor experiment was arranged in a completely randomized design with seven treatments and three replications. The treatments differed in application rates, types and dilution of liquid organic fertilizers. The PP compost had a thermophilic phase (t > 40oC) lasting for 15 days, which was three times longer than the PP bokashi. Accordingly, RComp(2:1) had a high EC (electrical conductivity) value (3.8 mS/cm) and organic matter (77.7%), and macronutrient concentrations of total N, available phosphorus and potassium were 26.3 g/kg, 13.6 g P2O5/kg and 63.0 g K2O/kg, respectively. Total aerobic plate counts in LComp(2:1) reached 2.5 × 107 CFU/mL. Meanwhile, L Boka(1:2) had an EC value of 19.8 mS/cm, and nutrient concentrations of total N, available phosphorus and potassium were 0.35 g N/kg, 0.09 g P2O5/kg and 9.93 g K2O/kg, respectively. Total humic and fulvic acids in LBoka(1:2) reached 2,300 mg/kg. The results of the trial rate of 0.5 kg RComp/m2 as a single or combined application with LComp(2:1) and LBoka(1:2) at diluted concentrations of total dissolved solids (TDS) 500 ppm gave a similar performance of plant heights, number of leaves, and yields of 1,278.9 - 1,425.7 g/m2, and were significantly different from those of the control treatment (526.8 g/m2).