Evaluation of the Use of Rice Bran Compost for Eco-friendly Weed Control in Organic Farming Systems

Abstract

Rice bran compost (RC) was evaluated under greenhouse and field conditions for eco-friendly weed control of vegetable crops in organic farming systems. RC was applied 7 days before spinach seed sowing, at the rate of 0% (control), 10%, 20% and 30% of soil (v/v) in the greenhouse and 2 kg m^-2 under field conditions. RC significantly controlled the number and dry weight of weeds, and the weed control potentiality was increased by the increased application of RC in both years. The efficacy of RC in reducing weed emergence and dry weight of broadleaf species was higher than grass weeds. Among the broad leaf weeds, Lamium amplexicaule L was the most sensitive to RC and was drastically reduced by the increased application of RC. Under field conditions, the total number of weeds and the dry weight of weeds were also significantly reduced with the application of RC, compared with the untreated control. The growth inhibition potentiality of water soluble fractions of RC was also tested with seed germination and radicle elongation of test species (barley, oat, tomato and lettuce). The concentration response curves for the test species were drawn by plotting the percentage of germination against the logarithm of the concentration. Considering the I25 value (defined as 25% inhibition of control) both for seed germination and radicle elongation, it was indicated that water soluble fractions of RC was more effective in the suppression of dicotyledonous species (tomato and lettuce) than monocotyledonous species (barley and oat). The results of the preliminary experiment with fresh rice bran under greenhouse conditions showed that fresh bran suppressed spinach seed germination when applied as 10% rice bran in soil but RC did not show a significantly negative effect up to 20% RC application, compared with the control. Moreover, RC enhanced spinach growth. Considering both the weed control potentiality and spinach growth enhancing ability of RC, the effective appplication rate of RC is between 10-20% of soil (v/v) for weed control as well as the successful growth of spinach. This research indicates that RC has the potential of being used as a natural herbicides.