The continued use of chemical fertilizers for crop productivity causes unexpected environmental degradation, including leaching of nitrate into ground water, surface runoff of phosphorus and nitrogen, and eutrophication of aquatic ecosystems. It has been suggested that organic farming system is a sustainable and eco-friendly approach to provide agronomic and environmental benefits particularly with regard to the improvement of soil fertility. Organic farming aims to build and maintain inherent soil fertility through the encouragement of biological processes. This means that organic ecosystems should depend on organic sources of nitrogen such as legumes, manures and liquid fertilizer. Prior studies reported the general role of soil organic matter(SOM) in nutrient storage and nutrient availability and explained how various SOM management practices can contribute to nutrient management in organic agriculture.
The consequent experiments were carried out to identify the current state of liquid fertilizer use and to optimize the its application for organic farming.
The first experiment was carried out to investigate the current status of liquid fertilizers used on organic and environmentally friendly farms. Component analysis of 41 types of liquid fertilizers produced and used in farms showed large differences in chemical properties among the samples. In addition, liquid fertilizers produced using the same ingredients showed differences in nutrient content, depending on the production method used by the farms.
The second experiment evaluated optimal conditions for the production of agro-fishery byproduct-based liquid fertilizers. During fertilizer production, Makkolli, yogurt, dry yeast and leaf mold were added to sesame oil meal, powdered bone, fish meal, and seaweed liquid fertilizers, as microbial resources. Inorganic nitrogen concentration in the liquid fertilizer was high in the dry-yeast treatment, regardless of the ingredient used. Addition of dry yeast, which is the most suitable microbial source, during liquid fertilizer production facilitated nitrogen mineralization. The addition of molasses during liquid fertilizer production resulted in a decrease in pH as the amount of molasses increased, while EC did not vary in relation to the amount of added molasses. Inorganic nitrogen concentrations in the liquid fertilizers were seen to decrease as the amount of molasses increased. As the concentration of fish meal added to the liquid fertilizer increased, the inorganic nitrogen concentration increased as well. However, 8 weeks after fermentation, there was no difference in inorganic nitrogen concentrations between the 20% and 30% concentration with fish meal treatment.
The third experiment was carried out to evaluate the effects of fish meal liquid fertilizer on cucumber growth and soil environment. There were no significant differences in cucumber plant height between the fish meal liquid fertilizer treatments and chemical fertilizer treatments. Also, the cucumber yield did not vary significantly between the concentrations of liquid fertilizers, and there were also no significant differences in the yield between the fish meal liquid and chemical fertilizer treatments. The soil microbial community varied in relation to the fish meal liquid fertilizer treatments. Microbial biomass was lower in the chemical fertilizer than in the liquid fertilizer treatment. Result of principal component analysis obtained from Ecoplate showed that fish meal liquid fertilizer treatments, no liquid fertilizer, chemical fertilizer, and no fertilizer were divided into distinct groups, with the no fertilizer treatment located furthest from the other treatments.
These results show that optimization of fermentation condition would enhance the quality of liquid fertilizers and fish meal liquid fertilizer could be used as an additional nutrient source in organic farming.