PLANT-BASED FERTILIZER FOR ORGANIC PRODUCTION

Abstract

A wide range of potential green-manure crops were tested for their productivity and concentration of plant nutrients, especially N, P, K, S and B. Selected green-manure crops were harvested at several developmental stages. Fresh wet, ensiled, and dried green manures were tested in pot and field experiments with several vegetable crops. The results showed that the plant species garden sorrel, dyer’s woad, and fodder radish had high P concentrations, and that cruciferous crops like dyer’s woad and fodder radish had high S concentrations. Dyer’s woad, salad burnet, and stinging nettle showed high concentration of B, whereas species like dandelion, chicory, and garden sorrel showed high concentration of K. In comparing plant species, plants were harvested at a developmental stage corresponding to maximum leaf/stem ratio. The pot experiments showed that green manures with high concentration of P and S increased the nutrient uptake and yield of cauliflower and kale. Although P increased the vegetable production, the results indicate that S was the main limiting growth factor. The field experiments showed that the vegetable production decreased when the C/N ratio of the green manure increased. It was concluded that differences in vegetable production were not due to the amount of N applied, but to the N availability. The overall conclusion of these experiments is that it is possible to produce green manures with high concentrations of S, K, P, and B, and low C/N ratios, and further, that these properties have great impact on the value of the green manure for vegetable production.