New Pelleted Plant-Based Fertilizers for Sustainable Onion Production

Pelletized plant-based fertilizers Ekofert K (red clover) and Ekofert L (lucerne) was compared to non-fertilized control and mineral N-fertilization (100 kg N ha-1) in sustainable onion cultivation (2012–2013). The organic fertilizers at pre-plant rates equivalent to 120, 180 and 240 kg N ha-1 were applied on a field fertilized with compost (25 t ha-1). The fertilizers Ekofert K and L significantly increased onion production as compared to the basic fertilization with compost alone. The increase in yield was favorably correlated with the applied fertilizer rates. The lowest rate of organic fertilizers ensured a yield at the level of mineral fertilization at the rate of 100 kg N ha-1 as single application. The higher rates of Ekofert K and L (180, 240 kg N ha-1) resulted in a marketable yield increase relative to single mineral fertilization. The use of organic as well as mineral fertilization increased nitrogen and chlorophyll contents in onion leaves, compared to the non-fertilized control treatment. The increase was positively correlated with fertilizer rates. The N-NO3 content in onion bulbs was in general not influenced by the application of organic fertilizers, compared to non-fertilized control treatment. Nitrogen content in the top soil (0–30 cm) was the highest after 5 weeks from incorporation of the fertilizers and diminished in following 4 weeks on average by 46% due to plant development and intensive nutrient uptake. After onion harvest, continued mineralization of soil organic matter and lack of uptake by plants increased average nitrogen content nearly to the level at stage of early plant growth. The N-NO3 content in soil increased with rates of the Ekofert fertilizers. In subsoil horizon (30–60 cm), the N-NO3 content was 2.5 times lower than in topsoil and significant only for the highest rate of the fertilizers.