The study was carried out in Oratórios, Minas Gerais State, Brazil, with objective of evaluating the plant nutritional state, yield and nutrients extraction by onion, cv. CNPH 6400, in organic system, submitted to rates of organic compost of swine manure. The experiment was arranged in a randomized block design, with four replications and the treatments consisted of five rates of organic compost (0, 10; 20; 30 and 60 t ha-1). The seedlings were transplanted on the 49th day after the sowing (DAS). Plants were harvested on 168 DAS and the maximum yield of marketable bulbs was 60.3 t ha-1, obtained with 43.4 t ha-1 of organic compost. The maximum yield of bulbs Class 3 was 33.346 kg ha-1, obtained with 32 t ha-1 of organic compost. In the Class 4 the yield was increasing and the Class 2 presented decreasing with the rates. The maximum yield of dry matter of bulbs was of 6.271 kg ha-1, obtained with 46 t ha-1. With 43 t ha-1 of organic compost, the export of nutrients by bulbs would be 116.65 kg ha-1 of N; 22.71 kg ha-1 of P; 117.65 kg ha-1 of K; 19.47 kg ha-1 of Ca; 8.31 kg ha-1 of Mg and 19.94 kg ha-1 of S. The application of 43 t ha-1 of organic compost is enough to obtain onion bulbs with great quality and yield. The cv. CNPH 6400 can be recommended for the organic system.
Allium cepa; organic fertilization; mineral composition; yield
