Plant density and nitrogen and potassium fertilization rates on yield of onion hybrids

An experiment was carried out in Sao Jose do Rio Pardo, the onion producing area in Sao Paulo State, Brazil,from March 07 to August 08, 2004. The objective of the research was to evaluate the effects of nitrogen and potassium fertilizer rates on yield of two onion cultivars, growing in different plant populations. The experimental design was in blocks with four replications in a 2x4x4x4 factorial cheme: cultivars (Optima and Superex), nitrogen (0; 50; 100 and 150 kg ha(-1) of N), potassium (0; 75; 150 and 225 kg ha(-1) of K2O) and plant population (60; 76; 92 and 108 pl m(-2)). The effects of N and K doses on yield were cultivar dependent. Average individual bulb mass increased with decreasing plant population and increasing nitrogen doses application. To reach 90% of the maximum expected crop yield of 71 t ha(-1) for 'Superex' and 64,8 t ha(-1) for 'Optima', nitrogen doses of 125 and 105 kg ha(-1) should be applied, respectively, without potassium fertilization.