Nutrient uptake and use efficiency of onion seed yield as influenced by nitrogen and phosphorus fertilization

The experiment was conducted at Kulumsa, South East Ethiopia, using four levels of nitrogen (N) (0, 50,100 and 150 kg N ha(-1)) and four levels of phosphorus (P) (0, 35, 70 and 105 kg P2O5 ha(-1)) fertilizers arranged in 4 x 4 factorial arrangements in randomized complete block design with three replications. The available P was increased after harvest due to the application of N and P fertilizer at the rates of 100 or 150 kg N ha(-1) and 70 or 105 kg P2O5 ha(-1). More specifically, nutrients concentration and nutrient uptake were significantly (p < .01) varied among treatment combinations and nutrient use efficiency was declined by increasing N and P after optimum rates. The higher physiological efficiency of N (53.47 kg kg(-1)) and P (580.41 kg kg(-1)) and the highest apparent recovery of N (19.62%) and P (2.47%) was recorded from application of 50 kg N ha(-1) and P at 70 kg P2O5 ha(-1) and the highest agronomic efficiency of N (10.78 kg kg(-1)) and P (15.25 kg kg(-1)) was recorded from N at the rate of 50 kg N ha(-1) and P at 35 kg P2O5 ha(-1), respectively. The combination of N at 100 kg N ha(-1) and P at 70 kg P2O5 ha(-1) was promising combination that generated highest net benefit 488,878.5 ETB (Ethiopian birr) ha(-1) with the highest marginal rate of return (36638%) and gave the highest seed yield (1858.82 kg ha(-1)) with yield increment of about 57.72% over the control.