Review on effect of Nitrogen and Phosphorous application on seed yield and nutrient uptake of onion (Allium cepa L.)

Onion is a herbaceous biennial monocot cultivated as an annual crop. The number of flowers opening on each day was influenced by hours of sunlight and concentration of phosphorous (P) and nitrogen (N). N and P treatments tended to lower bolting percentages. The yield of onion seed per plant increased as the nitrogen in the nutrient solution increased where seed stalks were produced. The effect of early dressings of N on crops grown under conditions when nights are becoming cooler is shown to allow the plants to reach to flowering stage early in the growing season. There is maximum response of onions to P fertilization in the range 0-52 kg ha-1. Plant roots take up nitrogen from the soil solution principally as nitrates (NO3-) and NH4+ ions. Nitrate is the preferred form for uptake by most of the most plants. It is usually the most abundant form that can be taken up in well-aerated soils. Nitrogen fertilizer application improves phosphorus uptake from the soil.