Effect of nitrogen and phosphorous application on seed yield and nutrient uptake of onion (Allium cepa L.)
Onion is an herbaceous biennial monocot cultivated as an annual. The higher seed yield in onion cultivars was due to the higher number of seed stalks per plant and to a wider umbel diameter which were influenced by application of N and P fertilizers. The number of flower opening on each day was influenced by the number of hours of sunshine and concentration of phosphorous and nitrogen. N and P treatments tended to lower bolting percentages. The yield of 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 a ‘bolting inducible’ 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 of N for uptake by most plants, and 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. Onion absorb phosphorous in the form of H2PO4- and H2PO4-. Too much phosphorus level affects plant growth by suppressing the uptake of iron, potassium and Zink. The availability of inorganic phosphorus is largely determined by soil Ph. Leaching losses of nitrate are growing crop cover to absorb the nitrates as rapidly as they are produced. Soil Ph drastically influences the reaction of phosphorus with the different ions and minerals. To increase the yield of onion seed the application of N and P fertilizer should be determined.