Optimum nitrogen supply is important for onion size. Nitrogen supports production of leaves and hence, increases the number of onion bulb scales and the size of the harvested bulb. Because these crops are shallow rooted with poor root branching, it is common practice to use split N applications to maximize uptake efficiency. Placement has been proven to be more effective than broadcasting.
Planting density is a very important management factor in determining bulb size in onion crops. In addition, good crop nutrition can help growers to achieve a desired diameter. Nitrogen, potassium and phosphorus are essential to influence onion bulb size.