EFFECT OF N- AND P-FERTILIZATION ON YIELD AND HARVEST TIME IN BULB ONIONS (ALLIUM CEPA L.)

Experiments on sandy loam has shown that in the earliest period of growth, when soil temperature is below optimum, supply of P to the onion plants is very important in order to promote rapid growth, high yield and full mature bulb in time.
The most effective method of P-supply regardless of the soil nutrient level has shown to be placement of P-fertilizers in the soil near to the plant at the same time and in connection with sowing/planting the crop.
Combination of P and N in a fertilizer like monoammoniumphosphate has shown to give the best utilization of P applied.
This method of fertilization has compared to broadcasting increased the yield with up to 8–10% and at the same time maturity was advanced one week.

Application of the optimum amount of N-fertilizer at the right time is at least as important to yield and quality of the bulb onions as optimum P-supply.
In experiments on sandy loam concerning increasing amounts of N as calcium nitrate the yield of marketable bulbs increased with N-application up to a total of 120 kg N per ha.
Further on there was a clear correlation between time of top fall-over and N-supply demonstrated by earlier maturing onions as the N-amount increased.
On average bulb onions supplied with 120 kg N per ha matured 9 days earlier than the O N treatment.

Plant analysis of N concentration in onion plants show a clear response of the N-amount applied.
Therefore also a correlation between percentage of N in plants at early growth might exist.
Further work may find methods to evaluate and predict the yield level and maturity time from plant analysis in onions.

Symposium on the Timing of Field Production of Vegetables

K. Henriksen

https://doi.org/10.17660/ActaHortic.1987.198.26