Ask Your Agronomist: Fertiliser regime for higher yields from onions

Q : I grow onions in Isinya, but production has been very low. Please advise on how to increase my yield.
Sanaipei

It is important to know where you will sell your produce to best know how to grow your onions.
Some of the factors you also need to consider before planting are the variety and quality, size, shape, colour, flavour, sweetness, skin finish and storage ability.
Onions have a relatively low nutrient uptake efficiency due to their shallow root system, characterised by thick roots with very few and short hairs.
It is, therefore, important to implement a fertiliser programme adapted to those conditions to help achieve optimum yields. It is also essential to time the applications of nutrients as close as possible to the rooting zone in frequency and readily available forms.
Onion nutrient requirement:

Applying fertiliser that provides balanced nutrition is necessary for achieving high yields and quality onions.
It is important not to over-apply nitrogen, particularly in bulb onions, as this can delay maturity, soften bulbs and lead to storage rots. In similar fashion to Nitrogen (N), most phosphorus is required early on in the plant’s development to ensure good root growth and to boost establishment.

Potassium is particularly important where high N rates have been applied, to help maintain yield by increasing dry matter and sugar accumulation in the bulb (better bulb size and weight).
Fertiliser regime:

Fertiliser application for onions should, therefore, start first week after transplanting, with an NPK regime for establishment of the crop. 40 per cent of the N, and K as well as calcium requirements should then be applied by the third to fourth week during the first top-dress.
The second top-dressing should then be done at the bulbing stage, supplying the rest of the nutrient needs. Calcium and boron are critical in ensuring a longer shelf life and preventing rots in the bulbs.

Onions prefer a nitrate form of nitrogen as opposed to ammonium forms, and therefore more of nitrate N source fertilisers such as in YaraMila Winner and YaraLiva Nitrabor will give better results – better bulb size and weight.

Please note that with this correct fertiliser application, it is important to adhere to all other good agricultural practices (weed management and crop protection), for best results.
For crop specific fertiliser recommendations, please consult the following agronomists in your area:

Western and Nyanza, Daniel Mui, 0702466343.

Rift Valley, Dennis Nyandaya, 0702466372.

Central, Stephen Kamau 
0728396204.

Peter Wekesa,
Senior Agronomist, Yara