Fertiliser application in onions

Red onions

The Red Striker F1 onion variety as demonstrated in a farm in Endarasha. Application of fertiliser close to the root zone improve the utilisation of nutrients by the plant.

Photo credit: Irene Mugo | Nation Media Group

Timely and appropriate fertiliser application ensures a healthy crop and higher yields. This is in addition to ensuring weed and pest and disease control. The onion crop should also get adequate water.

These are some of the management practices Desmond is keen on for a successful crop production cycle. In this article, we look at the nutritional requirements of onions.

It is necessary to apply balanced nutrition in order to get quality onions.

This starts by applying manure, which improves organic matter and soil structure.

It is important to conduct soil test analyses to determine the quantity of manure or nutrients required.

Fertiliser application should start in the first week or during transplanting.

It is important to use the right rates because too much fertiliser can cause plant overgrowth,  which can delay maturity. It at times makes the bulbs soft.

It is also important to understand that the onions have low nutrient uptake efficiency due to their shallow root system and few short hairs.

This therefore calls for timely application and close proximity to the rooting system.

If plating along drip lines, one should apply the fertiliser by drilling a furrow in between the lines. Care should be taken to prevent root damage.

Soluble fertiliser can be applied using the fertigation system – applying water and the fertiliser at the same time.

Onions prefer nitrate nitrogen over ammonium nitrogen, Because of that, they require more nitrate N-source fertiliser.

Insufficient nitrogen leads to stunted growth, whereas excess results in succulent plants that are more susceptible to frost damage and disease.

Late in the growing season, an excess of nitrogen causes delayed maturation and double centres. It is recommended to stop applying nitrogen at least four weeks before harvest.

To ensure proper root growth and uniform crop establishment, phosphorus is required early in the development of the plant.

The rate of phosphorus uptake remains relatively constant throughout the growth cycle.

Because phosphorus is immobile in soil and can be translocated from old leaves to the bulb during the bulb development and maturing stages, the majority of the phosphorus can be applied during planting up to the bulb development stage.

During bulb development, potassium is required to ensure expansion.

Calcium and boron are critical in ensuring a longer shelf-life and preventing rot in the bulbs.

As a result, it can be used as foliar fertiliser. It is important to adhere to good agricultural practices to get the best results.

The shallow root system necessitates careful water and nutrient management to ensure adequate availability.

Potassium, phosphorus and metal micro-nutrients, which are relatively immobile, are difficult for roots to access, whereas nitrogen and other mobile micro-nutrients tend to leach below the root zone.

Application of fertiliser close to the root zone improves the utilisation of nutrients by the plant.

Desmond is carefully implementing the fertiliser programme, based on his soil analysis and nutritional requirements of the ecrop.

In our next article, we shall look at fungal diseases affecting onions.