Use this formula to make fertilisers work for you

Workers at Kawanda spread manure in a vegetable garden. Photo/File 

What you need to know:

  • By applying fertiliser correctly, you will get the value of your money and a good harvest while at the same time help maintain the fertility of the soil.

Most farmers across the country are now weeding their farms as the rains continue to pound.

Many farmers supplement the nutrients required by the plants by using fertilisers, which are readily available in agrovets.

The benefits of fertilisers can only be realised when they are used in an efficient manner that is by minimising losses and maximising the gains in terms of the yields.

Therefore, as a farmer, how much fertiliser you apply, from which source, at what time and how you place the input on the farm is crucial.

There are four rights (4 Rs) in using fertiliser namely the right rate of application, from the right source, at the right time and to the right place.

Right rate
Crops require a certain amount of nutrients for optimum production. Part of these nutrients can be supplied from the soil, and the remainder must come from fertilisers.

Before applying any fertiliser, soil testing can help determine the portion of the crop nutrient requirement that is already available from the soil.

The right rate is the amount of fertiliser that you will need for the crop production season. Keep in mind that more fertiliser does not mean more yields. Therefore, don’t over or under apply fertiliser.

Right source
Choosing the right source of the material to deliver the nutrients is important. You should consider some key aspects such as; what source of nutrients would be the least expensive per unit of applied nutrient; if you should use organic source (compost or manure); when to use a controlled-release fertiliser; what sources can simultaneously deliver more than one-needed nutrient and when should you use a liquid form instead of a dry form.

When choosing the right source, bear in mind the ease of application of a nutrient and cost per unit. Also, consider the efficiency of the nutrients you are applying.

For instance, use a controlled-release nitrogen source to deliver small amounts of nutrients throughout the growing season, instead of larger amounts of nitrogen delivered in a few side-dressings from a soluble source.

The right source may be manure if the farmer would like to take advantage of the organic matter supplied along with the plant nutrients.

Right timing
The right timing of nutrients considers the growth pattern of the crop. Therefore, there is a natural change in nutrient demand during the season.

Crop development begins slowing from seed germination or transplanting, then increases through fruiting, and finally slows down at maturation.

Keep in mind the changes in crop growth and the demand for nutrient such that you time the fertiliser application with the crops’ needs.

For example, during the germination stage, the plant roots need to develop and therefore apply phosphorus as it is the critical nutrient required by the plant.

During the active vegetative growth, apply nitrogen as it boosts this crop stage. If you time your nutrient application well, you will reduce the likelihood of nutrient wastage.

Right placement
Place the nutrients where the plant will have the best access to them. The root zone is the right placement for most crops.

Also, most of the uptake of nutrients occurs through the root system. So, place the nutrients in the root zone to maximise the chances of them being absorbed by the plant.

The two general approaches of fertiliser placement are banding and broadcasting. Banding is when you place the fertiliser in bands in the soil, usually near the developing plant. Broadcasting is when you spread the fertiliser uniformly over the surface of the soil.

Whether you want to use banding or broadcasting will depend on the type of crop and the development or spread of the root system.

Broadcasting is usually most effective later in the season when roots of a row-crop have explored the space between the rows.

Right placement also relates to the form of the nutrient source, such as urea nitrogen. Nitrogen from urea fertiliser may be lost to the atmosphere when left on the surface of a soil with a high pH.

Therefore, to efficiently use urea fertiliser, incorporate/mix with the soil or apply a small amount of irrigation to move the mineral into the soil to reduce losses.

The same applies to other nutrients such as the placement phosphorous containing fertilisers. Phosphorous is immobile and, therefore, you should place it in bands near the roots of your crops.

Lastly, under certain situations and nutrients, apply the nutrients as a foliar. For example, when the soil pH is high, apply the micronutrients such as iron in form of foliar sprays.

These factors are often interrelated, for example, placement and timing of fertiliser may need to be addressed together.

By applying fertiliser correctly, you will get the value of your money and a good harvest while at the same time help maintain the fertility of the soil.