The dos and don’ts in wheat production

Peter Gambara

TRADITIONALLY, the winter planting season starts on May 1 annually; therefore, farmers countrywide are now busy with land preparation and planting. But there are certain things that farmers should be aware of in terms of planting methods, liming and fertilisers.

There are differences between using a seed drill and using a broadcast spreader and seed spreader.
Over the years, most A2 farmers resorted to using a broadcast spreader and seed spreader, as seed drills are difficult to get. Using a broadcast spreader is easy, cheaper and faster.
However, it has its disadvantages.

Firstly, it leaves the seed exposed and at risk of being devoured by birds.
This is true if a farmer takes time between broadcasting the seed and the first irrigation.
After broadcasting the seed, farmers normally use a roller or some light discing to incorporate the seed and fertiliser into the soil.

However, this is not 100 percent efficient as some seeds remain exposed.
When water is eventually applied, such seeds start to germinate, but eventually dry out and die.
Another disadvantage of broadcasting both fertiliser and seed is that the exercise leaves both inputs scattered all over.

Some seeds might actually fall way off the fertiliser, hence the roots will take time to reach the fertiliser. This will limit growth of the wheat in the initial stages. Broadcasting wheat also makes weed control difficult. Broadcast seeds tend to be thinner and produce a reduced plant population and slower germination than drilled seeds.

Delayed germination can actually lead to reduced tillering, hence a lower plant population.
A lower plant population will eventually lead to a reduced wheat yield.

A lower plant population results from the fact that, in using a roller or light disc to incorporate the seeds, some of the seeds are placed too deep such that they fail to germinate completely.
Another disadvantage of using a broadcast spreader relates to placement of phosphorus.
Phosphorus is immobile and will stay where it is placed.

If this phosphorus is placed where roots of the wheat cannot reach it, it will remain unused.
However, with drilled fertiliser, the phosphorus is banded exactly where the wheat roots will easily reach it.

This explains why most A2 farmers are content with lower wheat yields compared to their counterparts who would have drilled the seed, instead.
The slower germination also allows weeds to quickly sprout and start competing with the wheat for the available nutrients and space.

What are the advantages of using a seed drill over a broadcaster spreader?
Firstly, with drilling, seeds are placed at more uniform depths, hence are likely to germinate uniformly, unlike with broadcasting.

Secondly, a seed drill also places the seeds in line with the fertiliser, such that, as soon as the seeds germinate, the roots reach the fertiliser and start benefitting from the nutrients, unlike with broadcasting. Use of a seed drill will also result in a farmer using a lower seed rate (up to 20 percent) compared to broadcasting.

Whilst one needs 100 kilogrammes per hectare, using a seed drill, this increases to 120kg per hectare when using the broadcasting method.

This translates to an additional cost of US$30 per hectare. The pH of the land under wheat also needs to be managed.

Wheat tolerates a pH of between 6,0 and 7,0, with a target of 6,4 being ideal.
With the heavy fertilisers that we apply to maize, most of the land tends to be acidic, hence have a pH that is likely to be below 6,0.

A pH of below 5,5 increases the solubility of aluminium and magnesium particles and will negatively impact wheat growth and yield.

A very low pH might reduce root growth, resulting in stunted plants.
A low pH can also contribute to low water uptake and nutrient availability, thereby leading to low wheat yields.

There is, therefore, need to correct such a pH through the application of lime. A complete soil analysis would be ideal as it determines, not just the need to apply lime and how much, but also the exact amounts of both basal and top-dressing fertilisers that you will need to apply to the wheat crop.

However, if a complete soil analysis is not possible in the short period remaining, at least just do a soil pH test.

Most farmers use generally recommended rates of between 400 and 500kg of fertiliser per hectare.
However, the best solution is to have soil analysis determine the ideal fertiliser rates. Whilst most farmers are used to using the traditional 7:14:7 Compound D fertiliser at rates of around 500kg/ha, farmers should consider using the 8:23:23 basal fertiliser, instead.

It provides more phosphorus (P) and potassium (K) and has a slightly higher nitrogen (N) content.
However, this is not important as farmers will come in with top-dressing nitrogenous fertilisers later on during the life cycle of the wheat crop.

A bag of Compound D (7:14:7) is going for US$33,50 per 50kg, whilst a bag of Grainfert (8:23:23) costs US$44,75 per 50kg bag. This translates to US$335 at 500kg per hectare and US$358 at eight bags per hectare using the latter fertiliser.

But the wheat’s response to the Grainfert will definitely show that the crop has better nutrients than with the former. Farmers have the option of using either the traditional Ammonium Nitrate (AN) (34,5 percent N) or Urea (46 percent N).

Most farmers are used to applying AN as a top-dressing fertiliser. However, farmers should consider the use of Urea, instead. It is cheaper at US$37,50 per 50kg bag, compared to US$50,00 per 50kg bag for AN. Urea also has a higher nitrogen content (46 percent) than AN at 34,5 percent.

Since farmers in Zimbabwe use irrigation water during wheat production, it makes sense to use Urea as one can immediately apply water after applying the Urea, which easily dissolves it and prevents it from vaporising. Last but not least is the issue of scheduling in view of the shortage of electricity the country is currently going through.

ZESA has reiterated that it will ring-fence electricity to wheat farmers. Growers should also have enough manpower to quickly move pipes where necessary so as to minimise downtime.

* Mr Peter Gambara is an agricultural economist and consultant based in Harare