*Managing maize crop after emergence*

A farmer can apply top dressing at 2, 4 and 6 weeks after planting or at 4, 6 and 8 weeks after planting in maize depending on the state of the crop and soil type
Peter Gambara

MAIZE takes four to seven days to germinate in the warm temperatures that we experience during this time of the year in Zimbabwe. Most farmers are eager to establish how well a maize crop germinates after these seven days.

Several factors affect how well a maize crop germinates and these include the moisture level in the soil, the planting efficiency, the soil tilth and how deep the seed was placed.

In farming, most farmers learn by acknowledging their mistakes and knowing how to correct those mistakes in future.

In this article, I will look at what farmers should guard against at planting, that might reduce crop germination and how they should handle management issues of a maize crop that has germinated.

The germination percentage of a maize crop is established by dividing the seeds that germinated against those that were planted. If a farmer targeted 55 000 plants per hectare and only achieves 50 000, the germination percentage is 50 000/55 000 X 100 percent = 90 percent.

This germination percentage has a large bearing on the final maize yield. It simply means the crop only has a 90 percent chance to reach the potential yield level.

The summer season has started and most areas should receive rains within a few days after planting.

Maize requires at least 25mm rain in a three-day period to germinate.

Anything less might result in the planted seed rotting and failing to germinate.

Farmers should always observe the general rule about planting, they should either plant into soil that has adequate moisture to germinate the seed or if the moisture is not enough, they should plant into a dry soil and wait for the next effective rains.

Planting efficiency relates to how well the seed was placed in the soil.

A poorly prepared land might inhibit germination as some seed falls on weeds or is not covered by soil, even after using a planter. Therefore, farmers are encouraged to plant their maize into well-prepared soil.

By now, most lands are looking green from weeds that have germinated from the intermittent rains that we have been receiving since the start of the rainy season.

Where possible, farmers should re-disc their lands to achieve a fine soil tilth, free of weeds.

Planting depth affects germination. A shallowly planted maize crop is likely to be reached by rain showers and if these are less than 25mm in a three-day period, the germination process in the maize is triggered, but not enough to see the seed germinate.

Farmers should always avoid planting into soil that is almost dry, or half moist. They should only plant when there is enough soil moisture to germinate the seed.

Weather forecasts help, so that farmers can plant when rainfall has been predicted.

On the other hand, a too deeply planted maize seed is not likely to germinate, as the seed’s food reserves are not enough to see the emerging seed push through the soil.

Therefore, farmers should always try to place maize seed at the correct planting depth. Maize should be planted approximately 5 cm deep in a well-prepared soil tilth.

Once a maize crop has germinated, there are few ways to try and increase the yield to the desired level.

One of the most popular methods is gap-filling. Gap-filling involves placing seed along the lines, where the gap is bigger than the intended spacing.

Gap-filling should be done within 14 days from planting or one week from the first germination and since this is done manually/by hand, farmers can actually pre-soak the seed to quicken the germination process.

One of the most difficult tasks to perform, though, is to make sure the gap-filling maize is planted where it will reach the initially placed fertilisers.

It is easier where the initial planting was done by a planter, as the farmer just has to place the gap-filling maize along the line, but much more difficult where fertiliser was placed by hand/using a fertiliser cup.

Once maize has germinated, farmers should concentrate on ensuring rapid growth of the emerged plants.

This is done through two major means: ensuring that the field is weed free; and providing nitrogen through top dressing fertiliser to boost the crop’s growth.

I covered issues of weed control last week, and I will just re-emphasise here that maize should be kept weed free for the first six to eight weeks after germination.

This can be achieved through either the use of herbicides or weeding.

The more one delays weeding, the more competition that the crop suffers from the weeds for nutrients, water and light and the slower the growth of the maize crop.

Most basal fertilisers contain nitrogen. The mostly used basal fertiliser in maize is Compound D or Maizefert, which has an (Nitrogen, Phosphorus and Potassium) (N: P: K) composition of 7:14:7, meaning there is 7 percent nitrogen in the fertiliser.

This low level of nitrogen is just enough to see the seed emerge from the soil, but it is definitely not enough to see it through
to harvesting, hence the need for top dressing.

Where a planted crop receives heavy rains during the germination process, the nutrients in the planting fertilisers might be leached and the emerged plants will soon look yellowish.

This yellowish colour is also caused by low fertiliser applications or farmers having planted the crop without any basal fertiliser. There is therefore need for top dressing, or adding the nitrogen as the crop grows so that it remains green.

Generally leaching increases with heavy rainfall, however the lack of conservation works on most fields encourages water to accumulate on the land rather than run away to the rivers.

Unfortunately, a lot of farmers have ploughed up or not maintained contours on their lands, resulting in water failing to drain away from the lands.

Failure to maintain the existing contours results in water stagnating in the middle of the lands, break what remains of the contours and flooding the fields, sometimes washing away the crop. Stagnant water encourages more leaching.

This is the best time for farmers to maintain their storm drains and contours. Storm drains are like “big contours” that are placed at the top of the land to prevent water that might be coming from, say a hill rushing onto the land.

Contours on the other hand are placed at certain intervals in the land at slopes that will drain the water away from the land. Farmers should invite their AGRITEX officers to peg these storm drains and contours for them, if they are no longer visible or are non-existent.

Where an emerging maize crop shows yellowish signs, some farmers apply what they call “X”, which is a mixture of Compound D and Ammonium Nitrate.

However, farmers should be advised that the crop will only use the little nitrogen available in the “X” and the rest remains where it is placed.

The phosphorus and potassium nutrients are generally not mobile and will remain where they are placed.

A plant’s roots cannot obviously reach these nutrients if they are placed on the ground level. It is therefore a complete waste of money.

Farmers who split-apply their top dressing are more likely to achieve better yields than those who come in with a single application of top dressing.

A farmer can apply top dressing at 2 weeks, 4 weeks and 6 weeks after planting or at 4 weeks, 6 weeks and 8 weeks after planting in maize depending on the state of the crop and soil type.

A nitrogen boost at 2 weeks after emergence should be able to boost a yellowing crop, that is lacking vigour. Bear in mind also that a single top-dressing fertiliser can be easily washed away by heavy rains, especially in sandy soils.

Farmers should also start scouting for fall armyworm on a regular basis on their crop. This pest has caused considerable damage and continues to present most farmers with headaches on how to control it. I will talk more about scouting for fall armyworm and its control in subsequent articles.

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

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