For bumper maize harvest, top-dress when crop is knee-high

Wednesday August 14 2019
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A farmer applies fertiliser to maize crops in Uasin Gishu. Top-dressing and weeding go together because the removal of unwanted competitive plants is very important so that the fertiliser granules that boost the nitrogen. FILE PHOTO | NMG


Farmers continue to record low maize yields of between nine to 11 bags per acre against a target of 30 to 40 bags in most regions. This is partially blamed on poor farming practices.

Top-dressing is the application of nitrogen in granular fertiliser form to crops to boost the nitrogen available to the plant as it is growing.

Top-dressing and weeding go together because the removal of unwanted competitive plants is very important so that the fertiliser granules that boost the nitrogen, which should be placed at the base of the plant, are not taken up by the competing weeds, which would limit yields during times of high nitrogen demand from the maize plants.

Urea or CAN as a source of nitrogen boost for maize works best when it is applied at the correct crop growth stage and at the rate advised by the supplier (which usually is a spoonful per plant when done manually).

Ideally, this should be done when the maize is knee-high (about 18 inches tall), which means the plant’s root ball will have grown to around nine inches of depth under the soil.

Urea is the cheapest form of nitrogen but should only be used when rain is guaranteed so that the granules are dissolved and absorbed by the soil in 24-48 hours.


Beyond this, urea will hydrolyse and will be lost as gasses to the atmosphere. If rain is uncertain, CAN, whilst more expensive, is by far the better option.

Nitrogen and other nutrients are not taken up at a constant rate through the crop’s life. Many farmers apply fertiliser at around the three to four leaf stage, which is too early for the nitrogen requirement of the plant, so the knee-high or six to eight weeks post-emergence is the appropriate timing for the nitrogen boost for maize.

Weeding between the rows of maize should continue until the plants achieve their natural canopy. The canopy then suppresses further growth of weeds.

It is also worth noting that weeding during dry spells has a negative effect, in that the action removes soil moisture. So the best time to weed is when the rain is around and leave the weed trash along the lines to act as an umbrella during the drier periods.

Whilst embracing good farming practice, it is also best to weed before they flower so that they can’t seed, which would see them regrow.

Weeding by either hand or mechanically is possible, but the latter must be done with GPS guidance to avoid uprooting the planted maize through human error.

Most subsistence farmers intercrop maize with beans (or other leguminous crops). This has advantages as it helps reduce crop failure risk due to diseases, pests or drought, provides a cover crop within the rows to prevent weed growth and helps benefit the soil with some nitrogen fixing.

However, in the long-term, to achieve a good natural soil nutrient balance to maximise yields, it is much better to embrace crop rotation.

Robley is the managing director of FMD, the Massey Ferguson distributor for East Africa