Kenya continues to record low maize yields of between nine to eleven bags per acre against a target yield 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 fertilizer 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 fertilizer granules that boost the Nitrogen, which should be placed at the base of the plant, are not taken up by the competing weeds which will limit yields during the times of high Nitrogen demand from the maize plants.
Urea, or CAN as the source for the Nitrogen boost for maize work best when it is applied at the correct crop growth stage and at the rate advised by the supplier (which usually is advised as a spoon full per plant when done manually). Ideally this should be done when the maize is knee high (about 18 inches tall) which means the plants 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 within 24-48 hours, beyond this Urea will hydrolyze 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 life. Many farmers in Kenya apply fertilizer at around the three to four leaf stage, which is too early for the nitrogen requirement of the plant, so the knee high and six to eight week post emergence give the appropriate timing for the Nitrogen boost for Maize.
Weeding between the rows of maize should continue until the maize 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, in that the weeding action removes soil moisture, so best to weed when the rain is around and leave the weed trash in 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, to regrow. Weeding by either hand or mechanical weeding is possible, but mechanical weeding must be done with GPS guidance to avoid uplifting 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 ( disease/pest/ drought), provides a cover crop within the rows to prevent weed growth and helps benefit the soil with some Nitrogen fixing to help address monocropping issues, however in the long term to achieve good natural soil nutrient balance to maximized yields, it is much better practice to embrace crop rotation.
By Fergus Robley, the Managing Director of FMD, the Massey Ferguson distributor for East Africa.