The Sunday Mail
Peter Gambara
If you talk to anyone familiar with running short distance races, he/she will tell you that once the starter says “On your marks, set and go!”, all serious athletes should get a good start.
If you slip or fail to take off properly, you may never catch up.
Today, I would like to talk about how important it is for all farmers to make a good start as the season starts. As farmers start the new summer season, it is important to plant on time, getting the right plant population, applying the correct basal fertiliser rates, keeping weeds under control and applying the right amount of top-dressing on time.
Planting on time
All serious farmers should always ensure they have started well by planting their crops on time. Research shows that delays can contribute 0,3 percent to one percent yield loss each day planting is delayed.
A long season variety like SeedCo’s SC727, which was very popular with Command Agriculture-contracted farmers last year, can achieve up to 16 tonnes per hectare. But it requires 152 days to reach maturity and, ideally, farmers should plant it in early October for it to reach maturity by mid-March. Therefore, if a farmer were to plant it now, it means he/she will have delayed its planting by approximately 30 days, and that could lead to a yield loss of 48kg/day. It is also important to note that the more the delay, the higher the yield loss per day; hence the scale of 0.3 percent to one percent. Whilst delaying planting costs a farmer 48kg/day in October, that increases to at least 160kg/day if planting is delayed to late December/early January.
For each day a farmer delays planting this maize variety, a yield loss of 1,5 tonnes to 4,8 tonnes per month occurs.
A fortnight ago, SeedCo hosted an awards ceremony for its top-achieving farmers who got at least 10 tonnes per hectare last season. Taking the example of the SC727 maize variety above, it means by failing to take off with other farmers and being in the running to achieve 16t/ha, a farmer’s yield is already down to maximum potential of 11,2 tonnes.
Late planting also results in crops being exposed to pests and disease. Last year, late-planted maize was susceptible to fall worm/armyworm and stalk-borer. It is also more difficult to control weeds once rains start as rains tend to germinate the entire weed spectrum in the ground. Weeds will also be more intense, covering more ground harder to control.
Right plant population
Getting the right plant population is something many farmers take for granted. I remember how my mother would use a wire marked at 30cm intervals. The wire had visible joints at each interval. Farmers should know that inter-row spacing in maize is 90cm and the in-row spacing 30cm. That gives a population of approximately 37 000 plants per hectare. Whilst such a plant population is “fine” in natural regions III and IV, nowadays, agronomists say to achieve the desired 16t/ha, a farmer in a high rainfall area will need to plant between 50 000 and 70 000 plants/ha.
Since many farmers today use combine harvesters, it is not feasible to change inter-row spacing as most combine harvester heads use 90cm spacing. This means a farmer should use an in-row spacing of 20cm to achieve a plant population of 55 000 plants per hectare. At 90 percent germination, this will achieve about 50 000 plants per hectare. Once a farmer has achieved a lower plant population at planting, he/she has already slipped and will not catch up with those going for 16t/ha.
Correct basal fertilisers
Once a farmer has achieved a plant population of at least 50 000 plants per hectare, the next aspect he/she needs to watch is that the crop has adequate nutrients from fertilisers. The best way to know the amounts of each fertiliser required is to send soil samples for analysis at laboratories.
This year, Command Agriculture is giving farmers 10x50kg of compound D fertiliser per hectare. At that rate, farmers have no excuse whatsoever to fail to get a high yield.
Effective weed control
If a farmer has planted on time, achieved the right plant population and applied the right amount of basal fertiliser, the next aspect to watch is weed control. Weeds compete with crops for nutrients, water and light. Ineffective weed control can contribute considerably to yield reduction.
Many farmers make the mistake of trying to control weeds post-crop emergence. The best time to control weeds is before they emerge and that means targeting to kill the seed before it germinates or soon after it germinates. Once a weed germinates and is established well, it starts competing with the crop, depriving the latter of water, nutrients and light. However, should it become necessary for whatever reason to apply herbicides or control weeds post-emergence, this should be done not more than two weeks after crop emergence.
Ideally, maize should remain weed-free for the first eight weeks after emergence for best yield potential. For effective weed control, farmers should ensure they have used the right herbicide, mixed the herbicide correctly and applied it effectively.
I have seen many farmers rely on hardware shop assistants when asking for the best herbicide to apply. Shop assistants have no agricultural training and in most cases it is guess work. They just want to sell their products. The best person for information on seeds and herbicides is your agricultural extension worker (AEW, mudhumeni).
Besides, the best herbicide is determined by the weeds on the ground and their stage of growth, which is best assessed by the local AEW. Many farmers also make the mistake of not supervising their workers on mixing and applying herbicides.
A correct herbicide that is not mixed correctly is ineffective. Some people find it difficult to read labels and correctly translate. Spraying herbicides is also critical. A correctly mixed herbicide that is not applied correctly will not be effective.
Tractor drivers need to be trained on the correct speed/gears to use when applying chemicals. If the farmer is not present, some drivers rush through the task because they want to finish and rest. A tractor driver spraying a chemical should always work with an assistant who checks that the mixture being sprayed is actually coming out of the nozzles. It is common for boom-sprayers or knapsack sprayers to clog nozzles (with dirt) and prevent the mixture from coming out. If left unchecked, a driver will claim to have finished spraying a whole piece of land when nothing was coming out.
Top-dressing properly
Many farmers are aware that maize needs top-dressing fertilisers before tasseling for it to have good cobs. However, the important aspects include timing of the application and amount applied. The time of application makes a big difference to the yield potential, especially in sandy soils. For the best results, top-dressing fertiliser should ideally be split applied at least twice in red soils and three times in sandy soils. If applying 500kg/ha, at, say, four weeks, come back with another three bags (150kg) two weeks later and the balance of three bags (150kg) after another two weeks (four, six and eight week stages after planting).
Maize absorbs small amounts of nitrogen better over an extended period than large amounts at one time.
Maize requires only a fraction of its nitrogen requirements during the early stages, but its needs escalate rapidly once the crop reaches eight-leaf growth stage (knee height). The crop can grow from knee height stage to shoulder level (approximately 12 to 14-leaf stage) in about two weeks and reach tasseling/silking stage in another two weeks if conditions are favourable (i.e high rainfall, enough heat units and enough fertilisers).
Such rapid growth requires a large supply of nitrogen; hence, the general recommendation that a farmer should apply top-dressing to maize at knee height stage. Maize generally requires over half its nitrogen supply between knee height stage and tasseling stage, a period of approximately 30 days.
This means if you fail to top-dress the crop between knee height and tasseling stage, you will have deprived the crop of over half its nitrogen requirements and that has serious consequences on the yield level. The maize stalk becomes thin from knee height upwards, and a thin stalk will not be able to carry a heavy load of well-developed cobs, let alone two cobs per plant. Lastly, maize’s need for nitrogen does not end at tasseling. In fact, one-third of plant requirements must still be met by uptake during the kernel/grain development stage.
Nitrogen is actually crucial during ear and kernel development. If the plant fails to get this nitrogen from the roots, it cannibalises the leaves to provide nitrogen for kernel development.
This is what may cause leaves to turn yellowish during that stage. Therefore, it makes sense to still apply top-dressing fertilisers even after the crop has tasseled. The only compromise you can make is to reduce the amount to be applied. Like an alert athlete, farmers should make the right decisions right from the start to be able to achieve 16t/ha or more.
A slip on any of these aspects will make it very difficult to catch up with other “athletes”.
So farmers, “On your marks, set, go!”
Peter Gambara is an agricultural economist and consultant based in Harare. He wrote this article for The Sunday Mail
