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Golden Sibanda Senior Business Reporter
Zimbabwean farmers risk losing between 50 and 80 percent of potential maize yield if they fail to effectively control weeds among their crop in the first 10-12 weeks from germination, experts have warned.

According to Food and Agriculture Organisation, maize is the main staple food in Zimbabwe. It is cultivated in all five natural regions with NRs II and III accounting for about 84 percent of total maize production. NR IV has the largest area under maize but its yields are lower than those in NRs II and III. Experts contend that since maize is the main staple in Zimbabwe where population is growing at an average rate of 2,4 percent, farmers must take farming as a business and adopt best practices to optimise yields.

According to Seed Co, head agronomy and extension services, John Basera, farmers need to take charge of things they can control while managing those that they have no control over to realise the optimum benefits. He said there were 11 key things farmers need to observe in maize production, including weed control, soil condition, soil fertility, seed variety, population density, time of planting and moisture management. But one of the most important issues to note is the apparently simple issue of the potential negative effect of weeds on maize yield, which is a factor constraining farm productivity and adoption of farming as a full time business in Zimbabwe, especially in many communal areas.

“Annual yield losses due to weed problems can reach 50 percent. The crop must be weed-free in the first 10-12 weeks of the crop cycle, to enjoy a good head start against competition from weeds,” Mr Basera noted.

He emphasised the fact that failure to control weeds during the first five weeks of the crop cycle leads to a 50 percent yield reduction.  Mr Basera also said failure by farmers to control Shamva grass throughout the growing season, affected yields by 57-80 percent.

“Weeds compete immensely with a maize crop in the first weeks of the crop cycle. Never allow weeds to seed, it will enhance the weed seed bank and result in future weed control cost increases. One year of seeding makes seven years of weeding,” he said.

Fertiliser programmes for individual lands need to be adjusted in accordance with the respective soil fertility status.

Mr Basera said the maize crop required about 23kg N, 7-11kg P, 5-11kg K to produce 1 tonne. Achieving high maize yields requires an excellent soil fertility management programme, which is centred on adequate timing and placement of nitrogen, phosphorus, potassium and other micro-nutrients.

“Basal dressing should be applied at or before planting, while top dressing should be applied between 4 to 8 weeks after crop emergence. Split applications of top dressing fertilisers are recommended in lighter soils,” he said.

Mr Basera also noted that choosing the right maize variety was critical for farmers to achieve high and optimum yields. He said choosing the right maize variety contributed about 50 percent to the annual yields. Farmers, Mr Basera said, should also pay attention to issues of yield per plant, which should average from the three components and also yield per unit area — determined by the farmer’s ability to plant at optimum populations.

Maize growth rate also responds well to high daily temperatures experienced in October, November and December, as such, farmers should take advantage of this period, experts say.

“At least 40 percent of the HUs (Heat Units) is experienced during these three months, so it is critical for farmers to plant their crop as early as possible to capitalise on the HUs.”

Related to that, Mr Basera said farmers need to take advantage of early planting, as the length of the growing season becomes extended while pollination period may occur early before the mid-season dry spells. In addition, Mr Basera said soil organic matter (SOM) exerts numerous positive effects on the soil’s physical, biological and chemical properties.

This increases soil fertility by providing Cation Exchange Capacity (CEC) and acting as reserve of plant nutrients, especially nitrogen (N), phosphorus (P), and sulphur (S), along with other micronutrients, which are slowly released upon organic matter mineralisation. Mr Basera said thorough land preparation aids moisture conservation.  As such, he said wet ripping after 2-4 weeks, is critical to create a moisture bank.

“Due to climate change, water is increasingly becoming a limiting factor to yields.  High yields of maize often in the excess of 11 tonne per hectare can be achieved with irrigation. Where irrigation is available, higher yields can be obtained through early crop establishment before the onset of the rains.”