Ronald Rusere and John Basera

Improving crop productivity is a major driver as far as attaining food security and food surplus in concerned in Africa.

However, to achieve improved crop productivity, crop management should keep up with genetic gains in yield.  There are three themes to the farmer’s profit equation – input price, productivity and output price.  Unfortunately, a farmer does not have control over input price and output price but fortunately can manipulate those by improving productivity. If we get productivity right then profit and growth will ensue. Successful crop establishment is the first critical step of crop production and it contributes significantly to the success story of the farmer because that is where the yield gap begins. Crop establishment entails a series of events which include planting, germination, emergence and final crop stand. It depends on the interaction of many factors such as variety (seed quality), planting depth, population density management, temperature, moisture, good seed-soil contact, proper land preparation, nutrition and planting date.  A good beginning is the battle half won, a farmer should control these factors to the best of his/her ability so that crop the gets off to a good start. Yield potential is never as high as the day seed is planted, so the conditions have to be right in order to unlock that yield potential.  Planting is one of the crucial tasks that a farmer carries out and it is important that one achieves an optimum crop stand, with plant-plant uniformity of emergence in order to attain optimum yields. Any mistakes that occur at/during planting will result in yield loss and there’s no making up for lost yield. 

Variety selection

A smile after a bumper harvest starts with good decisions a farmer makes before the season and it forms the foundation of a good harvest. When a farmer chooses the right variety it is called tapping into the genetic gains phenomenon and it contributes to over 50% to the farmers success equation. Since yield is primarily determined by genetics, choose good resilient, high yielding varieties optimised for your agro ecological region and cropping system. Success lies in good seed selection and this can make or break a farmer’s season. It is one of the key decisions a farmer can make in a season. Select a variety with higher yield potential and good defensive traits such as drought and disease tolerance. Ultimately yield of maize will come from three things which are a long cob length the longer the cob the more the yield, a high row number (+16-20 rows) the more the yield and a shelling out percentage of 80-87%. The more the shelling out percentage the more the proportion of grain for the farmer. 

Planting date

We strongly recommend farmers to plant early with first rains and effectively. Crop should be established when a farmer recieves over 30-35 mm within a period of 2 -3 days provided land preparation was done prior.  Tap into the heat units which normally fall into the first three months of summer seasons in Southern Africa. Planting date influences profit margins as yield decreases with late planting.  Late planting will produce low yields, and is very risky, because the crop may suffer from drought stress at the end of the season; while pests (like fall armyworm, stalk borer) and foliar diseases (maize streak virus and HT) are more prevalent on late planted crops. On average, for every week that planting is delayed (after first effective rains), the yield loss is (120 kg) per ha. 

Every season has an optimal planting window that delivers maximum yield and farmers are advised to take advantage of early planting with the onset of the first rains and reap the potential yield benefits that come with planting early. 

Population density management

The seed bed should be fully utilised by ensuring that an optimum plant population is planted and this pays the bills for the farmer. Ideal plant spacing depends on type of crop, variety and the climatic conditions such as rainfall/ water availability.  Yield will come from yield/plant catered for by the breeders and yield/unit area component determined by the farmers ability to plant at recommended population levels for instance in maize 50 000-60 000 plants per hectare in high potential areas/ under irrigation and 37 000-44 000 in low potential areas, tobacco 15 000-18 000 plants/ha, cabbages 30 000-40 000 plants/ha, soyabean 350 000-500 000 plants/ha. Every one of those seeds should contribute to your final yield. Uneven spacing, skips in the field, missing opportunities from missing plants resulting from unsuccessful germination and emergence will reduce yield. Strive to achieve the optimum plant population that allows maximum realisation of yield potential.

Depth of planting

Planting depth is important towards achieving good seed-soil contact which promotes uniform crop emergence and stand which are the basis for good yields. It is not a matter of burying seed but placing seed at the right depth 3-4 cm in moist soils or 5cm under dry planting. Planting too shallow affects nodal root development in maize making it prone to the risk of root lodging and reduces root mass (floppy maize syndrome). 

A good nodal root system is essential in reducing early season root lodging and improves plant performance under drought stress later in the season.  Planting depth also depends on size of seed, with smaller seeds planted at a shallower depth than larger seeds. While the deeper the seed is placed the longer the seedling will take to emerge and the weaker the plant will be at emergence which may reduce plant vigour and yield. Farmers are urged to uniformly close the seed furrow during harrowing after planting, as air pockets tend to result in delayed emergence especially those using ox drawn harrows.

Optimum nutrition and fertiliser placement

Nutrition dictates health of the crop. At planting farmers should always apply appropriate amounts of basal dressing with N: P: K. Start up nitrogen will sustain crop for the next 21-25 days but then top dress later. The importance of enough early nutrition cannot be understated as it sets the trajectory towards high yield from the start. Shortages of nutrition at planting will limit yield potential. Fertiliser should also be placed precisely so that plant roots grow into the fertiliser. Place seed at least 2cm away from applied fertiliser as the fertiliser can burn seed however too far away could mean nutrients are too far away from the plant roots to be effectively absorbed during early root development. 

Adequate and uniform moisture

Uniform moisture is crucial for successful germination and emergence. A farmer should plant crop after receiving over 30-35 mm within a period of 2 -3 days provided land preparation was done prior A maize kernel needs to absorb water equal to 30% of its weight to initiate germination therefore all kernels must have equal access to water. Soyabean germination requires about 50% compared to 30% maize (soil moisture content + dry weight basis). 

It is important to place that seed down into adequate moisture, the more consistent moisture that is around the seed, the more consistent the germination and emergence. Excessive moisture levels are not conducive for germination as they limit oxygen concentration leading to a fraction of the seeds germinating. Variations in moisture in the field lead to uneven emergence. 

Adequate temperature 

Temperature is a key variable in influencing germination and growth of seedlings. The deeper the seed is placed the less effect direct sunlight and variable surface temperatures have on germination. Temperature along with depth will determine the duration of sowing- emergence period. Seedling vigour is most likely to be poor if the period between sowing-emergence is longer. Seeds should be placed in the best environment for them to thrive, in cool soils seeds lose vigour by taking too long to germinate. In poor saturated cold soils germination is affected resulting in stand loss.

Land preparation

Sets the tone for the season and it is the foundation to a good high yielding crop. Achieve a fine filth to create uniform seed bed, even under conservation tillage residue should be properly managed. Create a conducive environment which promotes quicker seed germination and faster root proliferation.  Poor land preparation causes uneven emergence resulting in yield loss. For a kernel of seed to absorb moisture quickly good seed-soil contact is crucial. Avoid working soils/planting when fields are too wet. 

The key to consistent individual cob weights and high yield in maize is attaining an even uniform crop stand. Poor planting conditions can result in the presence of a significant proportion of late emergers over a huge area and this will easily result in a reduction in yield negating the benefits of early planting. Late emergers will never catch up early emergers and a farmer needs to make sure that crop is planted in an environment that will lead to uniform emergence and development of adjacent plants after emergence. Uniformity of emergence is a critical aspect if one aims to attain high yields. 

Research by has shown that delayed emergence with 25% of crop emerging 10 days later than the rest can result in a 6% yield loss. Even if a farmer manages to achieve a full stand in terms of population, ultimately a crop with delayed/late emergers is at a competitive disadvantage with early emergers. 

The attainment of high yields requires great attention to agronomic detail therefore good crop management is one of the pre-requisites for successful crop production.  Make this season count by starting right! 

*Ronald Rusere is an agronomist and Dr John Basera is technical director (agriculture) at CBZ Holdings Limited.  He can be contacted on 0772 413 184