John Basera and Tegwe Soko
Wheat is the second most important cereal after maize in the food security basket in Zimbabwe. Flour’s easiness to produce various products such as bread, buns, biscuits and cakes has made the crop popular with the general populace. Its importance is broadly two pronged i.e. to the farmer and to the nation.
To the farmer
To the farmer it is one of the crop enterprises with a very lucrative return on investment. The return per dollar invested for wheat is about $2-$3 under high productivity levels. After investing $1 700-$2 000.00/ha (direct costs), a farmer can get a total gross income of about $4 000 (at 8 tonnes/ha and @$500/tonne), realising a gross margin of about $2 000/ha.
It is also a strategic component of double cropping or short rotation set ups, where a farmer grows maize in summer followed by wheat in winter.
We have always been encouraging farmers with irrigation to adopt the double cropping concept in order to improve their bottom and top line stories at farm level as well as to spread coverage of fixed costs per year. Growing wheat in winter also aid spread of cash flow on the farm.
The basic farm business principle is that farmers should have at least 2 major crop harvests per year supported by other complimentary crop sales/ventures after every two months such as vegetables. We generally recommend diversity in terms of crops and other non-crop ventures on the farm. This generally ensures smooth running of farming concerns.
Maize-Wheat-Maize or Soybean-Wheat-Soyabean are some of the common short rotations. The same machinery can be used to plant, spray and harvest both the winter and summer crops.
To the nation
Since the nation is in a drive for import substitution, producing wheat locally will result in forex savings which would otherwise be channelled to other more productive priorities of the economy.
The national annual wheat/flour requirement is above 350 000 MT and over the years Zimbabwe was producing less than a quarter of that. One can imagine the savings if this sum requirement is produced locally and also the implications on wheat value chain.
Producing wheat locally will create employment directly and indirectly in the upstream and downstream sides of the wheat value chain. Currently wheat contributes between 4-5 percent (a significant proportion) to the agriculture GDP.
Producing this annual national requirement locally will surely double if not treble its contribution to the agriculture GDP.
This week we are going to share some agronomic considerations to increase wheat productivity and as we prepare for the winter wheat production season.
There two overarching considerations for successfully increasing wheat productivity levels at farm level; Seed varietal choice and Religious adoption of Good Agronomic Practices.
Soils and climate
Wheat is a temperate crop and is best grown in winter under irrigation with optimum day temperatures of between 15-20OC and cooler nights giving the best yields.
There are some varieties that may be grown in summer (such as Sahai), but generally there is high disease, pest and weed pressure in summer accompanied by warmer temperatures that result in depressed yields (≤ 3t/ha), therefore, winter is the best time for growing wheat.
The crop is adapted to a wide range of soils. The soils must be well drained with an optimum pH range of 5.5-6.5 on a Calcium Chloride scale. Wheat yields are greater in the highveld (>1200 masl (metres above sea level)) and middleveld (800 – 1200 masl) with yield potential of 8 to 12 t/ha compared to the lowveld (<800 masl) where yields average of 4.5-7 t/ha under good management.
Land preparation and soil conditioning
The most suitable soil for wheat is one with:
A good effective depth with a fine tilth to ensure seed-soil contact. Good seed-soil contact ensure good crop emergence and stand which are the basis for good yields.
Favourable physical properties: Good internal drainage, an optimal moisture regime.
Chemical properties: Sufficient and balanced quantities of nutrients (NPK and other micro-nutrients/trace nutrients).
Biological properties: Good level of organic matter, and with beneficial micro-organisms.
The objective of soil tillage is to maintain the existing structure of soil or to improve the structure of poorly structured soils as well as addressing the three properties as mentioned above (physical, chemical and biological).
Lime can be applied if required to “sweeten” acidic soils to the pH optimum range. Lime application should be based on soil analysis prescriptions.
Gypsum improves soil physical structure i.e. removes hard setting clodiness, removes surface crusting and poor workability as well as supplying the soil with complimentary Calcium and Sulphur for good crop standing and growth.
There are several options of tillage which fall under two broad categories: conservational and conventional tillage which can be adopted in wheat production. The conventional tillage procedure follows the following steps:
Deep ploughing (ripping or chisel plough), liming and basal fertilizer application, discing and then followed by rolling. A roller can be pulled concurrently behind a disc harrow. Conservational tillage also known as zero/minimum tillage is another cheaper and more sustainable option which farmers can adopt.
Time of Planting.
The optimum time for planting winter wheat is between mid-April and the last week of May and even earlier in the Lowvelds. Sometimes planting time can be extended to mid-June but not normally recommended. Delayed planting results in a loss of about 50kg/ha/day after May. The first two weeks of May tend to give the best yields in the Highveld areas. Adhering to the optimum planting time has some agronomic explanations and rationales:
Early summer rain escape: Rains which come after the wheat has reached physiological maturity causes sprouting (grain germination in the ear) and result in down grading of the wheat due to a decline in baking qualities. So farmers are encouraged to plant early infact observing the optimum planting window.
Disease escape: disease pressure especially for rust diseases, normally rises when temperatures start to warm up around August and an early planted crop would have gotten a good head start without disease pressure.
Pest escape: likewise pest pressure such as aphids start to rise when temperatures start to rise. An early planted crop will have a good head start ahead of pest pressure.
One of the key considerations for the adoption of double cropping is early planting and early harvesting for both summer and winter crops. The farmer will now come in with his summer crop on time when wheat is planted and harvested early.
Wheat critical stages such as crop establishment, tillering, flowering and grain filling will coincide with the optimum growth conditions when the crop is planted early. For instance, for robust tillering i.e. for the plant to produce secondary stems (4 – 5 weeks after crop emergence) requires very cool conditions that normally occurs in May and June while Flowering (60 – 90 days) and Grain filling (> 90 days) must not coincide with frosty conditions to avoid flower and grain sterility.
The optimum plant population for wheat is 220-250 plants per m2. Seed rate depends on the seed size, germination percentage, planting conditions and planting method. To achieve optimum population density, generally, a seeding rate of about 110-125 kg/ha when drilling and 125-135 kg/ha when broadcasting with a spreader is recommended. To ensure good crop standability and yield, farmers should adhere to these optimum population densities. Diseases such as Powdery mildew are also minimized with good agronomic practices and adherence to optimum population levels.
Irrigation requirements and scheduling
Since there is very little or no rainfall during winter in Zimbabwe, irrigation is required to achieve a high yielding wheat crop. Generally the total gross amount of water required is 600 mm per ha (i.e. 6 mega litres per ha) depending on method of irrigation (Overhead irrigation with sprinkler or use of Centre Pivots) and must be applied as the crop requires it. The key points are:
- The soil must be brought to field capacity to the full potential rooting depth (about 1,2m) at planting to emerge the crop;
- A light irrigation must be applied at the 4th or 5th day after sowing, to break the crust to ensure good crop emergence;
- A light irrigation must be applied at 14 to 17 days after emergence to stimulate crown root development and tillering, and
- Irrigation thenafter must be applied to match crop water use. On sandy soils with low water holding capacities, irrigate frequently (7 to 9 day cycles with 30-35mm net). On clays and sandy clays, with good water holding capacities, irrigation may be less frequent with larger amounts (10 to 14 day cycles with 40-45 mm net). This is a general irrigation scheduling guide. For an informed irrigation scheduling, the use of a soil soil moisture sensors to evaluate the soil water content ahead and behind irrigation lines is a good aid to irrigation management. Irrigation is terminated when the neck of the ears/spikes/head (peduncle) turn yellow i.e. physiological maturity.
Wheat crop hardening
After the crop has emerged, the hardening stage begins. This induces crown root development as well as tillering. The recommended hardening period (irrigation is temporarily terminated during this stage) is 10 and 14 days in light and heavy soils respectively.
Top dressing fertilizer and herbicide application is done after a light irrigation which follows the hardening period, normally about 21 days after emergence.
The fertiliser regime management in wheat, like any other crop must be tailored to the soil fertility status, the yield potential and the grain quality requirements. Fertiliser regime management must be informed by soil analysis prescriptions. However, as a general guide, wheat requires a basal application of 400 to 500 kg/ha of a compound fertiliser (such as 7-14-7) and a top dressing of 400 to 500 kg of Urea or Ammonium Nitrate per ha. Both basal and top dressing fertilisers are broadcast.
Generally, 160 -190kg/ha of Nitrogen Units (N), 50-70 units of Phosphorous (P) and 30-50 units of Potassium (K) are adequate for optimum plant growth and yields. Basal fertilizer need incorporation into the soil by discing and should be applied after primary tillage.
The top dressing is usually applied in one application between 14-21 days after emergence on heavy soils, and in two applications of equal amounts at 14 and 35 days after emergence on sandy soils.
Top dressing should be applied after the hardening stage. Top dressing is essential for good leaf and general plant growth and ultimately the yield but also importantly for attaining good protein levels.
The minimum protein level requirement for “Premium” (Good quality) wheat is 11 percent. It is one of the considerations for grading and pricing of wheat. Attainment of good protein levels is also determined by varietal choice and general management. Application of Nitrogen after flowering can also boost the Grain Protein Content of wheat.
All fertility management practices must be based on proper full soil analysis recommendations by approved laboratories.
Farmers are advised to use some wheat specific post-emergence herbicide which should be applied after a light irrigation which follows the hardening period (2 WACE-Weeks After Crop Emergence). We also recommend farmers to apply specific herbicides against volunteer crops.
Farmers can consult agronomists and agrochemical companies for herbicide recommendations and it is important for farmers to read labels whenever they are applying herbicides.
Pests and diseases.
Aphids and stalk borers can attack wheat with aphids coming in earlier soon after tillering while borers can attack the plant from flowering onwards. Farmers must also be on the look-out for “Fall armyworm” given that wheat is one of the host crops to the pest. These pests can be controlled with appropriate pesticide sprays after scouting.
During the late grain-filling period, Quelea birds may consume much grain and reduce yields significantly if not attended to. A pesticide molecule called 9,10-Anthraquinone 50% WP (Bird Shield) has been developed, which can be used as a seed dressing or as a foliar spray at soft dough stage. Efficacy of this pesticide molecule can be enhanced by applying with a sticker and also a rainfast period of 4 hours or more. This pesticide molecule will act as a bird repellent. This is the best and the most efficient option. The other option is bird-scaring using bells, tins, whistles, discs/reflectors etc. by bird scaring gangs.
Diseases such as Leaf rust, Stem rust, Powdery mildew, Fusarium head blight and Take-all may cause significant yield reduction. Farmers must seek professional advice on how to control these diseases. It is always recommended to grow disease tolerant varieties and Seed Co wheat varieties such as SC Select are tolerant to these diseases. Generally two preventative fungicide sprays are recommended if farmers are located in disease prone areas and gives some form of insurance against climate change that can result in new disease pathotypes.
NB: Farmers are encouraged to scout their wheat crop for diseases, pests and deficiencies and make spraying decisions early when pest/disease can cause economic injury.
Consult Agrochemical companies for more information on chemicals. Always read chemical labels carefully, use safe practices and adequate protective gear during application.
A farmer must be a Crop Doctor, who takes time to investigate his fields in order to prevent problems and improve productivity. He walks his fields regularly, observing, inspecting, evaluating and interpreting the possible effect of the observations on crop growth. He diagnoses problems, seeks and proffer solutions.
Here are some tips on how to be a crop doctor:
Walk through your fields in a random manner, stopping every now and then to examine the soil, plants and surroundings. Be observant, be an investigator, think and take notes.
Examine at least ten places in the field when taking a general inspection, but if scouting for pests and diseases, it may be necessary to examine between 24 and 100 plants or more, depending on the pest and the size of field. Inspection pattern can be random, zig zag or diagonal pattern.
About the authors
(1) John Basera is Seed Co Agronomy and Extension Services Manager. He can be contacted on +263 772 413 184/ [email protected] (2) Tegwe Soko is Seed Co Group Wheat and Small Grains Breeding Programme Lead. He can be contacted on +263 772 516 669/ [email protected]