Increased soyabean production is necessary to meet an increasing domestic and global demand. Soyabean is one of the most common crops with multiple benefits to the farmer, the industry and the economy. However, current demand for soyabean in Zimbabwe far outstrips supply, opening opportunities for farmers and the industry to plug in the disparities.

Soyabean crop is used as an affordable source of protein for livestock feeds. It is also used in making cooking oil, margarine, soya chunks, soap, milk to name a few. It is one of the richest crops in terms of crude protein (ranging between 35-45%) and also contains 20% oil. Indeed soyabean contributes significantly to food security in Zimbabwe and it is therefore strategic to attain some level of autarky (or self-sufficiency) with regards to soyabean. The country requires about 220 000 Metric Tonnes of soyabean annually for food, feed and other industrial needs.

At national level, the crop is critical in attaining a complete food security basket for the general populace. Currently it contributes about 2 to 3% to the agriculture GDP and yet the agriculture industry contributes about 30% to the National GDP. Its contribution to the agriculture GDP can be more with increased production. The fact that the agriculture industry occupies a central space in the economy of the country [delete ,] cannot be overemphasized. The industry creates employment for at least 65% of the populace, directly and indirectly. This shows how essential it is to improve production and productivity levels of all the crops in the food basket such as soyabean in the country as well as non-food crops. Improving soyabean production will surely increase its contribution to the agriculture GDP.

We can also imagine the amount of foreign exchange saving the country will attain if the annual national requirement is produced locally.

At farm level, it is one of the short season crops with a lucrative return on investment. The general cost structure per ha ranges from $700.00 up to $900.00, at full absorption (all direct costs incorporated), i.e. at high management level. At this level a farmer will be targeting to get at least 3.5 tonnes/]ha and even up to 6 tonnes/ha, with Seed Co varieties. The minimum income a farmer can get using the ruling prices of $550.00 per tonne is about $2000.00 after a period of four and half months or less (depending on altitude and variety). It can be more with high productivity levels. It means a farmer can realise a gross return of at least $1100.00/ha, after 4-5 months. The break-even yield level for soyabean is about 1.7 tonnes/ha at the prevailing prices. A farmer can easily rake up to $3.00 per dollar invested.

A soyabean crop can be used for value addition on the farm, where own stockfeed can be formulated and mixed. Generally in livestock production systems, feeds constitute about 70% of the total cost structure. According to several studies, feed costs can be reduced by about 25% if a farmer can produce the feeds on the farm. This will ultimately enhance profitability levels of the livestock ventures. Other on-farm value addition options include soap, cooking oil, milk and soya chunks/mince production.

In addition to these top line stories, the soyabean crop is also compatible with long and short rotations. An example of a long rotation is maize (summer)-soyabean (summer) which is common in many non-irrigated farming systems. Soya (summer)-wheat (winter) is an example of a short rotation (also known as double cropping system) in irrigated farming systems. Both rotation setups are beneficial to the farmer.

Generally, the yield of a cereal crop which follows soya in a rotation is usually enhanced because of the residual nitrogen, since soyabean is a legume which fixes Nitrogen. A well-managed soyabean crop can leave a residual Nitrogen level of up to 90kg/ha, which benefits the next crop in a rotation.

The following table shows yields of wheat following maize and soya, and at different levels of applied Nitrogen.

Source: Seed Co Agronomy Manual, 2011

In rotations, the yield of maize/wheat following soyabeans is generally greater than following maize at both low and high levels of nitrogen application.

Other benefits of soyabean production

• The benefits from growing soyabean prior to maize include better moisture conservation due to the early maturity of soyabean and the canopy cover. In Zimbabwe, soyabean varieties are generally early to medium maturing (115 to 135 days from planting to physiological maturity).
• The soyabean crop can be used in the control of certain weeds, pests and diseases, especially in rotation systems with cereal crops.
• A soyabean crop can help the spread of peak work periods and early cash return in April or May and enhance farm cash flows. It should be noted that rotations as a cultural practice are a first port in Integrated Management of weeds, pests and diseases in most cropping systems.
• Soyabean rotates particularly well with winter-irrigated wheat, as it takes less time in the fields even when planted in November or early December.

Considerations for soyabean production

As we approach the summer season, we will publish practical tips on soyabean production in the Bumper Harvest column. This week, we will highlight general considerations, which have budgeting implications. This is the right time to plan for summer. 

Choosing the right variety

We always recommend for farmers to plant fresh certified seed every year. Certified seed is of high quality, with good and tested germination qualities. Certified seed is also screened of seed borne diseases-which can significantly reduce yield levels. Selecting a high yielding certified, fresh seed variety is the first and critical stage in attaining high productivity levels in soyabean production, just like any other cropping system. In frank and short terms, it is best to start with fresh certified seed every season.

There are two types of soyabean varieties: determinate and indeterminate. This refers to the way the plant grows i.e. the growth habit. Determinate cultivars grow vegetatively for about six weeks and then begin to flower, having put on 10 to 12 leaves. Once flowering begins, no further new leaves are produced on the main stem. Indeterminate cultivars, on the other hand, grow vegetatively for about six weeks then begin flowering when the main stem has about 10 leaves, but at the same time as flowering, the stem continues to grow for another three weeks or so, producing another five to seven leaves. Thus, the vegetative and reproductive growth periods overlap in indeterminate cultivars but not in determinate cultivars. Indeterminate cultivars also tend to grow taller than determinate cultivars. For these reasons, determinate cultivars are better suited to warm fast growing environments and sometimes irrigation maybe recommended.

When choosing a variety to grow in your particular farming region, the following considerations are critical:

• The variety must fit in a growing season of 4 to 5 months.
• The variety should give the highest yield for a farmer’s particular region.
• The variety must be resistant to lodging i.e. must have good standability at optimum population densities.
• The variety should have a longer period between physiological maturity (time when no more dry matter is added to seed) and pod shattering. This period is called shattering free period.
• High pod clearance to reduce losses when harvesting with a combine harvester or hand.
• A good variety must have a rapid stem dehydration. The stem must dry down concurrently with the pods.
• Resistance to diseases, especially red leaf blotch (Pyrenochaeta glycines) frogeye (Cercospora sojina), soyabean rust (  Phakospora pachyrhizi).

Soil condition and conditioning

Soyabeans are a legume plant suited to well drained soils with a relatively high clay content of more than 20%. The crop does not perform very well on weak/light sands but responds to manure. The crop is also sensitive to soil acidity because the bacteria which fixes nitrogen only thrives in a certain optimum pH range and is extremely sensitive to low pH (acidic soils). The optimum pH range is between 5.5 to 7 (CaCl₂ scale). Since soyabean is sensitive to soil acidity, we recommend farmers to sample their soils for analysis of the soil pH (acidity or basicity) in winter. If necessary, lime should be applied at the prescribed/recommended rates to bring the soil to an optimum pH level. In fact, we apply lime to sweeten acidic soils and the best time to do it is NOW (after harvesting).

Germination and emergence is enhanced by preparing the soil to a fine tilth and also by structuring poorly structured soils, normally by applying gypsum during land preparation in winter. Gypsum improves a soil’s physical structure i.e. removes hard setting clodiness, removes surface crusting/capping and poor workability as well as supplementing the soil with Calcium and Sulphur. However, gypsum application is determined by soil analysis. Again this is the most ideal time to do soil sampling and analysis i.e. after harvesting the summer crop.

Fertilisation

Soyabean grows well on residual fertiliser. A full soil analysis will determine the soil nutrient status and prescribe the rates and type of basal dressing to be applied. However, a general recommendation is to apply a pre-planting basal application of 200 to 300 kg per ha of soya blend or cotton fert/compound L. This basal dressing should be incorporated by discing it into the root zone/secondary tillage depth of 10-15cm. Soyabean also responds well to manure application. Since soyabean is able to obtain its nitrogen requirement through nitrogen fixation, we do not recommend nitrogen in the basal as well as in top dressing. Sometimes minimum nitrogen applications can be recommended especially after prolonged wet periods. Prolonged wet periods creates an anaerobic environment in the crop root zone and disturbs the functioning of the nitrogen fixing bacteria and usually result in yellowing of the crop. A light top dressing of about 75-100kg/ha after the wet spell is usually recommended in this case depending on soil type.

It is therefore essential to apply Rhizobium inoculant to the seed at planting. This inoculant is obtainable from Seed Co. A packet (80-100g) of Rhizobium inoculant is mixed in 1 L of water for every 100 kg of seed. However, a higher rate is preferable on sandy soils or in first year soyabean fields. Adding a few teaspoons of sugar will aid sticking the culture to the seed. In some cases a wetter can also be used.

Some farmers apply straight fertiliser combinations and averting rhizobium seed dressing.

Other critical considerations include weed control, disease and pest control to attain a good crop.

Parting shots

As we prepare for another bumper season, let us keep in mind the soyabean yield determinants which include soil conditioning, land preparations, time of planting, varietal choice, weed control and irrigation. Soyabean is indeed a lucrative crop to the farmer and strategic to the nation. You are invited to a field day at Mr and Mrs Pfachi Farm at plot 38, Fairview Farm, Mazowe on the 16^th of June 2017. Come and witness the fruits of religiously adopting Good Agronomic Practices. Also register for 11 Ton Plus Club and win big prizes this year.

About the authors

Author: Dr. John Basera and Dr. Hapson