1.0 Introduction Soybean
(Glycine max L.) belongs to the family Leguminosae. It is a short-day crop, which requires short days for ﬂowering. The crop is one of the most important sources of oil and protein and is commonly used in both human and animal diets. Soybeans contain approximately 40% protein and 20% oil on a dry matter basis. Although the oil is used primarily in edible products such as margarine and cooking oil, it is used industrially in such products as high-grade paints and pharmaceuticals. It can also be processed into soybean ﬂour and soybean milk. The soybean meal that remains after the oil is extracted is almost all used as a high protein livestock feed, but the meal can be further reﬁned to give various protein extracts for direct human consumption. In Zambia, it is grown by both commercial and small-scale farmers. Besides its uses given above, soybean contributes to improving the fertility of the soil. The crop ﬁxes atmospheric nitrogen into the soil due to the presence of the bacteria Rhizobium in its root nodules. The soybean crop is recommended to be grown in rotation with cereals. Though Soybean is widely adapted and is grown throughout the country, major production areas are found in agro ecological Region II of Lusaka and Central Provinces and parts of agro ecological Region III of Copperbelt Province.
2.0 Climatic and Soil Requirements
2.1 Climate Soybeans require medium amounts of rainfall. In Zambia, Region II is the most suitable with a rainfall range of 800-1000 mm annually. The optimum temperature range for soybeans growth and development is 22- 35 C. Very low temperatures, especially during ﬂowering, will reduce the oil content and yield.
2.2 Soil Types Soybean is well adapted to a variety of soils types. However, loose, deep and well-drained soils are ideal for optimum soybean production. But clay soils and compacted soils should be avoided. These soils are prone to waterlogging. Further, a hard crust surface may form when the soil dries aﬀecting emergence. The soil pH range of 5.5- 7 is ideal for optimal soybean production. If the pH is below 5, then lime could be applied. Application of lime will not only beneﬁt soybean production but subsequent crops.
3.0 Recommended Varieties.
One of the most critical decisions in growing soybeans is variety selection. The choice of variety is a key factor in proﬁtable soybean production. Many varietal characteristics, such as maturity, lodging, yield potential, promiscuity and disease resistance, must be considered when selecting varieties. The table below shows the recommended soybean varieties and their agronomic attributes;
Shattering, lodging, diseases
Good, resistant to major diseases
Non – promiscuous
lodging, shattering, most major diseases
4 Management Practices
4.1 Land Preparation
Land preparation can be started with winter ploughing which can be done in May-August. Farmers can also practice conservation tillage by making rip lines or digging basins. Farmers with access to appropriate equipment are encouraged to practice minimum or zero tillage.
4.2 Planting – In Zambia, soybeans should be planted within the month of December. Delayed planting may lead to a reduction in potential yield, while very early planting may lead to poor seedling establishment. In Region II, planting should be done in the ﬁrst two weeks of December, while in Region III, it should be done in the last two weeks of December. The recommended seed rate for soybean is 100kg/ha. However, as a safety measure against low germination, a slightly high seed rate is normally recommended i.e. farmers can use a rate of 110kg/ha. The ideal planting depth should be between 2.5 and 3 cm. It is recommended that soybean is planted in rows by drilling. The optimum row spacing is 45 or 70cm.
4.3 Weed Control
Soybeans are very competitive with weeds once the crop develops a canopy, but early emerging weeds can cause serious problems. In most cases, weeding can be repeated 2-3 times before the shade from the narrow rows suppresses later weeds. Note that poor weeding can reduce the yield by as much as 30%. Chemical control- this is the use of herbicide and is mainly practiced by farmers that can aﬀord the chemicals. Herbicides, if used properly, are a safe and eﬀective method to control certain weeds in soybeans. Important factors to consider when choosing a herbicide include:
1) type of weeds present, 2) stage of crop and weed growth, 3) herbicide persistence and crop rotation restrictions, 4) environmental considerations, and 5) herbicide costs. Farmers are advised to use commercially available herbicides for weed control in soybean and follow the manufacturer’s instructions on their use.
4.4 Fertilizer Use Soybeans take up relatively small amounts of nutrients early in the season, but as they grow and develop, the daily rate of nutrient uptake increases. Soybean is sensitive to boron toxicity and therefore the use of boronated fertilizers should be avoided. Top dressing is not necessary in soybeans because by this time the crop will be ﬁxing its own nitrogen. To enhance nitrogen ﬁxation, it is recommended, especially for non-promiscuous varieties that the seed is dressed with inoculum at planting. Inoculation initiates infection of the roots resulting in nodulation and then nitrogen ﬁxation by the crop. Promiscuous varieties such as Magoye may not require inoculum. On the hand, the non-promiscuous varieties such as Kaleya require to be inoculated. The inoculants can either be in liquid, slurry or peat form.
4.5 Crop Rotation Practices Soybean is eﬃcient at ﬁxing nitrogen from the air, and when grown under optimum management, it can signiﬁcantly enrich the soil and therefore crops grown in rotation with soybean beneﬁt from residual nitrogen. It is therefore recommended to rotate soybean with a cereal crop. However, it is important to note that soybean is susceptible to nematodes and therefore should not be grown in rotation with Solanaceous plants or other nematode susceptible crops.
5.0 Crop protection Soybean is susceptible to a few insect pests and diseases that reduce the yield and quality of the produce. There are measures that can be taken to minimize the damage.
5.1 Major Diseases and Control Measures Soybean production in Zambia is aﬀected by several fungal, bacterial and viral diseases. The crop is also aﬀected by nematodes. The following are the common soybean diseases.
5.1.1 Frogeye Leaf Spot (Cercospora sojina) This disease is prevalent in ﬁelds which are grown with soybean continuously. The common symptoms of the disease appear on leaves as lesions that are small, irregular to circular and grey with reddish-brown borders that most commonly occur on the upper leaf surface. In severe cases, the disease can cause premature leaf drop and will spread to stems and pods.
The symptoms on stems are not as common or distinctive as foliar symptoms and appear as narrow, reddish brown lesions that turn light grey with dark margins as they mature. The lesions on pods are circular or oval shaped and are initially red-brown and turn to light grey with a dark brown margin.
Control Measures Control measures include the use of resistant varieties, practicing crop rotation with non-hosts crops such as maize and wheat and use of recommended foliar fungicides applied during late ﬂowering and early pod set to pod-ﬁlling stages to reduce the incidence of the disease.
5.1.2 Bacterial Blight – is particularly prevalent during wet season and when diseased plant residues have not been incorporated properly. Symptoms vary from small yellow spots on the leaves to large yellow spots, dead lesions with yellow margins. Affected leaves usually drop early.
5.2 Major Pests and Control Measures A number of diﬀerent insects occur in soybean ﬁelds, but few are of economic importance and therefore do not warrant control measures. Some of the common pests are; termites, cutworms, stink bugs and leaf eating caterpillars. Control Measures In epidemic situations, chemicals are available to control most of these pests.
6.0 Harvesting Soybeans should be harvested as soon as it matures to avoid loss of yield through shattering. When fully mature, most varieties will change colour of the pods from green to golden yellow, and when shaken, the seeds should rattle, and .at least 50% of the leaves should have fallen to the ground. Additionally, the moisture content of the grain, is between 12- 14%. To minimise the risk of shattering, farmers should plant areas that they can manage to harvest before shattering starts as this may lead to yield loss. Varieties such as Magoye, should be harvested early as they take 7 and 10 days respectively to start shattering after maturity. The harvesting can also be done in the late hours of the afternoon when it is cool.
7.0 Post Harvest Handling and Processing
7.1 Threshing and Cleaning After harvesting and drying, threshing is done in order to remove the grain from the pods. This is done by pilling the plants on a concrete ﬂoor or tarpaulin and then beating lightly. After threshing, the soybeans grains are normally contaminated with debris such as soil, plant, small stones, weed seeds, or broken soybean seeds. The broken seeds and other impurities hinder drying operations, make post-harvest processing longer and more costly, lower the end-product quality, and serve as targets for postharvest disease.
7.2 Storage Clean threshed soybeans grain should be stored when the grain moisture content is between 10% and 12%. Before storage, soybean grain should be packed in bags made of either polyethylene or cotton ﬁbers. Ideally, bags should be stacked on wooden platforms in order to prevent direct contact of bags with the ﬂoor. The free space between the top layer of the stacks and the top of the storehouse should be at least 1 meter. The period of storage will depend on the intended use of the stored grain. If the stored grain is meant to be used as seed for next season planting, the storage room should be well ventilated to ensure low and stable temperature and humidity so as to minimise loss in seed viability. For grain meant to be sold at a later date, ensure that the storage conditions prevent grain deterioration through damage by pests.
7.3 Processing Soybean Most of the soybean grain produced is commercially processed into various products such as edible oil which include cooking oil, margarine and mayonnaise. However, small extraction machines are available for small scale processing for oil, milk and ﬂour. Beneﬁts of Modern Soy Products include the following: · Soy concentrates and isolates are easily digested by humans · Soy protein is equal to the quality of cow milk, meat and egg protein · Soy proteins are acceptable in almost all diets · Soy protein contain virtually no cholesterol and it is lactosefree