2.0: Agronomic Practices
2.0 Agronomic Practices
Improved agronomic and management practices for soybeans are critical since they influence soybean growth, development and yield. Soybean is is very sensitive to various stresses.
2.1 Agro-Ecologies
Soybeans are well adapted for production in all agro-ecological zones in Malawi. Malawi is agro-ecologically divided into 8 agricultural development divisions (ADDs). Five main landforms are evident in most of these agro-ecologies namely: Highlands, Escarpments, Plateau, Lakeshore, Upper Shire Valley and the Lower Shire Valley. The Plateau represents three quarters of Malawi at elevations of 750-1300 masl. Although the major soybean production districts are concentrated in the plateau, soybean virtually grows well in all agricultural development divisions. Soybean also grows well in warm, moist conditions with rainfall of 550-850 mm, well distributed over the growing season. Soybeans can also be grown under irrigation. If grown under irrigation planting should be done between May to June in low lying dry areas. It should be noted that soybean yields are reduced when grown off season due to photoperiod sensitivity of the crop. Yields are adversely affected by temperatures rising above 30oC or falling below 13oC for long period during flowering stage. This is detrimental to the formation of flowers and seed.
2.2 Soybean Varieties
There are more than eight soybean varieties currently grown in Malawi and have their recommended agro-ecologies based on their maturity period (Table 1 on page 5). These varieties were released in Malawi by the Agricultural Technology and Clearing Committee (ATCC). Farmers must select varieties that are adaptable and recommended in their respective agro-ecological areas. Maturity period and yield are important considerations when choosing a variety suited to a specific agro-ecology. Consider varieties that are early maturing rather than late maturing in areas with low rainfall like Salima and Shire valley. Although late maturing varieties have the capacity to give increased yields, it is risky to grow late-maturing varieties in drier environments because of late-season dry spells.
2.3 Source of Seed
The seed source should be known and reliable such as research institutions, registered agro-dealers, and registered seed producers with Seed Trade Association of Malawi (STAM). The seed should not be broken, shrivelled, diseased, purple stained, or contain off-types. Use high quality seed of the selected variety. It is common for soybean, even when stored properly, not to germinate after 12–15 months in storage since it loses viability. Therefore, use seeds that are not more than 12 months old to ensure good germination.
Sort out good seed for planting to ensure clean planting materials that are free from insect pest damage, disease infestation and weed seeds. Always buy soybean seeds from accredited seed companies or agro-dealers. Do not purchase seeds from open market the germination potential is not guaranteed. Poor quality seeds will not produce good yield.
2.4 Site Selection
Soybean can be planted in any soil that is suitable for growing maize but performs badly in poor sandy soils with low content of organic matter. Generally soybean is better suited to heavier soils than most other crops. Soils that easily compact and form a crust must be avoided for growing soybean because the protruding soybean seedling (hypocotyl) breaks easily under pressure. A fertile soil ensures that nutrients are available for the soybean crop and therefore minimizes the need for inorganic fertilizer inputs.
Therefore avoid :
Land on a steep slope
Land that is near a swamp or likely to have water logging conditions
Very sandy soil and areas with shallow surface soil to avoid drought stress
Areas with a lot of couch grass
Areas with a lot of shade to the soybean crop like under the trees
2.5 Land Preparation
A good contact between the seed and soil enhances rapid germination therefore proper land preparation is vital to ensure good germination and reduces weed infestation. Well-prepared land should ensure that weeds, shrubs and bushes are cleared.
Ridge or Flat Spacing: Farmers can plant soybean either on ridges or flat seedbed. If the farmer decides to make ridges, the ridges should be spaced at 75cm apart and make two grooves (20-30 cm apart) on a single ridge where the seed will be placed. If planting is on the flat surface, the recommended row spacing is 45 cm between rows.
2.6 Planting
Time of Planting: In Soybean production, early planting does not have the same positive effect on yield as is the case with crops such as maize. However, soybean requires enough soil moisture at planting. This is because soybean needs to absorb a minimum of 50% of their own mass in moisture (compared to 30% in the case of maize) before they begin to germinate. Sufficient soil moisture is thus necessary at planting. In Malawi, soybean can be planted in summer (December–April) and/or during winter (off-season) i.e. May/June and harvest around October) with irrigation or in dimbas under residual moisture. For the summer crop planting should be done with effective planting rains or soon rains are well established i.e. 30 mm of cumulative effective rains. Soybean should not be dry planted and should not be planted until it is clear that the rains have properly started. In winter season, planting to be done during May or June period but not later than July end. Timely planting helps in:
Greater number of main stem nodes and increased biomass
More rapid growth rate during pod setting
Potential for earlier flowering and therefore, a longer reproductive period
Greater grain filling rate, hence high yield
2.6.1 Use of Inoculants
Soybean production requires good supply of nitrogen for high grain yield. However, like many other annual legumes, the crop has the ability to meet most of its own requirement through biological nitrogen fixation after successful nodulation. Inoculants or rhizobia form a relationship with the soybean plant to form nodules or swellings that act as small factories for producing nitrogen. The decision to use inoculants on soybean before planting depends on the following:
The variety of soybean you have chosen to plant
The land cropping history
There are two kinds of soybean varieties; specific varieties and promiscuous varieties.
Specific soybean varieties require inoculants for them to perform well in the field where soybean has not been planted over the last three years. These varieties require specific rhizobia strain in the soil for them to form adequate nodules whilst promiscuous soybean varieties can easily associate with a number of rhizobia in the soil. If your field was planted with soybean in the last 3 years, then inoculation might not be necessary since the soybean will utilise the indigenous rhizobia left by the previous soybean crop. Currently, Tikolore is the only promiscuous soybean variety released for cultivation in Malawi.
The inoculant that is recommended is SOY inoculant. This inoculant is being produced and sold at Chitedze Research Station and Bvumbwe Research Stations. It can also be available in other research stations such as Lunyangwa, Chitala or Makoka if demanded. Arrangements can also be made to distribute inoculant to various ADDs. It is packaged in 50g packets which is enough for 10-15kg of seed. When inoculating the seed, the following procedure should be used:
1. Put soybean seed into a plastic pail.
2. Using a match inner box, weigh 5-10g sugar. The sugar acts as a sticker.
3. Mix sugar thoroughly with 200 ml of water. You can use a 300ml bottle to get the 200ml of water i.e. ¾ of 300ml bottle.
4. Then put the sugary water in a plastic pail with the soybean seed where the inoculant is then mixed with the seed until the seed is coated with the inoculum mixture. The sugary water helps the seed to be stacked with the inoculant. 50g pack of inoculant can cater for 10-15kg of soybean seed.
5. After thorough mixture of the seed with the inoculant, spread the inoculated seed on a tarpaulin or other clean surface under a shade (a tree) and leave for about 30 minutes to dry. The inoculated seed should be planted within 24 hours of inoculation in order to avoid killing the rhizobia.
NOTE:
Soybean inoculants require careful handling and storage. When you have inoculated your soybean seeds, planting should be done the same day (within 24 hours). The inoculant should be stored in cool dry place where the rhizobia cannot be killed. It is recommended that the inoculant be stored in a fridge, however, avoiding the deep freezer section of the fridge. Locally, farmers can keep the inoculant in a cool place for a short period of two to three weeks.
2.6.2 Planting
Planting soybean should be done on ridges or on flat land seed beds. Ridge planting should be done at 20-30 cm apart. Place one seed per planting station 5 cm apart to a depth of 2.5 cm. Flat planting should be done on rows spaced at 45 cm apart and 5 cm between plant stations.
2.6.3 Seed Rate
The required seed rate is 80 kg/ha for large seeded soybean varieties and 60-65 kg/ha for small seeded soybean varieties such as Tikolore.
2.6.4 Fertilizer Use
Most soils in Malawi are highly weathered and thus there is a very high variability of soil fertility and types among different sites. This means that not all soils in Malawi can sustain soybean growth and development and depending on their history, these soils have different rhizobial populations in them. As such, a good fertilizer recommendation for soybean production depends on a good soil test. Under normal conditions, soybean as a legume should provide itself with nitrogen through biological nitrogen fixation. Until nodulation occurs, the soybean plant depends on soil nitrogen for growth. Phosphorus is often the most deficient nutrient; therefore, apply optimum phosphorous fertilizer for good yield. Apply phosphorus using 2×50 kg bags for hectare of 23:21:0 +4S compound fertilizer available in Malawi. At planting or one week after planting, incorporate 18g fertilizer per meter length of the ridge/row into the made groove in the middle or between the two soybean rows in the ridge. If fertilizer application is delayed, it makes the crop grow vegetatively without making pods.
2.6.5 Plant Configurations in Intercropping
Soybean grows best when planted as a monocrop. However, when intercropped, plant component crops should be planted on alternate 4-5 rows. Farmers can also plant soybean in between maize planting stations, if the maize planting stations are spaced at 90 cm apart not at the current planting pattern of 25 cm in between planting stations of maize crop because soybean is sensitive to shading.
Intercropping two legumes that have different growth habits is a relatively new practice. It is an approach that takes advantage of beneficial interactions between the 2 legume crops. Successful doubled-up legume intercropping systems mostly involve pigeon pea. It has been established that pigeon pea grows very slowly for the first 2 months after planting. It follows that pigeonpea can be intercropped with either groundnuts or soybeans, without too much competition for water, nutrients and sunlight. Pigeonpea only starts rapid growth when either soybean or groundnuts are approaching maturity. When the groundnut or soybean matures in about 4 months and harvested earlier, pigeon pea continues to grow on its own in the field, forms pods, and will be harvested later. This way we ‘double’ crops and ‘double’ soil fertility benefits as both legume crops add soil fertility to the soil through biological nitrogen fixation and crop residues.
Establishment of Soybean-Pigeonpea (Doubled-Up) Cropping
Doubled-up legumes technology involves intercropping of herbaceous legumes such as groundnuts followed subsequently by a cereal crop such as maize in the second year. The following are details of the cropping pattern involved with the technology in year 1 and 2 (successively) in cases where legumes are grown in rotation with cereals, mostly maize in Malawi:
Year 1: Intercropping of one legume crop with a different legume crop
Year 2: Growing maize
All recommended practices in maize production should be followed to make sure farmer attain bumper yields. It is estimated that you can plant 1 kg of pigeonpea seed on 30 x 40 field.
