Narrate the agronomic practices of bean cultivation

1.Cropping system
-First step is to get the right variety for the region.
-Some varieties are pure lines e.g Canadian wonder.
-Land races which has genetic mixtures are found in farmers’ fields eg Rosecocco.
-Other varieties are bred at research stations e.g mwezimoja bred for dry areas, Mexican 142 for export market, red caricot. Etc. All the above varieties are determinate varieties and are mostly grown in pure stand rotated with other crops.
In areas of high rainfall indeterminate varieties which can be intercropped with maize, sorghum etc to support them are grown (Climb on).

2. Seed bed preparation
-Bean seeds are relatively large and therefore do not need a fine seedbed. Thus seedbed prepared for maize (medium tilth) is suitable for beans also.
-This allows seeds to be in good contact with soil to allow effective germination and emergence.

3.Time of Sowing
-Recommended to be sown early in the rains.
When intercropped, the crops should be sown on the same day.
-In low rainfall areas the combination of late sowing and use of late maturing varieties often leads to low yields primarily because of moisture stress during reproductive phase.
-In very dry areas late sowing may be of advantage because it gives soil sufficient time to accumulate soil moisture but use of early maturing variety is recommended.

Methods of Sowing
i. Commonly practiced method is dibbling. Holes are made randomly and about 2-3 seeds placed and covered with light soil.
ii. Oxen plough can be used to make planting furrows and seeds sown within the furrow at a given spacing
iii. For commercial farming planters are used with a modified plate to deliver the recommended seed rate. Work better when seeds are uniform in size.

4.Spacing and plant population
-If grown as pure stand, the recommended spacing is 45 -60cm x 10-15cm giving roughly 178000-200000 plants /ha with two seeds /hill or hole.
-In reality in the field farmers grow beans intercropped and spacing varies
Maize and beans in the same row and same hole taking the spacing of maize. The practice is not recommended.
-Maize and bean on the same row but different holes. Also maintains the maize spacing and results in lower bean population.
1: 1 ratio of beans and maize: One row of beans alternating with a row of maize
2: 1ratio of beans to maize. Two rows of beans alternating with one row of maize
2:2 ratio of beans to maize: Two rows of beans alternating with two rows of maize

Factors determining spacing in different areas
i. Amount of rainfall
ii. Weed control
iii. Labour availability and cost
Research indicate that there is low bean populations in farmers’ fields.

Reasons for low bean populations in fields
i. Use of seeds with low germination percentage
ii. Seeds which are disease
iii. Use of low seed rate or planting below the recommended rates
iv. Bean fly attack
v. Poor seed bed preparation and thus poor germination and emergence
vi. Water stress at germination. There can either be too much water (logging) or too little either of which can interfere with germination and emergence.

5. Fertilizer application
-Bean plants respond well to applied phosphates and depend on the history of the field.
-It also responds to applied nitrogen.
-Recommendation is to apply 100kg DAP as a starter fertilizer.
-It is recommended to inoculate the seeds with right strain of rhizobium to facilitate faster root nodulation. This is important in fields where beans are being grown for the first time, soil with low pH with limited native soil rhizobium. In inoculation bean seeds are wetted with culture material containing rhizobium, lime or lime+ phosphate or cellulose to correct soil pH.

6.Weed control
-Should be done in the first 4 -6 weeks after sowing as all weeding should be done in the vegetative phase.
-Clean seed bed preparation is needed.
-Weeding starts 1-2 weeks after seeding emergence and depending on the condition of the seed bed, amount of rainfall, one can do 2 -3 weedings before the plants start flowering.
-In the reproductive phase after flowering weeding may cause flower and pod dropping lowering the yield.
-Late weeding may also result in spread of diseases.
-Alternatively selective herbicides can be used but is not the best method as beans are often intercropped with narrow leaved plants such as maize and can be injured by herbicides that selects for narrow leaved plants.

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Titany answered the question on August 16, 2021 at 11:11