Introduction
Groundnuts have over the past centuries been a celebrated favourite
legume in Zambia. Groundnuts generally can be grown in most soil types however
climatic conditions and soil nutrients have a huge bearing on the yield output.
Groundnuts in Zambia can be grown for both commercial purposes and domestic
purposes. The commercial production is further classified into two separate
markets which are the vegetable market and the food processing market. The
Peanut butter manufacturing industry is the most popular for the latter. This
guideline seeks to equip growers to be able to efficiently grow groundnuts.
Commodity competition is now based on cost more than ever hence the need for Zambian
growers to obtain a low production cost.
Climatic
requirements
Temperature
Groundnuts require a high temperature and a frost-free period of about
160 days. They will not reach optimum maturity for a marketable yield to
justify commercial production in areas with fewer heat units during the growing
season. They are very sensitive to low temperatures and seeds should only be
planted when the minimum temperature stabilises above 18°C. Germination is 95%
at soil temperatures ranging from 18°C to 30°C. The suitable vegetative growth
temperature ranges from 20°C to 35°C. However, at 33°C this declines to 84%. A
favourable temperature for flowering and pod formation is about 28°C. Higher
altitudes with cooler climates are not suitable for groundnut production. Avoid
planting in dry soil and irrigating during cold spells or planting in cold, wet
soil.
Rainfall and
moisture requirements
Moisture is another critical factor for successful groundnut
production. Planting must be done on moist warm soils to speed-up the
germination process. Research has shown poor germination in drier soils.
Available soil moisture content is also commensurate with row width. Wider rows
are advisable in low-rainfall areas while the opposite is true in
higher-rainfall areas. Rainfall in the region of 500 to 700mm per annum will be
satisfactory for good yields of groundnuts.
Soil
requirements
Groundnuts grow best in well-drained, red-coloured, yellow-red and
red, fertile, sandy to sandy loam soils with a pH range of 5.5 to 7.0. Saline
soils are not suitable because groundnuts have a very low salt tolerance. Soils
with more than 20% clay and stones will result in poor yield and make
harvesting difficult. Shallow and compacted soils are not preferred as the
taproot of groundnuts can penetrate to the soil to a depth of about 2m.
Soil
preparation
Seedbeds should be prepared either on flat or widely ridged fields.
Primary soil cultivation is necessary on virgin soils or any other soil type to
remove debris and break the plough layer. A uniform seedbed with sufficient
planting depth and spacing, good germination, weed control and sufficient
moisture retention is imperative for good yields. All plant residues should be
incorporated well into the soil. Producers often grow groundnuts in a minimum
till system. This cannot be recommended as the soil layer where the pods
develop should be devoid of plant residue. Where plant residue is present, pods
rot diseases increase, influencing yield and quality. For successful groundnut
production, deep ploughing should be implemented.
The slope should be favourable and the field should be
well-protected from soil erosion through the construction of contours and field
waterways. Avoid using fields with too much clay and fields that were planted
to groundnuts the previous year. The field should be protected from soil
erosion by means of contour ridges and waterway channels.
Planting
The planting date for groundnuts in Zambia should be as soon as
enough rain has fallen and minimum temperatures are met, usually from
mid-October to mid-November. Late planting (from December onwards) results in
lower yields. Planting should occur during favourable soil and weather conditions.
Planting depths of 5cm to 7.5cm are preferred for better germination when soil
temperature is 18°C or above. The correct planting depth of 5cm to 7.5cm
ensures that the plant develops and produces optimally. The preferred
population density is 150 000 plants per hectare under dry land and 300 000
plants per hectare under irrigation. The best spacing between rows under
rainfed conditions should be 90 cm with a spacing of 4cm to 7cm between the
plants; and 30cm to 35cm under irrigation. The ideal intra row spacing is
between 50 to 75mm for all available cultivars.
One may apply basal fertiliser of Compound C (5:15:12) at a rate of
250kg/ha or alternatively Compound L (4:17:11). If these two cannot be found,
one may then apply Compound D (7:14:7) as a basal fertiliser however this
should be done as a last resort. After 8 - 12 weeks after planting, it is
recommended that one applies Calcium Sulphate/ Gypsum at a rate of 560kg/ha.
Irrigation
Most of the cultivated groundnuts in Zambia are under dry land.
Irrigation can be done in areas with limited soil moisture/low rainfall areas
so that production and quality can be maximised. The irrigation method will
depend on the available water resources and the available irrigation equipment.
Avoid application of excess moisture by ensuring that scheduled irrigation is
practiced. A great deal of moisture is needed before flowering and during pod
filling (moderate during flowering and no application is required during
ripening).
Groundnut is susceptible to a wide range of weeds that are in severe
competition with it for available soil moisture, soil nutrients, light, space,
etc., and others which serve as hosts for diseases. Weeds can result in low
yield and poor quality of the groundnut seeds, as well as making harvesting
difficult. Therefore, an integrated system, ranging from the chemical and
mechanical to the biological, should be used in order to prevent weed suppression.
Effective weed control implies good control of weeds throughout the growing
season.
1. Mechanical: Three
mechanical weeding operations are important (assuming no herbicides are
applied). The first is done prior to emergence of seedlings, which is usually
about seven days after planting. The second one will be performed at 21 to 28
days after planting, while the last cultivation is dependent on weed growth,
but should not be delayed later than 60 days after planting.
2. Chemical: Chemical weed
control is also recommended on groundnuts. Several herbicides are registered
for utilisation; however, the choice of herbicide and the concentration applied
will largely depend on the species of weeds involved and the level of
infestation. Below is a table with recommended Herbicides:
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Disease and pest control
Diseases in groundnuts can be classified as leaf, stem and pod
diseases, and particular viral diseases are also encountered. The most
prevalent diseases remain early leaf spot and Sclerotium stem rot. These
diseases are both difficult to control. Early leaf spot is recognisable by the
brown spots on the leaves which are surrounded by a yellow halo. Stem rot may
be identified by the white mycelium (fungal growth) in the stems, pegs and
pods. Both diseases are particularly devastating when the weather is warm and
the soil is moist. Below are tables which show how best to chemically deal with
Insects and diseases.
|
Insect problem |
Remedy |
|
Cutworms |
Decis 3.5 EC |
|
Aphids |
Dimethoate 40 EC |
|
Disease |
Remedy |
|
Seed Borne
diseases and damping off |
Vitavax Plus and
Thiram 80 WP |
|
Cercospora and
Leaf spot |
Benomyl 50 WP/
Bavistin, Folicur |
|
Phoma Leaf rust |
Chlorothalonil
50 SC/ Bravo |
|
Stem rot |
Benomyl 50 WP |
|
Root Stimulant |
Kelpak |
Other cultivation
practices
Rotational benefits Groundnuts, like other annual legumes in a
rotation, offer several cropping advantages for the producer. Groundnut yields
often increase when the crop is planted after non-legumes because of the
following factors:
• Disease and insect cycles become disrupted.
• Alternative herbicides can be used to kill grassy weeds.
• Soil nutrients are used efficiently.
Inoculation
Groundnut is a leguminous crop, and it has the ability to fix 60% to
70% of its nitrogen requirement from the atmosphere under ideal conditions.
Groundnut has a very specific relationship with Rhizobium bacteria and it is
essential that an inoculant should be used. Under good growing conditions,
groundnut is considered a relatively good nitrogen fixer, provided that it is
inoculated with an appropriate strain of Rhizobium. Other practices include
intercropping, use of good cover crops to improve the soil, organic matter
management, construction of diversion ditches, tilling and planting along
contours, construction of terraces, conservation tillage and improving soil
drainage.
Harvesting
Harvest maturity In order to determine the best harvest date, a
farmer must scout his/her crops on a regular basis, as the groundnut plant
usually gives an indication of when to harvest. The number of days to maturity
varies with cultivars. There are some characteristics that require close
attention and observation to determine harvest maturity, namely:
• Pod colour—inner walls
display a dark-brown colour as a result of darkening of the inner tissue of the
hull. When 75% of the pods of the selected number of plants have reached
maturity by showing the dark discoloration, harvesting can start. The outer
wall of the pods should display various shades on the inner cell layer when scraped
with a knife. The colours are white on the immature and yellow pods, and
orange, light brown or black on mature pods. Harvesting can be done if 70% of
the pods show the other colours except white.
• Seed colour—the colour
of seeds in the pods can also be used as an indication. Young, immature seed is
usually white in colour and changes to pink and dull pink as the seed matures.
• Leaves—the leaves
develop a yellow colour and are dry at the tips.
• Prevailing weather
conditions—these can influence the determination of the harvest date
because they influence quality. Drought determines the harvest date when the
soil is desiccated to such an extent that the plant withers and the seeds in
the pods begin to shrivel and take on a ripe appearance.
Such groundnuts must be harvested immediately.
Harvesting
methods
The digger-shaker-windrower is used to lift groundnuts and detach
them from the soil. Dig deep enough to prevent cutting pegs. Windrow-inverting
attachments orient plants as they leave the shaker so pods are primarily on the
top of windrows to permit greater air circulation and exposure to sunlight for
a shorter drying time. Windrowed groundnuts could be combine-harvested wet (35%
to 50% moisture), semidry (18% to 25%), or dry (8% to 10%). These pods could
reach a semidry condition (seeds rattle in pods) one to three days after
digging. Drying in the windrow to a moisture level of 8% to 10% requires five
to ten days of good drying weather. However, groundnuts remaining in windrows
for several days are more susceptible to weather damage than those that are
freshly extracted. Combining wet (green) or preferably semidry groundnuts,
followed by artificial drying, could result in better-quality nuts. Adjust
combines regularly to give better picking action when vines are tough, and
reduce picking action when vines are dry, to obtain good picking efficiency and
minimise mechanical damage to the hulls.
2. Manual
This method involves very careful operations that, if improperly
done, could result in some groundnuts being lost in the soil.
• Lifting or loosening the
groundnuts: This involves severing of the taproot below the soil surface
with a “blade” implement normally at a depth of 10cm to 15cm.
• The stacking process:
After several hours, groundnuts can be packed into bundles and stacked. It is
important to shake off loose soil before stacking. The stacks are formed with a
core of 15 to 40 plants placed on their leaves with the pods facing upward. A properly
formed stack will not lodge or become damp when it rains. The stacks are then
left on the land for four to eight weeks for final ripening and moisture loss
before being picked. Picking and shelling: This should be done with the correct
picker. The method of picking involves removing the pods from the entire plant.
Plants are fed into the picker and the shells are separated from the plants.
Close monitoring of the process is necessary in order to detect any defaults
that could affect the quality of the kernels.
• Shelling: Hand-operated machines are available for shelling groundnuts pods. Pods should be cleaned before being fed into the sheller. Close monitoring to avoid quality loss is also important during shelling.
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