Broccoli Farming In Kenya; Step By Step Guide
Broccoli is part of a large group of plants known as Cole Crops. The term “Cole” crops originated from the word caulis, meaning stem or stalk of a plant. Cole crops are biennials but are generally grown as annuals. In Kenya, Broccoli is growing in popularity especially amongst the middle class who are increasingly becoming health conscious. Large stocks can be seen stocked in major retailers.
Two crops per year are possible in most parts of the country, especially with continuous improvement in fast maturity and heat tolerance that extends the life of broccoli through all but the hottest parts of the season. It belongs to the crop family (Brassica oleracea), which includes cabbage, kale, cauliflower, kohlrabi and Brussels.
Climatic conditions for Broccoli Farming In Kenya
Broccoli requires moderate temperatures ranging between 0 oC and 29 oC. However, the optimum growing temperature range is between 15 and 22 oC. Optimum germination temperature is 29 oC. High temperatures (greater than 27 oC) delay maturity and increase vegetative growth. Cool temperatures (1.5-10 oC) hasten maturity and may induce “bolting”. Bolting is the term given when broccoli prematurely forms a flower stalk.
Soil requirements for broccoli farming in Kenya
Broccoli requires soils that can provide continuous water throughout the season. Well-drained, sandy loam soils are suited to early varieties. Loamy and clay loam soils are suited to late varieties because they are somewhat tolerant to poor drainage. Well-drained soils can be rotated frequently because club root is easier to control.
Planting broccoli in Kenya
Depending on the variety and region, broccoli can be grown throughout the year. On the Highveld the crop should not be sown between May and July because of the low temperature. Broccoli is generally transplanted as seedlings. Healthy one month old seedlings are recommended for transplanting purposes.
Broccoli seedlings management in Kenya
Seedlings should be grown in a well-aerated medium, which has good water holding capacity and at a pH of around 6.5. Generally, peat, bark and vermiculite mixes are used. Medium problems typically include excessive tannins and low air filled porosity, which results in poor drainage and the buildup of green mould. The medium should be pre-enriched and the seedlings should be fertilized. For optimum germination, the seedling trays should be placed in a germination chamber, at 20 °C with high relative humidity. The seedlings should be moved to the tunnel at the first sign of germination. The ideal temperature for seedling cultivation is 20 °C.
Seedling management is a critical factor in broccoli production, as the following factors related to
seedling production may result in physiological disorders:
- Incorrect sowing time.
- Cold temperatures, particularly below 7 °C.
- Cold grown seedlings.
- Over-fertilization of seedlings.
- Oversized seedlings at transplant.
- Temperature differences between the seedling nursery and the farm.
- A precision planter is recommended to place single seedlings at a uniform depth.
Broccoli plant population
A general spacing of between 20 000 and 40 000 plants per hectare is recommended.
The following points should be kept in mind when transplanting broccoli seedlings.
Firstly the seedlings must be transplanted and watered as soon as possible after they have been obtained from the nursery. Ideally seedling should be transplanted 5 weeks after sowing. Secondly the seedlings should be placed vertically into the ground and not sideways. This is to avoid a condition known as “J rooting”. This condition results in a J shaped root system that ultimately decreases yield and head size.
Thirdly the grower should ensure that seedlings are planted at the correct depth in a planting hole that has been formed into the ground prior to planting. If the seedlings are forced into the ground, without a hole being prepared for them to be inserted into, the root system may be damaged and the plant will experience stress resulting in poor yield. Once the seedling is placed in the hole the area should be firmed so that sufficient contact is made between the seedling and the soil.
When planting seedlings a choice can be made between the square method and the staggered method of planting. The staggered method is more advantageous as there is less competition between plants compared to the square method where plants are directly opposite each other, thus maximizing competition.
Broccoli Fertilizer Application
The soil is a resource that needs to be managed and monitored meticulously. It is essential that a grower have soil samples of the intended growing area analyzed by an accredited laboratory to determine the nutrient status of the soil. Based on soil analysis results a fertilization programme can then be developed. This programme is obviously specific for the type of soil that was sampled and subsequently analysed. This exercise should be done every season or every time a new crop is planted on the land.
In addition to having soil samples tested, the water quality should be analysed because water quality can have a direct effect on the growth of the plant. For example, irrigation water with high calcium levels can increase the soil pH.
The availability of water is critical for successful broccoli production. Irrigation may also be used to cool plants during periods of high temperature. Fertiliser could be applied through an irrigation system. Irrigation at the wrong time can cause problems such as head rot. Broccoli crops require a regular water supply of about 25 mm every 5 to 7 days during the growing season. Shortage of water is detrimental for head development.
There are many benefits to crop rotation including the suppression of diseases, insects and weeds. In addition, crop rotation improves soil fertility by allowing the soil to replenish its nutrients naturally, and soil structure improves because of the alternation between deep-rooted and fibrous-rooted crops. Crops within a family tend to be susceptible to the same pests, therefore, rotation of non-susceptible crops (or groups) for several years will allow all plant material to decompose and break pest cycles.
Without the presence of susceptible plant material, the number of disease and insect organisms will begin to diminish.
Crop rotation aids in weed control because the growth habit of each crop differs, which causes a decrease in the weeds’ ability to compete for space. Also, tillage practice and timing are different for dissimilar crops resulting in a decrease in the weeds’ ability to permanently establish. Another benefit of crop rotation for weed management purposes is with certain crops, there is a better chance at controlling different weeds. For example, in a broad leaf crop, grass control will be easier because of the use of grass killing herbicides and vice versa.
To create a crop rotation schedule, there are several things to be considered including types of vegetables grown, size of root system, size of planting rows, amount of fertility required for the crop and how much organic matter is left in the soil by the crop. Start designing the crop rotation by making a list of all vegetables to be grown and group them together by botanic relationship (e.g brassicacea, solanaceae).
Each year, change the location of the entire group within the field. This way, the same crop group will not be planted on the same piece of land two years in a row. Secondly, consider the size of the root system of the crop to be grown. Deep rooted plants will help to break up the soil, while shallow roots will not.
Thirdly, consider the size of the plant rows. The fourth consideration should be given to whether or not the crop to be planted is a heavy feeder. A heavy feeder will deplete the soils of nutrients quicker than a non-heavy feeder. The final consideration for a crop rotation is whether or not the crop will leave a lot of organic matter in the soil. Leaving organic matter behind is beneficial for replenishing the soil of nutrients lost to the crop while it was growing.
A long rotation of more than five years is better than a rotation of two years. Also, ask yourself the following questions when putting together a rotation: Is the rotation profitable? Are the yields sustainable? Does it make use of nitrogen produced by an earlier crop? Are herbicides residues left? Vegetable crops use a lot on nitrogen so it may be beneficial to plant a legume crop before broccoli.
Broccoli has an intermediate root depth that will aid in improving soil structure and aeration. This crop has small seeds which will require a fine seedbed. Therefore, previous crop residues will not be tolerated. If transplants are used, the roots can tolerate some plant residue, but too much residue will negatively affect root growth.
Perennial weeds should be controlled prior to planting. Herbicides recommended for use on Cole crops will not provide complete control of weeds. Therefore, it is important to grow Cole crops on soil where the weed seed population is low. The weed seed bank in the soil can be reduced by crop rotation, summer fallow, and the stale-seedbed technique. Care must be taken to avoid fields where residual herbicides from previous years persist in the soil as crop injury may occur.
Harvesting and handling
Harvest broccoli heads when bud clusters are tightly closed and the entire head is tight and firm. Heads that are loose or have individual flower clusters with yellow petals should not be picked. The terminall heads mature first. By removing the main terminal head, growth of the lateral heads (auxiliary buds) lower on the main stem will be promoted and production of smaller heads that can be harvested will commence. Since lateral heads develop unevenly, they cannot all be harvested at one time. Lateral heads must be harvested twice a week.
Broccoli heads are usually harvested with about 15 cm of the stem attached. After they have been cut off, part of the foliage is removed from the harvested shoots. The heads are from 5 to 25 cm in diameter and weigh from 100 to 800 g each. Side shoots from 5 to 10 cm in diameter and weigh from 100 to 500 g each. Broccoli intended for fresh consumption is often sold in bunches weighing about 450 to 600 g.
Broccoli heads mature at different times, resulting in two or three cuts needed to harvest a field.
Broccoli is harvested by hand and is often cut and packed into wax covered boxes in the field.
Broccoli heads are highly perishable and should be cooled immediately following harvest. In addition to icing, hydro cooling and forced air cooling can be used, but good temperature management must be maintained following cooling.
If held at 0 oC and near 100% relative humidity, broccoli can be stored for up to three to four weeks. Exposure to ethylene (from apples, other ethylene producing fruit or engine exhaust) will accelerate the yellowing of flower buds and reduce storage life and should be avoided.
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