1. BACKGROUND
Tomato scientific name Solanum lycorpersicum is a common vegetable of the Solanaceae family widely grown in Limpopo Province. Limpopo province with its warm climate is the major producer of tomatoes with an area of approximately 3 590 ha (DALLRD, 2020).
2. SOIL AND CLIMATIC CONDITIONS
Tomatoes prefer well aerated deep soils with high organic matter content; however, they are adaptable to a wide range of soils. Soil as a growth media should allow adequate root development to offer support to the plant, supply oxygen and mineral nutrients. The soil should be free of toxic elements. Compacted soils hamper root development. Root density is higher where there is high rate of diffusion. Optimal soil water and plant conditions increases root development of tomato plants. The tomato roots can develop as deep as 1.5m and as wide as the plant spacing allow.
Organic matter content is essential and serve as source of plant nutrition, and act as soil conditioner. It increases water and nutrients retention capacity and will also promote water infiltration, aeration, and root growth.
Tomatoes grow and produce best when average temperature ranges between 20 and 24 ◦C. Temperatures above 30 ◦C affect fruit set negatively. Night temperatures are critical for fruit set and should be between 15 and 20 ◦C. Average daily temperatures above 30 ◦C and the night temperatures is above 21 ◦C and result in poor fruit set which might affect tomato yield.
3. CULTURAL PRACTICES
Soil preparation
Profitability of tomato production is greatly influenced by soil preparation. The aim of soil preparation is to create conducive environment for tomato plants to develop optimal root system in a particular soil profile. The highest percentage of roots is found at the top 600mm although the root system of a tomato plant can penetrate up to 2m deep.
Soil preparation ensures that root development is not restricted and reduces the occurrence of soil compaction. If the soil is well prepared more oxygen will be available in the soil leading to better root development and higher yield. Tomatoes grown in a well-prepared field have more vegetative growth, reduced root disease prevalence and better water retention and an increased uptake of water and nutrients.
Plant requirements and soil type determine the choice of preparation system. No standard system can be recommended on all soil types, the clay content of the soil should be considered. When preparing sandy soil, the main focus will be to prevent erosion and compaction, whereas on heavier soils the focus will be on reduction of crust formation.
The soil preparation should be done to depths ranging from 200 to 400 mm. Ridging is an essential part of preparing soil for tomato production and should be done according to the land contours. Ridging a tomato plant keeps excess water away from the plant and improves the oxygenation of the root zone, increases soil depth and promote root development.
Planting
Planting of tomatoes commercially is done using seedling to avoid seed borne pathogens. Each cultivar has its own spacing requirement available from seed companies. Important factors to consider when deciding on plant population is the type of chemical spraying to be utilized or method to be used during crop growth.
Pest and disease control is a deciding factor. Lowest commercial planting is used in open land cultivation at between 12 to 18000 plant/ha and the highest is at 28-35 000 for open land production for processing market.
The population under protection is double that under open field production. Untrellised tomatoes in the open field is at 15 000 plant per ha. Recommended between row spacing is at 1,8m to 2,5 m. Tomatoes grown on the ground for informal and fresh markets should have enough inter row spacing of minimum 1,8 m to avoid damage during harvesting.
Fertilisation
Fertilisation program should be based on soil analysis. Ideal fertilisation levels required for tomato requires N (180-200 kg/ha), P (60-150kg/ha), K (300-400 kg/ha), Ca (250-300 kg/ha), Mg (50-60 kg/ha) and it is calculated using the 17–22-week application cycle. Nutrient withdrawal is determined by the phenological stage of the tomato crop. During vegetative growth from 0 to 5 weeks higher nitrogen is required by the tomato plant, and during the flowering stage (6-12 weeks) high calcium content is required and lastly during the fruit set and filling stage (12-20 weeks) high calcium and magnesium content are required.
Irrigation
The recommended irrigation method for tomatoes is drip or flood irrigation to manage the susceptibility of tomatoes to foliar diseases. The amount of water varies depending on climatic conditions. In cooler weather conditions tomatoes will require about 25mm of water per week and 50mm during very windy and dry weather. The root zone of the tomato plant spread into the soil at the similar rate to which aerial growth develops. The size of the root system needs to be taken into consideration when scheduling irrigation. Water usage is affected by phenological stage of the tomato plant. During fruit set water usage is at its highest and the lowest during ripening and harvesting.
Pests and Diseases
The common disease affecting tomatoes are early blight, late blight, powdery mildew, fusarium wilt, fusarium crown and root rot, Alternaria stem canker, pith necrosis, Gray leaf spot and bacterial spot.
Tomato is also affected by the notorious tuta absoluta which is highly resistant to most chemical pesticides and should be taken to manage resistance and ensures crop rotation and avoid growing Solanaceae crops in succession on same piece of land.
Tomatoes are very susceptible to root- knot nematode infections and may be attacked by Meloidogyne arenaria and Meloidogyne incognita.
4. Cultivar selection
Cultivar selection is dependent on market needs and the South African seed companies should cater for the following:
- Indeterminate fresh: long shelf life (large, medium, and small sizes)
- Indeterminate fresh: red cherries (round and oval shapes)
- Indeterminate fresh: yellow cherries (round and oval shapes)
- Indeterminate fresh: red cocktail (round and oval shapes)
- Indeterminate fresh: yellow cocktail (round and oval shapes)
- Indeterminate fresh: saladette (cylindrical and blocky shapes)
- Indeterminate fresh: truss tomatoes
- Determinate fresh: Long shelf life (large and medium sizes)
- Determinate fresh: Red cherries (Round and oval shapes)
- Determinate fresh: Saladette (Cylindrical and blocky shapes)
- Determinate: processors
- Determinate fresh tomatoes suitable for non-trellising
References
- Tomato production guideline sakata.co.za
- Vegetable production guide intelligro.co.za
- Hygrotech vegetable growth chart https://hygrotech.co.za
- A profile of the South African tomato market value chain (2020). dalrrd.gov.za
- Functioning pf the South African Tomato value chain: production, processing, challenges and opportunities. NAMC (2024).