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Nutrient management in tomatoes
Well-nourished tomatoes give farmers a good yield. A farmer should satisfy the crop’s needs by supplying enough nitrogen, phosphorus and potassium. Photos | George Katongole
What you need to know:
- Tomatoes are one of the most popular crops grown all over the world. They can be planted anywhere -- in yards or gardens. Tomatoes like to get off a good start with a really good nitrogen fertiliser which is a good boost for green growth.
Plants are most hungry for three nutrients — nitrogen, phosphorus and potassium.
Tomato is a heavy feeder of plant nutrients including nitrogen, phosphorous and potassium and it responds well to organic fertilisers. The amount of fertiliser applied is influenced by the fertility status of the soil, season and the cultivar.
Experts explain that tomato plants should be fertilised with organic (animal manure) and chemical fertilisers to be able to produce high yields consistently. In Uganda, the general recommendation is applying 60-120kg of nitrogen per hectare, 60-140kg of potassium and 60-120kg of phosphorous per hectare.
It is recommended that half of the fertiliser be applied as a basal dose and the remaining fertiliser can be added at first fruit set.
Nitrogen
The plants have a moderately high requirement of nitrogen. Nitrogen promotes better growth, a better flower and fruit set.
A minimum of 250kg per hectare of nitrogen (urea and Calcium Ammonium Nitrate – CAN) is recommended in high rainfall areas for high production.
Approximately a quarter of nitrogen is applied at planting while the remainder is applied in the first six to eight weeks of growth at two to three-week intervals. Further light dressings are applied over the next six or more weeks.
With emphasis on organic products, Doreen Nampamya, a research associate with Korea Program on International Agriculture (Kopia), who partners with National Agricultural Research Laboratories (NARL-Kawanda), where Kopia supports the growing of tomatoes, Chinese cabbage (pak choi), eggplant, cucumber and cabbage, among others, says there are alternative sources.
The cost of Urea is Shs120,000 per 50kg bag.
The richest organic sources of nitrogen are manures, ground-up animal parts (blood meal, feather dust, leather dust) and seed meals (soybean meal, cottonseed meal).
“Nitrogen is needed in greatest amounts because it is normally the most readily lost nutrient in the soil,” Nampamya says.
She explains that nitrogen concentration in any manure varies not only with the kind of animal, but also with the kind of bedding used, the age of the manure and how it was stored.
Ground-up animal parts and seed meals generally have the highest concentrations of nitrogen and are more consistent in their nitrogen concentration.
Potassium
Tomato also requires high levels of potassium. Adequate levels of potassium (Muriate of potash – MOP) result in improved colour, taste, firmness, sugars, acids and solids of the fruit. Plant cells are also strengthened.
Nampamya notes that a minimum of 60kg of potassium should be applied per hectare.
A 50kg bag of potassium-based fertiliser is sold at Shs180,000 in most agri-shops.
In the world of organics, phosphorous sources include certain manures, as well as bone meal and pulverised rock phosphate.
Other richer sources are; seaweed, wood ashes, and the minerals greensand and granite.
Phosphorous
Phosphorous promotes root development, early flowering and fruit set while ensuring more vigorous growth. Nampamya says that a total of 40-60kg of phosphorous is recommended per hectare.
She explains that some commercially available organic fertilisers are blends of one or more individual organic fertilisers, which can offer a balance of all three major nutrients.
“But farmers should read the labels carefully to understand nutrient concentrations in the particular blends,” she says.
Micronutrients
Nampamya explains that tomatoes also require micronutrients for growth and development. Deficiencies of magnesium, calcium and molybdenum are common in acidic soils while boron and copper deficiencies are not often found in tomatoes.
However, if boron deficiency occurs, it results in fruit cracking, pitted and corky areas, deformed shape, malformation and uneven ripening. Iron has been found to be deficient on calcareous, alkaline soils or after heavy application of lime. Manganese deficiencies are mainly found in calcareous soils.
She advises farmers to apply, GrowCal, a micronutrient source that is sprayed on the plants. It is applied at a ratio of 60mls in 20 litres of water.
