Agronomic Practices of Irrigated Crops and Problems Associated With Irrigation

Crops, whether rain-fed or irrigated, are usually planted on the field and taken care of from establishment to harvesting and processing before they are finally consumed by the consumer.

Regardless of the time of planting, the care of crops remains similar, except for some crops that may require special practices during their growth stages. The agronomic practices of irrigated crops are the main focus of this article.

Read Also: Major Genetic Differences between Tropical and Temperate Livestock Breeds

Agronomic Practices of Irrigated Crops

Agronomic practices refer to the care provided to planted crops before, during, and after the establishment of the farm. All crops require specific agronomic practices, and crops that can be irrigated are no exception. The agronomic practices for some irrigated crops are discussed below.

1. Cabbage (Brassica oleracea var. capitata)

i. Scientific name: Brassica oleracea var. capitata
ii. Family: Brassicaceae or Cruciferae
iii. Cultivars: Sugarloaf, Drumhead (flat), Cape Spitskool. Consult seed retailers for more options.

Cabbages grow well in most well-drained soils rich in organic matter, with an optimum pH range of 5.5-6.1. If the pH falls below 5.5, lime should be applied one month before planting.

Cabbage can be grown year-round, except in some areas. Cool, moist conditions are ideal. Mature plants tolerate temperatures as low as -3°C, though prolonged exposure to temperatures between -1°C and 4°C may induce bolting.

The optimum temperature for cabbage growth is 18°C, with a maximum of 24°C and an average minimum of 4.5°C. Excessive wet conditions followed by dry spells can cause head bursting, while warm summer conditions increase susceptibility to aphid infestations and cabbage diamondback moths.

i. Land Preparation

Land preparation includes clearing and tillage, which may be done manually (using a machete or hoe), mechanically (using bulldozers or stumpers), or chemically (using non-selective herbicides in no-tillage systems).

After clearing, tillage loosens the soil, mixes in fertilizer, and prepares a favorable environment for crop establishment. Primary tillage involves loosening the soil and incorporating organic material or fertilizer. Secondary tillage creates finer soil and shapes the rows.

ii. Seed Amount

Approximately 450 g/ha is required for planting.

Five seedbeds of 10 m x 1 m each can accommodate 1 hectare. Mix 60 grams of compound fertilizer (N:P:K) per m² into the seedbed soil.

iii. Transplanting

Transplant after 4-6 weeks during the cooler part of the day.

iv. Spacing

Space plants 45-60 cm between rows and 30-45 cm within rows, resulting in a plant population of 49,300-74,000 plants/ha.

v. Planting Time

Cabbage can be planted throughout the year.

vi. Growth Period

1. Seedbed: 4-6 weeks
2. Field: 4-5 months, depending on the variety.

vii. Fertilizers

Organic fertilizers are ideal, but N:P:K 15:15:15 at 50 kg/ha can be applied to enhance vegetative growth.

viii. Harvesting

Harvest when heads are firm. Hybrid cultivars typically mature almost simultaneously.

ix. Expected Yield

Yields of greater than 25 tons/ha are possible, depending on the cultivar and management.

x. Pests

1. Aphids: Control with Dimethoate 40 EC (10 ml/10 liters of water) when observed on a few plants.
2. Spider Mite: Control with Nuvacron 40 (50 ml/10 liters of water) when first signs appear.
3. Diamondback Moth: Control with Carbaryl 85% WP (20 g/10 liters of water).

xi. Diseases

1. Damping Off: Caused by Rhizoctonia, Pythium, Phytophthora, and Fusarium. Control by pre-dusting seeds with Thiram.
2. Downy Mildew: Control with Ridomil MZ 72 (25 g/10 liters of water) during routine spraying, especially in February to April.
3. Black Rot: Caused by Xanthomonas campestris. Control with Copper Oxychloride 85% (40 g/10 liters of water).
4. Soft Rot: No control possible.

2. Tomato (Lycopersicon esculentum)

i. Scientific name: Lycopersicon esculentum (L.)

ii. Family: Solanaceae

iii. Varieties: Roma, Rossol, Floridade, Rodade, Money Maker, Red Khaki, Heinz, Ife Plum, Ronita, Marglobe, Valiant, Ibadan Local, etc.

Tomatoes grow well in a range of soils, from sandy loams to clays, with a soil depth of at least 60 cm. The soil should be well-drained, with an optimum pH of 5-6.5. Lime should be applied when the pH falls below 5.

Tomatoes are very frost-sensitive and require warm weather for 4.5 months. Seed germinates best at temperatures between 15-25°C. Maximum growth occurs when day temperatures do not fall below 21°C and night temperatures stay above 15°C.

High day temperatures can cause blotchy ripening and soft fruit, while low temperatures can result in poorly shaped and poor-quality fruit.

i. Land Preparation

Land preparation involves clearing and tillage, as described for cabbage, using the appropriate tools and methods based on the farm’s requirements.

ii. Humidity

Hot, dry spells followed by heavy rain can cause fruit cracking, while moist, overcast weather may result in fruit splitting and disease.

iii. Seed Amount

About 160 g of seed/ha is required.

iv. Spacing

1. Determinate varieties: 1 m between rows and 30 cm within the row.
2. Indeterminate varieties: 1-1.2 m between rows and 30-45 cm within the row.

v. Planting Time

The best planting time is from March to November. Transplant tomatoes after 6-8 weeks in the nursery. Seedling trays are recommended to reduce transplant shock.

vi. Cultural Practices

Indeterminate varieties should be staked or trellised to improve quality and yield. Side branches should be removed, leaving one or two main stems. This improves fruit size, quality, and facilitates spraying and harvesting.

vii. Trellising/Staking Methods

1. Poles: Strong poles and 2 or 3 horizontal wires.
2. Poles with strings: Strong poles with a top horizontal wire and strings to suspend plants. Poles should be 1.5 m in length, with 0.30 m buried.

viii. Growth Period

Tomatoes can take up to 6 months from sowing to harvesting, depending on cultivar, management, and growing conditions.

ix. Fertilizers

Apply N:P:K 15:15:15 at the rate of 50 kg/ha.

x. Harvesting

Harvest begins 4 months after transplanting, usually by hand-picking ripe fruits.

xi.Expected Yield

Tomatoes can yield 30 tons/ha or more, depending on the cultivar and management.

xii. Pests

1. Red Spider Mite: Control with Metasystox 25 EC (10 ml/10 liters of water) when first observed.
2. Thrips: Control with Malathion 50 WP (10 g/10 liters of water).
3. Nematodes: A 4-year rotation with non-sensitive crops is recommended.

xiii. Diseases

1. Leaf Blight: Caused by Phytophthora sp.. Control with Bravo 500 or Milraz 76 WP and Dithane M45.
2. Early Blight: Caused by Alternaria solani. Control as for Late Blight.
3. Wilts: Caused by Fusarium oxysporum, Rhizoctonia solani, and Verticillium dahlia. Heat treatment and Thiram dips can control.
4. Bacterial Canker: Caused by Corynebacterium sp.. No control, except for hygiene and heat treatment.
5. Leaf Spot: Control with Dithane M45 or Copper Oxychloride 80%.
6. Mosaic Virus: Control by spraying against vector insects such as whitefly using Cymbush 20 EC, Metasystox 25 EC, or Malathion.

Read Also: Crossbreeding as Tool for Tropical Livestock Improvement

Problems Associated with Irrigation

Irrigation offers several advantages for crop production, but it also presents various challenges, including:

1. Build-up of pests and diseases
2. Seasonality of water sources
3. High cost of equipment
4. High cost of system installation
5. Need for skilled personnel
6. Topography of the land

The success of crop production depends on the effective management of agronomic practices. Proper management leads to better yields, while poor management results in low productivity. Farmers should always adhere to best practices for improved crop success.

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