Malawi has abundant water resources and potential irrigable land, and among the irrigable places available are the Lower Shire, places that lie on the lake shores (Karonga, Nkhata Bay, Salima, and Nkhotakota), and Lake Chirwa Plain. Irrigation in Malawi is very important as it helps to address the challenges of food insecurity and poverty. These challenges are caused by erratic rainfall distribution, resulting in prolonged dry spells, droughts, and floods, whose occurrence has increased over time due to climate change. This has negatively affected rain-fed agriculture. In addition to that, food demand in Malawi has been increasing progressively due to the absolute increase in population, which is estimated at an annual growth rate of 2.8%.

The potential area available for irrigation amounts to 407,000 hectares, by estimate. Currently, the area irrigated is estimated at about 104,600 hectares, of which 54,284 hectares are irrigated by smallholder farmers. This demonstrates how much we can extend beyond the limits and the prospective that is in irrigation. The overall objective is to enhance economic growth and development through irrigated agriculture production and productivity.

Site selection for irrigation development

There are factors to consider when selecting a site where you want to develop your irrigation system. These are physical, economic, and social factors.

Physical factors are, in other words, the factors in the abiotic environment that influence the growth and development of organisms in biological communities. An expert site selection team will be able to review many of the key factors that can positively or negatively impact your development site choice.

These factors are: reliability and closeness to the water supply; land slope and soil characteristics; risk of flooding; protection of the crop and equipment from theft and damage by livestock.

Economic factors: these affect the allocation, distribution, and utilization of the resources used, along with the commodities produced by farming. Economic factors are internal and external factors in the market that affect the economy.

These factors include ease of vehicle access if surveying and engineering work are required, and ease of access to markets for the supply of inputs and the sale of products.

Social factors can be defined as a generative approach that, through networking, food production, and the practice of local welfare, generates bonds and restores lifeblood to urban and rural communities.

These factors include farmer organization, land tenure issues, and water rights issues.

Irrigation methods

The following are common methods of irrigating crops:.

1-Watering can/bucket irrigation

Watering cans or bucket irrigation is extensively used by smallholder farmers. This method works best on small farms that are close to a water supply, particularly where there is limited availability of water or where the well re-fills gradually. Water should not be applied directly from the bucket, for this can lead to injury to plants, specifically young plants.

2-Basin irrigation

A basin is a level area of land bordered by earth embankments that is fully flooded during irrigation. Basins can be flat, either sunken or raised, or ridged. This method of irrigation, in all cases, requires well-leveled ground. Basin irrigation is appropriate for a wide range of crops.

Some of advantages of basin irrigation

a) Achieves a precise quantity of water with a minutest labour input if the beds are well levelled.

b) ensures water conservation through nominal runoff.

c) Basins last for a lengthy time once they are established. Extended ponding and crop damage can occur in poorly managed flat beds.

There is a risk of soil erosion due to the application of water at high speed.

3-Furrow irrigation

Furrows are generally used in farms that have a large uniform field where long-term furrow establishment is possible. They are not applicable in plots that are of irregular shapes. As the water flows in the furrow, it is gradually absorbed into the bottom and sides of the furrow, soaking up the soil. The length of the furrow depends on the type of soil and the slope of the land, but in most cases, the length is not less than 50m. It is imperative to use the appropriate shape of furrow, furrow spacing, and length.

The following are some of the advantages:

a) Moderate to high irrigation efficiency.

b) There is less danger of leaching nutrients from the soil than with basin methods.

c) Crop stems are not wetted

d) Even soils that form a surface crust when flooded can be irrigated as water moves laterally from the furrow into the ridge below the level of plant growth.

The disadvantages of furrow irrigation are:

a) Erosion can occur if the slope is too steep.

b) Labor requirements may be high as the streams must be carefully regulated to achieve uniform water distribution.

c) Salts from the soil or water supply may concentrate on top of the ridge and eventually cause damage to young crops.

d) The lateral spread of water in coarse-textured soils may not be enough to wet the soil between the furrows.

Cautious land levelling is essential for uniform furrow slope and shape.

4-Sprinkler irrigation

Sprinkler irrigation is a method that resembles rainfall as water is applied to the soil. This method can be used for various crops, soil types, and geographic locations. The system can work on a land slope of up to 12%. The system can be used where the water flow rate is limited.

The advantages of a sprinkler irrigation system include:

a) Can be used on steep slopes and uneven ground.

b) can be used on a wide variety of crops.

c) The labour requirement is low.

d) Ensures high efficiency as the water is applied evenly over the irrigation area, if managed appropriately.

The disadvantages of a sprinkler irrigation system are:

a) The high capital cost of the equipment.

b) High operational and maintenance costs for the pump and field equipment.

c) Irrigation is affected by high winds.

d) Evaporation losses can be high.

e) Sprinkler nozzles are easily blocked if sediment-laden water is used.

5-Micro (drip) irrigation

Microirrigation involves various technologies that ensure water is applied to a specific area of the field. It uses less water and ensures a good crop yield. It can also be used for fertigation, a process where fertilizers are applied through irrigation water. This system achieves even distribution of nutrients, and actual crop nutrient requirements can be met since an incremental supply of nutrients is possible. In drip irrigation systems, irrigation frequency is much higher than in any other system, which ensures a high moisture level in the soil. However, maintenance and purchasing costs for equipment are very high.

5-Sub-surface irrigation

In this method, the water supplied to the plant comes from the underground by controlling the level of water that occurs naturally in shallow grounds. Water flows through the action of capillaries to the shallow. Consistent drawing down of water is important to escape water logging of the plots and crop damage.

Guidelines for selecting an appropriate irrigation method

The following are factors to consider when selecting an irrigation method:

a) Natural conditions: soil type, slope, climate, and water supply.

b) Types of crops to be grown.

c) Type of technology; this will directly affect the labour required and skills needed to maintain the system.

d) Previous experience with irrigation and levels of training.

e) Costs and benefits: some methods require more resources to install, so they are used in crops that are highly economical.

The selection of an irrigation method must take into account all the above-mentioned factors. It must not be based only on physical or technical criteria.