Maize Water Requirements and Irrigation Systems
How to design an irrigation schedule for maize, and what irrigation systems are available?
To avoid stressing the crop, farmers need to design an appropriate irrigation schedule that covers the water demand of maize in different developmental stages throughout the season. Continuous water stress will affect the crop’s growth, robustness, and resistance to other abiotic and biotic stresses and will finally reduce the crop yield.
An irrigated crop in the dry season will require between 5 and 7 tonnes of water per hectare, while for the whole growing season, the total amount fluctuates between 6 to 9 tonnes of water per hectare.
Irrigation scheduling for maize
The amount of water delivered to the plants through the irrigation system depends on the following:
- Soil type (soil water-holding capacity, soil moisture content)
The soil type should not be neglected when calculating the water amounts needed. For example, sandy soils may require up to 8 times more water than other soil types
- Environmental conditions and rainfalls (will affect the intensity of evaporation and will balance the input of water needed from irrigation)
- Variety and yield goals-expectation
- Planting date (earlier sown crops will need less water through irrigation)
- The efficiency of irrigation. Generally, it is better to use a medium to small amount of water per application, especially in lighter soils. More specifically, in the guidelines for maize farmers, the government of Australia points out that applications of 25mm were more effective than large irrigation sessions with more than 33 mm of water.
In months with high temperatures and less or no rainfalls, the water demands of well-grown maize plants can reach 60 mm per week (roughly 2-3 litres per day). The farmer can use the water balance approach to find the right amount of water that needs to be added with irrigation and form the most appropriate schedule per field
To reinforce and correct the calculation results obtained with the above-mentioned method, the farmer can use soil moisture sensors. The tensiometers are the cheapest but most trusted option (cost a few hundred dollars). Of course, we should keep in mind that the installation and maintenance of such sensors could cost up to 110 dollars per year
Growth stages and water requirements of maize
It is very important for the farmer to know how the crop’s water demand fluctuates during the growing season and which are the most crucial periods when water needs must be satisfied sufficiently. Depending on the availability of irrigation water, the farmer may apply from 3 to 9 (or to 11 for light soils) irrigation sessions during the maize growing season. The first irrigation needs to be applied before or right after sowing to improve the soil water content and help seeds germinate. In all cases, 1 to 3 more irrigation sessions should cover the plant’s needs at the end of the vegetative season and the flowering, keeping soil moisture up to 60%. Usually, the water supply stops after the flowering stage. It is crucial to keep in mind that any irrigation plan that does not entirely cover the crop’s needs during each growth stage will result in some yield loss
The water demand of the plants changes through the growing season. As the plants develop larger leaf surface, the demand for water rises as well, approaching maximum water use when the canopy has fully grown (40-60 days after planting). Maize reaches its peak water demand and is highly sensitive to water scarcity during the flowering stage and early grain fill (60-95 days after planting). This means that a severe water deficit at that stage will negatively affect the fertilization, grain number per cob, and as a result, the final yield of maize (4). More specifically, if the soil moisture during this period remains at the wilting point for 1-2 days or 6-8 days, the final yield may be reduced up to 20% and more than 50%, respectively. On the contrary, maize is more tolerant to water shortage during the early vegetative growth stages (until 40 days after planting) and the stages of late grain fill and ripening (after 110 days from planting).
Overwatering (waterlogging) can also cause significant problems and negatively affect the final maize yield. Especially during flowering, it can reduce a plant’s yield by over 50% (4).
Irrigation Methods used in maize
- Furrow and Basin irrigation
These two methods are applied in areas with ample water resources and restrictively only in fields with a slope lower than 0.5%. In case there is a great danger of soil degradation and erosion, both methods should be avoided. Much attention is needed in heavy soils with bad drainage and in fields with high salt content (maize is very sensitive). Finally, during the warmest months of the year, there is going to be high water loss due to evaporation.
- Irrigation with Sprinklers (rain spray-gun irrigation)
It is one of the most widely used irrigation methods in maize, especially in large fields. Such systems require pipes that can operate in quite high pressure (more than 8 bars). The sprinkles usually deliver water at a flow rate between 18 to 30 m3 per hour (30.000 litters per hour). The irrigation with sprinklers modifies the microclimatic conditions around the plant’s canopy and may decrease leaf transpiration and temperature (Cavero, 2016). Based on experimental results, the application of irrigation with sprinklers during the night may increase 10% the final yield of the plants (Cavero, 2018).
This technique has three main problems. Firstly, there is a lot of water loss due to wind drift and evaporation. Secondly, as the maize plant grows, it becomes harder for the equipment to move through the field without damaging the crop if the sprinklers are not installed on the field surface. At this point, we should mention that such permanent installation has a quite high cost, and the farmer should take that into consideration before deciding. Finally, this method increases the water and humidity in the canopy of maize plants, creating favorable conditions for fungal infections.
Additionally, irrigation with rain spray can create some problems in the pollination and fertilization of maize plants when the application takes place during the flowering period (the most crucial period with the highest water demands). To overcome some of these difficulties, farmers may choose to combine this method with basin irrigation. They use the sprinklers in the early stages when the plants are still short and change to basin irrigation in later stages.
More and more farmers choose to water their maize fields by using above-ground drip-irrigation thanks to the higher water saving (25-55%), the increase in water use efficiency of maize, and finally, the higher yields produced under this system (10-50% yield increase) (5, 2, Lamm & Trooien, 2003.). Compared to the sprinklers, drip irrigation has an extra advantage that it does not wet the leaves of the plants, thus reducing the risk of fungal diseases. The system has been successfully tested and used for over a decade in different climates (temperate and sub-humid zones).
Moreover, the use of drip irrigation offers the opportunity for the farmer to apply fertigation (application of fertilizers through the irrigation system). Usually, the drippers used have a flow rate of 1 liter per hour. The irrigation pipes are usually placed in every other row of maize plants, and the drippers are 1.4 -1.6 meters apart from each other. In some regions of Italy, farmers successfully use a version of the conventional drip-irrigation system called LPS (Low-Pressure System) that allows the irrigation of larger fields (30 hectares). The flow rate of the drippers in an LPS system is 0.6 liters per hour (6).
The farmer should take into account the efficiency, the sustainability but also the cost of each irrigation system in order to make the best decision. In all cases, it would be useful to consult your local licensed agronomist and keep a record of the efficiency of the irrigation plan that you apply each year. It is important to keep in mind that there is no golden rule or a fixed recipe of success that fits all fields, and the farmer may need to experiment in order to find what suits best for his/her field and crop.