All flood irrigation systems require intensive and accurate preparation of the land prior to planting. Accurate levelling of the fields is essential.
On larger basin and flood irrigation systems, this can only be achieved using a laser-controlled levelling apparatus. This type of land treatment is expensive and generally not available to remotely situated small-scale farmers.
The levelling of flood basins and short furrows can be achieved by the farmer with normal farming implements. Training and education are, however, important. An efficient flood irrigation scheme can provide water more efficiently than alternative systems, such as a sprinkler system. A poorly managed flood irrigation scheme wastes considerable quantities of water. If irrigation application is inefficient, reduced yields can be expected.
For short furrow irrigation, the level furrows can easily be set out using simple equipment such as a hose and water to align the furrows.
The furrow bed can also be levelled by filling it with water and removing humps and bumps by hand as the water slowly seeps into the soil. More extensive land levelling is needed for other types of flood irrigation.
For short furrow and similar systems, it is significantly easier to manage irrigation by using fixed applications. (The same depth of irrigation water is applied with each application.) Scheduling is simplified and one of the following models should be used to control irrigation:
Both the time lapse between irrigations at a point, and the application depth are fixed. The system relies on using some groundwater, and rainfall, to keep supplying the plants with water. Irrigation applications provide slightly less than the peak water demand of the plant.
Each time that a certain quantity of water has been used and the soil has dried out to a certain measurable extent, water is applied to bring the soil water back to the field capacity.
On smaller systems, furrows and border irrigation can be set out using profile boards to establish levels. On larger commercial farming systems, expensive laser levelling in conjunction with large machinery will be more common.
Next month we shall look at sprinkler irrigation. This series is published with acknowledgement to the ARC Agricultural Engineering for the use of their manuals. Visit www.arc.agric.za for more information.