Grain Guide 2018

General irrigation tips Successful, sustainable crop irrigation goes hand in hand with a holistic approach to the whole farm. In this holistic approach, soil physics and chemistry, water retention capacity of soil, type of crop, cultivars, physiological stage of the plant, plant health and root systems, among other things, are taken into account. Knowledge of the resources and how they react, as well as the crop requirements, are critical to consider while planning which crops to cultivate. Adapt scheduling and administration to line up with these resour­ ces and crop requirements. Check the delivery of the irrigation pivot and take the trouble to regularly maintain the pivot, pumps and other irrigation equipment. Soil properties will determine how much water should be administered. Use good remote sensing to ensure that water distri­ bution, infiltration and run off are managed effectively. Prevent run off at all times by improving water infiltration and scheduling. By cover­ ing the soil with crop residue, the infiltra­ tion is increased and run off is decreased. Sometimes adding gypsum can also con­ tribute to increasing the infiltration rate. For effective irrigation scheduling, it is essential that there be no compacted lay­ ers in the soil profile and that the season is started with a full profile. Starting with a full soil profile limits seedling damage when the profile has to be brought up to drained upper limit (DUL) within a season. This limits waterlogging of small and young plants and poor nutrient absorption under anaerobic conditions. Barrier layers in soil cause anaerobic conditions, which trigger nematode and nutrient issues. Sometimes it might be necessary to carry out wet rip actions to ensure that the soil is draining and to prevent the issues mentioned above. Effective irrigation scheduling is very important throughout the season. Try to administer larger quantities of water at a time, with longer periods in between so that the soil has time to dry somewhat and oxygen can enter the soil. The root zone in the soil and the depth of the roots should support you in your deci­ sion on how much water to administer at a time. It is also important to know when (physi­ ologically) the plant reaches its water requirement peak. Some crops, for instance maize, have three periods that are sensitive to stress conditions due to water shortages. Plant health should also be monitored continuously, because sick plants use less water. If sick plants receive too much water, the situation will worsen substantially and total crop yields will decrease. Monitoring of soil with respect to salts becomes critical in an attempt to farm sustainably. Remote sensing as well as soil sampling can be done at GPS points. Make sure that there is enough water available to meet the top crop requirement. Water should not be taken away too soon at the end of the cash crop season. If water is taken away too soon, grain may ripen too soon and kernel weight could be compromised. Therefore, optimal irrigation scheduling should be done throughout the season, otherwise damage might occur. Calibrate the irrigation pivot at least once a year to ensure that the dosages on the ground are even and so that you know how much water is administered per hectare. Pietman Botha, agricultural consultant Also read the article about practical tips for your centre pivot, written by S Koster and P Botha, in the SA Graan/Grain of October 2017. Scan this QR code to see. 110 GRAIN GUIDE 2018 Irrigation