— 26 IREC Farmers' Newsletter No. 200 — Spring 2018 0 10 20 30 40 50 60 70 80 90 100 Irrig. 1 Irrig. 2 Irrig. 1 Irrig. 2 Irrig. 1 Irrig. 2 Irrig. 1 Irrig. 2 Irrig. 1 Irrig. 2 Border Rivers Border Rivers Gwydir (Weemelah) Gwydir (Weemelah) Gwydir (Moree) Gwydir (Moree) Namoi Namoi Sth NSW Sth NSW Requirement Efficiency (%) Requirement Efficiency Single siphon Double siphon Optimising irrigation performance of the irrigation events improved application efficiency, as shown in Figure 4. Requirement efficiency Requirement efficiency shows how well the soil deficit has been met, i.e. how well the soil profile has been filled. This measure does not have to be 100% but if it is not, deficit irrigation is occurring, i.e. we are not filling the profile completely along the length of the field. Across the trials, 60% of the irrigation events had a requirement efficiency of 100% (Figure 5). This was due to the irrigation time being too long, causing siphons to continue to run once water reached the tail drain and the profile to keep filling. It is important to consider application efficiency and requirement efficiency together. For the irrigation events measured in the trials, a high requirement efficiency often resulted in lower application efficiency. Information collected by a Norwood irrigation advance meter, together with other irrigation data and soil nitrogen tests after two irrigations, enabled nitrogen loss in tailwater to be determined. Figure 4. Application efficiency of measured and optimised irrigation events Figure 5. Requirement efficiency of individual irrigation events for single and double siphon treatments — 26 IREC Farmers' Newsletter No. 200 — Spring 2018 Save water and nitrogen on cotton