— 25 IREC Farmers' Newsletter No. 200 — Spring 2018 0 5 10 15 20 25 30 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 kg N/ha Single siphon Double siphon Opt. single Opt. double Nitrogen losses in tailwater Tailwater samples were taken from a single furrow in each treatment. They were analysed for total nitrogen and nitrogen concentration. In all cases except one site there was only a small amount of nitrogen in the tailwater for these events. There was up to 7 kg N/ha in the tailwater in the single siphon treatment compared with up to 13 kg N/ha in the double siphon treatment (Figure 2). This indicates that the placement of pre-plant nitrogen was well managed by the growers, being below furrow level in the bed or hill. Double siphons resulted in greater losses of nitrogen and this was related to the higher volumes of tailwater produced. Optimising the irrigation events reduced the amount of nitrogen lost in the tailwaters. The nitrogen in the tailwater can be lost to the atmosphere within 24 hours so the water should be applied to other fields immediately and not held in storages. Irrigation performance Application efficiency The application efficiency of each individual irrigation event measured in the trial is presented in Figure 3. An application efficiency of 80% should be considered as a standard for minimum performance. Three-quarters of the irrigation events measured had an application efficiency of less than 80%, indicating significant room for improvement in irrigation management. It should be noted that an application efficiency of greater than 90% is achievable under furrow irrigation. The SISCO computer model identifies the required flow rates of water and the cut off times (when siphons are pulled) to match the soil’s infiltration characteristics. Using the model results in improved irrigation performance through maximising application efficiency and uniformity of distribution, which in turn reduces runoff and deep drainage, thereby reducing nitrogen losses. Figure 3. Application efficiency of individual irrigation events for single and double siphon treatments Figure 2. Quantity of nitrogen in tailwaters (kilograms of nitrogen per hectare) for individual irrigation events — 25 IREC Farmers' Newsletter No. 200 — Spring 2018 Save water and nitrogen on cotton