22 IREC Farmers' Newsletter No. 199 — Autumn 2018 Nitrogen application Nitrogen use has been increasing over time across the industry and in the 2016–17 season there was a wide range of applications rates and techniques. Rates varied between 170 kg N/ha and 456 kg N/ha. Application timing ranged from 100% applied pre-crop to 100% applied post -planting. Similarly, application methods ranged from deep banding, either with urea or anhydrous ammonia, to some under the plant line or some beside the plant line. Some growers were spreading and working into the bed or hill, while others were spreading and hoping rain or irrigation would take the nitrogen into the soil profile. While applied nitrogen accounted for 9.8% of yield variation, there were significant interactions with location as shown in Figure 6. Analysis of the 2016–17 data on fertiliser application showed that for any amount of nitrogen applied over 250 kg N/ha, the question of whether it was economically worth the application must be asked (Figure 7). Whether this applies for other seasons is yet to be determined. The trend lines show the variability within the data set. The data suggests that nitrogen should be managed within the respective crop and season and with realistic seasonal yield potential. Good information from a bad season The 2016–17 season for southern-grown cotton was probably one that most growers would choose to forget and not rehash. However, the advantages of pulling together information about the majority of growers’ fields and some key drivers of yield can aid education and management decisions in the future. In spite of the challenging field preparation and growing conditions (extreme maximum and minimum temperatures in the early part of the season and again at late flowering), the season showed how bad things can get and that cotton crops can still be viable. From the data collected it would appear the optimum cotton crop in the 2016–17 season was likely to have been grown on spaced hills, after a summer fallow and planted with the variety Sicot 74-6B3F around the second week of October. Nitrogen would have been monitored through the season and application rates of nitrogen around 250 kg N/ha would have been adequate. The data also raises questions that warrant further research about cotton production in the southern regions, such as: l  the effect of excessive applied nitrogen on crop termination, defoliation and picking period, and the consequent effect on quality l  the impact of farm design and bed shape as it relates to crop rotation, irrigation efficiency, compaction and water infiltration In spite of the challenging field preparation and growing conditions, data from the 2017–18 season show how bad things can get and cotton crops can still be viable. Figure 7. Cotton yield as a function of total nitrogen applied (kg N/ha) in the southern cotton growing region, 2016–17 Yield (bales/ha) Total nitrogen (kg/ha) R2 = 0.62 Carrathool Coleambally Griffith Hay Jerilderie Regression line Trendline Whitton-DP Location Yield (bales/ha) Total nitrogen (kg/ha) Carrathool Coleambally Griffith Hay Jerilderie Whitton-DP Location Figure 6. The relationship between cotton yield and total nitrogen applied at various locations in the southern cotton growing region, 2016–17