19 IREC Farmers' Newsletter No. 199 — Autumn 2018 Location Rotation Nitrogen Sowing date Variety Bed shape Individual drivers 23.6% 11.9% 9.8% 3.2% 6.4% 4.3% Combination of drivers Rotation 28.9% — — — — — Nitrogen 24.2% 17.2% — — — — Sowing date 31.8% — — — — — Variety 25.8% — — — — — Bed shape — 13.1% — — — — Interacting drivers Location x rotation 30.9% — — — — — Location x nitrogen 27.9% — — — — — Location x sowing date 35.3% — — — — — Location x variety 27.8% — — — — — Few cotton gins — most of the southern cotton industry is serviced by three main gins located in the Murrumbidgee region, two of which only started in ginning in 2015. Diverse soils — soil types in the south vary much more than in the north. Northern cotton farms are primarily situated on uniform grey clay soils with a smattering of red-brown earth soils. In the south, cotton is grown on a much wider range of soil types and variation can often be within one field. Irrigation techniques — since many farms have come out of rice or vegetable production, there is a greater diversity of irrigation techniques with bays and siphons being the two main water delivery systems. Row configuration — given the production history of the region, there is diversity in row/bed width ( 1.0, 1.5, 1.8 and 2.0 metres) and row spacing (0.75, 0.9 and 1.0 metres). Limited machinery —many farmers have used existing farm machinery to ‘try’ cotton before undertaking significant capital expenditure on specific cotton row crop machinery. Understanding southern cotton In light of the diversity of farming backgrounds, techniques and machinery in the south and in order to not ‘re-invent the wheel’, the creation of a database was proposed to try and pick up the key attributes for successful cotton farming in the southern region. With agreement from cotton growers involved, data was provided on an individual field basis by the three cotton gins in the Murrumbidgee Valley and by many agronomists, as authorised by the farmers. Of the approximately 42,000 hectares of cotton production in the two valleys in 2016–17, farmers signing up to contribute to the database accounted for 31,384 ha. Agronomists were able to provide basic field data for 23,797 ha, however 692 ha was screened out of the analysis due to significantly low yields (less than 6 bales/ha). Thus, 23,105 ha of the district total of 42,000 ha or 55% of the southern cotton region was included in this analysis. The 2015–16 cotton growing season in the south was the most successful of all the seasons in the district’s short lifetime. Data from Rivcott Gin reports average yields of 11.3 bales/ha in 2015, 12.6 bales/ha in 2016, and 8.6 bales/ha in 2017. Figure 1. Griffith airport daily maximum, minimum and rainfall for the 2016–17 season (Source: Bureau of Meterology) Table 1. The percentage contribution of drivers to variance of yield in the southern cotton region for the 2016–17 season. A dash (—) means contribution to variance was not significant. Degrees celcius Rainfall (mm) Rainfall Max T Min T 2016–17 season The peculiarities of the season were highlighted when it started raining in May 2016 and over 525 mm of rain fell in the months May to October, compared with the long-term average of 230 mm for the same period. Under these wet circumstances, growers were trying to prepare fields for the 2016–17 cotton growing season. Daily maximum and minimum temperatures and rainfall are shown in Figure 1. Extreme temperatures (hot and cold) were experienced in early to mid-December and hot temperatures in mid-January to mid-February. The main yield drivers for the 2016–17 season, as identified by information collected in the database and listed in Table 1, are: l location l rotation l nitrogen rate l sowing date l variety l bed geometry. Some drivers influenced variance of yield individually, as well as in combination with other drivers. There were also interactions between drivers that contributed to yield variance (Table 1).