Climatic and agronomic conditions
Australian Crop Report: December edition
Rainfall from August to October 2019 was generally extremely low to well below average across most cropping regions in New South Wales, southern Queensland, northern Victoria, north-eastern cropping regions in South Australia and northern cropping regions in Western Australia (Map 1). Over the same period, rainfall in northern cropping regions in Queensland, western South Australia and southern Western Australian was generally below average to average, which was largely the result of below average rainfall during October.
Maximum daytime temperatures during late winter and spring were generally above average in most cropping regions. In contrast, there were numerous frost events and lowest minimum temperatures on record in southern Australia in September.
November rainfall, as at 26 November 2019, was around average in most summer cropping regions in northern New South Wales but below average in almost all summer cropping regions in Queensland (Map 2).
Map 3 shows modelled root zone (0 to ~1 metres) soil moisture in millimetres for cropping zones in New South Wales and Queensland as at 25 November 2019.
The modelled root zone soil moisture for November 2019 indicates stored soil moisture levels are extremely low in summer cropping regions. (Map 3).
Due to the extremely low levels of root zone soil moisture, planting and yield prospects for dryland summer crops will be almost entirely dependent on in crop rainfall during the remainder of the growing season.
According to the latest three-month rainfall outlook (December to February), issued by the Bureau of Meteorology on 21 November 2019, rainfall in summer cropping regions in New South Wales and Queensland is likely to be below average (Map 4).
The outlook for maximum and minimum temperatures for summer 2019–20, indicates higher than average daytime and night-time temperatures are likely in cropping regions in New South Wales and Queensland.
Map 5 shows the shire-scale forecast of grain sorghum yields obtained from the University of Queensland's Queensland Alliance for Agriculture and Food Innovation (QAAFI). These forecasts are based on soil moisture conditions and the seasonal outlook, including the most recent trend in the Southern Oscillation Index (SOI). It is important to note that final sorghum crop yield is affected more by in-crop rainfall and temperatures during crop growth than by the soil moisture at the time of sowing.
At the beginning of November 2019, the forecast indicated a generally below average outlook for the 2019–20 sorghum crop (Map 5).
The water available for crop growth can come from water stored in the soil during the fallow or from in-crop rain. On average, the total water requirement to achieve the national 5-year average sorghum yield of 2.85 tonnes/ha is 290 millimetres, based on a conversion rate of 15kg of grain sorghum per millimetre of water. See recent analysis published by the Grains Research & Development Corporation (GRDC) for more detail.
The QAAFI estimates of the probability of exceeding the long-term grain sorghum yield is based on rainfall information up to the end of October and does not incorporate significant rainfall deficiencies in November. As such ABARES has undertaken an analysis to determine the chance of achieving 290 millimetres of water availability (Map 6). This analysis is based on available soil moisture as at 25 November 2019 and estimates of rainfall totals for December to February derived from the Bureau of Meteorology’s latest rainfall outlook . The probability of achieving 290 millimetres of water availability provides a good indication of the prospects for grain sorghum production .
At the end of November 2019, the chance of achieving 290 millimetres of water availability was low in summer cropping regions. The highest chance (25%) is in the northern and eastern part of the Queensland summer cropping region and some eastern parts of the New South Wales summer cropping region. In other summer cropping regions in northern New South Wales and Queensland, the chance of achieving 290 millimetres of water availability are lower than 25%.
It is important to note that the crop yield associated with a specific level of water availability varies across regions with variations in soil characteristics (the QAFFI analysis presented in Map 5 does account for regional variations in soil characteristics). As a result the implications of 290 millimetres of water being available may be quite different across regions. Additionally, in some seasons the responsiveness of crop growth to water availability will be better than average (around 28kg/mm) and in other years it will be worse (around 6kg/mm) as responsiveness depends on factors such as temperature, humidity and the timing of rainfall.