Climatic and agronomic conditions
Australian Crop Report: September edition
Rainfall from August to October 2020 was generally average to well above average across most cropping regions in New South Wales, northern Queensland, Victoria and South Australia (Map 1). Rainfall in southern cropping regions in Queensland was below average to average. Over the same period rainfall was generally severely deficient to below average in Western Australia, which was largely the result of extremely low rainfall during October.
Despite variable rainfall in June and July, close to average yield potentials were preserved across most cropping regions due to a draw down of soil moisture reserves built up during late summer and autumn.
November rainfall, as at 18 November 2020, was generally extremely low to below average in most summer cropping regions in northern New South Wales and Queensland (Map 2). While drier than normal conditions during the first 18 days of November have allowed the harvest of winter crops across northern New South Wales and Queensland to proceed without delay, these dry conditions have constrained spring planting of summer crops.
Map 3 and Map 4 show the relative levels of modelled upper layer (~0.1 metres) and lower layer (~0.1 to ~1 metres) soil moisture for summer cropping zones on 18 November 2020. Soil moisture estimates are relative to the historical long-term average (1911 to 2016) and presented in percentiles.
Upper layer soil moisture responds quickly to seasonal conditions and often shows a pattern that reflects rainfall and temperature events in the days leading up to the analysis date. Lower layer soil moisture is a larger, deeper store that is slower to respond to seasonal conditions and tends to reflect the accumulated effects of events that have occurred over longer periods.
Relative upper layer soil moisture on 18 November 2020 was generally extremely low to well below average for this time of year in most grain sorghum growing regions (Map 3).
The modelled root zone soil moisture on 18 November 2020 indicates stored soil moisture levels were average to below average in most grain sorghum growing regions in Queensland and northern New South Wales (Map 4). Some southern parts of these regions in New South Wales were above average to well above average.
Soil moisture and rainfall over the entire growing season will determine planting opportunities and crop production outcomes for dryland summer crops. With extremely low upper layer soil moisture and variable levels of root zone soil moisture, the favourable rainfall outlook for the remainder of the growing season will need to be realised to achieve current forecast summer crop production during 2020–21.
According to the latest three-month rainfall outlook (December to February), issued by the Bureau of Meteorology on 19 November 2020, rainfall in summer cropping regions in New South Wales and Queensland is likely to be above average. In summer cropping regions, there is a 75% chance of receiving between 100 and 300 millimetres across most grain sorghum growing regions in New South Wales and Queensland, with totals up to 400 millimetres in some northern parts of these regions in Queensland (Map 5).
The outlook for maximum and minimum temperatures for summer 2020–21, indicates higher than average daytime and night-time temperatures are likely in cropping regions in New South Wales and Queensland.
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.
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 18 November 2020 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 2020, the chance of achieving 290 millimetres of water availability was relatively high in many summer cropping regions. The highest chance (75%) 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 is between 50% and 25%.
Note: Chance of achieving 290 millimetres of water availability is displayed for sorghum producing shires only.
Source: ABARES & Bureau of Meteorology
It is important to note that the crop yield associated with a specific level of water availability varies across regions with variations in soil. 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.