Climatic and agronomic conditions
Australian Crop Report: June edition
Rainfall during the February to April period affects the development and yield prospects of summer crops, and the soil moisture available for the planting of winter crops. Rainfall for the 3-months to April 2021 was above average to extremely high in most cropping regions in New South Wales and Western Australia, and average to well above average in cropping regions in Queensland. In contrast, rainfall during this 3-month period was extremely low to average in most cropping regions in Victoria and South Australia (Map 1).
For May 2021, rainfall has been generally average in New South Wales and Queensland, well below average to average in Victoria and South Australia and average to well above average in Western Australia (Map 2).
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 cropping zones across Australia for May 2021. 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. Upper layer soil moisture is important at the beginning of the winter cropping season since plant germination and establishment utilise this moisture. 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. Crop development in areas of above average lower layer soil moisture are typically less reliant on in-season rainfall than in areas with below average lower layer soil moisture.
Month-to-date relative upper layer soil moisture for May 2021 was around average for this time of year in most cropping regions in eastern and western Australia (Map 3). However, relative upper layer soil moisture was extremely low to below average in cropping regions in western Victoria and South Australia.
Relative lower layer soil moisture for May 2021 was average to extremely high for this time of year in most cropping regions in central and northern New South Wales, southern Queensland and Western Australia (Map 4). In contrast lower layer soil moisture was below average to extremely low for this time of year in cropping regions in southern New South Wales, northern Queensland, Victoria and South Australia.
The rainfall outlook presented in Map 5 provides an indication of how favourable conditions for agricultural production are likely to be over winter. A combination of expected rainfall and stored soil moisture provides an indication of potential crop yields at the end of winter. In areas with below average soil moisture at the end of autumn, a favourable rainfall outlook for winter would suggest that these cropping regions are likely to receive sufficient rainfall to support crop establishment and growth over the next three months.
The latest three-month rainfall outlook (June to August), issued by the Bureau of Meteorology on 3 June 2021, suggests that winter rainfall is more likely to be above average in most cropping regions in New South Wales, Victoria, Queensland and South Australia, and below average in cropping regions in Western Australia (chance of exceeding median is less than 45%) (Map 5).
Analysis of the Bureau of Meteorology's monthly and seasonal rainfall outlook products indicates that it is likely rainfall will not be evenly distributed over winter, with higher than average rainfall more likely in June in most cropping regions and less favourable conditions more likely during the remainder of winter. If realised, higher than average rainfall during June is likely to consolidate opening season rainfall totals recorded in Victorian and South Australian cropping regions during late May and provide a welcome top up to soil moisture levels and assisting with the germination and establishment of dry sown crops.
There is a 75% chance of between 50 and 100 millimetres of winter rainfall across the majority of Australian cropping regions, with a 75% chance of between 100 and 200 millimetres across the west and south of Western Australia and southern cropping regions in New South Wales, Victoria and South Australia (Map 6). It is highly likely these forecast winter rainfall totals will be sufficient to sustain crops through to spring across the majority of Australian winter cropping regions.
There is a 75% chance of rainfall between 25 and 50 millimetres in some northern Queensland cropping regions. Many of these north Queensland regions also had low soil moisture at the start of winter and three-month rainfall totals in this range would make it difficult for crops in these regions to make it through to spring.
The outlook for maximum and minimum temperatures for June to August 2021 indicates that daytime and night-time temperatures are likely to be slightly above average in most Australian cropping regions. The current temperature outlook for winter will benefit plant growth, particularly benefiting the germination and establishment of later sown crops. However, warmer than average temperature during winter also presents a potential downside risk to grain and oilseed production in those areas that planted early into ideal soil moisture conditions. Mild winter temperatures will speed up the time to maturity which could potentially see crops flowering in August and early September when they are highly susceptible to yield losses due to a late frost.
Potential crop yield is determined by soil moisture at planting and rainfall received during the growing season. Estimates of water availability over a growing season, provide an indication of potential crop yield which can be used to inform crop production forecasts. Map 7 shows modelled water availability levels that have a high chance of occurring by the end of October 2021.
The crop yield associated with a specific level of water availability varies across regions with variations in soil characteristics. The indicative estimates presented in Map 7 assumes a relatively conservative conversion rate of 16kg of wheat per millimetre of water and a standard soil evaporation loss factor of 110 millimetres. The implications for yield of the analysed threshold values of water availability will differ across regions, as responsiveness of crop yield to soil water availability depends on factors such as temperature, humidity, soil nutrition and the timing of rainfall.
On average, the total water requirement to achieve the national 5-year average wheat yield of 2.0 tonnes/ha is 235 millimetres, based on a conversion rate of 16kg of wheat per millimetre of water. The total water requirement to achieve 3.0 tonnes/ha, 2.5 tonnes/ha, 1.5 tonnes/ha, 1.0 tonnes/ha and 0.5 tonnes/ha based on this same conversion rate have been estimated to be 295, 265, 205, 175 and 140 millimetres, respectively.
ABARES estimated the winter cropping areas likely to achieve 295, 265, 235, 205, 175 and 140 millimetres of water availability. These indicative estimates are based on modelled plant available soil moisture as at 30 April 2021, recorded rainfall totals as at 24 May 2021, an estimate of rainfall totals with a 75% chance of falling during winter derived from the Bureau of Meteorology rainfall outlook released on 27 May 2021 and assumed average September and October rainfall totals.
As at 24 May 2021, based on modelled plant available soil moisture as at 30 April 2021 and expected rainfall throughout the growing season to the end of October 2021 the analysis presented in Map 7 indicates average or above yield potential across much of New South Wales, southern Victoria, south-eastern Queensland, central and southern South Australia and much of Western Australia. This average or above yield potential is highly dependent on the timing and intensity of rainfall event during the growing season, particularly in Western Australia where soils have a lower moisture holding capacity. Across parts of northern Victoria, northern Queensland and eastern South Australia, modelled water availability analysis indicates that below average yield potentials are more likely by the end of October 2021.