Climatic and agronomic conditions
Australian Crop Report: June edition
Autumn rainfall in 2020 was above average to extremely high in most cropping regions in New South Wales and Victoria, and average to well above average in cropping regions in South Australia. In contrast autumn rainfall was extremely low to below average in most cropping regions in Queensland and Western Australia (Map 1). However, rainfall during February and March in Queensland and Western Australian cropping regions provided generally favourable conditions leading into the winter crop season in these regions.
During May 2020, rainfall was generally average to below average in most cropping regions (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 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 in May 2020 was around average for this time of year in most Australian cropping regions (Map 3).
Relative lower layer soil moisture in May 2020 was average to extremely high for this time of year in most cropping regions in the eastern states and South Australia. In contrast lower layer soil moisture was average to extremely low for this time of year in Western Australian cropping regions (Map 4).
The rainfall outlook presented here provides an indication of how favourable conditions for agricultural production are likely to be over winter. The latest three-month rainfall outlook (June to August), issued by the Bureau of Meteorology on 4 June 2020, suggests that winter rainfall is likely to be above average in most cropping regions in Queensland and New South Wales and there are roughly equal chances of higher or lower than average winter rainfall in most other cropping regions in Australia (Map 5). It is likely rainfall will not be evenly distributed over winter with lower than average rainfall likely in June in most cropping regions and more favourable conditions in the remainder of winter.
Map 7 shows modelled water availability levels that have a high chance of occurring by the end of October 2020. Water available for crop growth comes from water stored at sowing time and in-crop 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 2020, recorded rainfall totals as at 31 May 2020, an estimate of rainfall totals with a 75% chance of falling during winter derived from the Bureau of Meteorology latest rainfall outlook released on 4 June 2020 and assumed average September and October rainfall totals.
The crop yield associated with a specific level of water availability varies across regions with variations in soil characteristics. The indicative estimates presented above, abstract from this complexity by assuming a conversion rate of 16kg of wheat per millimetre of water and a standard soil evaporation loss factor of 110 millimetres. As a result the implications of the analysed threshold values of water availability may be quite different across regions. Additionally, in some seasons the responsiveness of crop growth to water availability will be better than average (around 22kg/mm) and in other years it will be worse (around 6kg/mm) as responsiveness depends on factors such as temperature, humidity, soil nutrition and the timing of rainfall.
Note: Modelled water availability is displayed for cropping regions only.
Source: ABARES & Bureau of Meteorology