Australian Crop Report: December edition
Rainfall from August to October 2018 was generally extremely low to well below average across most cropping regions in southern New South Wales, Victoria, and eastern South Australia (Map 1). Over the same period, rainfall in cropping regions in northern New South Wales, Queensland, western South Australia and Western Australian was generally average to above average, which was largely the result of above average rainfall during October.
Maximum daytime temperatures during spring have been generally above average in most cropping regions and numerous lowest on record minimum temperature were recorded in southern Australia in September.
November rainfall, as at 27 November 2018, was around average in summer cropping regions in Queensland and New South Wales (Map 2).
Map 2 Australian rainfall percentiles, 1 to 27 November 2018
Note: Rainfall percentages are displayed for summer cropping regions only. Rainfall for 1 to 27 November 2018 relative to the long-term record and ranked in percentiles. This analysis ranks rainfall for the selected period compared with the historical average (1900 to present) recorded for that period.
Source: Bureau of Meteorology
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 22 November 2018.
The modelled root zone soil moisture for November 2018 indicates stored soil moisture levels are highly variable in summer cropping regions. In north-eastern cropping regions in New South Wales and parts of northern and western cropping regions in Queensland, soil water levels range from 50 to 100 millimetres. For other cropping regions in northern New South Wales and Queensland soil water levels mostly range from 0 to 50 millimetres (Map 3).
Map 3 Modelled root zone soil moisture, as at 22 November 2018
Note: Root zone soil moisture is displayed for summer cropping regions only.
Source: Bureau of Meteorology
Prospects for dryland summer crops in areas of low root zone soil moisture will be highly 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 29 November 2018, there is no strong tendency toward either above or below average summer rainfall in cropping regions in New South Wales. Summer rainfall in Queensland is more likely to be below average than above average (Map 4).
The outlook for maximum and minimum temperatures for summer 2018–19, indicates hotter than average daytime and night-time temperatures are likely in cropping regions in New South Wales and Queensland.
Map 4 Rainfall outlook, December 2018 to February 2019
Note: Rainfall outlook is displayed for summer cropping regions only.
The map shows the likelihood of exceeding the 1990–2012 median rainfall. Median rainfall is defined as the 50th percentile calculated from the 1990–2012 reference period.
Source: Bureau of Meteorology
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 2018, the forecast indicated a generally below average outlook for the 2018–19 sorghum crop (Map 5). Areas in central and eastern Queensland are showing between 50% and 80% chance of exceeding the median shire sorghum yield, while southern sorghum growing areas of New South Wales showed between 70% and 80% chance of exceeding the median shire sorghum yield. Remaining areas in Queensland and northern New South Wales showed between 10% and 40% chance of exceeding the long-term median shire sorghum yield. However, the forecast was made early in the growing season and a wide range of possible yields exist.
Map 5 Probability of exceeding long-term median grain sorghum yield
Note: Probability of exceeding the long-term sorghum yield, given SOI phase was "rapidly rising" at the end of October.
Source: Queensland Alliance for Agriculture and Food Innovation
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 probability of exceeding the long-term grain sorghum yield obtained from QAAFI is based on rainfall information up to the end of October and does not incorporate significant rainfall events in November. As such ABARES has undertaken an analysis to determine the chance of achieving 290 millimetres of water availability. This analysis is based on available soil moisture as at 22 November 2018 and estimates of rainfall totals for December to February derived from the Bureau of Meteorology’s latest rainfall outlook to determine the impact of November rainfall on the prospects of grain sorghum production (Map 6).
At the end of November 2018, the chance of achieving 290 millimetres of water availability was highest (50 to 75%) in the northern part of the Queensland summer cropping region and the eastern part 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 25% or lower.
Map 6 Chance of achieving 290 millimetres of water availability
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 characteristics. The analysis presented in (Map 6) assumes a simple conversion rate of 15kg of grain sorghum per millimetre of water across the entire analysis area (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.
Table 4 Rainfall in major cropping districts, median and actual, August 2018 to October 2018
|District||District no.||August median|
|New South Wales|
|NW Plains (W)||52||19||19||21||7||33||51|
|NW Plains (E)||53||30||31||29||12||40||68|
|NW Slopes (N)||54||37||40||36||26||54||67|
|NW Slopes (S)||55||41||29||41||34||54||63|
|N Tablelands (N)||56||42||32||46||46||69||88|
|CW Plains (S)||50||30||12||27||11||30||32|
|CW Plains (N)||51||23||17||21||9||28||42|
|CW Slopes (N)||64||36||31||34||31||44||41|
|CW Slopes (S)||65||45||27||39||21||42||46|
|C Tablelands (N)||62||45||35||40||40||48||57|
|C Tablelands (S)||63||59||39||53||43||65||65|
|SW Slopes (N)||73||62||29||51||25||48||22|
|SW Slopes (S)||72||114||84||95||47||95||48|
|Lower North East||82||118||113||94||41||95||36|
|W Darling Downs||42||20||32||22||8||46||86|
|E Darling Downs||41||24||19||30||15||54||101|
|Moreton S Coast||40||29||17||34||22||66||169|
|Upper South East||25B||57||68||48||13||38||22|
Notes: Median rainfall is calculated over the period 1900 to August 2018. Australian rainfall districts are shown in Map 8 of the Australian crop report.