Soil temperature for sowing decisions
Author: Laura Forward, Meridian Agriculture
When preparing to sow pasture paddocks, either in autumn or spring, the main consideration is usually moisture. In autumn, it’s all systems go as soon as we get some decent rainfall, while in spring it’s often a question of how soon we can get on the paddock without getting the tractor bogged. The other key consideration is soil temperature, which is frequently missed despite it playing a huge role in whether or not your sowing is successful.
In the autumn, we are generally considering the temperature requirements of temperate grasses (ryegrass, phalaris, etc.) and legumes (clovers and sometimes lucerne). The optimal topsoil temperature ranges for these species are listed in Table 1.
In spring, we are most often considering summer crop species such as brassicas/forage rape, maize, millet or sorghum. The temperature requirements for these species are listed in Table 2. If spring sowing phalaris – a fairly common practice – the temperature guidelines for grasses in Table 1 will apply.
Table 1: Top-soil temperature requirements for autumn-sown species
Most grasses | Legumes | |
|---|---|---|
Above 10° | Yes | Yes |
Between 5° and 10° | No | Some will strike, but will be |
Below 5° | No | Yes |
Table 2: Top-soil temperature requirements for spring-sown species
Brassica | Maize | Millet | Sorghum | |
|---|---|---|---|---|
Below 8° | Will begin to strike, | No | No | No |
Between 8° and 12° | Yes | Will strike, | No | No |
Between 12° and 15° | Yes | Yes | No | No |
Between 15° and 18° | Yes | Yes | Ideal is 15° | No |
Above 18° | Yes | Yes | Yes | Yes |
When measuring soil temperature in preparation for sowing, there are two easy methods:
- Use a temperature probe/soil or meat thermometer – put this into the ground to about 10 centimeters deep, in an area that is representative of your paddock (not under a tree, etc.) at around 10 am for three consecutive days. The average of those three measurements is the soil temperature
- If you have a soil moisture probe, or one near you on the network, this will give you a live reading of the current soil temperature.
The Agriculture Victoria soil moisture probe network provides real time soil and moisture data for many soil probe sites across the state. Looking at historical soil temperature (about three years of data is available for most pasture sites) is useful to see when critical temperatures generally occur and can be used as a guide as to when plants may need to be established.
References
Jim Moir. (2020) Advances in Plant Sciences. New Zealand Journal of Agricultural Research 63:3, pages 269–271.
Serafin, L., 2022. Moving summer crop sowing early or late - risks and rewards on the Liverpool Plains. Grains Research and Development Corporation.