Seasonal soil moisture condition assessment for Victorian dairying areas
Autumn 2019 update
Dale Boyd and Dale Grey – Seasonal Risk Agronomists, Agriculture Victoria
Agriculture Victoria has installed several soil moisture probes on a range of soil and pasture types across Victoria in dryland sites.
Soil moisture probes have helped with making early decisions in the cropping industry for some time, with monthly analysis produced as an enewsletter.
In the last two years, monitoring sites on dairy farms in Jancourt (Western District), Longwarry (West Gippsland) and Yarram (South Gippsland) have set up and monitored when there is data available.
Refer to map on the left for the location of soil moisture probes on all pasture grazing sites.
The probes used to measure the soil moisture are capacitance types and are 80 centimetres long with eight internal sensors to provide soil water content values and temperature every 10 centimetres.
Each probe collects information on water infiltration after rain events and on plant water used to grow dry matter (particularly in the absence of rain).
The probes are factory calibrated in a light soil medium but are currently not field calibrated to the soil type they have been installed in. The scale does not represent millimetres but only relative soil moisture values.
Over time and a range of seasons, the data will eventually show maximum and minimum soil moisture capacity. A percentage of plant-available water can be calculated for any point in time (per cent of full profile).
Different soil types at each site means they cannot be directly compared to other sites and are best assessed individually. All sites are currently useful in showing relative movement/use of moisture down the profile for various soil types and pasture species.
The following highlights key recent soil moisture level observations up until the end of May 2019, as well as future insights for each of the three individual dairying sites of Jancourt perennial pasture, Longwarry chicory and Longwarry perennial pasture.
The Yarram site is now back online transmitting soil moisture data.
Jancourt perennial pasture, South West Victoria
Soil moisture conditions have been improving at the Jancourt site since March.
Rain measuring 118 millimetres in May has allowed the soil moisture profile to fill to depth and the deepest sensor at 80 centimetres is wet.
With another 20 millimetres of rain in early June, the speedograph will continue to show moisture increases and is likely to be now over 80 percent.
There is some scope to absorb further rain in the 10–40 centimetre zone but if further rainfall totals of above 20 millimetres and limited pasture growth, this site is likely to go through winter with wet conditions.
Longwarry chicory and Longwarry pasture, West Gippsland
The moisture profiles measured at Longwarry have been low during the second half of summer and have only just started to build up in May after a dry March and April.
Rain measuring 50 millimetres in the last week of May has deposited moisture down to 60 centimetres and is now back on track to continue to build up moisture profiles for winter.
Yarram perennial pasture and Yarram prairie grass, South Gippsland
The moisture profiles measured at Yarram have been relatively low in spring and summer, and slowly building up in autumn.
Rain measuring 60 millimetres in the last week of May has resulted in positive moisture increases in the soil profile of around 25 percent.