Current seasonal soil moisture condition assessment for Victorian dairying areas
Dale Boyd, Seasonal Risk Agronomist, Agriculture Victoria
Agriculture Victoria has installed several soil moisture probes on a range of soil and pasture types across Victoria in dry land 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 15 months new monitoring sites on dairy farms in Jancourt (Western Districts), Longwarry (West Gippsland) and Yarram (South Gippsland) have been monitored. Refer to map below. Refer to map of location of soil moisture probes on all pasture grazing sites.
The probes used to measure the soil moisture are capacitance typesand are 80 centimetres long with eight sensors internally 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 (percent 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 soil moisture level observations made this year, as well as future insights for each of the five individual dairying sites - Jancourt perennial pasture, Longwarry chicory and perennial pasture, and Yarram perennial pasture and prairie grass.
Jancourt perennial pasture, South West Victoria
The Jancourt site was saturated through winter but with a dry September, this perennial pasture used over half the water in the soil profile. Moisture consumption continued during October and November but rain in mid-October delayed depleting the reserves by about one week.
Current soil moisture levels are slightly higher than this time last year, but remaining moisture is not as freely available as it is to be sourced from deeper depths. Without further rain, the paddock could be out of plant available water early next year and reduced pasture production will result from harder to access soil moisture.
Longwarry chicory and Longwarry pasture, South Gippsland
The moisture levels at Longwarry have been reset to field capacity after high rainfall in November that boosted moisture profiles by 25 to 40 per cent. Several other rainfall events have continued to top up the profile. Current moisture levels are better than this time last year.
With the soil holding the maximum amount of moisture at the start of summer, the season length appears promising for pasture production.
Yarram perennial pasture and Yarram prairie grass, West Gippsland
The moisture profiles measured at Yarram have been relatively low through winter and early spring. Since November moisture levels have increased 25 to 50 percent with the better improvements occurring on the perennial pasture sites, compared to the Prairie grass which was at a lower status.
It is always a good sign to see moisture profiles increasing in spring to extend growth further into summer, but further rain is required to continue growth. Seasonal conditions observed up until November on both Yarram sites have been challenging.