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Soil Moisture Monitoring
7 September 2018
Volume 5 Issue 6

The rain and grain project, with the use of soil moisture monitoring probes, provides real time soil water content data.  Monitoring sites have been commissioned in cropping regions throughout the state by Agriculture Victoria. The sites record soil water content at one source point from 30 centimetres down to one metre as a reference point for a paddock.

Sites monitored include: Merrimul, Ouyen, Speed, Kerang, Birchip, Normanville, Lah, Bangerang, Taylors Lake, Coonooer Bridge, Raywood, Elmore, Youanmite, Hamilton, Lake Bolac and Sale.
Locations of Agriculture Victoria soil moisture monitoring sites

To access information provided in the graphs, log onto the website:  Login and password are both: dpi

Recent rain and SMM observations:

After a good start to August with some timely rains, the second half of the month returned to a drier pattern north of the divide which saw the continued run of below average decile rainfall.
The exception continues to be the South-West region and the West-Wimmera where rain has continued to be average or above and in some areas even creating water logging conditions.
Generally, rainfall of less than 25 millimetres during August in the Mallee (Map 1) and just a touch over that in Central Victoria and the Wimmera has generally not permitted deeper moisture penetration and the connection to last season moisture is either poor or is hard to determine from sensor data. Frost conditions have further compounded crop issues and are still being assessed for full impacts.
Areas with no or very little soil moisture improvement during this growing season have suffered significant yield impacts and have an immediate need for rain to salvage any crop yield potential. Paddocks are now in a large moisture deficit and have a total reliance on early September rain to fill this deficit and keep crops growing. Deep soil moisture may have little benefit if is decoupled from the top horizon with this seasons moisture infiltration depth.  Roots appear to be restricted in growth and development and other paddock issues of root disease are showing up in the dry conditions.  The current weather outlook for September by 12 climate models scanned by The Fast Break’s Dale Grey suggest a drier to average rainfall outlook for spring.
Areas that did not receive the December 2017 rains last year have paddocks that started the season with limited soil moisture reserves. With no improvement during the growing season these crops have little to no yield prospects north of the divide.

Rainfall was the weakest in the far north-west, with areas in the south-west, and far north-east the wettest.

Graph 1. BoM rainfall month date

The month to date rainfall map for August (2018) indicates the areas that had less than 25 millimetres for the month and these districts have had no deep soil moisture improvement in August and July.

Decile map from march to the end of may shows all parts of the state are below average decile except the south west

Map 2. BoM 1 April 1 to 3 Sept 3 rainfall totals for 2018 growing season.
Large areas in the Mallee are yet to register 100 millimetres for this growing season and in the Wimmera and North Central rainfall totals just over 100 millimetres on medium to heavy soil types have had limited moisture penetration.

The growing season rainfall Victorian map indicates the extent of cropped area that has below average yield potential with sensor data indicating where deep soil mositure the exists is either poorly connected restricting crop growth or not able to be utilised by this seasons crop.

Water balance model has good soil moisture conditions in the south west but marginal in the wimmera and mallee

The AWRA soil water balance model from the BoM reflectsthe seasonal performance of cropped areas with any of the darker blue colour still with yield potential. 

Speedo assessments

Soil moisture speedo values have generally reduced over the past month of August in the Mallee.  Central Victorian sites are the lowest, with all three being around 25 percent but some are holding steady with the moisture levels, but are now at levels much lower than this time last year. Most sites North of the divide are now show the signs of moisture depletion, which is later than expected for the season but reflects the low plant growth and water uptake.

Paddocks in the South West have either improved soil water values or have reached field capacity.

Last season, there was a range of crops grown, many of them non-cereals, so take note of the description below each speedo gauge to help explain the current soil moisture status because if that crop has influenced the current reading then it has been listed. This season 2/3 of the crops monitored are cereals.


Soil Moisture: Werrimul just over 50%, Ouyen about 80%,Speed 70% Normanville & Gippsland under 50%, Birchip & Brim 30%, Sheep Hills & Youanmite 50%, Taylors Lake almost 100%, Coonooer Bridge and Raywood  25%, Elmore just over 20%, Lake Bolac 40% and Hamilton 100%.
Speedo soil moisture graphs
No improvement in soil moisture conditions this month.  Currently at 60%
No improvements to soil moisture conditions in the past month and currently at 85%
Soil moisture is at 70% and this time last year it was a 90%
Current soil moisture is at 40% but this time last year it was at 90%
Birchip smm speedo 30 percent and last year was 50 percent
Currently 30% down from 80% this time last year.
Sheep Hills about 50%, down from more than 85% this time last year..
Taylors Lake 100 per cent, after only sitting at about 50 percent this time last year.

Note - Last years annual pasture had limited moisture use and December rains infiltrated to depth and the moisture content has been validated with soil coring and physical inspection of soil.  Paddock next door growing canola last year appears to have a much drier profile and would be more typical of district soil moisture levels.

North Central
Coonooer Bridge sitting juder under 25 per cent, compared to more than 50 per cent this time last year.
Raywood sitting just over 25 per cent, compared to about 75% this time last year..
Two years summed soil moisture graph, showing moisture carry over from 2016 for crop growth in 2017. 2018 the summed soil moisture conditions are at 25 percent.

Year summed soil moisture graph from Raywood is the data set used to produce the Raywood speedo. Moisture conditions are over 50 per cent down on this time last year. There have been two instances this growing season (highlighted in blue circles) where rainfall has infiltrated to the moisture sensors. Soil moisture levels are currently similar to the start of the growing season in April. Moisture is being rapidly taken up by the wheat crop because this is one Ag Vic monitoring site that has a connection to deeper soil moisture reserves.  There are limited soil moisture reserves deposited by the harvest rains indicated by the brown circles.

Raywood seperate trace soil moisture graph. 12 month view

Moisture infiltrated down to 50 centimetres with harvest rains last year.  Moisture has infiltrated down to 50 - 60 centimetres this winter and connected-up the soil moisture reserves from harvest. Moisture depletion by the wheat crop last season indicates that this crop will run out of moisture without significant September rain as there is no more moisture below 50 - 60 centimetres. This has been validated by soil coring this winter.

Elmore at 30%, compared to about 50% this time last year
North East
Youanmite about 50%, after almost being 75% this time last year.
Gippsland about 45%, similar to this time last year.
Gippsland Pasture
Giffard West Perennial pasture (still to confirm upper and lower limits so no speedo available)
Summed graph of all 8 sensors for 2018 till current for Giffard West in GIppsland monitoring pasture..

The Gippsland pasture site next door to the cropping site had all the moisture depleted in March by pasture growth, while the cropping site had deep soil moisture conserved with no crop growth over summer.  It appears like many other areas, that limited rain over winter has either failed to connect-up or the connection is poor, reducing wheat crop growth and yield potential.

South West
Lake Bolac 45%, compared to about 13 % compared to this time last year.

Lake Bolac pasture individual trace soil moisture graph - 12 months

After six  months of no moisture changes in summer and autumn, highlighted in yellow is the moisture infiltration down to 100 centimetres with the above average growing season rainfall which provides a positive outlook for spring growth in this South-West region.

Hamilton about 100%, compared to about 100% this time last year.
Irrigation – Irrigated Cropping Council trial block Kerang
2018 individual sensor graph. Moisture profile is full and just starting to use water at 10-20cm.

Summed sensor graph (10 - 40 centimetres) from Kerang irrigation site winter 2018.

Pre-irrigation of the paddock in April provide a timely emergence of the oat crop in autumn and a full profile through winter. In early August soil moisture was being depleted by the oaten hay crop. The first spring irrigation has recently been applied, triggered when soil moisture was starting to be depleted at 50 centimetres (red oval).  When this movement at this depth occurs, it is because soil moisture reserves above this depth are depleted to where they are no longer ready available to plant.


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