Nitrogen use efficiency project: Soil moisture monitoring throughout the
high rainfall cropping zones of Victoria
Since 2012, Southern Farming Systems has been conducting research into improving the efficiency of
nitrogen use in high rainfall zone (HRZ) farming systems, as part of the Carbon Farming Futures initiative.
The project aim is to improve nitrogen use efficiency (NUE) – the efficiency with which soil nitrogen is
converted into grain N – by reducing nitrous oxide (N2O) emissions and maintaining farm productivity.
The highest losses of N2O occur after nitrogen fertiliser is applied, particularly when supply exceeds crop
demand or when the soil is waterlogged. Improving NUE should result in less nitrogen lost from the soil,
resulting in both environmental and economic benefits. To access the soil probe information represented
in this report, please visit the SFS website:
http://www.sfs.org.au/AOTG-Soil-Probe-farmworks-map.
AOTG 56
In order to monitor and assess soil temperature and moisture conditions, SFS has installed 62 soil probes
located across the major soil types of the high rainfall zones of Victoria and Tasmania. The probes record
soil temperature and moisture in 10 cm increments down to a meter below the soil surface, every 15
minutes. Graphs of this data are available on the SFS website, allowing farmers to monitor their local
soils, and make informed decisions regarding the risk of nitrogen losses at any proposed nitrogen
application date.
RECENT OBSERVATIONS:
Although the season began well for most areas in the Western Districts, rainfall within the last six weeks
has been low, which has caused the seasonal outlook to plummet compared to earlier predictions in May.
At this stage, the 2014 season (shown by the purple line) is now below decile 5 or the median value at
both Westmere and Penshurst.
Penshurst - 2014 Growing Season Rainfall Deciles
Decile 2
Decile 5
Decile 8
Actual
800
700
Cumulative Rainfall (mm)
600
Decile 8
Decile 5
500
400
Actual
300
200
Decile 2
100
0
1-Apr
1-May
1-Jun
1-Jul
Figure 1a. Penshurst growing season decile, 2014.
1-Aug
1-Sep
1-Oct
1-Nov
1-Dec
Westmere Site - 2014 Growing Season Rainfall Deciles
Decile 2
600
Decile 5
Decile 8
Actual
Cumulative Rainfall (mm)
500
400
Decile 8
Decile 5
300
Actual
200
Decile 2
100
0
1-Apr
1-May
1-Jun
1-Jul
1-Aug
1-Sep
1-Oct
1-Nov
1-Dec
Figure 1b. Westmere growing season decile, 2014.
The graphs below are generated from 4 trial paddocks within the AOTG 56 project, in which the timing
and product choice of fertiliser is varied, to determine whether application timing can be improved.
Reading the summed graphs: the information recorded by the soil probe is used to generate a graph
which shows the total amount of soil moisture from 30 cm to 100 cm in the soil profile. This total
moisture level is shown by the red line, and records moisture continuously from installation until the
present month, while the blue bars at the top of the graph show the rainfall that occurred during this
period. The graphs below show a selected time period based on the 2014 season, and comparisons with
the 2013 season if applicable.
Reading the stacked graphs: the moisture information from the probe is used to generate a graph which
shows the moisture level at each 10 cm increment. The top purple line represents the 10 cm moisture
probe, while the bottom red line represents the moisture recorded at 1 m in depth. The blue bars at the
top of the graph show the rainfall that occurred during this period. The upper limit of water holding
capacity is termed “field capacity” while the lower limit is termed the “wilting point”. These levels are
shown by the driest to date, and the wettest to date points reached on the soil moisture graphs.
Bairnsdale Probe
Figure 2a shows the summed moisture data recorded by the moisture probe located at the Bairnsdale
trial site from November 2013 until the present. Moisture levels over summer and throughout most of
the 2014 growing season were high, due to consistent rainfall earlier in the season than in 2013. Soil
moisture decline in August was alleviated by 29 mm of rain, but the moisture level has fallen significantly
since the beginning of September, showing the Revenue wheat crop has begun to draw large amounts of
water reserves from the profile. Crop water use is causing a much greater decline in soil moisture at this
time point when compared to last year, due to lower rainfall later in the season, and a greater crop
rooting depth allowing higher soil moisture reserved to be drawn upon by the crop.
1/11/2013
1/1/2014
1/5/2014
1/9/2014
Figure 2a. Summed moisture data recorded by the moisture probe located at the Bairnsdale trial site.
Figure 2b below shows the stacked soil moisture data recorded by the moisture probe located at the
Bairnsdale project site. As shown above, soil moisture during the season remained high, until midSeptember. Moisture levels to 60 cm in depth have declined significantly due to crop use. Soil moisture
below 60 cm remains largely unaffected, although a slight decline can be seen since October 1st.
1/5/2014
1/7/2014
1/9/2014
Figure 2b. Stacked moisture data recorded by the moisture probe located at the Bairnsdale trial site.
Yatchaw Probe
Figure 3a shows the summed moisture information recorded by the moisture probe located at the SFS
focus paddock site at Yatchaw from January 2014. High moisture levels earlier in the year have declined
since mid-August, and have continued falling rapidly from the beginning of September onwards. This is
chiefly due to the lower rainfall experienced in August compared to last year, 145 mm to 47 mm. This
decrease in rainfall has caused a significant increase in declining soil moisture levels, due to the greater
reliance and use of stored soil water, by the crop.
1/4/2014
1/5/2014
1/6/2014
1/7/2014
1/8/2014
1/9/2014
1/10/2014
Figure 3a. Summed moisture data recorded by the moisture probe located at the Yatchaw focus paddock.
Figure 3b shows the stacked moisture information recorded by the moisture probe located at the SFS
focus paddock site at Yatchaw. Moisture levels in the top 60 cm of the profile have declined from a high
level at mid-August, with stored water being drawn from up to 50 cm in depth, and with most from the
top 40 cm in depth. Moisture levels below 50 cm remain unaffected, and appear to have increased
slightly over time.
1/5/2014
1/7/2014
1/9/2014
1/10/2014
Figure 3b. Stacked moisture data recorded by the moisture probe located at the Yatchaw focus paddock.
Winchelsea 1 Probe
Figure 4a shows the summed moisture information recorded by the moisture probe located at the SFS
focus paddock site at Winchelsea from November 2013 till the present. Soil moisture was relatively high
at the start of the season due to early rainfall in January replenishing the profile. This high moisture level
continued until early September, when the Revenue wheat crop suddenly used an enormous amount of
stored soil water. The moisture profile is now at the driest level since probe installation in 2012, and is
well below the moisture level shown last year at the beginning of October (see red circles).
1/9/2013
1/1/2014
1/3/2014
1/5/2014
1/7/2014
1/9/2014
Figure 4a. Summed moisture data recorded by the moisture probe located at the Winchelsea focus
paddock.
Figure 4b shows the stacked moisture information recorded by the moisture probe located at the SFS
focus paddock site at Winchelsea. Rainfall events after sowing had little effect on soil moisture at depths
below 30 cm, suggesting those depths were at field capacity due to early rains. However, crop water use
since mid-September has dramatically reduced water levels in the top 70 cm of the profile, and is also
being drawn at a slower pace from the 80 and 90 cm levels. This Revenue wheat crop is already drawing
soil moisture from 90 cm in depth.
1/10/2013
1/1/2014
1/3/2014
1/5/2014
1/7/2014
1/9/2014
Figure 4b. Stacked moisture data recorded by the moisture probe located at the Winchelsea focus
paddock.
Werneth Probe
Figure 5a shows the summed moisture information recorded by the moisture probe located at the SFS
project site at Werneth. Moisture levels during the growing season were high, until water use by the faba
bean crop began in September. This water use has combined with minimal rainfall to decrease the
moisture stored in the soil profile, although the water use has been far less than the wheat crops shown
in Figures 3 and 4, and less than the wheat crop shown in Figure 2. However, similar to the Winchelsea
site, moisture at the start of October 2014 is less than the moisture at October 2013 (see red circles).
1/9/2013
1/1/2014
1/3/2014
1/5/2014
1/7/2014
1/9/2014
Figure 5a. Summed moisture data recorded by the moisture probe located at the Werneth focus
paddock.
Figure 5b below shows the stacked moisture information recorded by the moisture probe located at the
SFS focus paddock site at Werneth.
Crop water use commenced at the beginning of September, and has been drawing water from up to 60
cm in depth. Water use of this crop has not been as dramatic as the wheat crops shown above at other
sites.
4/8/2014
1/9/2014
29/9/2014
Figure 5b. Stacked moisture data recorded by the moisture probe located at the Werneth focus paddock.