Farmers inspiring farmers
Seasonal soil moisture and nitrogen availability
Dr Cassandra Schefe1 and Stephen Lowe2
Riverine Plains Inc
Stony Creek Vineyard
1
2
Key points
• Soils in the Rutherglen region of Victoria are
highly variable.
• Most soils across the region increase in clay
content in the subsoil, which has a limited
capacity to supply water to plant roots.
• The distribution of plant-available nitrogen
(nitrate-nitrogen) throughout these soils
is variable, with some soils having a high
concentration of nitrogen (N) near the soil
surface, while others store nitrogen at depth.
• Sampling for deep soil nitrogen (DSN) by
combining all soil from 0–60cm depth does not
give a clear picture of where nitrogen is located
throughout the profile.
Background
During June 2015 the North East Catchment
Management Authority (NECMA) with funding from
the Australian Government’s National Landcare
Programme, enabled Riverine Plains Inc to install and
monitor soil moisture probes in cropping paddocks at
11 sites across the Rutherglen region of Victoria through
the Soil Moisture Probe Network Project.
The objective of this project was for growers to
understand how knowledge of stored soil moisture
can inform their decisions about applying fertiliser.
For example, if the soil profile has sufficient moisture,
growers might decide to apply enough nitrogen during
spring to satisfy the full crop requirement. However, if
there is limited stored soil moisture, growers might only
apply a smaller amount of fertiliser, as the crop would
be entirely dependent on opportune rainfall events to
take it through to harvest.
In addition, measurements of DSN post-harvest and
pre-sowing means the amount of nitrogen mineralised
during summer can be accounted for when planning the
nitrogen strategy for the following season.
The Sustainable Agriculture Victoria: Fast-Tracking
Innovation initiative made possible with the support of
66
RESEARCH FOR THE RIVERINE PLAINS 2016
the Foundation for Rural and Regional Renewal (FRRR)
together with the William Buckland Foundation allowed
the sampling of DSN (broken into incremental depth
samples) at each of these sites. By connecting the
results from soil nitrogen sampling to soil moisture status,
growers can predict if the stored nitrogen will be available
to the crop through the year, or if it will be lost through
leaching (due to accumulation of nitrogen at depth under
high soil moisture conditions).
Aim
The aim of this project was to increase our
understanding of nitrogen availability and movement
across, and between, seasons and to appreciate
how nitrogen availability is intimately related to soil
moisture status.
Method
Soil moisture probes were installed at 11 sites across
the Rutherglen region during June 2015. Probes were
removed during harvest (November 2015) and in
preparation for sowing (late March 2016).
Each probe measured up to four depth intervals (10, 30,
50 and 90cm below the soil surface), with values logged
every two hours. The data was manually downloaded
from each probe on a regular basis. Gaps in the dataset
occurred if the probe was damaged.
Deep soil nitrogen sampling was carried out at each
of the soil moisture probe locations during June and
December 2015, and April 2016 (Figure 1). The June
sampling was carried out at a time when many growers
across the region undertake DSN sampling to identify
how much nitrogen they need to apply to meet crop
demand through spring. The December sampling,
post-harvest, provided a measure of post-crop residual
nitrogen, and the April sampling provided information
on the amount of nitrogen lost or mineralised (becoming
more plant-available) during the summer months; ready
for sowing.
Sampling at each of the 11 soil moisture probe sites
consisted of one core sample, which was split into
increments (0–10, 10–20, 20–30, 30–60 and 60–100cm)
before being submitted to the laboratory for analysis of
mineral nitrogen (nitrate + ammonium) and total nitrogen
(includes organic and inorganic forms — i.e. the total
nitrogen soil bank).
Corowa
Gooramadda
Wahgunyah
Rutherglen
Brimin
Boorhaman
North
Norong
Chiltern Valley
Chiltern
Peechelba East
FIGURE 1 Locations of the 11 soil moisture probes installed across the Rutherglen area
By measuring both mineral nitrogen and total nitrogen
growers can appreciate the role of organic forms of
nitrogen in cycling and mineralisation processes.
As the nitrogen samples collected were not replicated,
they cannot be statistically analysed. As such, the
results presented provide an indication of nitrogen
availability, however as they are sampled from one point
in the paddock, there is the possibility the results are not
representative of the rest of the paddock.
Results
Soil moisture and available nitrogen
Please note the graphs included in this section have
not been plotted on a common axis, so take care when
comparing the values between sites.
The laboratory results for the ammonium fraction were
highly variable and potentially unreliable. As such,
they have been excluded from the analysis, with just
the nitrate-nitrogen fraction of mineral nitrogen being
presented.
The monthly rainfall data for Rutherglen is presented in
Figure 2 to provide context to the soil moisture results
presented. While there was plentiful rainfall during
winter, spring was dry. The rainfall during December
and January contributed to replenishing stored soil
moisture, however there was little follow-on rainfall
during February and March.
Monthly rainfall (mm)
90
80
70
60
50
40
30
20
10
0
Jun 15
Jul 15
Aug 15 Sep 15 Oct 15 Nov 15 Dec 15 Jan 16 Feb 16 Mar 16
FIGURE 2 Monthy rainfall recorded at Rutherglen, June 2015–March 2016
RESEARCH AT WORK
67
East Rutherglen
Carlyle
Jun-15
50
Dec-15
Apr-16
Nitrate-N (kg/ha)
Nitrate-N (kg/ha)
Farmers inspiring farmers
40
30
20
10
0
Location:0–10
Springhurst/Lilliput
10–20
20–30
Soil depth (cm)
30–60
60–100
Dec-15
Apr-16
150
100
50
0
Location:
Rutherglen
0–10 East
10–20
20–30
30–60
60–100
Soil depthCanola,
(cm) stubble burnt
2014 crop and stubble practice:
2014 crop and stubble practice: Wheat, stubble burnt
2015 nitrogen applied: 9kg N/ha MAP, 37kg N/ha urea
2015 nitrogen applied: 8kg N/ha MAP, 101kg N/ha urea
Timing of 2015 in-crop nitrogen application: Mid-June
Timing of 2015 in-crop nitrogen application: Late July, early August
2015 stubble management (post-harvest): Stubble burnt
2015 stubble management (post-harvest): Stubble burnt
Plains throughout most of the
Soil moisture was Browns
non-limiting
2015 cropping season at Springhurst/Lilliput, Victoria,
Dec-15
Apr-16
until 80the season dried off duringJun-15
September,
at which
point60soil moisture started to withdraw down to 50cm.
Rainfall
40 during November wet the profile somewhat, to a
Norong
depth
of 30cm, however the
soil Central
had dried out in the top
20
10cm0 layer by sowing (Figure 3).
Cornishtown
The East Rutherglen
site maintained high soil moisture
levels through the season, until mid-September 2015
Jun-15
Dec-15
Apr-16
50
when
the season turned dry (Figure 5). While the
40
10cm
soil layer showed strong extraction of stored soil
30
moisture, only a small change is seen at 30cm, due to the
20
Dugays
Bridge
high subsoil clay content
at this
site. However, the large
10
decrease
in
plant
available
soil
nitrogen
(nitrate-nitrogen)
0
0–10 to December
10–20
20–30
30–60
60–100indicates
Jun-15
Dec-15
Apr-16
from 70
June
2015 (post-harvest)
Soil depth (cm)
60
plants were extracting nutrients (and therefore water) to
50
a depth
40 of at least 60cm.
30–60
Jun-15
60–100
Dec-15
Apr-16
Nitrate-N (kg/ha)
2
2
2
2
Nitrate-N
(kg/ha)
Nitrate-N (kg/ha)
Soil moisture (mm) 6/0
il moisture6/0(mm) Soil moisture (mm)6/0
Soil moisture (mm)6/0
Soil moisture (mm)
5/
5/
5/
5/
20
2
20
20
01
Nitrate-N (kg/ha)
Nitrate-N
15
15
15(kg/ha)
5
7/
7/
7/
7/
07
07
07
07
/2
/2
/2
/2
01
01
01
01
5
5
5
5
18
18
18
18
/0
/0
/0
/0
8/
8/
8/
8/
20
20
20
20
15
15
15
15
29
29
29
29
/0
/0
/0
/0
9/
9/
9/
9/
20
20
20
20
15
15
15
15
10
10
10
10
/1
/
/
/
1
11
11
1/
1/
/2
/2
20
20
01
01
15
15
5
5
22
22
22
22
/1
/1
/1
/1
2/
2/
2/
2/
20
20
20
20
15
15
15
15
2/
2/
2/
2/
02
02
02
02
/2
/2
/2
/2
01
01
01
01
6
6
6
6
15
15
15
15
/0
/0
/0
/0
3/
3
3/
3/
/2
20
20
20
01
16
16
16
6
20
15
10cm
30cm
50cm
90cm
1030
South West Rutherglen
25
5
20
015
10–20
20–30
30–60
60–100
Jun-15
Dec-15
Apr-16
10 300–10
Soil depth (cm)
5
25
0
20
Springhurst/Lilliput
15
10
10cm
30cm
50cm
90cm
5
30
0
FIGURE
levels at 20–30
Springhurst/Lilliput,
Victoria
25 3 Soil moisture
Springhurst/Lilliput
0–10
10–20
30–60
60–100
20
June 2015–March
2016
Soil depth (cm)
15
10
Jun-15
Dec-15
Apr-16
60 5
50 0
40
Dugays Bridge
30
20
10cm
30cm
50cm
90cm
1030
025
20 0–10
10–20
20–30
30–60
60–100
Carlyle
15
Soil depth (cm)
10
5
FIGURE
4 Plant-available (nitrate) soil nitrogen levels, at
Jun-15
Dec-15
Apr-16
0
50 /Lilliput, Victoria June 2015–April 2016
Springhurst
Dugays Bridge
40
30
30 20
25
20 10
15 0
10
5
0
40
30
10cm
0–10
30cm
10–20
20–30
30–60
Norong
SoilCentral
depth (cm)
10cm
30cm
RESEARCH
FOR THE RIVERINE PLAINS 2016
20
10
50cm
50cm
90cm
60–100
90cm
Nitrate-N (kg/ha)
20–30
30
20
The June
2015 nitrate-nitrogen sampling showed a large
10
amount
0 of nitrogen (170kg N/ha) at the 0–10cm depth
0–10
20–30
30–60
before 101kg
N/ha 10–20
was applied
as urea
during60–100
late July/
Norong
depth
(cm)
early August (Figure 6). Soil
This
indicates
plants potentially
had access to 271kg N/ha during late winter. As it was quite
Jun-15
Dec-15
Apr-16
35 at this time, it is likely
East
Rutherglen
wet
some
of this nitrogen was lost as
30
25
gaseous-nitrogen
due to denitrification (gaseous-nitrogen
20
30cm
90cm
loss),
while
the
rest
was taken up10cm
by the
crop.50cm
Conversely,
15 30
Wahgunyah
10
25
the lack of change in DSN (60–100cm) indicates that while
5 20
the
0 crop
15 may not have used this nitrogen, it is unlikely to
0–10
10–20
20–30
30–60
60–100 Apr-16
Jun-15
have10
leached deeperSoil
due
to the high
clayDec-15
content at this
35
depth (cm)
5
site. 30
Summer
mineralisation
resulted
in
almost
40kg N/ha
0
25
East Rutherglen
20 to the following crop.
available
Nitrate-N (kg/ha)
10–20
26
26
26
26
/0
/0
/0
Nitrate-N
Nitrate-N
(kg/ha)
Soil moisture
(mm)(kg/ha)
Soil moisture (mm)
il moisture (mm)
Soil moisture (mm) /05
Soil moisture (mm)
5/
5/
5/
/2
20
20
20
01
15
15
1
5
5
7/
7/
7/
7/
07
07
07
07
/2
/2
/2
/2
01
01
01
01
5
5
5
5
18
1
18
18
8
/0
/0
/0
/0
8/
8/
8/
8/
20
20
20
20
15
15
15
15
29
29
29
29
/0
/
/0
/0
09
9/
9/
9/
/2
20
20
20
01
15
15
15
5
10
10
10
10
/1
/1
/
/
1
1
1/
1/
1/
1/
20
20
20
20
15
15
15
15
22
22
22
22
/1
/1
/1
/1
2/
2/
2/
2/
20
20
20
20
15
15
15
15
2/
2/
2/
2/
02
02
02
02
/2
/2
/2
/2
01
01
01
01
6
6
6
6
15
15
15
15
/0
/0
/0
/0
3/
3/
3/
3/
20
20
20
20
16
16
16
16
0–10
Nitrate-N (kg/ha)
2015 crop and yield: Wheat, 5t/ha
Nitrate-N (kg/ha)
2015 crop and yield: Wheat, 3.9t/ha
The June352015 nitrogenSoil
sampling
showed a large bulge
depth (cm)
30
of nitrate25(plant-available nitrogen) at 30–100cm depth,
which is 20
likely due to accumulation of nitrogen over time,
15
(Figure 4).
10 This bulge largely disappeared by the post5
harvest sampling,
with limited nitrogen remaining by the
0
0–10
10–20
20–30
60–100
pre-sowing sampling.
While the
crop 30–60
may have
used
Indigo
depth (cm)
some of this DSN, it is likelySoil
at least
some of the nitrogen
in the 60–100cm layer was lost through leaching while
Jun-15
Dec-15
Apr-16
25
Springhurst/Lilliput
soil moisture
levels were
high throughout the season.
68
Jun-15
200
15
10
305
250
20
15
10
5
0
10cm
0–10
10–20
20–30
30cm
30–60
50cm
90cm
60–100
Soil depth (cm)
Carlyle
10cm
30cm
50cm
90cm
10cm
30cm
50cm
90cm
30
25
FIGURE
5 Soil moisture levels at East Rutherglen, Victoria
20
June 15
2015–March 2016
East Rutherglen
* The sharp
10 drop in soil moisture in late February is due to a damaged probe.
5
0
Jun-15
Dec-15
Apr-16
200
Carlyle
150
30
100
25
50
20
15
0
10
5
0
0–10
10–20
20–30
30–60
SoilNorong
depth (cm)
60–100
30cm levels,
50cm at
90cm
FIGURE
6 Plant-available soil10cm
nitrogen
East
40
Rutherglen, Victoria June 2015–April 2016
30
20
10
Soil moisture (mm)
10
0
16
/2
0
/2
0
26
/0
5
/0
3
15
22
2/
02
/2
0
/2
0
/1
2
/1
1/
20
10
/2
0
29
/0
9
/2
0
/0
8
18
/2
0
Soil moisture (mm)
20
10
/0
5/
20
0
26
200
150
100
50
6
Soil moisture (mm)
30
0 25
20
15
10
5
0
0
01
26
/
05
/2
3/
2
15
/0
02
/2
01
01
6
5
60–100
2/
2/
2
/1
90cm
Nitrate-N (kg/ha)
50cm
30–60
22
10
/1
1/
20
15
15
Soil depth (cm)
20
15
20–30
/0
9/
29
20
15
18
/0
8/
20
15
20
15
10
5
0
10–20
Nitrate-N (kg/ha)
/2
0
/0
3
15
22
2/
02
/2
0
/2
0
/1
2
/1
1/
20
10
/2
0
29
/0
9
/2
0
/0
8
18
/2
0
0–10
35
30
25
20
15
10
5 40
0 30
16
16
15
15
15
15
15
15
30cm
FIGURE 9 Soil moisture levels at Browns Plains, Victoria June
2015–March 2016
60–100
6
01
15
/
03
/2
6
01
2/
02
/2
5
01
22
/
12
/2
15
10
/1
1/
20
5
01
29
/
09
/2
5
01
18
/
08
/2
5
7/
07
/
20
1
5
01
Dec-15
Apr-16
60
40
20
0
0–10
10–20
20–30
30–60
Soil depth (cm)
60–100
FIGURE 10 Plant-available soil nitrogen levels, at Browns
Plains, Victoria June 2015–April 2016
50
40
30
20
25
20
0
15
10
5
0
10
5/
/0
26
Apr-16
Indigo
Nitrate-N (kg/ha)
Dec-15
Jun-15
80
20
6
15
/
03
/
20
1
6
2/
02
/
20
1
5
20
1
12
/
20
1
22
/
29
10
/1
1/
15
/0
9/
20
15
20
18
7/
/0
07
8/
/2
01
5
15
5/
5
Soil depth (cm)
Soil moisture (mm)
30–60
Nitrate-N (kg/ha)
20–30
Jun-15
25
Dec-15
Apr-16
20
15
10
5
0
RESEARCH AT WORK
0–10
10–20
20–30
Soil depth (cm)
30–60
60–100
Nitrate-N (kg/ha)
10–20
Jun-15
/2
05
7/
07
10
30
0
25
Nitrate-N (kg/ha)
0–10
35
30
25
20
Cornishtown
15
10
5
10cm
30cm
50cm
90cm
0
30
0–10
10–20
20–30
30–60
60–100
25
20
Soil depth (cm)
15
10
FIGURE
8 Plant-available soil nitrogen levels, at Wahgunyah,
5
Victoria0 June 2015–April 2016
26
/
7/
07
Nitrate-N (kg/ha)
Soil moisture (mm)
20
07
/
15
90cm
Apr-16
Figure 10 shows nitrogen distributed to depth during
June, with the highest concentration in the 10–20cm
soil layer. It appears plants were extracting nutrients
through the profile, based on the low levels of nitrateCarlyle
nitrogen present during December, and may have almost
depleted all nutrient reserves by harvest. Mineralisation
Jun-15
Dec-15
Apr-16
during
50 the summer months has provided some nitratenitrogen
prior
to
sowing,
although
this
is
primarily
only in
40
Browns
Plains
30
the 0–10cm layer, as would be expected.
7/
20
3/
/0
02
2/
50cm
Nitrate-N (kg/ha)
2
15
16
15
15
15
15
15
15
/2
0
/0
5
26
16
6
/2
20
2/
01
15
15
/1
10
29
22
30cm
20
Browns Plains
0
/0
/1
1/
9/
/0
/0
18
10cm
10
26
20
20
20
8/
/2
07
7/
15
15
5
01
15
5/
/0
26
50
40
30
40
20
30
10
0
20
Dec-15
25
South West Rutherglen
20
The 15
10cm soil moisture sensor at Browns Plains was
10
10cm
30cm remaining
50cm
90cm
faulty,30
so is not shown in Figure
9. The
data
5
shows25
0 plants were extracting moisture down to a depth
0–10
10–20
20–30
30–60
60–100
20
of at least
50cm and likely a bit deeper, while the 90cm
15
Soil depth (cm)
layer 10
shows a heavy clay layer with minimal potential to
5
extract0water (Figure 9).
/2
0
16
/2
0
15
/0
3
/2
0
16
15
/2
0
22
2/
02
/1
2
/1
1/
20
15
15
/2
0
10
/0
9
15
/2
0
29
/0
8
18
7/
07
/2
0
15
15
/2
0
26
Soil moisture (mm)
30
The June
20 nitrate-nitrogen samples show an accumulation
in the100–10cm soil layer, with little nitrogen at depth
(Figure0 8). As plants can freely extract water down to at
least 50cm, it is likely the crop extracted nutrients from
that layer also, which is supported by the absence of
detectable nitrate-nitrogen in the 30–60cm soil layer. The
lack of change in nitrate-nitrogen levels at the 60–100cm
Dugays Bridge
layer indicates plants are
not extracting from that layer,
which is supported by Figure 6, indicating the deep soil
Jun-15
Dec-15 extraction
Apr-16
layer may
be high in clay, Wahgunyah
with little penetration
70
60 or nutrients by plant roots.
of water
Jun-15
26
/0
5
90cm
Nitrate-N (kg/ha)
Soil moisture (mm)
50cm
soil moisture
at which point
the crop started to run the soil moisture levels down
(Figure 7). Although a soil pit was not available at this
site, it appears to be free draining and lighter textured
down to at least 50cm, with plants accessing moisture
down to 50cm with ease. The fact the 50cm layer
had a large range between the upper and lower limits
Norong
(field capacity and permanent
wilting point) indicates a
lighter texture, compared with 10cm
the previous
site at90cm
East
30cm
50cm
40
Rutherglen, which is known to have a high clay content.
6
3/
20
1
/0
20
16
15
2/
90cm
60–100
60–100
30
2015 stubble
management (post-harvest): Stubble burnt
20
30cm
30
2015 stubble
management (post-harvest): Stubble burnt
Soil moisture (mm)Nitrate-N (kg/ha)
50cm
60
Apr-16
30–60
70
60
50
40
30
20 40
10
0 30
Timing of 2015 in-crop nitrogen application: June, September
/0
5/
10cm
20
3/
2
2/
2
15
/0
0
Location:
Browns Plains
FIGURE 7 Soil moisture levels at Wahgunyah, Victoria June
2015–March 2016
Wahgunyah
Dec-15
20–30
90cm
Soil depth (cm)
10
26
Timing of 2015 in-crop nitrogen application: Granular urea during
June, liquid during August
01
6
60–100
01
6
60
90cm
10–20
50cm
West Rutherglen
2015 nitrogen applied: South
87kg N/ha
urea
Nitrate-N
Soil moisture
(mm) (kg/ha)
50cm
Apr-16
0–10
30cm
2015 nitrogen applied: 46kg N/ha urea, 27L N/ha Sulsa (liquid
urea — 100L/ha of product applied)
20
16
20
3/
/0
15
Dec-15
10cm
2015 crop and yield: Wheat, 5t/ha
/0
5
16
/0
3
/2
0
16
2/
20
15
16
20
2/
90cm
Norong Central
2014 crop and stubble practice: Canola, stubble burnt in windrows
25
20
15
The 10
Wahgunyah site maintained high
5 the season until mid-September,
through
0
50cm
Apr-16
2015 crop and yield: Wheat, 4.25t/ha
Soil moisture (mm)
90cm
Dec-15
2014 crop and stubble practice: Canola, stubble burnt
Carlyle
50cm
Jun-15
35
30
25
20
15
40
10
5
30
0
20
(kg/ha)
Soil moistureNitrate-N
(mm)
16
/2
0
15
/0
3
/2
0
/2
0
2/
02
22
90cm
16
50cm
15
15
30cm
/1
2
15
10
29
18
26
/1
1/
20
/2
0
15
/0
9
/2
0
15
/0
8
7/
07
/2
0
15
/2
0
/0
5
/0
3
/2
0
16
10cm
30
25
20
15
10
5
0
Location: Wahgunyah
15
2/
20
90cm
16
50cm
Soil moisture (mm)
East Rutherglen
2
22
1
29
18
7
26
Norong Central
35
30
25
20
15
10
5
0
69
10cm
0–10
10
10–20
20–30
60–100
16
/2
0
16
/0
3
2015 crop and yield: Wheat, cut for hay 5t/ha
70
0–10
10–20
20–30
30–60
Nitrate-N (kg/ha)
16
6
20
01
/0
02
3/
/2
20
15
22
2/
/1
2/
/1
1/
20
15
15
15
20
29
10
/0
8/
/0
9/
20
15
5
01
/2
07
18
35
30
25
20
15
10
5
0
0–10
20
16
/0
3/
/2
01
6
02
15
2/
/1
2/
20
15
20
15
22
10
/1
1/
20
15
9/
/0
26
7/
/0
5/
20
15
Nitrate-N (kg/ha)
Soil moisture (mm)
Dec-15
6
01
/2
03
5
01
/2
90cm
60–100
6
30–60
20
1
Soil depth (cm)
Apr-16
50cm
02
/
20–30
5
10–20
12
60–100
Wahgunyah
Browns Plains
15
/
FIGURE 14 Plant-available soil nitrogen levels, at Carlyle,
Victoria June 2015–April 2016
2/
Apr-16
0–10
20
1
Dec-15
90cm
60–100
30cm
22
/
Jun-15
RESEARCH FOR THE RIVERINE
PLAINS
2016
South
Rutherglen
SoilWest
depth
(cm)
)
0–100
35
30
25
20
15
10
5
0
/0
Nitrate-N (kg/ha)
26
Apr-16
0
11
/
Norong
0
10cm
10
/
10
40
40
30
30
20
20
10
10
0
5
20
50cm
30–60
Norong Jun-15
50
9/
20
1
Victoria30June 2015–April 2016
0–10
FIGURE 13 Soil moisture levels at Carlyle, Victoria June
Carlyle
2015–March 2016
/0
0–100
30
10cm
30cm
50cm
90cm
25
20
20
10
15
0
0–10
10–20
20–30
30–60
60–100
10
Norong Central
5
Soil depth (cm)
0
10cm
30cm
50cm
90cm
FIGURE
4012 Plant-available soil nitrogen levels, at Cornishtown,
20–30
29
40
29
Apr-16
20
15
Dec-15
8/
Jun-15
5
Indigo
30cm
70
60
50
40
30
20
10
0
Soil depth (cm)
8/
20
1
5
0
10–20
/0
50
0–10
/0
Apr-16
June
10cm
18
90cm
18
50cm
/2
01
5
30cm
5
10cm
30
FIGURE
2511 Soil moisture levels at Cornishtown, Victoria
20
2015–March
2016
15
* Soil moisture
sensor not working during early March 2016.
Cornishtown
10
Carlyle
15
10
5
30
0
25
20
15
10
5
0
07
3/
20
16
Dugays Bridge
7/
60–100
07
/2
01
20–30
30–60
Soil depth (cm)
90cm
7/
10–20
50cm
Nitrate-N (kg/ha)
Soil moisture (mm)
0–10
30cm
20
15
10cm
The crop at the Carlyle site appears to have had limited
access to soil moisture (Figure 13), with the 0–10cm
Norong Central
sensor being the only one to show clear change with
rainfall or crop water extraction. This indicates the site
Apr-16
is located
on a heavy clay, and/orJun-15
has a Dec-15
high amount
of
35
30
run-off — both of which would limit the amount of rainfall
25
Rutherglen is supported by the
infiltrating
to depth. ThisEast
suggestion
20
15
nitrate-nitrogen
values shown in Figure 14, which reveal
10
30cm and
50cm
90cm
5
the nitrogen
is mostly stored in10cm
the 0–10
10–30cm
30
0
25
layers, with0–10
only minimal
to 60cm.
10–20 nitrogen
20–30 moving
30–60 down
60–100
20
As most
of
the
nitrate-nitrogen
is
in
the
topsoil
layers,
Soil
depth
(cm)
15
10
this, with
additional in-crop nitrogen, are likely being
5
utilised0 by the crop. However it is likely that significant
denitrification occurred on this site during the wet winter,
which may have been subject to prolonged waterlogging
due to its inability toSouth
drain
water.
The amount of nitrateWest
Rutherglen
nitrogen mineralised during summer was surprisingly
Jun-15 have
Dec-15
Apr-16
low, suggesting
the soil sample may
been
taken
30
from an
25 area of bare ground, from which there was limited
20 matter (OM) to drive the mineralisation process.
organic
5/
100
30
50
25
200
15
10
5
0
2015 stubble management (post-harvest): Stubble burnt
/0
16
/0
3
/2
0
16
/2
0
15
22
10
29
2/
02
/2
0
15
15
/1
2
/1
1/
20
15
/2
0
/0
9
15
/2
0
18
/0
8
15
/2
0
15
7/
07
/0
5
Springhurst/Lilliput
This correlates well with the nitrate-nitrogen values (Figure
12). While there was measurable
nitrate-nitrogen
10cm
30cm
50cm
90cm to
depth 30
during June, East
although
probably
less
than
optimum
Rutherglen
25
in the 0–10cm
layer, the crop depleted the nutrient stores
20
15
to depth
by harvest. However, the stores of nitrogen in
10
Jun-15
Dec-15
Apr-16
the topsoil
were replenished with summer
mineralisation
2005
0
Cornishtown
of nitrogen.
150
Timing of 2015 in-crop nitrogen application: Late June, August
26
Nitrate-N
Soil moisture
(mm) (kg/ha)
content with depth, based
on the staged decrease in soil
Soil depth (cm)
10
moisture at each depth from late September to the start of
0
November, with the November rain event only impacting
on the 10cm layer.
2015 nitrogen applied: 74kg N/ha urea
Nitrate-N(mm)
(kg/ha)
Soil moisture
5/
20
15
Apr-16
/0
Dec-15
26
Jun-15
Timing35of 2015 in-crop nitrogenWahgunyah
application: Late June
30
25
2015 stubble management (post-harvest): Stubble burnt
20
15
10cm
30cm
50cm
90cm
40
10
The soil
moisture
graph
from
the
Cornishtown
site
(Figure
5
30
0
11) indicates
a soil profile that gradually increases in clay
0–10
10–20
20–30
30–60
60–100
20
)
2015 nitrogen applied: 58kg N/ha urea
Nitrate-N (kg/ha)
15
2014 crop and stubble practice: Canola, stubble burnt in windrows
Nitrate-N (kg/ha)
/2
0
2/
02
/2
0
15
15
/1
2
/1
1/
20
22
29
18
Location: Carlyle
Wahgunyah
2015 crop and yield: Wheat,
5t/ha
26
0–100
30–60
90cm
26
26
(kg/ha)
Nitrate-N
26
/0 (mm)Soil moisture
(mm)2(kg/ha)
Soil moistureNitrate-N
(mm)
6/
Soil moisture
Soil moisture (mm) /05
Soil moisture (mm)
/0
5/
0
/2
5/
5/
5/
20
0
20
20
20
15
15
15
15
15
7/
7/
7/
7/
7/
07
07
07
07
07
/2
/2
/2
/2
/2
01
01
01
01
01
5
5
5
5
5
1
1
8/
8/
18
18
18
08
08
/0
/0
/0
/2
/2
8/
8/
8/
01
01
20
20
20
5
5
15
15
15
29
29
29
2
2
9/
/0
/0
9/
/0
0
9
9
0
9/
9/
/2
/2
9/
20
20
01
01
20
15
15
5
5
15
1
1
10
10
10
0/
0/
11
11
/1
/1
/1
1/
1/
1/
/2
/2
20
20
20
01
01
15
15
15
5
5
22
22
22
22
22
/1
/1
/1
/1
/1
2
2
2/
2/
2/
/2
/2
20
20
20
01
01
15
15
15
5
5
2/
2/
2/
2
2
02
02
/0
/0
02
2/
2/
/2
/2
/2
20
20
01
01
01
16
16
6
6
6
15
15
15
15
15
/
/
/0
/0
/0
03
03
3/
3/
3/
/2
/2
20
20
20
01
01
16
16
16
6
6
90cm
50cm
2014 crop and stubble practice: Wheat, stubble burnt
/2
0
3/
20
Apr-16
10
/2
0
15
15
/0
9
/0
8
/2
0
15
15
7/
07
/0
5
26
16
0–100
30cm
Soil depth (cm)
0
/2
0
3/
20
90cm
Apr-16
Norong
Location: Cornishtown
Apr-16
Dec-15
Farmers inspiring farmers
16
0–100
Jun-15
70
60
50
40
30
40
20
30
10
0
20
/2
0
90cm
Nitrate-N
Soil moisture
(mm) (kg/ha)
Apr-16
200
150
100
50
0
0–10
0
60–100
0–10
10–20
16
/2
0
16
15
30
20
10
16
30
25
/0
5
26
Soil moisture (mm)
16
5/
2
20
26
/0
3/
/0
15
16
26
/0
5/
2
20
03
/
15
/
Nitrate-N (kg/ha)
Soil moisture (mm)
1
2
26
/0
5/
/0
15
Dec-15
70
60
50
40
30 4
20 3
10
0 2
20
3/
/2
2/
02
20
2/
/1
20
/1
1/
10
20
9/
/0
29
22
Jun-15
71
Apr-16
ha)
60
Apr-16
ha)
RESEARCH AT WORK
Dec-15
1
16
15
15
15
15
20
8/
/0
18
/2
7/
07
20
South West Rutherglen
Springhurst/Lilliput
Jun-15
/2
/2
0
15
/0
3
/2
0
16
2/
02
/
Apr-16
FIGURE 18 Plant-available soil nitrogen levels, at Norong
Central, Victoria June 2015–April 2016
5/
FIGURE 16 Plant-available soil nitrogen levels, at Indigo,
Victoria June 2015–April 2016
01
5
35
30
25
20
15
10
5
0
15
60–100
Dec-15
35
South West Rutherglen
30
Jun-15
Dec-15
Apr-16
25
10cm
30cm
50cm
90cm
20
30
15
25
10
20
5
15
0
10
0–10
10–20
20–30
30–60
60–100
5
0–10
10–20
20–30
30–60
60–100
Soil
depth
(cm)
0
Soil depth (cm)
/0
Soil depth (cm)
30–60
2
Norong
Nitrate-N
Soil moisture
(mm)(kg/ha)
5
20–30
20
15
20
12
/
15
20
22
/
10
60–100
3
Norong Central
*Soil moisture sensors not working in early March 2016.
Nitrate-N (kg/ha)
10
10–20
6
/2
02
2/
22
30–60
/1
1/
9/
29
/0
18
/0
8/
/2
07
7/
20–30
Soil depth (cm)
01
6
/0
15
15
0–10
01
15
/1
2/
20
15
20
/1
1/
10
29
18
/0
/0
9/
8/
20
20
15
15
5
10–20
01
5
01
5
0
0–10
20
15
0
26
16
01
/2
10
4
FIGURE 17 Soil moisture levels at Norong Central, Victoria
June 2015–March 2016
Apr-16
20
0
90cm
20
26
25
50cm
Soil moisture (mm)
30
Apr-16
30cm
Jun-15
Dec-15
16
15
22
2/
02
/1
2
/2
0
15
15
/1
1/
20
10
/2
0
15
29
/0
9
/2
0
15
18
/0
8
/2
0
15
7/
07
15
40
3
2
2
1
1
20
3/
/2
02
2/
/1
2/
20
01
6
15
15
20
22
10
/1
1/
01
5
9/
2
29
/0
01
5
18
/0
8/
2
5
01
/2
07
7/
FIGURE 15 Soil moisture levels at Indigo, Victoria June 2015–
March 2016
Indigo
Jun-15
Soil moisture (mm)
Soil moisture (mm)
/2
0
/0
5
60–100
07
/0
15
Nitrate-N (kg/ha)
7/
20
3/
/2
02
20–30
30–60
Soil depth (cm)
90cm
Soil moisture (mm)
16
6
01
15
2/
/1
22
2/
50cm
40
Dec-15
10cm
5/
2
10–20
30cm
Jun-15
50
/0
0–10
01
5
5/
2
20
20
/1
1/
10cm
25
40
20
20
15
0
10
5
0
26
/0
15
15
20
10
9/
/0
29
18
7/
/0
07
8/
/2
20
15
5
01
15
20
5/
/0
26
Nitrate-N (kg/ha)
Soil moisture (mm)
60
20
60–100
3
2
2
1
1
Dugays Bridge
100
5/
30–60
Apr-16
While the soil moisture results indicate that the plant
10cm
30cm
50cm
90cm
50 30
roots
may not have gone much past the 30cm layer, due
25
0
to the
wet
conditions,
the
nitrate-nitrogen
at depth was
0–10
10–20
20–30
30–60
60–100
20
15
decreased
by harvest,
by plants
Soil depth
(cm) or through losses to
10
depth (Figure
18). Moreover, although nitrogen supply
5
0 was replenished during summer, presumably
at depth
through mineralisation, the amount measured at depth
is surprising given most mineralisation processes occur
in the top 0–10cm layer of soil, with limited movement
to depth. One possibility may be that the location for
the April samplingCornishtown
was a stock camp during the summer
Norong Central
months.
/0
20–30
15
22
10
29
18
10–20
Dec-15
most of the winter, as shown by the 10cm depth layer
having a higher soil moisture content than the deeper
layers (Figure 17).
This can only occur if the topsoil has
East Rutherglen
a greater clay content than the subsoil, and so can hold
more water (which is unlikely), or if the soil is saturated,
Jun-15
Dec-15
Apr-16
200 free-standing water. Saturation is likely, as the 30cm
with
150 also held more water than it would otherwise.
layer
Soil moisture (mm)
16
/0
3
/2
0
16
/2
0
2/
02
/2
0
15
15
/1
2
/1
1/
20
15
/0
9
/2
0
15
/0
8
/2
0
15
7/
07
/2
0
15
/0
5
26
Nitrate-N (kg/ha)
Soil moisture (mm)
0–10
15
10 nitrate-nitrogen
Soilvalues
depth (cm)
The soil
shown in Figure 16
5
support0 this observation. The even distribution of
nitrogen through the profile during June indicates easy
movement of nutrients down the profile, while the lack
of measurable nitrogen post-harvest indicates the
crop used this nitrogen within season, with leaching
of nutrients below the measured depth also possible.
Brownsnitrogen
Plains
Movement of mineralised
over summer was also
measured, with the 10–20cm depth recording as much
IndigoJun-15 Dec-15 Apr-16
nitrate-nitrogen
as is in the surface
0–10cm layer.
80
Nitrate-N (kg/ha)
/0
15
The Indigo site looks to be quite free draining down to
at least 30cm, as shown by the 10cm and 30cm depths
in Figure 15, showing similar soil moisture storage. The
range in soil moisture storage
Carlyle(difference from wet to dry)
in the 10cm and 30cm layers, and the rapidity with which
the profile wet and drained, indicates
thisDec-15
soil isApr-16
likely to
Jun-15
have 50
a high gravel content.Cornishtown
While infiltration decreased
40
down to 50cm, there were still some plant roots at depth,
30
as seen
by water extraction by
the 30cm
crop during
early
10cm
50cm
90cm
20
30
October
2015
after
the
10cm
and
30cm
layers
were
10
25
20
depleted
of soil moisture.
0
a)
20
16
90cm
3/
16
20
2/
0
2015 stubble management (post-harvest): Stubble burnt
/2
0
16
/2
0
/0
3
15
2/
20
16
Soil depth
(cm) July
Timing10
of 2015 in-crop nitrogen
application:
26
0
20
2015 nitrogen
applied:10–20
10kg N/ha
MAP, 46kg
N/ha urea
0–10
20–30
30–60
60–100
Nitrate-N (kg/ha)
90cm
Jun-15
35
30
Location:
Norong Central
25
20
2014
15 crop and stubble practice: Wheat, stubble burnt
Springhurst/Lilliput
10
2015
5 crop and yield: Wheat, 3t/ha
0
10cm
30cm
50cm
90cm
2015 nitrogen
MAP,
92kg
N/ha 60–100
urea
0–10 applied:
10–208kg N/ha
20–30
30–60
30
Soil depth
(cm)
Timing 25
of 2015 in-crop nitrogen
application:
Late July, late August
20
2015 stubble
management (post-harvest): Stubble burnt
15
10
5
0
The Norong
Central site appeared to be waterlogged
26
Apr-16
Nitrate-N (kg/ha)
Dec-15
2015 crop
5 and yield: Feed wheat, 3.5t/ha
30
50cm
60–100
/0
3
/2
0
2/
02
/2
0
15
15
/1
2
/1
1/
20
Jun-15
30
Wahgunyah
25
Location:
Indigo
20
15 and stubble practice: Wheat,
10cm
30cmburnt
50cm
2014 crop
stubble
40
10
Nitrate-N (kg/ha)
Soil moisture (mm)
90cm
30–60
Wahgunyah
South West Rutherglen
50cm
20–30
Soil depth (cm)
22
29
10
/2
0
15
15
/0
9
/0
8
/2
0
15
/2
0
7/
07
/2
0
/0
5
30–60
Soil depth (cm)
0
26
20–30
20
15
10–20
18
Soil moi
0–10
10
15
16
/2
0
16
/0
3
15
2/
20
20
0
35
30
Nitrate-N (
25
20
15
10
5
0
Farmers inspiring farmers
100
0–10
10–20
20–30
30–60
60–100
Soil depth (cm)
East Rutherglen
90cm
16
2014 crop and stubble practice: Lucerne, two-way disc before
cropping
16
/2
0
/0
3
Dec-15
Apr-16
Jun-15
10cm
30cm
Dec-15
50cm
90cm
40
30
/2
01
0
Apr-16
re (mm)
35
3030
2525
2020
re (mm)
20
20
15
15
N (kg/ha)
isture (mm)
30 30
07
10
7/
07
/2
Soil moisture (mm)
20
20
15
03
/
15
/
30
Wahgunyah
10cm
30cm Dec-15
50cm Apr-16
90cm
Jun-15
RESEARCH
FOR THE RIVERINE PLAINS 2016
25 25
N (kg/ha)
72
01
7/
26
6
6
02
/
2/
22
/
10
/
29
/
18
/
7/
26
FIGURE 22 Plant-available soil nitrogen levels, at Dugays
Bridge, Victoria June 2015–April 2016
40
26
/0
5/
90cm
60–100
20
1
5
12
/
20
1
5
11
/
20
1
5
50cm
30–60
Soil depth (cm)
20
1
5
20
1
20–30
09
/
07
/
20
5/
/0
10–20
30cm
Apr-16
20
1
10cm
Dec-15
South West Rutherglen
100
07
/2
01
5
Soil moisture (mm)
5/
2
3/
15
/0
30
25
20
15
10
5
0
/0
90cm
20
16
6
01
2/
Jun-15
0 0–10
Cornishtown
South West
Rutherglen
90cm
01
Soil moisture (mm)
15
20
5/
7/
/0
15
/0
20
3/
/2
02
2/
02
/2
20
15
2/
20
15
/1
1/
10
29
22
/1
5
/0
9/
2
01
5
01
8/
2
50cm
Norong Central
70
60
5040
40
30
30
2020
10
10
0
15
Soil depth (cm)
Apr-16
26
16
6
01
15
20
2/
/1
22
10
/1
1/
20
15
15
20
9/
29
/0
18
/0
8/
/2
20
15
5
01
15
07
7/
5
7/
07
/2
01
5/
2
/0
26
Nitrate-N (kg/ha)
16
20
3/
/0
15
30cm
FIGURE 21 Soil moisture
levels
at Dugays Bridge, Victoria
Dugays
Bridge
June 2015–March 2016
Soil moisture (mm)
Apr-16
6
2/
02
/2
01
5
12
/
20
1
15
20
10
/1
1/
22
/
5
29
/
09
/
20
1
5
18
/
08
/
20
1
5
01
7/
07
/2
5
20
1
26
/
05
/
3/
2
01
6
100
Dec-15
Soil moisture (mm)
90cm
Jun-15
35
Wahgunyah
30
Norong Central
25
20
10cm
30cm
50cm
90cm
1540
10
Jun-15
Dec-15
Apr-16
35530
0
30 20
0–10
10–20
20–30
30–60
60–100
25
Soil depth (cm)
20 10
15 0
FIGURE
20 Plant-available soil nitrogen levels, at Norong,
10
Victoria
5 June 2015–April 2016
0
0–10
10–20
20–30
30–60
60–100
Nitrate-N (kg/ha)
Nitrate-N (kg/ha)
Apr-16
/0
6
01
/2
03
FIGURE 19 Soil moisture levels at Norong, Victoria June
2015–March 2016
Norong
10cm
30
25
20
15
10
5
0
08
/
2/
15
/
02
12
/2
/2
01
01
6
5
15
20
10
22
/
9/
29
/0
/1
1/
20
15
15
20
8/
20
/0
26
7/
0
7/
5/
/0
15
15
0
30
25
20
15
10
5
0
Dugays Bridge
18
10
5
60–100
Soil moisture (mm)
15
30–60
Soil depth (cm)
01
20–30
90cm
5
10–20
50cm
5
0
The nitrate-nitrogen
results (Figure 22) show the crop
accessed almost all available nitrogen reserves by
harvest, with little nitrogen remaining in the profile at the
end of the season. The poor mineralisation of nitratenitrogen during summer indicates most of the ‘potentially
mineralisable nitrogen’ fraction in the total soil nitrogen
bucket was accessed. This means the 2016 crop would
require larger nitrogen inputs to meet its yield potential.
20
20
3/
/0
02
2/
22
16
6
01
/2
20
/1
2/
/1
1/
20
15
15
15
20
29
10
/0
9/
20
8/
/0
18
0–10
20
30cm
The Dugays Bridge soil moisture probe indicates this site
is likely to be free draining, which would be expected as
it is close to the Murray River (Figure 21). As such, it is
unknown if there is any
lateral water movement from the
Springhurst/Lilliput
river at the 50cm and 90cm deep soil layers. However,
10cm
30cm
50cm drawing
90cm
when the 10cm and 30cm sensors
started
30
moisture
25 during September, the 50cm sensor showed
slight 20
drawdown, as did the 90cm sensor. This indicates
15
roots were
accessing water at depth.
10
20
1
30
0
20
20
3/
15
5
01
/2
07
10cm
40
10
16
100
20
18
90cm
Norong
30
Soil moisture (mm)
Apr-16
Nitrate-N (kg/ha)
26
7/
/0
3/
5/
20
20
16
15
Soil moisture (mm)
The 50
soil moisture profile at Norong showed a high
capacity
to store and release moisture from the 10cm
0
Carlyle
0–10
20–30
30–60
60–100
depth, due
to a 10–20
light-textured
topsoil
(Figure
19).
Soil depth (cm)
10cm texture
30cm
50cm
90cm
However, there was likely a large
change
into
30
the subsoil,
with a large increase in clay content. This
25
would20
explain
why the moisture release range of the
15
30cm 10
and 50cm soil layers is similar, and relatively small
5
(small 0difference between wet and dry moisture levels).
The decline in soil moisture in the 30cm and 50cm depth
during mid-October indicates plants were accessing to
Cornishtown
this depth, with the nitrate-nitrogen
values supporting the
soil moisture results (Figure 20). While some nitrogen
Jun-15
Dec-15
Apr-16
may50be lost to depth, it is likely plants used most of the
40
nitrogen.
5/
22
29
18
15
2015 stubble management (post-harvest): Stubble burnt
100
90cm
2015 nitrogen applied: 18kg N/ha DAP
Timing of 2015 in-crop nitrogen application: None applied
2015150
stubble management (post-harvest): Stubble burnt
100
2015 crop and yield: Wheat, 2.5t/ha
/0
/2
0
2/
02
/2
0
/1
2
/1
1/
20
/2
0
10
/0
9
/2
0
/0
8
/2
0
7/
07
6/
05
Jun-15
26
15
15
15
15
15
Location: Dugays Bridge
200of 2015 in-crop nitrogen application: June, August
Timing
Nitrate-N (kg/ha)2
3/
20
50cm
2015 nitrogen applied: 9kg N/ha MAP, 74kg N/ha Urea
/2
0
16
15
2015 crop and yield: Wheat, 4t/ha
Apr-16
30cm
30
25
20
Location:
Norong
15
10
2014 crop
practice:
Wheat, stubble burnt
5 and stubbleEast
Rutherglen
0
Soil moisture (mm)
10cm
Soil moisture (mm)
90cm
Apr-16
40
20
10
0–10
10–20
20–30
30–60
60–100
/
15
2/
22
16
/2
0
/0
3
15
2/
02
/2
0
16
15
/2
0
/1
2
22
29
10
/1
1/
20
15
15
/2
0
15
/0
9
/2
0
18
/0
8
/2
0
15
15
7/
07
16
/2
0
16
15
/0
3
22
2/
02
/2
0
/2
0
/1
2
10
/1
1/
20
15
15
15
/2
0
15
29
/0
9
/2
0
15
18
/0
8
/2
0
15
7/
07
16
6
20
01
15
2/
/0
02
3/
/2
20
2/
/1
22
10
/1
1/
20
15
15
15
9/
20
15
/0
29
18
/0
8/
/2
20
01
5
15
07
7/
Example of the value of incremental soil sampling
Rutherglen, 2015
20–30
12.7
30–60
18.9
200
100
25
20
50
15
0
10
6
20
1
6
03
/
15
/
2/
02
/
20
1
12
/
22
/
20
1
5
5
20
1
5
11
/
20
1
09
/
10
/
18
168.0
29
/
/0
8/
20
15
Nitrate-nitrogen
Average soil nitrate-nitrogen
(kg/ha)
levels across incremental depths
67.2
150
60–100
30
0
Soil moisture (mm)
/0
26
0–10
Soil depth (cm)
10–20
Nitrate-N (kg/ha)
Dec-15
Depth
(cm)
isture (mm)
Nitrate-N (kg/ha)
Jun-15
20
15
10 1
TABLE
5
from East
0
01
5
01
6
3/
2
15
/0
2/
2
01
6
at South-west
10
5
30cm
50cmof nitrate90cm
The Springhurst/Lilliput
site has 10cm
a larger
amount
30
0
0–10
10–20
20–30
30–60
60–100
25
nitrogen at depth than the east Rutherglen (Table 2).
/2
60–100
Carlyle
50
/2
0
/0
90cm
15
50cm
2/
0
01
5
2/
2
01
5
22
/1
10
/1
1/
2
01
5
9/
2
29
/0
01
5
8/
2
01
5
18
/0
7/
2
7/
0
01
5
5/
2
26
/0
Apr-16
Browns Plains
10–20
20–30
30–60
25 0–10
20
Soil depth (cm)
15
10 24 Plant-available soil nitrogen levels,
FIGURE
5
Rutherglen,
Victoria June 2015–April 2016
0
0
Based on the 0–100cm depth average of 56kg N/ha at
East Rutherglen in Table 1, a grower may decide to apply
more nitrogen to the crop soon after sowing. However,
based on the 0–30 and 30–100cm averages, which show
Wahgunyah
plentiful nitrogen in the
surface soil available for plant
uptake, the grower may decide to apply less nitrogen
Dec-15
Apr-16
early35in the season, reserving someJun-15
for topdressing
later
30 the season if the conditions (and soil moisture
during
25
availability)
allow, as thereCornishtown
is little nitrogen available at
20
15
depth for plants to access through spring.
26
15
Dec-15
30cm
40
10
07
16
3/
/0
02
/2
20
01
6
15
22
2/
/1
2/
20
15
20
/1
1/
15
29
10
/0
9/
20
18
/0
8/
/2
07
7/
20
15
5
01
15
Jun-15
Soil moisture (mm)
Nitrate-N (kg/ha)
FIGURE 23 Soil moisture levels at South-west Rutherglen,
South 2016
West Rutherglen
Victoria June 2015–March
30
25
20
15
10
5
030
Soil moisture (mm)
26
60–100
Soil depth (cm)
90cm
Two 0examples
from the June 2015 dataset are shown
30
0–10
10–20
20–30
30–60
60–100
in Table
1 and Table 2 to demonstrate the value of
20
incremental
sampling. Soil depth (cm)
10
7/
30–60
90cm
50cm
10
/0
5
16
/2
0
15
50cm
30cm
Splitting cores into more than two increments would
Jun-15
Dec-15
Apr-16
70
become
cost-prohibitive, however even the simple
60
change
can provide useful information
50 to two incrementsWahgunyah
on 40
nutrient availability, resulting in more informed
30
decision-making
and greater environmental
stewardship.
10cm
30cm
50cm
90cm
20
Nitrate-N (kg/ha)
20–30
/0
3
/2
0
2/
02
30cm
90cm
Feedback
to date from this project is that some growers
0
are already changing the way they carry out their
sampling, with the soil core being broken up into at
least two increments (0–30cm and 30–60cm) to better
Dugays Bridge
understand where the nitrogen is stored.
Soil moisture (mm)
10–20
16
15
/2
0
22
/1
2
15
15
10
/1
1/
20
/2
0
29
/0
9
15
/2
0
/0
8
15
0–10
20
5/
/0
18
7/
07
10cm
15
10
5
0
26
/2
0
15
/2
0
26
/0
5
Nitrate-N (kg/ha)
Soil moisture (mm)
20
15
1030
525
020
50cm
incremental depth sampling
10cm
26
Soil moisture (mm)
0
The increase
in nitrate-nitrogen down to 60cm indicates
nitrogen can be easily leached in this soil (Figure 24).
While plants are likely to take up most of this nitrogen, as
roots accessed this depth,
there
is potential for nitrogen
Norong
Central
to be lost deeper in the soil profile. This is seen from
the April sampling, where the nitrate-nitrogen values
Jun-15
Dec-15
Apr-16
35
increased
at the 60–100cm soil depth. This demonstrates
30
the ability
of this soil to
move nutrients to depth.
25
South West Rutherglen
30cm
40
The incremental
depth sampling was carried out to help
30
growers
appreciate the averaged deep nitrogen sample
20
has limitations.
Nitrate-N (kg/ha)
Norong Central
The soil moisture profile of the South-west (SW)
10cmhad
30cm
50cm capacity
90cm
Rutherglen
site indicates this soil
plentiful
40
to store
and
release
water
for
plant
growth,
with
plants
30
accessing
moisture
down
to
at
least
50cm,
if
not
deeper
20
(Figure
10 23).
Soil moisture (mm)
2015 stubble management (post-harvest): Stubble burnt
20
Timing of 2015 in-crop nitrogen application: July
10cm
practice for sampling DSN is to take a
core soil sample down to 60cm or 100cm, homogenise
the sample and take a subsample from that for laboratory
analysis. This effectively provides an average nitrogen
sample for the whole core. While this provides an
indicator of stored nitrogen across the whole season, it
doesn’t provide any information on when the plants will
Norong
be able to access this nitrogen.
/2
0
16
/0
3
15
2/
02
/1
2
22
10
29
/0
9
/0
8
18
7/
07
/2
0
16
/2
0
15
/2
0
15
/1
1/
20
/2
0
15
15
/2
0
/2
0
15
15
/2
0
26
/0
5
2015 nitrogen applied: 10kg N/ha MAP, 46kg N/ha urea
30
25
20
15
Importance
of
10
5
The accepted
0
/0
5
90cm
5/
50cm
20
30cm
5/
Soil moisture (mm)
10cm
30
25
20
15
Location:
South-west Rutherglen
10
5
2014 crop
and stubble practice: Canola, stubble burnt in windrows
0
2015 crop and yield: Wheat, 4.9t/ha
/
/
10
/
29
/
18
7/
/
26
/
15
2/
/
/
10
/
29
/
18
7/
/
26
22
Carlyle
Dugays Bridge
Average 0–30cm
= 82kg/ha
East Rutherglen
Average 0–100cm
= 56kg/ha
Average 30–
Jun-15
Indigo
100cm
= 17kg/ha
Dec-15
10cm
50cm
Apr-16
15.1
30cm
90cm
RESEARCH AT WORK
73
Farmers inspiring farmers
TABLE 2 Examples of the value of incremental soil sampling
from Springhurst/Lilliput, 2015
Depth
(cm)
Nitrate-nitrogen
(kg/ha)
0–10
21.0
10–20
15.4
20–30
13.4
30–60
42.0
60–100
49.3
Average soil nitrate-nitrogen
levels across incremental
depths
Average 0–30cm
= 17kg/ha
Average 0–100cm
= 28kg/ha
Average 30–100cm
= 46kg/ha
If a grower used the results from the 0–100cm sample
(28kg N/ha), a decision could be made to apply a lot
of nitrogen early during the season due to a perceived
nitrogen deficit through the profile. However, if the core
was split into the 0–30cm and 30–100cm layers, the grower
would identify the shortfall of nitrogen in the top layers,
but also see there is some nitrogen sitting at depth, which
could contribute to finishing the crop off in a favourable
season without additional nitrogen being applied.
Total nitrogen vs available nitrogen
The results presented to date mostly focus on the
available soil nitrogen (measured as nitrate-nitrogen),
which is the form of nitrogen crops access during the
growing season. Another form of plant-available nitrogen
is ‘mineral nitrogen’, which includes both nitrate (NO3)
and ammonium (NH4) forms of nitrogen, which is a more
complete measure of available nitrogen. However,
as some of the ammonium results received during this
project were questionable, the ammonium results were
omitted.
A key part of the nitrogen story for crop production is
the cycling of nitrogen through organic (plant matter,
decaying roots, microbial biomass) and inorganic
(nitrate, ammonium) forms. To this end, we measured
the total soil nitrogen in addition to the available/nitratenitrogen to understand the size of the complete soil
nitrogen ‘bucket’, which is already in the soil, additional
to any fertiliser applied.
The real challenge lies in estimating the nitrogen
mineralisation rate — the rate at which the organic (plant
unavailable) nitrogen is transformed into plant-available
forms. The mineralisation process depends heavily
upon environmental factors including temperature and
moisture, and also varies according to the type and
amount of plant residue present on the ground.
A comparison of total nitrogen vs plant-available nitrogen
is presented in Figure 25. Figure 25 illustrates an
accumulation of organic nitrogen (represented as totalnitrogen minus nitrate-nitrogen) in the 0–10cm layer,
which is expected as this is where most of the nutrientcycling microbes are located.
To provide context as to the size of this organic nitrogen
‘bucket’, nitrate-nitrogen is plotted alongside, and barely
registers on the scale of this graph.
Nitrate-nitrogen (%)
0.20
Total nitrogen (%)
0.18
0.16
Nitrogen (%)
0.14
0.12
0.10
0.08
0.06
0.04
0
0–10
10–20
20–30
30–60
60–100
0–10
10–20
20–30
30–60
60–100
0–10
10–20
20–30
30–60
60–100
0–10
10–20
20–30
30–60
60–100
0–10
10–20
20–30
30–60
60–100
0–10
10–20
20–30
30–60
60–100
0–10
10–20
20–30
30–60
60–100
0–10
10–20
20–30
30–60
60–100
0–10
10–20
20–30
30–60
60–100
0–10
10–20
20–30
30–60
60–100
0–10
10–20
20–30
30–60
60–100
0.02
Norong
Central
Dugays
Bridge
South west Wahgunyah
Rutherglen
Carlyle
East
Rutherglen
Browns
Plains
FIGURE 25 A comparison of total nitrogen vs plant-available (nitrate) nitrogen
74
RESEARCH FOR THE RIVERINE PLAINS 2016
Indigo
Cornishtown Springhurst
Lilliput
Norong
Observations and comments
Although all of the sites for this project lie within the
Rutherglen region, there is a range of soil types. However,
the duplex, texture-contrast soil type dominates, with a
sharp increase in clay content in the subsoil. This means
water is strongly held in this zone and is only extracted for
plant use after the topsoil layers are depleted of moisture.
The sites vary in both the amount of nitrate-nitrogen
stored in the soil, and the depth at which it is stored.
As the traditional DSN measure doesn’t account for the
distribution of nitrogen, it is worth considering splitting
DSN samples into two increments — a 0–30cm and a
30+cm depth sample. This will provide more accurate
information on the availability of nitrogen as the season
progresses, supporting better and more timely fertiliser
application decisions.
The nitrate-nitrogen component is only a small
proportion of the total soil nitrogen, with the large pool of
soil organic nitrogen being responsible for the ongoing
cycling and mineralisation throughout the season and
during summer.
While the soil moisture results presented here show a
dry soil profile going into the 2016 season, as this report
is being written the ground outside has turned to mud,
thanks to the fantastic rain received during early May. With
between 60–80mm rainfall across the region, it certainly
will go a long way towards refilling the soil profile!
Acknowledgements
This project was carried out in partnership with the
North East Catchment Management Authority (NECMA)
with funding from the Australian Government’s National
Landcare Programme and Sustainable Agriculture
Victoria: Fast-Tracking Innovation, an initiative made
possible with the support of the Foundation for Rural
and Regional Renewal (FRRR) together with the William
Buckland Foundation.
Many thanks to the growers who participated in this
project.
Contact
Dr Cassandra Schefe, Riverine Plains Inc
T:(03) 5744 1713
E:[email protected]
RESEARCH AT WORK
75