The following is a very interesting case study about using
all three elements the H2Grow companies bring to the table, informing the
grower of soil variability and then adjusting inputs to match soil
requirements.
The paddock studied is located at Greenvale Pastures near
Methven. It was EM soil surveyed by Agri Optics NZ Ltd to provide data on field
soil variability. This area was then divided into zones based on the deep soil
profile results from the EM soil survey. HydroServices used the GPS points
provided from the EM soil survey to ground truth the 6 different zones and then
set up monitoring sites with a neutron probe in each as shown in the map below.
 |
Figure 1: An EM soil
survey map with neutron probe sites marked, for a Water Holding Capacity (WHC)
trial conducted by Agri Optics and HydroServices.
|
As a result of HydroServices ground truthing, the full point
and stress point was ascertained for the six different soil characteristics at each
of the different EM zones. Table “A” shows the different water holding
characteristics at different locations, along with the EM reading at that point
and total area within the paddock in that zone. As you can see from the table there was a
large variation in water holding capacity between the different sites.
|
Table A
|
Full Point (mm)
|
Stress Point (mm)
|
DualEM
0-60cm
|
Zone Area
(ha)
|
|
Site 1
|
187
|
139.5
|
4.77
|
0.6
|
|
Site 2
|
233
|
178
|
6.05
|
3.0
|
|
Site 3
|
228
|
178
|
5.77
|
5.4
|
|
Site 4
|
232
|
178
|
6.20
|
7.2
|
|
Site 5
|
181
|
134
|
5.44
|
3.6
|
|
Site 6
|
106
|
70
|
5.01
|
0.6
|
In the season of the case study the pivot watering this block did not have variable rate irrigation (VRI) installed. With HydroServices providing weekly monitoring throughout the season the irrigation applications were well managed using the conventional irrigation system. Through this the grower was able to keep water up to the lighter zones (zone 1 and 5) to stop any potential yield loss on those areas due to water stress.
At harvest time the yields where mapped and yield data
processed by Agri Optics, enabling it to be viewed on our VA Gateway software
platform. The map below shows yield variations in the crop of autumn-sown Phoenix
wheat with the six locations marked. After harvest the yield in the different
sites was then compared to see how they matched up relative to each other and to
what the grower expected.
 |
Figure 2: A Yield
map of Phoenix Wheat harvested after the first season of the trial, with the
neutron probe sites marked on it.
|
From the results in table “B”, it can be seen that the
heaviest parts of the paddock (where you would have expected the highest yield)
underperformed when compared to the lighter soils which received the correct
amount of water.
|
Table B
|
Full Point (mm)
|
Stress Point (mm)
|
Wheat Yield (t/ha)
|
EM 0.60m (ms/m)
|
EM 1.5m (ms/m)
|
Zone Area
(ha)
|
|
Site 1
|
187
|
139.5
|
17.56
|
4.84
|
10.95
|
0.6
|
|
Site 2
|
233
|
178
|
12.31
|
9.28
|
16.30
|
3.0
|
|
Site 3
|
228
|
178
|
13.26
|
8.18
|
15.02
|
5.4
|
|
Site 4
|
232
|
178
|
15.58
|
7.85
|
14.71
|
7.2
|
|
Site 5
|
181
|
134
|
16.48
|
5.18
|
12.52
|
3.6
|
|
Site 6
|
106
|
70
|
10.00
|
3.80
|
10.32
|
0.6
|
By over watering the heavier soils not only was the excess
water potentially wasted with an increased risk for leaching nutrients but
there was also a yield penalty in the order of 3-4 t/ha. At $400/t for wheat
this would equate to a loss of $1200-$1600/ha.
The following winter Lindsay NZ (formally Precision Irrigation) retro-fitted Growsmart Precision VRI on the pivot, enabling the different soil zones to be irrigated with water
application matched to soil characteristics and crop needs. Any variability in
crop yield was then down to agronomic factors other than water. Due to watering
in the different EM zones, yield variations and crop ripening evened out. This allowed
management to concentrate on other factors which had influenced on the final
yields.
 |
Figure 3: The yield
map from the season following Growsmart VRI being installed on the pivot, showing
the variation due to differences in EM soil characteristics had been minimised.
|
For any more information about this blog or more information
on EM surveying or to have your EM survey ground truthed by HydroServices
please get in touch (to email click on the personal profile pictures on the right).
Chris Smith (chris@agrioptics.co.nz) - Agri Optics NZ Ltd
