Friday 12 June 2015

"The Whole Shebang" - EM Mapping, Soil Moisture Measurement and VRI

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