Understanding the Variability of Yield Potential

CropPro has been partnered with Bourgault Industries on their research farm since 2015. The SWAT MAPS agronomy program has allowed Bourgault to showcase their variable rate technology.

Figure 1. SWAT Zones for Bourgault field 13

The backbone of any precision agronomy program is yield potential. How do we define it, manage it, and map it? How can we improve our accuracy?

At CropPro, it all starts with the SWAT MAPS. Each field is mapped with a truck mounted SWAT BOX system that collects high resolution data in the field. That data is then converted to a ten zone Soil Water And Topography SWAT MAP. This map classifies areas of the field that have similar soil properties so they can be treated effectively. These maps of soil potential are the most important step of realizing optimized yield potential.

The SWAT MAP shows how water behaves on the surface but to dial in a fields true yield potential we need to know what is happening at root level and below.

Figure 1 shows SWAT zones on Bourgault field 13: red zones represent eroded knolls with low organic matter; light green zones represent water holding zones with high organic matter and dark green zones can be limited by excess moisture.

In-field weather station technology provides that window. In 2020 we installed 3 weather stations with soil moisture probes across the field. One each in zones 1, 5 and 9 to observe how much plant available water is present and how root activity differs in each zone.

Figure 2. In field weather station and soil moisture probe

The soil moisture probe is equipped with 6 depth sensors at 10, 20, 30, 50, 70 and 100cm. The daily change in moisture values at each sensor is an indication of root activity at that depth. The dry conditions this year reversed the trend of normal root growth. In a normal year we would see root growth in the dryer zones 1 to 5 reach deeper for soil moisture where zones 9 and 10 may not because of adequate or excess moisture. This year those dryer zones couldn’t get established and didn’t have the strength to reach below 50cm where zones 9 and 10 were forced to go deeper for moisture.

Figure 3. Soil moisture sensor graph from Field 13 Zone 10 (left) and 1 (right). Wavy lines represent root activity. Roots at Zone 1 struggled to reach the 70 and 100cm depth where in Zone 10 there is root activity down to 100cm.

Figure 4. July 2020 plant available water map for Field 13. Stars mark station placement

The late season rains gave the soil moisture profile a much-needed recharge. Unfortunately, the above average fall temperatures and increased weed pressure have left moisture values at about 50% of what they were last year.

The SWAT WATER maps use these soil moisture probe readings to model water variability for the field. Now we can fine tune the yield potential for each zone based on its water holding capacity.

One of the most underutilized ways to evaluate yield potential is the harvest data itself. The Bourgault research farm now has three years of complete, processed and cleaned yield data to work with. This allows us to go beyond looking at single year yield and create multi year maps that give us a better idea of long-term trends in yield performance.

In 2020 the addition of the CropScan sensor for mapping protein, soil moisture content gave us additional high-resolution data to work with. Protein maps give us a better picture of what is happening with nitrogen use and how we can affect grain quality.

These are powerful tools for analytics.

Figure 5. CropScan protein map

Figure 6. Multiyear yield for Field 13 normalized to an average of 100bu/ac

The more information our agronomists have the better able they are to provide a fertility recommendation that matches the productivity of the field. We can compare multiple years of yield like in Figure 7 and see that yield performance can differ drastically with environmental conditions.

Figure 7. Canola yields from two years compared to the target yield by SWAT ZONE on Field 13

In 2019 above average moisture conditions allowed the dry zones 1-3 to exceed their target yield. In the dry challenging conditions of 2021, yields were well below targets except in zones 8-10 where water storing capacity is much higher.

In 2020 the CropScan sensor was used to collect protein data from the wheat at harvest. This was used to summarize the average percent protein for each SWAT ZONE and compare it to the yield.

The average protein percent for the whole field was above average but the highest values were in zones 1 and 2 where availability was limited. We can use information like this to adjust the amount and timing of nitrogen applications in future.

Figure 8. Wheat yield compared to percent protein summarized by SWAT ZONE.

By combining the use of multiple forms of technology on a single farm and putting that data to use, we can focus on the true yield potential of each field.

Danielle Epp

Water & Yield Specialist

danielle@swatmaps.com