Soil WHC from Seed to Yield – Part 2
In part 1 of this 3 part blog series, we saw how the variability in the soils water holding capacity (WHC) affected our germination and emergence. Read Part 1 here.
Part 2: In-Season Plant Growth Development
This week we will look deeper into in-season plant growth and how the same WHC factors can influence the crop development throughout the entire season. Some things we need to consider are:
- How is root development affected by WHC?
- Does nitrogen loss vary by the difference in WHC?
- Does nutrient availability change with WHC?
All of these factors above have a direct impact on plant development, and ultimately yield. Using the same field example from Part 1 of the blog, let’s look at the difference in WHC or Plant Available Water Capacity (AWC) in each of the different soil types within the field. Using the Virtual Profile system in the CropMetrics Virtual Optimizer (VO) software, we are able to establish the specific AWC in each management zone. The simple to use Virtual Profile system allows us to customize each zone based on default soil type values or specific textural analysis soil sample results while also allowing the user to import any type of management zones to begin with. For this field we are using EC mapped zones, and we have identified a plant AWC of 5.40 inches as the low in zone 1, and a high of 7.20 inches in zone 3. See the image below. Does this variance in AWC really affect plant growth development? Or better question, will Variable Rate Irrigation (VRI) influence a noticeable change in how we manage the crop?
The AWC established above is calculated on a 3 foot rooting depth which we have identified from our CropMetrics soil moisture probe in the majority soil type. This was taken at the corn crop’s VT growth stage estimated by the VO crop growth models and ground truthed by the local Precision Data Specialist (PDS). The moisture probe also shows us a recommended irrigation application rate of 1 inch for the majority soil type. Using this information, the VO VRI software automatically creates a VRI Rx that looks like this:
Notice the application rate range is 0.82”-1.09”, with the average majority soil type receiving the designated 1 inch that the moisture probe recommended. Does the variance in application rates make enough difference to the WHC and the actual plant growth development? Let’s analyze further by looking at actual soil moisture measurements from multiple moisture probes in the field. The probe data on the left (Probe A) is from the grower’s regular application rate of 1 inch in the heaviest soil type (Zone 3). The probe data on the right (Probe B) is from the grower’s VRI application rate of 0.82” in the same soil type (Zone 3). You don’t need to be an expert at understanding soil moisture probe data as we will simplify what this means.
Each line in the graph is measured soil moisture at the soil depth indicated on the left side of graph. The spikes or increases on each line are precipitation events, rain or irrigation. The stair step decreases are the daily water use by the plant. The decline activity at each soil moisture depth indicates the crop rooting activity. Focus on the red circled areas of each graph. Probe A shows little activity at 12” and almost no activity at 20-36” depths. This is caused from over-watering a particular soil type, and in this case, 1 inch irrigation was too much water for Zone 3 and was creating an anaerobic effect to the plant. However, when reducing the application rate to only 0.82” using VRI, we are able to create a more viable growing environment for the plant which in turn created more rooting activity throughout the entire soil profile, all the way down to 36 inches. Which plants do you think are healthier? Which plants will utilize more nutrients? Which plants will YIELD more?
VRI is a simple to use tool that can be implemented on any brand or age of center pivot today. VRI is one single tool that can influence more factors affecting plant growth development than any other tool available. Many times growers attempt to start managing variability in the field using variable rate seeding and/or nitrogen applications. That is often setting limitations up front. However, if we can first improve our water management on each acre, we will create a much healthier growing environment for the plant and will see greater overall improvements. Managing WHC, and the variability of WHC on each acre utilizing a low cost solution like VRI will affect plant growth development significantly, improving yield and maximizing profitability across the entire field.