Calling in the SWAT team of crop fertility planning


If you’re like many western Canadian grain farmers, you put the bulk of the year’s fertilizer on in the spring. That practice means you need the most informed data in front of you before the growing  season to determine how much of which nutrient goes where — preferably as close as possible to amount needed to achieve the maximum possible yield.

What’s the best way to get to that rate? We’ve had access to combine-generated yield maps, variable rate application equipment, and satellite imagery for a long time. Several different companies have developed their own approach to prescription mapping, all on some variation of using these tools, plus perhaps some other layers, such as soil texture, soil tests, and more.

CropPro Consulting, based in Saskatchewan takes the SWAT approach: looking at yield potential and fertilizer needs from the ground up using soil, water, and topography (SWAT).

As Wes Anderson, senior fertility specialist with CPC, explains the SWAT model is less about delineating low, medium, and high yield zones, and more about understanding the root cause of yield and normalized difference vegetation index (NDVI) variability.

A yield map tells you what happened in any given year (or year over year) but doesn’t really explain the why, he says.

“Low yield can be for many, many different reasons. Seeding mishaps, salinity, insects, flooding — but they all should be managed differently,” Anderson says. “A traditional (VR) model might delineate an eroded knoll with a saline depression (as the same), but really they should be managed completely differently.”

Anderson says that field mapping and fertility planning has evolved from those early years of satellite maps, where he says they now create prescriptions from the ground up (not the sky, down) starting with electrical conductivity (EC) mapping, then building the layers with topography and a water model for a deep understanding of the soil. It’s all in the name of not mapping for low, medium, or high yield potential, but instead mapping a field’s potential responsiveness to a fertilizer application and water-driven yield potential.

Does the SWAT model completely eliminate the need for NDVI or aerial imagery? Anderson says not necessarily. “It frankly depends on the application. In crops where you’re going to be making decisions (and applications of nutrients)  in-season, NDVI imagery is a great fit, because you need to know what’s happening right now.” But in Western Canada we’re potentially applying 100 per cent of nutrients up front, at seeding, and that management scenario is more informed by the ground’s potential than what you may see on an image.

Listen to the full interview with Wes Anderson, senior fertility specialist with CropPro Consulting below:

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