The proliferation of precision ag practices across North America is pushing more and more growers to begin soil testing – and those who already are, to ramp up their efforts. A common question they encounter: Which is better, grid sampling or zone? Our experts outline the pros and cons of each... and uncover some surprising middle ground along the way.
If you ask Markus Braaten which is better, soil testing by grid or by zone, don’t expect a quick response. According to the manager of agronomic precision services with Agri-Trend Knowledge Team...it depends.
“Grid sampling is looking at the soil attributes in a particular grid point,” he says. “There are two problems with this: Does that grid point truly represent the spatial variability of that particular attribute? I’ve done soil tests on a quarter-acre grid that had a four-fold difference in potassium levels.”
The second problem is that grid samples only tell the story of the soil, not other factors that could shine light on the cause of variability, such as topography, drainage, water-holding capacity, etc. “It assumes productivity is purely the function of what I can see on a soil test,” he points out. “But oftentimes what I see on the soil test impacts productivity, but it doesn’t dictate it.”
However, there are situations in which grid sampling is the best and most cost-effective option, says Braaten. “When you’re considering a management strategy that addresses a soil attribute such as pH and the decision whether to lime, the best way to understand that is to do a grid sample.”
The challenge, then, is determining the right grid size. “No soil attribute adheres to a perfect grid, so this can become the problem,” he cautions.
To help growers navigate this question, we’ve polled the experts to come up with an overview of the pros and cons of each, and a look at how this trend will evolve in the future.
Don't miss Part 2 in this series!