Iowa State’s Antonio Mallarino came to the Info Ag conference in St. Louis with a gauntlet to throw down:
“We have lower grain prices, stable fertilizer prices,” he said, “and real or perceived serious agricultural impacts on water quality.”
Mallarino’s pitch: Better soil testing pays. Yield levels must be considered.
“Yield can vary greatly in fields,” Mallarino told the crowd. “It varies a lot in many fields, especially in the corn belt.”
He began his talk by pointing to soil sampling as the most common and important error in soil testing for phosphorus and potassium.
“Labs get the blame most of the time, but the sampling most often is the problem,” Mallarino said.
Where do the sampling problems crop up? Depth consistency issues, the number of composite samples in a field, and the location of samples.
Some of the problems come from assumptions behind common sampling methods, he told the crowd.
“The theory is that soil formation factors and topography may influence nutrient levels, and soil physical properties may influence yield potential,” Mallarino said. “The problem is that …50, 60, or 70 years of management have masked the impact of these things.”
Different soil sampling methods can produce very different prescription maps he said, showing the slide above.
In most fields there is a lot of variability, Mallarino said. On top of that, few sampling methods consider yield as they should.
He prefers unaligned or random grid-point sampling, and he’s an unashamed advocate of devoting more resources to the practice.
“Farmers are spending a lot of time on a lot of things and need to spend the time on core sampling,” he said.
Mallarino said that one of the reasons he pushes greater sampling is instead of two, three samples, with fifteen, twenty, they can trust that sample more.
“This is important for profits, for efficacy, for conservation of resources,” he said.
“The main takeaway is, don’t apply phosphorus to high-testing soils,” Mallarino said. “It is not good for farm profitability, efficient fertilizer use, or water quality.”
Precision ag professionals have a responsibility to tell clients to spend money where it really counts, he said.
“Soil sampling is expensive—that’s what people tell me... You should tell them to invest in soil sampling,” Mallarino said. “Good technologies will not work well with the wrong fertilizer recommendations.”
“A great technology, used wrong, is still wrong.”