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Determining how much fertilizer to apply this spring is a lot like determining how much oil your tractor needs.
“You pull the dipstick and check the oil, right? What’s the dipstick on your soil? Soil samples and the soil test,” says Ray Ward, president of Ward Laboratories in Kearney, Neb.
But Ward says you need to interpret that soil test in relation to crop removal.
“When the crop is growing, it’s taking up nitrogen, phosphorus, potassium and other nutrients in the plant tissues. When you harvest the grain, the plants nutrients are removed from the field,” he says. “Then you do it again the next year and when you do it for 50 years, think about what you are doing to your soils. You need to replace the nutrients.”
With residue decomposing at the top of the no-till soil structure, that’s where you have your highest levels of fertility, Ward says. Fertility levels will decrease as you move downward in the soil.
“Some people say that what you have is nutrient stratification and you need to do something, but that’s good because the nutrients are up where the plant needs it,” Ward says.
He suggests taking 8-inch soil samples at the same time, depth and conditions each year, and then track back the fertility tests to see trends over time. If you see higher levels of fertility, cut back. If you see them falling, increase the amount of fertilizer.
For testing levels of chloride and nitrate…