Soil sampling after harvest

Knowing the existing soil nutrient levels in the fields can help cut down on your fertilizer bills. Charlie Wortmann is a soil fertility specialist at the University of Nebraska. He recommends testing soil once every four years.

The process can be done in several ways, but he says the samples should represent fields, or areas within fields no larger than 40-acres for the best accuracy. Take one sample of soil from 12 sampling points for each part of the field.

"Often you do that by management zone," says Wortmann. "You know that there are some differences in soil, or management history, or yield, and so you look at different parts of the field differently to see if they need different management."

In maybe once every ten years, do grid soil sampling where one sample is taken every two-to-two-and-a-half-acres.  Because it’s more intensive, the results can be put into spatial information tools like GIS to create a map of nutrient availability across the field.

Wortmann says soil testing should determine at least five important properties.

"First we want to look at pH and organic matter, definitely phosphorous, potassium, zinc. So, those are the five most important properties, at least for us in Nebraska," he says. "And, of course you can test for other nutrients and other properties, but that’s sort of our basic package."

Fall is a good time for soil sampling. It allows more time to get results back from the laboratory, and use the information in designing the fertilizer management program for next year.