Soil Test Results in Hand: Now What?

Sep 27, 2023

Crop management should be based on current soil test results
The Federated agronomy team repeatedly declares the value of soil testing – and if you’ve followed their recommendations, you have soil test results to interpret. Here’s how.
Your first option is to contact your Federated Agronomist and let them translate – and make recommendations – but it’s also good to understand the report apart from the information Federated’s ag team provides.
Recall that soil sampling can be done in several ways: grid sampling with 2.5 or 5-acre grids, zone sampling, and composite sampling. Loen noted that samples should be taken at least every four years on every field.
At the time a soil sample is submitted, you can note crop rotation and yield goals – up to three different options – as well as previous crop and intended crop (with a “multitude of crop options,” Loen said).
Craig Loen, Federated’ Osceola ag sales rep, outlined noteworthy facets of soil test results:
The summary results will be charted on page 1 of the report. Note that any recommendations from the lab are for crop removal alone. “You are not necessarily building up the soils if the results on page 1 are low to medium,” said Loen. Plus, higher yields require higher nutrient replacement for the next crop.
Page 2 of the soil test results will include an ag lime section, under soil amendments, that will give you the amount of ag lime needed to raise the soil pH to the buffer pH (listed on pg. 1).
Note that neutral pH is 7.0, and a pH of 6.5-6.9 is optimal for most crops. Lower pH is acidic soil; higher than 7.0 is alkaline soil. “Most of Federated’s soils are acidic; the lower the buffer index, the higher the lime requirement (tons per acre) needed to raise the pH to optimum ranges,” said Loen.
When pH is in the right range, nutrients are available to the plants, not tied up in the soil; they are in soil solution for mass flow to the plants through their roots. Additionally,  herbicides are more effective when the pH is right – low pH reduces their efficacy.
Another important section on the test results report lists macronutrients – nitrogen (N), phosphate (P2O5), potassium (K2O).
N (46-0-0) and P2O5 (18-46-0) are 46% products, so divide the stated N and P2O5 numbers by 0.46 to get the needed lbs./ac. of urea or Super U™ and DAP for your particular crop and yield goal.
Potash (0-0-60) is a 60% product, so divide the stated K2O number by .60 to get the needed lbs./ac.
Talk to your Federated Agronomist to set up soil sampling or with questions about results already received. This information from Midwest Labs offers additional insight into interpreting results.

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