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The PSNT from Field to Lab: How to Ensure Accurate Results

Daniel Kaiser and Fabian Fernandez

Once you’ve taken the soil samples in the field, it’s time to send them to the lab for analysis. Good soil management from field to lab is imperative to getting accurate results from your samples. Watch Extension Soil Fertility Specialist Dan Kaiser explain best management practices for the PSNT test from the field to the lab, and read on for more advice.

What kind of bag should I use to store and submit my samples?

Your three choices for storing and submitting soil test samples are hardware bags, Ziplocs or bags provided from your soil lab. Ziplocs work well for wet soil, as the bags won’t degrade with the moisture and they keep the soil moisture intact. However, soil in Ziploc bags will not readily dry and if stored in a warm place can serve as an incubation chamber for soil microbes, resulting in a chance in the nitrate concentration of the soil sampled. In order to minimize change in nitrate values, keep the samples cool.

Most soil labs prefer samples be submitted in a bag that they provide because they’re set up to handle those bags throughout the lab process. Some of these bags are lined, meaning no air is exchanged in the bag, which can reduce aeration and drying. The goal no matter what type of bag you choose should be to minimize microbial activity so the nitrate levels in your sample remain at the same levels that you sampled from the field.

Should I dry my sample?

This depends on how quickly you can submit the samples to the lab. If you can bring the samples to the lab right away, you won’t need to dry the samples. Most labs have rapid drying capabilities, which get rid of the soil moisture and virtually stop microbial activity in the soil.

If you can’t get to a soil lab right away, you may need to dry the samples on your own.

Do I need to mix my samples? 

Soil labs only use one to two grams of the soil sample you submit, so mixing and homogenizing your sample is imperative. This way you ensure that the small sample that is tested represents the nitrate levels of your entire sampling area.

How do I interpret my results?

Generally, a result of 26 ppm means a field has all the nitrogen it needs. Results showing 21 to 25 ppm will be adequate. No need to apply supplemental N. At 20 ppm and below, a field needs supplemental nitrogen. When deciding how much N to apply, look at the history of the field, past management practices and weather thus far in the growing season. In corn on corn fields, we recommend applying between 40 and 70 pounds of nitrogen. With corn following soybeans, apply between 30 and 50 pounds.

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Support for this project was provided in part by the Agricultural Fertilizer Research & Education Council (AFREC).

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