Published on 02/03/16

UGA expert advises farmers that it's not too late to soil sample their fields

By Clint Thompson

Of the mindset that it’s “better late than never,” University of Georgia Cooperative Extension soils and fertility specialist Glen Harris advises Georgia farmers to take samples of the soil in their fields for analysis before applying fertilizer.

“It’s tempting to say, ‘I just won’t bother soil sampling this year,’” Harris said. “But with budgets tight like they are, you just don’t want to guess what fertilizer you need, even if you sample late this year.”

According to Harris, it’s commonplace for Georgia’s producers to sample their fields every year to see the levels of nutrients still in the ground and what nutrients farmers need to be mindful of adding during the upcoming growing season.

Some farmers have just concluded the last growing season with their peanut and cotton harvests, and Harris is worried that some farmers won’t take the time to properly sample their soils.

With commodity prices low for cotton, corn and peanuts, soil sampling provides producers, at an inexpensive cost, a proper reading of the level of nutrients in the soil.

“Why pay money for additional fertilizer needs if you don’t have to? You can guess that you might need 100 pounds of potassium per acre on cotton, but what if you find out you’re a little better off than you originally thought, and you only need 50 pounds? That makes a big difference over a lot of acres,” Harris said. “I think our growers understand the importance, and they’re sampling every year.”

Sampling a field involves collecting soil 6 to 8 inches below the soil line. In fields with reduced tillage, Harris says it’s only necessary to take the top 4 inches.

The key to a proper soil test is to collect a representative amount of the whole field, Harris said. “Avoid weird spots like a ditch. If you get a representative sample and send it off to the lab, they only use a tablespoon of soil to represent the big area, so you want to be careful to sample an area that best represents that field,” Harris said.

UGA Extension recommends sampling be done in the fall, right after crops are harvested. But in circumstances like the previous growing season, during which rain was prevalent during harvest time, a delay in harvest could push sampling back to January and even February.

Harris cautions farmers about sampling high parts of fields. If certain areas of a field stay wetter than others, farmers have a tendency to sample high parts of a field that are easy to get into, he said. This can produce an inaccurate soil test because nutrients can change from the top of a hill to the bottom.

He also recommends that growers grid sample their fields, which involves collecting samples on specified blocks of acres within a field. Instead of one representation, the grower has multiple samples, usually on 2.5-acre grids, that provide a more defined level of variability throughout the field. This is especially helpful with pH and liming, as variable-rate fertilizer applicators can supply accurate levels of lime or nutrients in the soil where they are most needed.

“The beauty of doing it the first time is that you find out how much variability you have in that field. If you have no variability, it makes no sense to use variable-rate (applicators), but that rarely happens in south Georgia,” Harris said.

Harris insists that all 16 nutrients a plant needs to produce high yields are important. Some are classed as micronutrients, such as boron, zinc and manganese, because plants don’t need much of them, he said.

“All nutrients are important to the growth of a plant. For different crops, we have different ways of supplying those nutrients and some are more important for certain crops than others,” Harris said.

To learn more about soil testing in Georgia, visit

Clint Thompson is an agriculture writer based in Tifton, Georgia.