It may seem early to be thinking about spring fertilizer application, but fall or winter is the best time to take soil samples for spring and summer forage crops, Dwayne Beaty, University of Arkansas area extension agronomist, said.
"Waiting until spring for soil testing leaves little time to plan for important fertilizer and limestone application decisions. In addition, he said there are other benefits to soil testing in the fall or winter.
“The majority of soil tests go in to the soil testing labs in the spring,” he said. “You can get a more timely turnaround on the analysis by doing it in the fall. It is also better to put out phosphorus and potassium in the fall because you have the wintertime for the P and K to move into the ground and become available for the plant. Certainly, if you need to apply lime, fall is the best time to apply it so the nutrients will be available in the springtime for plants to use it.”
Vance Hambelton, University of Missouri agronomy specialist, added, “After the growing season, the plants have already used what they are going to use and there is not going to be a change or loss in nutrients."
To get a good sample, Hambelton said he recommends taking several sub-samples.
“If you are testing a 20 or 40 acre field, for one soil sample, you need to have 10 to 20 core sub-samples over that entire field from the surface down to 6 inches deep. Mix all the sub-samples together, pull out a representative sample – about a cup to a pint – from the mixture, and take that to be tested.”
Hambelton said taking sub-samples provides a better representation of the whole field. However, he said producers should avoid taking sub-samples in areas that are not typical of the entire field, like watering areas or shade trees.
“You will get a misrepresentative sample if you test in those areas because more manure and urine are deposited in those areas and it won’t be representative of the whole field,” Hambelton said.
Beaty said he recommends producers soil test every three to five years. In some situations, however, he said more frequent testing may be necessary.
“If they have to put out a lot a pH, they could test again after two years to see where they are to do some advance planning,” Beaty said. “Lime is such a high input; it needs a little more planning than the fertilizer.”
Producers also may use soil testing for tax planning purposes, Hambelton said. He said by testing in the fall, producers not only have information about their fertilizer and lime needs for the upcoming year, but also they can pre-buy fertilizer and put the cost on this year’s tax return.
