Wayne Flanary, Regional Agronomist
The high prices of phosphorus and potassium fertilizers last year had growers reducing application rates. Now is the time to soil test and determine the application rates for your next year’s crop.
Soil tests are good for three to four years. Soil test values will not make great changes within this time frame if properly sampled. Therefore, old tests will still be good to use. If you have tests older than four years, then it is time to retest.
Soil testing is a better way of determining nutrient needs than using crop removal. With crop removal, plants can take up more nutrients than they actually need. Also, areas across the field yield differently creating additional variability of trying to replace what was removed.
Be sure to soil test at six to seven inches deep. The calibration research was conducted at this depth and you need to follow the same practice.
If you sample too deep you can dilute soil test values and this will give you low readings. Too shallow can give too high of readings. This is important with phosphorus, and potassium in determining liming needs.
Point samples are composite cores mixed together to obtain a representative test from a small point area generally geo-referenced. The key is taking enough samples to represent this point. The point sample then is used to make geo-referenced spread maps which adjust rates as spreading equipment moves across the field.
Also, sampling from an area representing several acres should have multiple cores taken to create a composite sample to represent an area. We recommend taking a soil test on more than 20 acres. Also, just taking one core sampling to represent an area will not be accurate. Use multiple sampling soil cores to represent an area. The more, the better.
Our high yields will be removing nutrients from the soil and will be trucked to town as grain. It is important to stay on top of this as we move into the future. Some University professors predict that we will grow 300 bushel corn in the not too distant future.
The soil test boxes can be picked up from local Extension offices. Many soil tests are already being taken and are being sent to the University of Missouri Soil Test Lab. Also, many dealers are also sending soil tests to commercial labs.
Fall is a good time to have soil samples taken before application of phosphorus and potassium fertilizers. Our general recommendation is to soil sample in fall, then always sample in fall. If sample in spring, its best to continue to sample in spring. But, if you need tests, its best to get things sampled when you can get to the field. The priority is to get the tests.
For more information, contact Wayne Flanary at 660-446-3724 or Heather Benedict at 660-425-6434, Regional Agronomists, University of Missouri Extension.
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