Publications Plus online catalog
This Land
50 Ways Farmers Can Protect Their Groundwater
50 ways 57 ways 60 ways

2. Test the Soil

Soil testing

Soil testing helps you find the balance—applying enough fertilizer to maintain productivity without applying so much that it becomes uneconomical or environmentally hazardous.

To ensure that your soil test is accurate, collect samples to the proper depth—7 inches when testing for pH, phosphorus, and potassium. Collect an adequate number of samples, typically from each 2-1/2-acre area.

Collecting samples Collect samples from precisely the same areas of the field that were sampled in the past and collect samples at the proper time—late summer and fall. Sampling every four years is strongly suggested.
testing for N Because of nitrogen's high mobility in the soil, testing for N has not been consistently reliable. However, the drier parts of the Corn Belt have had some success with both the early spring nitrate-nitrogen test and the pre-sidedress nitrogen test.
Tissue testing Tissue testing of young cornstalks is not reliable for indicating nitrogen availability in the field, but tissue testing of mature cornstalks shows promise. Iowa State researchers reported that the end-of-season cornstalk test deserves attention as a tool to compare and refine N fertilizer recommendations.
monitor nitrogen levels Research indicates a close link between chlorophyll content and nitrogen content in the leaves. Therefore, some specialists in the drier parts of the Corn Belt recommend that you monitor nitrogen levels with a chlorophyll meter beginning a little before tasseling. These specialists suggest you use the chlorophyll meter to schedule your last 50 pounds of nitrogen per acre, not your first.
soil tests for phosphorus and potassium In contrast to testing for nitrogen, soil tests for phosphorus and potassium are well-established and quite effective for determining P and K needs. The most useful test for phosphorus is the P-1 test, while the most frequently used and best-calibrated test for potassium is ammonium acetate exchangeable K.

University of Illinois Logo