Did your soybeans or alfalfa not yield what you were expecting this year? Well fall is the perfect time to pull soil samples and see what’s going on under ground. Whether it is soil fertility or testing for soybean cyst nematodes (SCN); these are both factors that can drive yield.
In soybeans, SCN can cause 30% yield loss overtime and knowing the levels in your field can help explain some of the losses. If you haven’t sampled in a while or never have sampled your fields now is the time to do this. The Nebraska Soybean Board is sponsoring free SCN testing this fall into next year. These samples are processed at the University of Nebraska Plant and Pest Diagnostic Lab. To sample pull 15-20 soil cores at 6-8 inches across your field or in low yielding areas. These samples can be pulled at any time and in any previous crop, it does not have to directly follow soybeans. Once you have the samples collected these can be sent to Nebraska Plant and Pest Diagnostic Lab or you can contact your local extension office for more information. While you are out pulling some samples for SCN, cruise over and check out your alfalfa fields as well.
If you saw lower yields this year in your alfalfa then soil sampling may be the next step. If you visually have no signs or losses, then it’s time to look under ground. Soil fertility is key to maintaining yield and alfalfa fields should ideally be sampled each year to check pH, potassium, and phosphorous levels across all soil textures. Note, if your field is sandy, eroded, or highly weathered, you may want to test for sulfur as well. It is important to remember that compared to row crop ground or grass hay, nitrate-nitrogen is not a concern with alfalfa’s ability to fix atmospheric nitrogen. With that said, digging a few plants up and checking nodulation will provide some insight to plant/soil health as well.
To collect your soil samples this fall you will need to collect soil cores at 8 inches or if the field was previously sampled at 6 inches stay with the historic depth for comparison. Soil samples pulled at 8 inches are used to determine soil pH, lime need, phosphorus, potassium, and sulfur. When pulling the samples it is very important to be at an accurate depth, because values change the deeper or shallower we go in the profile. For example potassium and pH may increase, decrease or remain the same with deeper samples, causing confusion when attempting to apply lime or potash. You can use a file or a sharpie marker to measure 8 inches on your soil probe to make it easier, when pulling cores.
When sampling there are a few ways you can decide to pull the cores: by soil type, grid, or representative samples for every 40 acres. For alfalfa fields, by soil type or representative samples for every 40 acres would be the most cost effective choices. When pulling samples you will need to pull 10-15 random soil cores across your soil type or 40 acre area to be represented. Those soil cores need to be mixed together in a plastic bucket. From there take about a pint of soil and place in a bag to be analyzed. Repeat this process across the field for every 40 acres or by the soil types in your field. You can also sample smaller areas for more accurate results depending on time and cost.
Then package and label samples for submission. Once you have your results reach out to your fertilizer dealer, agronomist, or extension educator for more information and how to build a profitable alfalfa program. So whether you are pulling soil cores for alfalfa or testing your soybean fields for SCN levels, get out and sample your fields this fall if possible.