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Soil sampling: Develop a plan, get the kits and get it done

Delbert Voight and Nicole Carutis Published on 31 January 2015

The basis for high crop yields comes from a proper crop nutrition program and fundamental soil testing.

Recent surveys indicate that 20 percent of the fields in Pennsylvania do not have a current soil test. With high crop yields, the plant food contained in the soil is depleted more rapidly.

A 200-bushel corn crop pulls 80 pounds of phosphorus (P) and 60 pounds of potassium (K) out of the soil, which is why it is important to get a benchmark as to what nutrients are left. Low K can result in yellowing corn leaves, stalk rot and an increase in mycotoxin susceptibility.

Low pH and low P can result in purpling of the leaves and numerous ear malformations from lack of fertility, all of which could have been avoided with a simple soil test.

Soil test kits available from local extension offices are the best way to indicate the relative amounts of food available for plants. Here are a few points to consider:

  • Have a plan. Determine a method for your farm that allows for timely three-year testing or shorter. Remember, P and K do not move in the soil as much as nitrogen and thus can be managed more consistently.

  • Take samples yourself or be sure a consultant with proper training is collecting them.

  • You need to ensure that the 10 to 15 acres one bag is designed to represent does just that. Errors occur when the sample is taken without regard to ensuring it represents the area to be tested. Some growers try to stretch a bag to more than 15 acres, and that reduces the confidence that the test is accurate.

  • Plan a day to gather the samples. Frozen soil slows down the process. With ATVs and other devices, it should generally be a fairly speedy process. Label the bags first, get them in a box in order, then take them to the lab or local drop-off location for analysis.

  • Don’t forget that those no-till fields need a surface pH test as well to get a handle on any acid roof that might form over repeated N applications. On no-till ground, pastures and alfalfa, take a 2-inch soil sample and test for pH.

    This can be done with at-home testing kits. I recommend the Cornell pH test kit. This might be the most important aspect of your fertility plan.

  • When lime applications are needed on your entire farm, lime one-quarter to one-third of your fields each year. This eliminates one tremendous bill and ensures that pH is maintained for the whole farm.

How many soil test kits do you need? This information should be well outlined for producers that soil test regularly, but sometimes management zones can change slightly over time or with the addition of new data to the system.

When selecting soil testing areas, or management zones, first consider the lay of the land. The top of the knoll is likely going to have a different soil than the bottom of the slope.

Are there any abnormal areas? Wet spots, sinkholes or other irregular areas of the field should not be part of the sample. Sampling zones should be no more than 10 acres in size. The more information available, the more soil sampling zones can be tailored to the needs of the farm business.

Another layer in determining sample areas can be defined by the soil type. A map of soil types for your operation can be found using the NRCS Web Soil Survey. Further information that might influence management zones for a producer is field history and yield data.

If one field has been managed as two fields in the recent past, two different soil tests may show differences in this management although the fields have now been joined.

The data available for collection in crop production seems infinite. There are other ways of soil sampling that may be used in different situations. The most important concept to remember is that one soil sample should contain multiple cores from throughout one field or area. One soil core is not representative of typical field conditions and may skew the big picture on your farm.  FG

Delbert Voight and Nicole Carutis are forage crop educators with Penn State University; this article was first published in the Penn State Extension newsletter, 2014.