Keeping Nutrients in the Field and Out of the Water

Don’t guess, soil test!
The best way to know the fertility level of a field is to soil test. As soil test phosphorus increases, the dissolved phosphorus in runoff increases. This form of phosphorus is readily available as a food for algae and other aquatic weeds in lakes and streams. Optimal soil test phosphorus for field crops is about 25-35 ppm. Take a look at your soil test reports to see how your fields compare.

Soil tests should be taken a minimum of every three to four years. However, if you are just starting a soil testing program, sample every one to two years to get an idea on how nutrients change in your system.

Apply nutrients based on soil test results and crop needs
The soil test is the producer’s road map to nutrient management. Reports from the Michigan State University Soil and Plant Nutrient Laboratory include MSU fertilizer recommendations. However, if your soil test was from another lab and you would like to convert to MSU recommendations, simply enter the lab results into the MSU Fertilizer Recommendation Program. This program can also be used to get fertilizer recommendations when a crop has changed. Questions on interpreting soil tests can be directed to Michigan State University Extension field crop senior educator George Silva at or 517-543- 4467. Additional information on MSU soil fertility research is available at the MSU Soil Fertility Research website.

Keep nutrients in the rootzone
Getting the right amount of fertilizer on the field is the first step. The next is keeping it there. Fertilizer that has escaped from the rootzone will not benefit the crop or the producers bottom-line. When manure is applied, injecting the manure or incorporating it within 48 hours will protect nitrogen and phosphorus. Fall applied dry fertilizers should also be incorporated. Soils with macrospores or large cracks can lose nutrients to the tile lines. This is a concern with no-till fields and liquid manure that has the consistency of water. Breaking up the soil macrospores prior to application can decrease nutrient movement to the tile lines. Banding commercial fertilizers instead of broadcasting can also decrease risk of nutrient loss.

Fall is a great time to soil test. Take a look at the fertility levels of fields, determine the optimal rate for the 2016 crop and examine the nutrient management options to identify any practices that can be adopted to keep the nutrients in the field and available to the crop.

Soil sampling summary

  1. Sample uniform areas within the field that are 10 acres or less:
    • Soil types, topography, management history.

  2. Collect 20 cores from sample area at the appropriate depth using a zigzag pattern.
    • Tilled systems, sample at tillage depth.
    • Long-term, no-till, 6-7 inches and another sample at 2 inches for determining pH.
    • Pastures with no tillage, 4 inches.

  3. Thoroughly mix the soil cores in plastic bucket.
  4. Fill a soil sample box with composite sample (about 1 cup).
  5. Complete the MSU Soil Test Information Sheet.
  6. Send samples to MSU Soil and Plant Nutrient Lab, 1066 Bogue St. Room A81, East Lansing, MI 48824-1325
  7. For more information visit the MSU Soil and Plant Nutrient Laboratory website.

Source: Marilyn Thelen, Michigan State University 

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