Soil pH and aluminum toxicity

Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.

This spring, several wheat fields have came to our attention where spots had a pH near or below 5.0. Under these conditions, aluminum is in a soluble form and is taken up by crops, inhibiting cell division in plant roots and reducing growth. Plants with aluminum toxicity may also experience calcium or magnesium deficiencies and appear stunted with chlorotic (yellowish tissue rather than green) areas.

When scouting your fields this spring, look for areas of reduced plant growth and chlorosis. Occasionally, small acidic spots develop in fields. Acidic spots tend to develop first in low areas as calcium and magnesium are leached from the soil. When poor growth occurs in small areas of a field, it is important to determine the cause. These can be indicators of increasing acid conditions in the field as a whole, and the need for liming. Dolomitic limestone, which contains both calcium and magnesium carbonate, should be applied on acidic soils that are magnesium deficient. Additionally, proper soil pH is important to promote favorable microbial activity and maximize the availability of micronutrients.

Mineral soils in Michigan tend to become acidic over time from precipitation (which has an average pH of 5.7), the decomposition of soil organic matter, the weathering of clay minerals, the application of nitrogen fertilizers, and the leaching of calcium and magnesium. However, soil pH does not change rapidly in most soils and acid soil conditions can be prevented with monitoring. Soil pH should be determined at least every three years. We recommend collecting 15-20 soil cores from a relatively uniform area to represent no more than 25 acres. Non-uniform areas (different soil type, topography, management history, etc) should be sampled separately. To correct low soil pH, apply lime based on soil buffering capacity (cation exchange capacity) or buffer soil pH test. Particular “problem spots” in your field should be avoided when testing the field overall, and should be tested separately to determine the nature of the problem in that particular part of the field. Plant tissue samples can also be collected from the good and bad areas of the field to allow comparison.

For soil pH or plant tissue nutrient analysis, samples can be submitted to the MSU Soil and Plant Nutrient Laboratory or dropped at your local MSU Extension office. Protocols for proper tissue sampling can be found at: http://www.css.msu.edu/SPNL.

To send samples directly to the laboratory, the address is:

Soil and Plant Nutrient Laboratory
A81 Plant and Soil Sciences
Department of Crop and Soil Sciences
Michigan State University
East Lansing, Michigan 48824-1325

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