Growing plants depend on soil for water, nutrients, and root growth. Additional nutrients should be applied when essential elements are at low levels. When nutrients are limited, plants will often show distinctive deficiency symptoms. Extreme deficiencies will lead to death of the plant. By the time nutrient deficiencies appear, yield potential may be greatly reduced.
In contrast, high levels of nutrients can also reduce plant growth, and if toxic levels are reached cause plant death. High levels of one element can also result in a corresponding shortage of another nutrient. Early symptoms of a low nutrient level or imbalance are seldom evident. When the level of an essential plant nutrient is below that required for optimum yields or when there is an imbalance with another nutrient, additions of the limited nutrient will be needed. A soil test is essential in determining nutrient levels in the soil.
Before planting a crop, sample the soil and have it tested for nutrient levels. A reputable soil test laboratory, such as the University of Minnesota laboratory will give fertilizer recommendations based on the soil, crop and desired yield goal. The University lab tests for phosphorous (P) potassium (K) and pH (acidity of the soil) for $12.50 per sample. Micronutrient tests are available for additional costs but are not generally recommended for homeowner use. For growing production crops in the field, a sample can represent from 5 to 20 acres depending on the field situation. Make sure the sample represents the area you wish to fertilize - for example, gardens should be sampled separately from lawns.
Soil tests provide the basis for evaluating the fertilizer needs of most field and vegetable crops as well as landscape plants. This includes lawns and gardens. For information on taking a soil sample listen to script number 286. For soil test forms and sample bags contact your local Extension Service office or the University of Minnesota Extension Service Soil Testing Laboratory at 612-625-3101.
Reviewed by Brad Carlson 2009.
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