Signs of a Lack of Nitrogen in Soil

Causes

• Nitrogen is often one of the first nutrients to become deficient in soil. According to the University of Minnesota Extension, long-term planting, even with crop rotation, can deplete the soil of nitrogen. In sandy soils, excessive rain can cause nitrogen to leach away. Heavy and frequent rains can also lead to denitrification, which makes nitrogen unavailable to plants. A low pH, which indicates acidic soil, can make it difficult for plants to absorb nitrogen.

Symptoms

• Nitrogen deficiency generally causes plants to turn a light green color, becoming increasingly yellowish as the deficiency becomes more severe. The older leaves -- those at the bottom of the plant -- can become completely yellow and die from the leaf tips inward. Specific symptoms vary depending on the particular crop, and can include poor kernel fill, stunted growth and low-grain protein. Be sure you know what healthy plants are supposed to look like before you attempt to diagnose nitrogen deficiency.

Considerations

• Many nutrient deficiencies cause similar symptoms. Yellowing leaves, for example, can be caused by a lack of magnesium, sulfur or molybdenum, just to name a few. The symptoms of nitrogen deficiency can also be similar to injury from propanil, imidazolinone and sulfonylurea herbicides. This can make picking out the specific problem tricky, and the best way to tell if nitrogen is lacking in your soil is to get a soil test from your nearest university extension office. The test results include nutrient levels, pH levels and recommendations for soil amendments.

Solutions

• Organic materials used as fertilizer, which include alfalfa, wood chips, corn stalks and various animal manures contain nitrogen, and their addition to soil can help to replenish this nutrient. Many commercial fertilizers also contain high nitrogen levels. Look for products with the words "ammonium," "nitrate" or "urea" on the packaging.