Crop Nutrient Status


soybean field

A mixed bag is occurring this year. Some farmers have col, dry soil while others are getting too much rain. Variable weather conditions mean there are a variety of nutrient problems. The most common complaint seems to be slow growing soybeans. Soybeans planted into heavy cereal rye combined with cold nights is resulting in slower soybean growth, especially if it is dry (slow nutrient release). As summer progresses, temperatures should warm up the soybeans should catch up. Rye residue conserves moisture and keeps the soil in a more ideal range for optimal plant and microbial growth later in the season when temperature get hotter, high 80’s and 90’s.

There are several nutrient issues farmers can scout for this year. On corn and soybeans, Boron (B) and Calcium (Ca) deficiency symptoms are noticeable. On corn, look for parallel lines or just slight zipper effects on the outside of the leaf to identify B deficiency. Boron is needed to get calcium into the plant. After nitrogen and potassium, Ca is the most needed plant nutrient. Calcium is a major regulator, activating over 146 key enzymes in a plant. On soybeans, it is harder to see. Look for slight leaf imperfections around the outside edge. For B, soluble forms of B can easily and cheaply be tank mixed with herbicides and fungicides.

On Calcium (Ca), look for imperfections on the interior of the leaf, between the outer leaf edge and the midrib. Again, a zipper effect or parallel lines. Ca deficiency is easier to spot on corn than soybeans. Soybeans sometimes appear to be crinkled or have lots of veins. On both corn and soybeans, healthy plants should have dark green broad leaves that are smooth with few veins. Scouting corn leaves, nutrient deficiencies start showing up when the plant leaves are not flat and they start to become wavy. Corn and sorghum deficiency symptoms are more obvious than soybeans. Calcium can either be applied as lime, gypsum, or as a soluble foliar spray. The cheapest way is with lime or gypsum before or after planting.

A key element that is becoming more deficient is Sulfur (S). Sulfur (S) deficiency and nitrogen deficiency are intertwined. Sulfur deficiency is often associated with yellow streaking corn leaves. Adequate S is needed to make amino acids and proteins. If the nitrate and ammonium levels in a plant get too high, that is due to incomplete conversion to protein. When this happens, expect more insect damage. Insects attack plants that are not as healthy and have excess nitrogen in the leaves. Insects can not digest full proteins, so they will not feed on healthy plants. If you have both Ca and S deficiencies, gypsum contains both elements and it will not change your soil pH. Try to get the white or pink gypsum if possible. Black and gray gypsum has heavy metals in it and is not as effective.

Since glyphosate (Roundup) is used so extensively, most plants are deficient in Manganese (Mn). Glyphosate ties up Mn. Manganese sulfate with some fulvic acid is commonly now foliar sprayed on soybeans. Manganese deficiency symptoms are easy to spot. Soybeans leaves will have dark green veins with yellow between the leaves. Sometimes the leaves can turn brown and black if the problem is severe.

On sandy soils, yellow soybean leaves are a common due to magnesium (Mg) deficiencies. For optimal growth and photosynthesis, plants need magnesium (Mg). Magnesium is often lacking on sandy soils. Epsom salt (magnesium sulfate) plus fulvic acid can be applied to make the plant leaves greener. An element not often discussed is iron (Fe). Iron is needed to active the chlorophyll enzyme. Iron comes in many different chemical valences but the Fe2+ valence is the only one the plant can use. When soil conditions are cold and or cold and wet, the right valence of iron is often lacking. Applying iron oxide (rust) with a fulvic acid as foliar spray can solve this problem. Tomato plants turn a healthy dark green color within hours after this treatment.

In corn, for zinc (Zn) deficiency symptoms look for lily white midribs. Zinc activates 300 enzymes and Zn deficiency could be responsible for 10-30% yield reductions. For copper (Cu), look for excess brace roots. Copper is needed to make lignin, so Cu deficiency plants are more likely to lodge or have stalk rot. Three final nutrients needed to optimize nitrogen use efficiency: molybdenum (Mo) is needed for optimal nitrogen protein synthesis, cobalt (Co) is needed for soybeans nodulation, and nickel (Ni) is used to activate the urease enzyme. Healthy plants with adequate plant nutrition have fewer diseases and less insect damage.