The end of May and early June has traditionally been the time for corn nitrogen (N) side dressing. Farmers now put N on pre-plant, at planting (pop up directly on the seed), beside the seed (2x2, 2x4 inches), or later with high boys and ‘Y’ drops. Corn is a big user of N but N may not always be what is limiting. Recent research shows that majority of corn nutrients are processed by soil microbes first which efficiently then feed the plants.
In a healthy soil, feeding microbes directly may be more cost and nutrient efficient than feeding corn. While we can feed the corn inorganic (no carbon, N) elements, new research shows corn can absorb amino acids and proteins directly. Many Extension publications are outdated without this new information. If you question how this is possible, think about how herbicides work in plants. Glyphosate (Roundup) is a large molecule (much larger than amino acids) absorbed by plants.
Soybeans and corn are two plant species infected by Arbuscular Mycorrhizae Fungi (AMF). There are about 250 species of AMF and they are a “Keystone” species, essential to human and animal survival. They are like hair extenders on plant roots, increasing the root surface area 20X, bringing back essential plant nutrients in exchange for sugar. Recent discoveries show AMF ingest bacteria and leak out amino acids and proteins that can be transported directly back to a plant. Healthy soils full of microbes create a healthy banquet for plants to feast on, either directly (microbes themselves) or indirectly though microbial soil wastes absorbed by the tips of growing plant roots.
In this biological system, organic nutrients (carbon-based fertilizer) are more plant energy efficient than inorganic (no carbon, traditional fertilizer). The plant has to supply energy and carbon to convert simple inorganic nutrients into carbohydrates and proteins. If it is already an amino acid or protein, that is plant energy saved so the plant can use that energy for other things. As humans interested in food for ourselves, we hope the majority of that saved energy is used to increase crop yield. Unfortunately, plant yield is generally the last thing to increase. Plants spend energy growing, defending themselves from pests (insects, diseases, weeds) and improving the soil for future generations (somewhat similar to humans building better homes and farms). To get the highest yield; soils have to be healthy, aerobic, have good soil structure, and have good drainage. The soil microbes and plants work together, investing energy and carbon (humus and active organic matter) to make their home a better place to live.
If microbes are so important to plant and soil health, how might our fertility system be changed to improve microbial growth? Adding humic acid (3%) and glucose (3%) to fertilizer have proven effective at improving Nitrogen Use Efficiency (NUE). Our current NUE is only 30-50%, so a lot of N gets wasted. Adding humic acid increases the retention of soil N and the glucose (molasses) is a complex sugar that forms the backbone for microbial amino acid and protein synthesis. While these products might not immediately increase corn yield, they do greatly increase NUE, which can save farmers money on fertilizer costs. Corn yields will increase once the soil environment becomes healthier.
Sulfur (S) is another element that is needed to improve NUE. Sulfur is needed by microbes to form essential amino acids like cysteine and methionine. If your corn leaves have yellow streaks, sulfur may be missing. With the Clean Air Act, our soils are getting less S out of the air for free and are becoming more S deficient. Gypsum or calcium sulphate is a good source of both Ca++ and SO4- for plant growth. Calcium is a major regulator of over 140 plant enzymes that regulate reproduction. The sulfur is needed for amino acid production.
The 4R’s for gypsum are the right rate, 250-300#; right source, wall board grade or mined gypsum (not flue gypsum); right place, broadcast on corn or soybeans; right time (this is critical), 30-40 days before the corn tassels or soybeans bloom. Both and calcium and sulphate can get tied up in the soil. The soil microbes need these critical elements in the right form at the right time to get the best results. Improving soil health is a journey, not a destination.