Fertilizer and Micronutrients
A micronutrient is an element essential for plant growth but is required in very small amounts. Until recently, farmers have been able to rely on the natural quantities found within the soil for adequate crop production. With yields continuing to increase, micronutrient availability will develop a more important role in complete fertilizer programs for top yields. Key points to remember in the consideration of micronutrient fertilizers include:
• The category of micronutrient includes the boron, manganese, zinc, copper, iron, molybdenum, nickel, and chlorine. Today the most commonly applied micros are boron, manganese, and zinc.
• While all crops require micronutrients in some amount, not every operation or field is guaranteed to see a response if they are applied. Yield response revolves around overall management and therefore manage the basics first (correct hybrid, N-P-K-S, lime, etc.).
• Poor conditions or management (drought, compaction) can induce micronutrient deficiency even if the environmental supply is optimal.
• Micronutrients are need in such small amounts that a deficiency and toxicity are not far apparent. Growers should work closely with their fertilizer suppliers to apply micronutrients in the proper form, at the right rate, and in the correct place for utilization.
• Deficiencies that are serious enough to become visible are very rare and in many cases have never been seen in Iowa.
• A combination of crop scouting, soil tests, and tissue tests will likely be required to diagnose low micronutrient levels.
Micronutrients have a variety of roles within a plant.
- Boron is an important component of cell walls and reproductive structures. If a deficiency occurred, it would be most likely in soils that are low in organic matter, sandy, or highly weathered. Drought can also cause decreased boron uptake.
- Manganese plays a role in plant enzymes, germination, and photosynthesis. Heavy, poorly-drained soils with higher pH are most susceptible to manganese shortages.
- Zinc is required for protein synthesis, metabolic reactions and early growth. Springs that lead to cool wet soils in combination with high soil pH or excessive soil P levels can lead to a zinc deficit.
- Copper activates enzymes and catalyzes certain reactions with a plant. Very small amounts of copper are required for crop production but if there were a deficiency it would be found in high organic soils.
- Iron is essential for energy transfer, nitrogen fixation and chlorophyll formation. We see iron deficiency as bright yellow/green chlorosis and is most common in areas of high pH and organic matter.
- Molybdenum is key for nitrogen management within the plant. Acid soils are more likely to show this deficiency and it can be fixed by correction of pH.