Micronutrients are essential plant nutrients that are found in trace amounts in tissue, but play an imperative role in plant growth and development. Without these nutrients, plant nutrition would be compromised leading to potential declines in plant productivity. Of the 17 elements essential for plant growth, eight are micronutrients: boron (B), chlorine (CI), copper (Cu), iron (Fe), manganese (Mn), molybdenum (Mo), zinc (Zn) and nickel (Ni).
There is increasing interest from the agricultural community in micronutrient fertilization for a variety of reasons including: 1) soil erosion and long-term cropping have resulted in the removal of micronutrients from soils; 2) increasing crop yields generally leads to greater micronutrient removal rates in grain and other harvested products; and 3), the widespread replacement of micronutrient-rich manures with mineral fertilizers has reduced micronutrient addition from fertilizer sources. Collectively, these factors have led farmers to question whether micronutrient fertilization may now be required to meet the changing demands of crop nutrition.
The Tri-State Fertilizer Recommendations state that in general, soils in Michigan, Indiana and Ohio have adequate amounts of micronutrients to support crop growth. The only reported micronutrient deficiencies in this region have been with B, Cu, Mn and Zn. These deficiencies can cause plant abnormalities, reduced growth and sometimes yield losses. Over the past 40 years, there have been ongoing efforts to evaluate the effect of micronutrient fertilization on field crop yields. Here we have compiled all available studies conducted by Ohio State University which examined the effect of micronutrient fertilization on field crop yields in Ohio.
We found a total of 194 trials that tested a micronutrient fertilized treatment (or set of treatments) relative to an unfertilized control treatment. Five micronutrients were evaluated independently (B, Cu, Mn, Mo, or Zn) in these trials, while some of these trials evaluated a combination of micronutrients. There was a total of 17 alfalfa trials, 33 corn trials and 144 soybean trials (Table 3). These field trials were conducted in a total of 17 Ohio counties (Figure below).
This historical summary of micronutrient trials in Ohio demonstrates that yield responses to micronutrient fertilization are not common. In fact, the only responses observed with micronutrient fertilization occurred when Mn was applied to soybean (9 out of 144 trials) and when boron was applied to corn (1 out of 9 trials). While infrequent, it is important to keep in mind that probability of a yield response to micronutrients is much greater in scenarios where deficiencies are known, or suspected to be more prevalent, for example, in sandy, acidic or peat soils.
The infrequency of yield responses to micronutrient fertilization in Ohio has limited the development of reliable soil and plant tissue tests as diagnostic tools that can accurately predict when to apply micronutrient fertilizer. Accordingly, farmers should use all available tools to monitor micronutrient availability in their fields including: scouting for visual deficiency symptoms, soil testing and plant analysis, monitoring yield maps and assessing environmental conditions. When considering micronutrient fertilization, it is always a good idea to leave an unfertilized strip as a check or control. This will allow you to compare areas that received a micronutrient fertilizer vs. an area that did not. Yield monitors or weigh wagons can help you determine if the micronutrient fertilization increased yield and provided an economic benefit.
To read the full review of the effect of micronutrient fertilization on field crop yields in Ohio, click here.