Soil Health, Micronutrients and Macronutrients. (Part 2)

By Dusty Sonnenberg, CCA, Ohio Field Leader, a project of the Ohio Soybean Council and soybean check-off.

Macronutrients can impact micronutrients. Carbon is a key macronutrient. “Carbon is probably the most limiting element in our soils,” said Hoorman. “It takes 100 pounds of carbon each day to produce a 200 bushel per acre corn crop. This carbon used by plants comes from the both the atmosphere and the soil. The carbon cycle occurs in both the plant and the soil. During photosynthesis plants take in CO2 from the atmosphere into the leaves and give off O2. Roots take in O2 from the soil and give off CO2 back into the soil. When soils are tilled in the fall, there is a loss of soil carbon in the form of CO2. This is carried away, and not available to the growing crops.”

Nitrogen (N) is another important macronutrient. “Every 1% organic matter contains 1000 pounds of Nitrogen,” said Hoorman. “We are only between 30-50% efficient at keeping the N in the soil. Because of denitrification due to poor soil structure we can lose up to 60% of the N. We can lose 20-30% of the N by leaching. It is similar with Phosphorus (P). Poor soil structure makes us only 10-50% efficient with Phosphorus. About 50-70% of the P is tied up in organic matter. About 90% can run-off during the most intense rainfall events. Of that P loss, about 30% is lost due to surface erosion, and the other 70% is leaching down through the tile water. This is lost due to poor soil structure and the water not being retained in the soils.” Some of the soil structure issues are a result of soil compaction.

Some soils are having issues with Potassium (K). In those soils, K is being applied, but the test results show the K levels dropping. “There is a concept called Potassium Induction which occurs in saturated soil conditions and K gets caught up in the clay soil particles,” said Hoorman. “Farmers broadcast the K on their fields and then use vertical tillage to lightly incorporate it, but if the soil moisture conditions are not right then a hard pan of soil compaction occurs at about 1-2 inches and with the wet falls we have been having, K is getting tied up.”

Nutrient deficiencies in plants can be confused with one another as well as other growing season issues in the plant. “A white midrib on a corn leaf can be an example of a Zinc deficiency,” said Hoorman. “We observed a lot of Zinc deficiency for two reasons this year. We had a relatively dry fall, winter, and spring. Most micronutrients come available when we have reducing conditions and the soil is wet. Another thing that ties up Zinc is glyphosate. Along with Zinc, glyphosate ties up, Manganese and Iron. One way to mitigate the impact of glyphosate use on micronutrients is to plant Oats. Oats is a cover crop that can help counteract the impact of glyphosate.”

Increasing soil organic matter is also very important in improving micronutrient availability to plants. “Organic matter buffers the pH and makes the nutrients in a form that is plant available. It increases the water and nutrient holding capacity of the soil” said Hoorman. “Organic matter is one of the chelators of micronutrients to put them in a form that the plants can use. We need the nutrients to be in a reduced for that the plants can use and works by stripping off the Oxygen. Magnesium, Manganese, Calcium, Copper, Iron, and Zinc are helped by organic matter to be kept in a form that is plant available.”