by Jake Munroe
A recent study conducted at Purdue University has demonstrated the importance of micronutrients for high-yielding, modern corn hybrids. The study showed that high-yield corn hybrids take up not only more nitrogen, but also greater amounts of micronutrients such as iron, zinc, copper, and manganese. Furthermore, at higher rates of N fertilization, these micronutrients are stored in greater quantities in the grain, which results in greater export off of fields.
According to one of the study's authors, micronutrient levels have not traditionally been considered in cash cropping. Despite their critical roles in plant growth and reproduction, micronutrients have often been assumed to be at adequate levels in the soil. "But if you are in a cash crop situation where you're producing bigger plants and more grain," says Tony Vyn, professor of agronomy at Purdue and study co-author, "you are exporting more nutrients away from the field at harvest. If you're not replacing them, the soil is going to be depleted over time."
While the study did not find that plant density had a large effect on micronutrient uptake, increased nitrogen rates resulted in higher yields and greater uptake and allocation of micronutrients to the ears. In other words, when yield is driven by high nitrogen availability, micronutrient uptake keeps pace, accordingly. This is why it is critical to think about micronutrient levels for high production corn; shortages can limit yields.
Dr. Vyn suggests putting zinc in with your starter fertilizer or mixing it into bulk phosphorus fertilizers. He adds that iron and copper are typically at sufficient levels in soil, and that manganese can be supplied via foliar sprays. For more information on the study, visit https://www.agronomy.org/publications/aj/abstracts/105/6/1645.
It is also important to consider how other factors, such as soil mineral balance and soil organic matter levels, affect micronutrient availability. For example, zinc, which controls production of plant growth hormones (auxins) that govern leaf size, may be present in sufficient levels, but its uptake can be stifled by excess phosphate. Zinc, along with many other micronutrients, is also much less available for plant uptake at an alkaline pH, due to chemical reactions that make it insoluble. Finally, mycorrhizal fungi, which are decimated by excessive tillage and low organic matter, play a critical role in supplying zinc to plants.
Boron, another micronutrient, is very important for reproductive growth as well as sugar movement within plants. As it is a negatively charged mineral, boron, like nitrates and sulfur, can easily leach from the soil. Organic matter holds onto boron in the soil and makes it available for corn for when it is needed most (e.g. during tasseling, silking, and pollination). In soils with low organic matter or under intensive irrigation, a pre-flower boron application can be very cost-effective. It is interesting to note the protagonistic relationship between boron an calcium, noting that calcium uptake requires the presence of available boron.
So, be sure to know where you stand with micronutrient levels in your soil, and use tissue testing in season to identify deficiencies. Don't let a lack of micronutrients hold back your yield.
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