Managing For Higher Corn Planting Densities

Climate LLC and Monsanto Company partner through funding research programs with Professor Fred Below of the University of Illinois and Field Research Technician and PhD student Brad Bernhard to accelerate the development of strategies to manage higher corn planting densities.

Corn yields have increased significantly since the 1930s largely due to genetic improvement and better crop management. Grain yield is the product of the number of plants per acre, kernels per plant, and weight per kernel. Of the three components that make up grain yield, the number of plants per acre is the factor that the farmer has the most direct control over. Kernel number and kernel weight can be managed indirectly through proper fertility, weed, pest and disease management to optimize plant health, and weather also plays a major role. Currently the average U.S. corn planting density is just under 32,000 plants per acre and has increased 400 plants per acre per year since the 1960s. If this trend continues, the average U.S. corn planting density will reach 38,000 plants/acre in 15 years and 44,000 plants/acre in 30 years. Successfully utilizing digital ag tools to predict the fertility needs as densities continue to increase will require integrated experiments.

Plant Density Impact on Plant Structure

Field experiments conducted in 2016 and 2017 examined the effect higher planting densities have on above- and below-ground corn plant biomass. At a given planting density, there are roughly 12-15 tons per acre of above-ground biomass and only around 0.5 tons per acre of below-ground biomass. Surprisingly, those roots below ground support nearly 30 times more biomass above ground. The vast majority of an average corn plant’s root system is concentrated within a 7-inch horizontal spread, indicative that there is little below-ground competition across the rows, and that below-ground competition is largely within the row. When planting densities increase, more carbon material is sequestered above ground but not below ground. Individual corn plant root systems get significantly smaller as planting densities increase (see picture). Creating roots takes a considerable amount of energy and resources from a plant. Thus the smaller the root system a plant can get by with, the better. However, smaller root systems require better crop management.

Fertility Management Considerations at Higher Planting Densities

Narrower row spacings can be used to increase the distance between plants within a row and provide greater coverage of leaf area across the ground area. At a given planting density, using a 20-inch row spacing leads to larger root systems than when plants are grown in a 30-inch row spacing. However, ever-increasing planting populations are resulting in smaller and less expansive root systems available to acquire nutrients. Placing nutrients directly in the root zone at the right time using the correct source and rate increases the probability that roots will take up and utilize those nutrients. Integrating this understanding of seeding rates, row spacing and product placement with advanced fertility management practices such as predicting fertility needs with digital agriculture approaches to help manage the right source, right rate, right timing and right place for nutrient management is critical to maximize grain yield and input efficiency at higher planting densities.

About The Authors

Dr. Fred Below is a professor of Crop Physiology at the University of Illinois. Dr. Below creates strategies to teach farmers and agricultural professionals the value of crop management decisions, and develops systems to sustainably produce high-yielding corn and soybeans. He evaluates environmental, genetic, and management factors that impact the productivity of corn and soybeans.

Brad Bernhard is a field research technician and PhD student under the advisement of Dr. Fred Below in the Crop Physiology Laboratory at the University of Illinois. Brad’s research focuses on in-season fertility using different fertilizer sources and application methods. In addition, he is investigating ways to manage higher corn planting densities using narrower row spacings along with characterizing hybrids for use in these more intensive cropping systems.