By Keru Chen
Corn yields in the United States have increased 2.3 fold over the past 40 years.1 This drastic increase in return is the result of improvements in both corn hybrid genetics and management practices.
One management practice that has changed significantly is optimum plant population, or how many plants are planted on each acre. Optimum plant population is critical for best yield because it allows for the best allocation of resources. If the population is too low, it will lead to a waste of the resources (land, fertilizer, water, etc.). On the flip side, a population that is too high will lead to high plant-to-plant competition and result in weaker plants that are more vulnerable to extreme weather conditions or diseases. Recently, research from Kansas State University showed that the average optimum plant density increased 7,500 plants/acre in the last 30 years. The researchers concluded that 9% of total corn yield gain in the US could be attributed to increased plant population.2 The increasing optimum plant populations have been an effective strategy for increasing grain yields because there are more plants. With more plants, there are more ears per acre and higher plant density that allows the corn leaves to intercept and use more of the available sunlight.
Despite the benefits of increased plant population, crowding is also a stress to the corn plant. Therefore, many genetic improvements in corn hybrids were needed to make them suitable for higher plant densities. For example, modern hybrids have more erect leaf structure, which makes them more tolerant of being crowded close together. In the meantime, erect leaves allow light to pass through the canopy and increase radiation use efficiency. High plant population increases the possibility of stalk lodging, the breakage of the stalk below the ear. The loss of yield due to stalk lodging ranged from 5-25% in US.3 This breakage is due to thinner stalk, which caused by limited light, nutrition, and water per plant at a high plant population. The vigor of the cells in stalk is dramatically reduced and more likely to be fed by European corn borer. Lower ear height and reduced tassel branch number have contributed to lower the risk of stalk lodging at high population.4
In addition to being tolerant of high plant populations, modern hybrids have changed in other significant ways. One of these changes has been an increase in the length of time the corn ear is growing. After flowering, the vegetative growth (leaves and stems) ends and reproductive growth (ear) begins. During the reproductive growth, the corn plant increases in weight by 50%. Modern hybrids are known to have a longer reproductive stage, which provides more time for photosynthesis, the essential process for accumulating dry weight. About 80% of the final dry weight of the ear comes from photosynthesis that occurs during reproductive growth. The other 20% is from carbohydrates that were stored during vegetative growth and then are remobilized to the ear. In addition to a more extended reproductive phase, the leaves of modern hybrids also stay green for a longer period of time. This allows for more photosynthesis and higher yields.
The changes in hybrid genetics and management practices are important considerations when working with crop growth models. Because of this, CiBO Technologies continues to conduct our own field trials to ensure that our model parameters reflect current agriculture. With this knowledge, the CiBO team packages crop science and agronomy knowledge into the software to accurately predict crop performance in different environments. Beyond that, CiBO’s crop growth model leverages environment factors and topographic factors with update genetics and management practices to capture field variability and provide a more precise prediction on yield.
The simulation helps AgriBusinesses better understand the outcomes of different management practices and provides key inputs to understanding crop performance. Comparing these different scenarios allows businesses to know the right place, right time, and right crop to put on their field to maximize their crop yield.
1. USDA Quick Stats. Link
2. Assefa et al., 2018. Analysis of Long Term Study Indicates Both Agronomic Optimal Plant Density and Increase Maize Yield per Plant Contributed to Yield Gain. Scientific Reports Volume 8: 4937. Link
3. Nielsen. Stalk Lodging in Corn: Guidelines for Preventive Management. Agronomy Guide, Purdue University Cooperative Extension Service. Link
4. Wei et al., 2018. Exploiting SPL genes to improve maize plant architecture tailored for high-density planting. Journal of Experimental Botany. Volume 69: 4675–4688. Link
About Keru Chen
Keru Chen is a crop scientist at CiBO Technologies. Throughout her career, she has been focused on nitrogen and phosphorus dynamics in the corn plant, as well as the environment, management, hybrids interaction respond to nitrogen and phosphorus application. She holds a Ph.D. in Agronomy from Purdue University.