Henry J. Mascagni Jr. and Brenda Tubaña

Corn grain yield and seed quality depend on the interaction of management and climate. Although an adequate number of plants is needed for maximum yield, too high a population may reduce yield and produce additional plant stress. Hybrid traits such as root and stalk quality help determine the optimal number of plants needed to produce maximum yield. Another important trait influencing optimal plant population is ear flex, or the ability of the plant to adjust ear size based on growing conditions. Because ear size may increase when growing conditions are good, fewer flex-ear plants are required for maximum yield. For fixed-ear hybrids, high plant populations required for maximum yield in good years may depend on a hybrid’s drought tolerance. Severe moisture stress with higher plant populations may affect plant growth and plant health. Hybrid choice and seeding rate may also affect the optimal nitrogen rate. To maximize yield potential and profitability, more research is needed on optimum seeding rates and nitrogen requirements for commercial hybrids currently being marketed.

Field experiments were conducted in 2013 and 2015 on a Sharkey clay at the Northeast Research Station near St. Joseph to evaluate the influences of seeding rate and nitrogen rate. A fixed-ear hybrid Dekalb DKC 66-97 and a flex-ear hybrid REV 28HR20 were evaluated at four seeding rates and nitrogen rates. Seeding rates were 26,400, 30,800, 35,200 and 39,600 seeds per acre, with targeted populations of 24,000, 28,000, 32,000 and 36,000 plants per acre. The harvested plant populations were within 5 percent of the number of seed planted in each instance. Corn was planted on March 21, 2013, and March 30, 2015. Nitrogen fertilizer was applied at the two-to-three-leaf stage at rates of 200, 250 and 300 pounds per acre. The trials were conducted under irrigated and non-irrigated conditions each year, with four furrow irrigations in 2013 and three furrow irrigations in 2015.

Rainfall was well distributed each year, resulting in good grain yields in the non-irrigated trials (Figure 1[BRC1] ). Average grain yields generally increased for the fixed-ear hybrid as seeding rates increased regardless of soil moisture status, ranging from 150.6 to 178.6 bushels per acre in non-irrigated trials and 161.9 to 200.4 bushels per acre in irrigated trials. Flex-ear average grain yields across seeding rates ranged from 174.1 to 183.3 bushels per acre non-irrigated and 183.3 to 198.4 bushels per acre irrigated. Optimal seeding rates for the flex-ear hybrid were 26,400 seeds per acre in non-irrigated trials and 30,800 seeds per acre in irrigated trials. Optimal seeding rates for the fixed-ear hybrid were 30,800 seeds per acre in non-irrigated trials and 39,600 seeds per acre in irrigated trials. Nitrogen use increased as seeding rates increased for each hybrid in all trials (Figure 2), with little interaction among the variables studied. Responses to nitrogen rates across seeding rates were similar for both hybrids.

Because of relatively good rainfall distribution, conditions were conducive for plant development even without irrigation. The flex-ear hybrid has the ability to increase ear size at low plant populations when growing conditions are good, thus reducing the optimal number of plants required for maximum grain yield compared to hybrids that have fixed-ear traits. Ear size was measured, and in general, the flex-ear hybrid produced larger ears than the fixed-ear hybrid, particularly at the lower seeding rates.

In situations with lower yield expectations, fewer plants may be required for maximum grain yield, particularly when planting a flex-ear type hybrid. In these cases, growers can reduce seed cost by planting fewer seeds per acre.

Henry J. Mascagni Jr. is a professor at the Northeast Research Station in St. Joseph, and Brenda Tubaña is the Jack E. and Henrietta Jones Professor in the School of Plant, Environmental and Soil Sciences.

(This article appears in the summer 2018 issue of Louisiana Agriculture.)

FIGURE 1. Influence of seeding rate, averaged across N rates, on grain yield for corn hybrids on nonirrigated and irrigated Sharkey clay at St. Joseph, averaged across 2013 and 2015.

FIGURE 2. Influence of nitrogen rate and seeding rate, averaged across hybrids, on grain yield on nonirrigated and irrigated Sharkey clay at St. Joseph, averaged across 2013 and 2015.