Corn yield and seed quality depend on management, climate and the interaction of these factors. In Louisiana in recent years, lack of rain combined with high temperatures have caused yields to suffer. Successful, non-irrigated corn production should include optimum plant population and proper hybrid selection. Excess plant population may increase the rate of soil moisture depletion, reduce yield potential and increase risks from aflatoxin contamination of the grain.

Hybrid characteristics such as drought tolerance and ear type are two traits that interact with plant population. Ear type can be determinate (ear size is fixed), indeterminate (ear size varies) or some variation of the two. Indeterminate or flex-ear hybrids have the ability to adjust ear size depending on growing conditions. Therefore, fewer plants are required for maximum yield compared to fixed-ear hybrids. More importantly, fewer plants need less soil water. This is important in dry years, particularly on drought-prone soils, where yield potential may be reduced and risks from aflatoxin contamination increase. Planting flex-ear hybrids at relatively low plant populations may be the best production strategy.

Field experiments were conducted in 2000 on a Tensas/Alligator clay at the Louisiana Delta Plantation near Jonesville, La., and in 2001-2003 on Sharkey clay at the Northeast Research Station near St. Joseph, La., to evaluate the influence of irrigation, hybrid and seeding rate on yield and optimum plant population.

Furrow-irrigation treatments were scheduled using the Arkansas Irrigation Model, a computer program. Treatments included a non-irrigated control and irrigation at 1.5- and 2.5-inch soil water deficit (SWD). The 1.5-inch SWD is considered well-watered, and the 2.5-inch SWD moderately well-watered.

Hybrids evaluated were Pioneer brand (PB) 33K81 (a fixed-ear hybrid), PB 3223 (a semi-fixed ear hybrid) and Golden Acres (GA) 8460 (a flex-ear hybrid). These hybrids were selected based on yield potential and differences in ear development traits. Seeding rates were 20,000, 25,000, 30,000, 35,000 and 40,000 seeds per acre. Recommended cultural practices of the LSU AgCenter were followed.

There was an observable relationship between yield potential and optimum plant population in this four-year study, with optimum plant population increasing as yield potential increased. In 2003, highest yields occurred, and the relationship between yield and plant population was most obvious. Yields were highest for the well-watered, 1.5-inch SWD trial at 165 bushels per acre followed by the moderately well-watered 2.5-inch SWD trial at 151 bushels per acre and non-irrigated trial at 140 bushels per acre.

Averaged across seeding rates, yield rank among hybrids was PB 3223 followed by GA 8460 followed by PB 33K81. At lower yield potentials (non-irrigated and 2.5-inch SWD), yields for the fixed-ear PB 33K81 and semi-fixed ear PB 3223 generally increased with plant population up to about 30,000 plants per acre, while maximum yield for the flex-ear hybrid GA 8460 occurred at or fewer than 25,000 plants per acre. When soil water was not limiting (in the 1.5-inch SWD), maximum yields occurred at about 30,000 plants per acre regardless of hybrid.

These findings suggest that when yield expectations are high, optimum plant populations are about 30,000 plants per acre regardless of hybrid type (fixed- versus flex-ear). In situations with lower yield expectations, however, fewer plants may be required for maximum yield, particularly when planting a flex-ear type hybrid. In these cases, producers can reduce seed cost by planting fewer seeds per acre.

Rick Mascagni, Professor, and Robert Bell, Research Associate, Northeast Research Station, St. Joseph, La.

(This article was published in the summer 2004 issue of Louisiana Agriculture.)