Plant Population Effects on Corn Hybrids Differing in Ear Growth Habit and Prolificacy

Terminology characterizing differences in ear growth habit and prolificacy is commonly used by seed companies to relate corn (Zea mays L.) hybrid yield potential to varying plant populations. Little information is available to document the significance of various ear response types associated with commercially available Corn Belt hybrids. The objective of this study was to assess hybrid × plant population interactions of commercial corn hybrids differing in ear growth habit and prolificacy. Field experiments were conducted in 11 environments in Ohio during 1990 and 1991. Four hybrids (LH119 × LH51, B73 × LH38, LH132 × DM2, and LH123 × LH93) chosen to represent different responses to plant population associated with ear type were compared at three plant populations (16 000, 24 000, and 32 000 plants/acre). Grain yields, ears per plant, and stalk lodging varied with hybrid and plant population in both years. The semiprolific hybrid and the fixed and flex single ear hybrids exhibited similar yield response to plant population across a wide range of environmental conditions. In 1990, grain yields were greatest for the flex (LH51 × LH119) and fixed (B73 × LH38) single ear hybrids and semiprolific (LH123 × LH93) hybrid at 32 000 plants/acre and the prolific (LH132 × DM2) hybrid at 24 000 plants/acre; whereas in 1991, under drier, hotter conditions, yields for all four hybrids were greatest at 24 000 plants/acre. Prolificacy was most pronounced in LH132 × DM2 and at the low plant population; it was least evident in LH119 × LH51 and at the high plant population. Stalk lodging was greatest in the prolific and semiprolific hybrids and at the high plant population; it was negligible in the fixed single ear hybrid and at the low plant population. Although the prolific hybrid exhibited relatively high yields under stress in 1991, its greater predisposition to lodging limits its potential use in Eastern Corn Belt environments where diseases and weather conditions make stalk quality a major factor in hybrid selection. The relatively minor role that hybrid × population interactions played in determining grain yield compared with environment, hybrid, and plant population main effects suggests that hybrid differences in ear growth habit and prolificacy are of limited importance in determining optimum plant populations. Research QuestionSeeding rate recommendations vary among corn hybrids for grain production. Seed companies often relate hybrid differences in plant population response to variation in ear growth habit and prolificacy (ear size and number) among hybrids at varying plant population. According to some companies, a “fixed-ear” hybrid is associated with a relatively determinate ear size that limits its potential to compensate for variation in plant population and growing conditions. In contrast, a “flex-ear” hybrid has a more indeterminate ear size, which can adjust for differences in plant population and environment. Prolific hybrids with the potential to produce more than one ear per plant may be even less sensitive to variation in plant population than single ear flex hybrids. The primary objective of this study was to evaluate the response of corn hybrids differing in ear growth habit and prolificacy to varying plant populations. Hybrid performance was evaluated across a range of production environments representing different soil types and climatic conditions in Ohio. Literature SummaryWith the exception of what has been reported in seed company marketing literature, little information is available comparing the relative advantages of hybrids with different ear types at varying plant populations under different environmental conditions. The breeding and agronomic implications of prolificacy have been extensively investigated by plant breeders. Most of this research, however, has involved experimental lines and populations with varying degrees of prolificacy, which may not be representative of commercially available hybrids. Study DescriptionThe study was conducted in 11 environments on four soil types in Ohio during 1990 and 1991. Four corn hybrids characterized as single-ear flex (L119 × LH51), single-ear fixed (B73 × LH38), semiprolific (LH123 × LH93), and prolific (LH132 × DM2) were grown at three populations (16 000, 24 000, and 32 000 plants/acre). Precipitation at the six locations in 1990 was 2.6 to 9.6 in. above the 30-yr average, whereas at the five locations in 1991, it was 2.7 to 8.4 in. below normal. Applied QuestionDid hybrid differences in ear growth habit or prolificacy (ear size and number) influence the plant population levels required for greatest grain yields? Hybrids responded differently to plant population according to varying growing conditions over the 2 yr (Table 1). Under the favorable growing conditions of 1990, the two single-ear hybrids and the semiprolific hybrid, averaged across locations, required a higher population (32 000 plsnts/acre) than the prolific hybrid to achieve the greatest yields. In 1991, however, under hotter, drier weather conditions, plant population response among hybrids, averaged across locations was not markedly different, with all four hybrids achieving highest yields at 24 000 plants/acre. The prolific hybrid outyielded the three other hybrids under moisture stress and at low plant population because of its ability to produce grain on a second ear and minimize barrenness. At 16 000 plants/acre, the prolific hybrid averaged 1.9 and 1.4 ears/plant in 1990 and 1991, respectively, but it required a higher plant population for greatest yield potential. At higher population, especially 32 000 plants/acre, the prolific and semiprolific hybrids lodged more than did the single ear hybrids. This greater potential for stalk quality problems may warrant seeding rate recommendations that are suboptimal for grain yield. Table 1Grain yields, ears per plant, and stalk lodging of four hybrids at three plant populations averaged across six environmentsin 1990 and five environments in 1991 in Ohio. 19901991HybridPlantEars/Ears/(ear type)populationYieldplantLodgingYieldplantLodging1000bu/%bu/%plants/acreacreacreLH132 × DM2161561.86 31531.44 5 (prolific)241771.42 81611.13 9321801.18181631.0017LH123 × LH93161471.37 31421.07 4 (semiprolific)241721.09 31530.98 9321811.04101510.9315LH119 × LH51161511.02 11410.98 2 (flex)241811.00 31520.95 5321891.00 71540.88 5B73 × LH38161291.08 11260.96 3 (fixed)241611.03 21410.92 4321751.00 31440.87 6