Impact of Hybrid Selection, Planting Date and Seeding Rates on Dryland Corn in Western Nebraska

Impact of Hybrid Selection, Planting Date and Seeding Rates on Dryland Corn in Western Nebraska

Figure 1. Field of early-planted corn that dried up due to drought conditions during the early season in 2017 (left). Areal imagery of the study conducted in 2019 (right).
Figure 1. Field of early-planted corn that dried up due to drought conditions during the early season in 2017 (left). Areal imagery of the study conducted in 2019 (right).

Corn is a critical part of dryland crop rotations in western Nebraska and is typically grown either as continuous corn or after winter wheat in a three-year winter wheat-corn-fallow rotation. Many farmers prioritize planting irrigated acres first, often delaying planting dryland corn until after the USDA Risk Management Agency’s final planting date (May 25) for full insurance coverage.

The May 25 planting cutoff date is applied across Nebraska. Many corn growers in western Nebraska perceive this policy as unfair due to the shorter growing season and often better grain yield observed in late-planted corn. During the 2017 early season drought, many farmers in Chase County lost their early-planted dryland corn (Figure 1). Others in the region reported better yield of late-planted dryland corn.

In response, this two-year study was designed to evaluate the effects of planting dates on dryland corn and examine whether hybrid selection and seeding rate recommendations might change as planting dates are delayed.

Figure 2. Weather conditions during the 2018 and 2019 growing season at Grant
Figure 2. Weather conditions during the 2018 and 2019 growing season at Grant

On-Farm Strip Trial at Stumpf Farm, Grant

A strip trial was conducted at the Henry J. Stumpf International Wheat Center at Grant during the 2018 and 2019 growing seasons on a 75-acre field. The predominant soil type at the site was Kuma silt loam. The trial was managed using no-till practices and a fertility program based on 150 bu/ac yield goal. In 2018, the previous crop was corn, while in 2019 the previous crop was winter wheat.

Four seed corn companies provided their best performing dryland corn hybrids:

  • Dekalb DKC51-20RIB (101-day)
  • Croplan 4079SS (100-day)
  • Golden Harvest G03C84-5122-EZ1 (103-day)
  • Pioneer P0589AMXT (105-day)

Four hybrids were planted at five planting dates:

  • 2018 – May 1, May 10, May 20, May 30, June 10
  • 2019 – May 4, May 10, May 16, May 31, June 6

Within each planting date block, hybrids were planted at five seeding rates: 7,000, 11,000, 15,000, 19,000, and 23,000 seeds/ac. Each hybrid by planting date and seeding rate combination was replicated three times and planted into 60 x 150 foot strips. The middle 12 rows (30 feet) of each strip were harvested for yield.

Better Yield with Early Planting

Early-planted corn yielded better regardless of the hybrid and seeding rate (Figure 3, Tables 1 and 2). The yield penalties for May-planted corn, however, were much lower in 2019 due to above average precipitation in August and September (Figure 2). For example, yield penalties for late-planting corn ranged from 0.5-1.0 bu/ac/day in 2018 and were only 0.2-0.4 bu/ac/day in the 2019 growing season (Figure 3, Table 1 and 2).

Early-planted corn yielded better regardless of the hybrid and seeding rate (Figure 3, Tables 1 and 2). The yield penalties for May-planted corn, however, were much lower in 2019 due to above average precipitation in August and September (Figure 2). For example, yield penalties for late-planting corn ranged from 0.5-1.0 bu/ac/day in 2018 and were only 0.2-0.4 bu/ac/day in the 2019 growing season (Figure 3, Table 1 and 2).

Planting in June caused sharper decline in grain yield. Between May 31 and June 10, yield decreased 18-24 bu/ac in 2018 and 8-10 bu/ac in 2019 (Table 1 and 2). The higher yield penalty in 2018 is likely associated with below average rain in August and September (Figure 2).

Yield penalties for planting after May 25 (cutoff date for full insurance coverage) but before May 31 were 0-5 bu/ac in 2018 and 0-2 bu/ac in 2019, depending on the seeding rate (Table 1 and 2).

Good Response to Higher Seeding Rates

The optimal seeding rate is the one that provides the best return (yield/profit) on the investment (seed/seed price). Thus, increasing seeding rates beyond point of maximum net return will result in economic losses. This point changes depending on the environment (i.e., yield goal) and is usually observed at the seeding rate where corn yield starts to plateau.

Assuming the price of seed corn to be $280 per bag (80,000 seeds) and $3.50 ($3.85-$0.35 for harvest and hauling)/bu price of corn grain on the market, increasing seeding rate by 2,000 seeds/ac costs $7/ac and needs to provide more than a 2 bu/ac yield increase to be economically justified.

In 2018, corn responded well to high seeding rates (more than 17,000 seeds/ac), especially at early-planting dates (early- to mid-May) while increasing seeding rate beyond 17,000 seeds/ac was seldom economically justified at late planting dates (Figure 4, Table 1 and 2).

In 2019, yield increased 6-10 bu/ac for each additional 2,000 seeds/ac regardless of the planting date, suggesting that economically optimal seeding rates were beyond the highest seeding rate evaluated (23,000 seeds/ac).

Hybrid-Specific Responses

Dekalb, Croplan and Pioneer hybrids had similar overall yield in both 2018 and 2019, while Golden Harvest under-performed in 2018 and over-performed in 2019 compared to the other three (Figure 5).

Corn hybrid rankings, however, changed depending on planting date and seeding rate (Figure 6, Table 3 and 4). In 2018, Croplan performed the best when planted in mid-May with seeding rates of more than 15,000 seeds/ac; the Dekalb hybrid had the best yield when planted in early-May at high seeding rates (more than15,000 seeds/ac) and when planted in June; the Pioneer hybrid yielded the best when planted at low seeding rates of less than 15,000 seeds/ac in May. In 2019, Pioneer was best in early-May at high seeding rates, Dekalb was best in June at high seeding rates and Golden Harvest had the best yield in every other scenario.

Take-Home Messages

Our data strongly supports earlier planting in dryland corn. Fairness of RMA policy towards western Nebraska farmers, however, is subject to debate. In both the 2018 and 2019 growing seasons, small yield penalties occurred between May 25 (the cutoff date for full crop insurance) and May 31, while sharp decline in yield was observed when corn was planted in June, especially in 2018 when precipitation in August and September was below average.

There was strong response to seeding rates higher than the currently recommended 15,000 seeds/ac. Previous modeling studies by Nebraska Extension Specialists Bob Klein and Drew Lyon showed that a harvest population of 12,500 plants per acre provided the best economic returns in dryland corn production in western Nebraska. We are reluctant to recommend increasing seeding rates of more than 15,000 seeds/ac as both the 2018 and 2019 growing seasons had above average precipitation. In semi-arid regions impacted by intermittent periods of drought, such as in western Nebraska, evaluating response of dryland corn to seeding rates in a drier year would be necessary.

Hybrid selection showed once again to be one of the most important decisions in dryland corn production. In addition, hybrid-specific responses to planting dates and seeding rates can cause large yield differences and also need to be understood. Multi-year evaluation would be beneficial to better understand the climate variables that contribute to one hybrid yielding better than the other.

Table 1. Yield (bu/ac) of dryland corn in 2018 growing season as affected by planting date and seeding rate. Shaded cells represent the area beyond the maximum net return (seed corn = $280/bag, corn grain = $3.50/bu).
Planting Date
Seeding rate (sseds/ac)1-May6-May11-May16-May21-May26-May31-May5-Jun10-Jun
23,000 114 113 110 109 106 104 99 88 75
21,000 111 110 109 107 105 104 99 87 73
19,000 107 108 107 106 105 103 98 86 71
17,000 103 104 105 103 103 101 97 84 68
15,000 98 99 100 98 99 97 93 80 64
13,000 92 92 93 91 90 90 87 75 60
11,000 84 84 84 81 79 81 79 69 55
9,000 74 74 73 71 69 71 71 62 49
7,000 63 63 62 60 59 62 62 54 43
Table 2. Yield (bu/ac) of dryland corn during 2019 growing season as affected by planting date and seeding rate.
Planting Date
Seeding rate (sseds/ac)1-May6-May11-May16-May21-May26-May31-May5-Jun10-Jun
23,000 150 147 144 144 144 143 140 136 132
21,000 143 140 137 137 137 136 134 130 125
19,000 136 133 131 130 130 129 127 123 118
17,000 128 126 123 123 123 122 120 116 111
15,000 120 118 114 114 115 115 113 109 104
13,000 111 109 106 106 107 107 106 101 96
11,000 102 99 96 96 98 99 98 93 87
9,000 92 89 86 87 88 90 89 84 79
7,000 82 79 76 76 79 80 80 75 70
Table 3. The highest yielding corn hybrid for a given planting date and seeding rate in 2018; Dekalb DKC51-20RIB (D), Croplan 4079SS (C), Golden Harvest G03C84-54122-EZ1 (GH) and Pioneer P0589AMXT (P).
Planting Date
Seeding rate (sseds/ac)1-May6-May11-May16-May21-May26-May31-May5-Jun10-Jun
23,000 D D D C C C C C D
21,000 D D D C C C C D D
19,000 D D D C C C C D D
17,000 D D D C C C D D D
15,000 P P P P P D D D D
13,000 P P P P P P D D D
11,000 P P P P P P D D D
9,000 P P P P P P P D D
7,000 P P P P P P P P P
Table 4. The highest yielding corn hybrid for a given planting date and seeding rate in 2019; Dekalb DKC51-20RIB (D), Croplan 4079SS (C), Golden Harvest G03C84-54122-EZ1 (GH) and Pioneer P0589AMXT (P).
Planting Date
Seeding rate (sseds/ac)1-May6-May11-May16-May21-May26-May31-May5-Jun10-Jun
23,000 P P D GH GH D D D D
21,000 P P GH GH GH GH GH D D
19,000 P P GH GH GH GH GH GH D
17,000 P P GH GH GH GH GH GH GH
15,000 P P GH GH GH GH GH GH GH
13,000 GH GH GH GH GH GH GH GH GH
11,000 GH GH GH GH GH GH GH GH GH
9,000 GH GH GH GH GH GH GH GH GH
7,000 GH GH GH GH GH GH GH GH GH
Figure 6. Hybrid-specific yield responses to planting date and seeding rates during 2018 and 2019 growing seasons at Grant.