Collaborating Producer: Koos & Barbara Bos, Peace River
Research Coordinator: Dr. Akim Omokanye
From: Peace Country Beef & Forage Association 2016 Annual Report
Plant population refers to the number of plants per acre; planting or seeding rate refers to the number of seeds planted per acre. Optimum plant population depends on factors such as hybrid, moisture stress level, soil fertility, and yield goal. In the Peace, for silage or grazing, the suggested seeding rate has been 30,000 kernels per acre for years and the recommendation is based on studies carried out elsewhere, outside of the Peace region. A few producers seed more than the 30,000 kernels/acre suggested seeding rate in the Peace. We are aware that more plants per acre should equal more ears/acre which should be beneficial for optimizing yield. On the other hand, kernel numbers per plant and weight per kernel eventually decrease with increasing plant populations. PCBFA conducted on-farm studies on seeding rates for 2 years to determine how corn yield responds to plant population.
The trial site was at Koos & Barbara Bos, near the Peace River Airport in 2015 and 2016. The site has had corn for some years, so no fertilizer was applied to the corn crop in both years.
Demonstration strip design was used in large plots. DuPont Pioneer 39F44 corn hybrid (Roundup Ready corn) with 2000 corn heat units (CHUs) requirement was seeded in 2015 and in 2016, we used DuPont Pioneer P7213.
We used a 12-row corn planter at 22” seed row spacing to seed. There were 4 treatments (seeded kernels per acre) consisting of approximately:
1) 38,000 kernels/acre
2) 36,000 kernels/acre
3) 34,000 kernels/acre
4) 32,000 kernels/acre
Seeding was done on May 17 in both years (2015 & 2016). Roundup® was used to control weeds.
Corn forage yield was determined from several 23.8’ row lengths when most cobs were at the half milk line stage. Plant height was measured and the number of ears per plant counted at harvest. We also determined final plant population. Notes were also taken on cob development and kernel stage. Wet corn forage samples (whole plant) were analyzed by A&L Canada Laboratories Inc., London, Ontario.
Results & Discussion
Final Plant Population, Plant Height & Number of Ears
In the 2 years (2015 & 2016), the mean percent stand (final population divided by seeding rate) was 94% (ranging from 91% to 100%) and there was no consistent difference in the final population recorded following the different seeding rates tested. This indicates that seed germination, emergence and vigor were very good for all seeding rates. It is important to note that final populations are usually expected to be lower than the seeding rates due to germination problems, emergence problems, or subsequent plant mortality.
Plant height is an important component which helps determining the growth attained during the growing period. The mean plant height over both years (2015 & 2016) was significantly affected by seeding rates (Table 1). Plant height decreased from 225 cm for 32,000 kernels/acre to 190 cm for 38,000 kernels/acre, the result of the competition-density effect of plant populations.
The number of ears per plant was similar for all seeding rates and the average was 2 ears per plant. However, we observed that lower seeding rates showed better cob development. Lower seeding rates also attained about 3/4 milk-line stage at harvest compared to the highest seeding rates (38,000 kernels/acre), which seemed to have milk-line just about the half mark
Corn Forage DM Yield
Over the 2 years (2015 & 2016), the mean corn forage DM yield increased from 3.8 tons DM/acre for the lowest seeding rate (32,000 kernels per acre) to 4.4 tons DM/acre for the mid-range seeding rate (36,000 kernels per acre), after which it decreased to 3.8 tons DM/acre for the highest seeding rate tested here (38,000 kernels per acre). Though we used different varieties in both years and we did not calculate the economical optimum plant population for various seed costs and corn silage prices, the decrease in corn forage DM yield beyond 36,000 kernels per acre probably suggests that we could increase the seeding rate from the 30-32,000 kernels per acre that is currently suggested for producers in the Peace, to 36,000 kernels per acre for grazing or silage purposes.
The forage crude protein (CP) did not show any consistent response to increased seeding rates (Table 1), indicating that plant population may not play any significant role in corn forage CP content. For a gestating beef cow, the forage CP values obtained for all seeding rates were enough for this category of beef cow, which requires 7% CP at mid-gestation and 9% CP at late-gestation.
The forage energy (%TDN) varied from 66% for 32,000 kernels/acre to 63% for 38,000 kernels/acre (Table 1). All seeding rates had the 55-60% TDN required by a gestating beef cow, depending on its pregnancy stage.
The minerals tested here, in most cases, were similar for all the seeding rates (Table 1).
The optimum final plant population is that which best balances the benefit of more ears per acre (since ears form about 60% of corn total DM yield) with the disadvantage of smaller ears and lighter grain. Over the 2 years (2015 & 2016), forage DM yield peaked at 36,000 kernels/acre. This therefore seems to suggest that up to 36,000 kernels could be used as a corn seeding rate without much compromising on forage protein, energy and minerals for a dry gestating beef cow. Please note that stalk health and integrity often falter as plant population increases beyond some maximum threshold as we observed for the highest seeding rates used in this tests (38,000 kernels/acre). The primary exception to what we observed here would be those soils or growing conditions that severely limit yield potential (e.g. low moisture).