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Corn Seeding Rates Trial

Updated: Jun 26, 2023

Collaborating Producer: Koos & Barbara Bos, Peace River

Research Coordinator: Dr. Akim Omokanye

From: Peace Country Beef & Forage Association 2015 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 seed rate has been 30,000 kernels per acre for years and the recommendation has been based on studies carried out elsewhere, outside of the Peace region. In collaboration with Koos & Barbara Bos, PCBFA carried out a trial to examine optimum seeding rate for corn grazing or silage production.


The trial site was at Koos & Barbara Bos, near the Peace River Airport. The site has had corn for 6 years and has not received any fertility in the last 4 years, so no fertilizer was applied to this year’s corn crop.

DuPont Pioneer 39F44 corn hybrid (Roundup Ready corn) with 2000 corn heat units (CHUs) requirement was seeded on May 17 with a 12-row corn planter at 22” seed row spacing. There were 4 treatments (seeded kernels per acre) consisting of:

1) 38,049 kernels/acre

2) 36,146 kernels/acre

3) 34,425 kernels/acre

4) 32,858 kernels/acre

Spraying to control weeds was done with Roundup®. According to Alberta Agriculture and Forestry (, the calculated CHUs from seeding date (May 17) to corn forage harvest date (October 6) was 2005 for Peace River area, while the long-term average for the same period (May 17-October 6) was 1904.

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 cobs per plant counted at harvest. 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


Plant height (Table 1) - Corn seeded at 32,825 kernels per acre grew taller than other seed rates at harvest. Seeding at 34,425 to 38,049 kernels/acre produced similar plant heights.

Forage yield (Table 1) - Wet forage yield was higher for both 38,049 and 36,146 kernels/acre seeding rates (14 tons/acre) compared to other seeding rates. The forage dry matter (DM) yield appeared to be slightly favoured by seeding at 38,049 kernels/acre (4.0 tons DM/acre) compared with other seeding rates. But overall, the differences between seeding rates were negligible.

Forage Quality

Protein (Table 1)- The forage protein content appeared to be slightly higher for the lowest seed rate 32,858 kernels/acre ( 12% CP) than other seed rates. Generally, the protein requirements of a dry gestating cow, 7% CP at mid-pregnancy and 9% CP at late-pregnancy were met by all seed rates, but only the lowest seed rate (32,858 kernels/acre) had adequate protein that is needed by a lactating beef cow (11% CP). So, this means that the lowest seed rate (32,858 kernels/acre) had adequate protein for beef cattle.

Macro minerals (Table 2)- The forage Ca content varied from 0.16% Ca for both 34,425 and 32,858 kernels/acre to 0.21% Ca for 38,049 kernels/acre. The forage Ca content appeared to decrease slightly with increased seed rates. Only 38,049 kernels/acre had adequate Ca for a dry gestating cow, which requires 0.18% Ca, while others fell short of meeting this category of a cow’s Ca requirement. All seeding rates failed to meet the 0.42% Ca needed by a lactating beef cow.

For the forage P content, increased seeding rates appeared to have slightly increased forage P. All seed rates had sufficient P for a dry gestating cow, but none of the seed rates had adequate P for a lactating beef cow.

The forage K, S and Mg respectively varied from 1.05-1.19% K, 0.08-0.10% S and 0.18-0.21% Mg for the seed rates. The forage Na content was same for all seed rates (0.01%). The Mg (0.12% Mg) and K (0.60% K) requirements by a dry gestating beef cow have been met by the four seed rates. For a lactating beef cow, forage K content was adequate, while none of the seed rates had sufficient Mg for a nursing cow. Both S and Na requirements by mature beef cattle were not met by any of the seed rates.

Detergent Fibers & relative Feed Value (Table 3) - The forage fiber content, ADF & NDF, is a strong predictor of forage quality, since it is the poorly-digested portion in the cell wall. The ADF & NDF appeared to be lower for the lowest seed rate (32,858 kernels/acre) than other seed rates. The RFV combines estimated NDF and ADF into a single index. The RFV obtained were well within the suggested RFVs for beef cows (90-115 RFV).


(Table 3) - Energy gives the ability to use the building blocks for growth and other productive purposes. Using Total digestible nutrients (TDN), the rule of thumb is 55-60-65; this rule says that for a mature beef cow to maintain her body condition score (BCS) through the winter, the ration must have a TDN energy reading of 55% in mid pregnancy, 60% in late pregnancy and 65% after calving. The forage TDN obtained in this study varied from 63-66% TDN, indicating that all seeding rates provided sufficient TDN needed by a dry gestating cow (mid-late pregnancy).

Conclusion – The highest seed rate (38,049 kernels/acre) just slightly had more forage DM than other seed-ing rates. But generally, seeding rates did not have any significant influence on forage DM yield. In terms of forage quality, the lowest seeding rate (32, 858 kernels/acre) seemed to favour protein and detergent fiber contents and this is reflected by the highest relative feed value (RFV) obtained for the lowest seed rate (32, 858 kernels/acre).

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