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Determining Optimum Nitrogen Rates for Corn

Updated: Jun 26, 2023

Trial Site: Fairview Research Farm

Research Coordinator: Dr. Akim Omokanye

From: Peace Country Beef & Forage Association 2016 Annual Report

One of the most costly and important inputs in corn production is nitrogen fertilizer. The objective of this project is to help develop appropriate N rate recommendations for corn. In order to become more confident with this new nitrogen rate recommendation approach we will continue building the response data-base with more nitrogen trials during the next few years.


The study site was at the Fairview Research Farm (NW5-82-3W6) on RR #35, MD of Fairview. The soil test at 0-6” soil depth done at Exova laboratory (Edmonton) prior to seeding showed an organic matter content of 7.1%, a pH of 5.5 (acidic) and an electrical conductivity of 0.35 dS/m. The field was cultivated before seeding.

The treatments mentioned below were arranged in a randomized complete block design in 4 replications.

The treatments consisted of 3 corn types and 4 N fertilizer rates as provided below:

Three (3) Corn types:

1. RR hybrid (A4414RR)

2. Conventional hybrid (Master Graze)

3. Open-pollinated (Catt)

4 N-rates (lbs N/acre):

1. 0 N lb/acre

2. 60 N lb/acre

3. 100 N lb/acre

4. 140 N lb/acre

Each corn type was tested with the 4 N rates. Regardless of the N rates applied, all corn types received a uniform application of 30 P + 66 K + 0 S (lbs actual/acre).

Seeding Rate & Date: 30,000 kernels/acre, May 17

Seeding Method: We used a 6-row John Deere corn planter at 30” row spacing.

Pre-emergent used was Roundup Weather Max. In-crop was done with Basagran Forte @4-6 leaf stage.

The amount of rainfall received from seeding to killing frost was 13.8 inches.

Date of first killing frost: September 4

Total corn heat units from seeding to Killing frost: 1711

In-crop spraying was with Basagran Forte.

Measurements taken at harvest: plant height, final plant population, number of ears/plant and forage yield and quality. Field notes were taken on ear development and kernel stage at harvest.

Results and Discussion

Number of ears/plant (Table 1)

The number of ears per plant averaged about 3 ears/plant for 0, 60 and 100 lbs N/acre and this appeared to increased to about 4 ears/plant for 140 lbs N/acre.

The number of ears/plant was similar for all corn types and this averaged 3 ears/plant for each of the corn types tested.

Overall, except for the highest N rate (140 lbs N/acre) which seemed slightly increased over other rates, number of ears was not generally affected by corn types and N fertilizer rates.

Plant height (Table 1)

All corn types and N rates had similar plant heights. Though Catt, an open pollinated variety, seemed to have the potential to grow taller than Master Graze and A4414RR.

Moisture (Table 1)

The forage moisture content at harvest was similar for all corn types as well as for all N rates applied. The forage moisture content varied from 79-80% for N rate and from 78-80% for corn types.

Forage Crude Protein (Table 1)

The forage crude protein (CP) content was similar for the 3 corn types, varying from 11.5% CP for A4414RR to 12.3% CP. Both fertilizer N rates of 100 and 140 lbs N/acre showed significant CP improvement over 0 lbs N/acre. The application of 60 lbs N/acre did not improve forage CP content over 0 lb N/acre rate. The CP required for a gestating cow is 7% in the second trimester and 9% in the third trimester.

Looking at the protein values in Table 1, the protein requirements of these categories of cows have been sufficiently met by all corn types at any particular N rate.

Forage DM yield (Figure 1)

For each corn type, N application rates had significant effects on forage DM yield. The forage DM yield increased with increased N rates for all corn types. The response to applied N rates was more for A4414RR than Master Graze or Catt. The highest N rate (140 lbs N/acre) increased DM yield by 2.8, 1.4 and 3.4 tons DM/acre over check (0 lb N/acre) respectively for A4414RR, Master Graze and Catt.

Figure 2 shows the mean DM yield (across corn types) for N rates. The DM yield seemed to respond linearly to increased N rates. The application of 60 - 140 lbs N/acre fertilizer improved DM yield by 0.7 to 2.5 tons DM/acre.

Forage Energy

The forage energy (%TDN) was generally above 65% TDN for all corn types at all N rates including the control (0 lb N/acre) (Figure 3). This shows that the energy (%TDN) requirements of a gestating cow of 55% at mid-pregnancy stage and 60% at late-pregnancy have been exceeded.


Corn responds well to nitrogen, so adequate availability of nitrogen is critical to profitable corn production. However, excess nitrogen adds unnecessary expense and increases the risk of nitrate movement to groundwater. In the present study, the forage DM yield increased with increased N rates for all corn types. The highest N rate (140 lbs N/acre) increased DM yield by 2.8, 1.4 and 3.4 tons DM/acre over check (0 lb N/acre) respectively for A4414RR, Master Graze and Catt. We observed N deficiency in some plants with 0 lb N/acre. The deficiency first appeared on the lower leaves, manifested as yellowing, beginning at the tip of the leaf and proceeding down the midrib.

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