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Cover Crop Cocktails for Forage Production - Effects of Species Mixtures and Seeding Rates

Research Coordinator: Dr. Akim Omokanye

Location: Fairview Research Farm

From: Peace Country Beef & Forage Association 2020 Annual Report

Funded by the Canadian Agricultural Partnership - Government of Alberta

In northern Alberta, interest is still growing amongst beef cattle producers, in the use of a multispecies annual crop mixture for forage production. Such mixtures could increase forage production, improve water and soil quality, increase nutrient cycling, moisture conservation, and crop productivity. Cover crop species for cocktails can be selected from a diversity of plant categories, such as cereals/grasses, brassicas, legumes, and forbs/herbs, which correspond to different plant functional groups and traits (e.g., biological N-fixation, deep root system for nitrogen scavengers). Each crop species in a mixture may reach maturity at slightly different times, therefore providing available immature forage continuously through the growing season.

Objective: To determine seeding rates that optimize forage production, while simultaneously maintaining diversity of species for maximum ecosystem benefits.

Methods

Experimental Site: Fairview Research Farm (NW-5-82-3-W6M) on RR #35, MD of Fairview. Site soil information from 0-6” depth at seeding: pH = 6.2, organic matter = 4.7% and electrical conductivity = 0.21 (dS/m). Before the fall of 2018, when the site was sprayed out with Roundup at 1.0 L/acre and tilled, the previous crop was alfalfa hay for over 15 years.

Experimental design: Factorial design (9 x 3) with 4 replications in plots measuring 8 m x 1.8 m.

Treatments: The cover crop mixture treatments ranged in diversity from 2 to 8 plant species (Table 1). Mixtures were designed to include different functional groups. Haymaker oats and Maverick barley were included as controls.

Each of the mixtures and the 2 cereal controls were seeded at 3 different seeding rates, which are:

a) Recommended monoculture seeding rate (N)

b) 125% monoculture seeding rate (N125)

c) 150% monoculture seeding rate (N150)

A substitutive approach (i.e., proportional replacement design) was used, such that seeding rates for each species in the mixture was proportional to their recommended monoculture seeding rate. The seeding rates for individual species in the mixture were then determined by dividing each recommended seeding rate by the total number of species in the mixture (e.g., divide by 4 for the 4 species mix).

The seed in each cocktail mixture was weighed and mixed in an envelope prior to seeding. Mixed row seeding method was used. The legumes were inoculated at seeding.

Seeding was done on May 29 using a Fabro plot drill into 9” (about 23 cm) row spacing.

Soil temperature at seeding was 12°C.

Fertility (actual lbs/acre): 50 lbs P2O5 per acre only.

Results

Forage Dry Matter Yield

Both controls (barley and oats) seemed to be affected negatively by increasing seeding rates (Figure 1). For the mixtures, there appeared to be an inconsistent response to increasing seeding rates across the mixtures generally. For the 2-way mixes, forage DM yield increased slightly from N to N125 and thereafter fell sharply at N150. Mixtures that responded positively to increasing seeding rate to a point (N125) before stabilizing or decreasing are: 3-, 5-, 6- and 8-way species mixes. The 7-way mixes on the other hand decreased with increasing seeding rate. Overall, 2-way species mix at N and N125, 3-way species mix at N150, and 6-way species mix at N125 and N150 all produced above 9000 lbs DM/acre. Other species mixes and rates had lower than 9000 lbs/acre.


Forage Quality

In terms of forage CP, there isn’t much of a variation between seeding rates for the each of the controls used in this study. Oats however appeared to have more CP than barley at each seeding rate, and both oats and barley did not appear to vary much from normal (N) to higher (N150) seeding rate (Table 1). Both 2– and 3-way species mixtures did not vary much with increasing seeding rate. However, 4-, 5–, 6– and 7-way species mixtures showed tendencies to producer lower CP with increasing seeding rate. On the other hand, 8-way species mixtures maintained its level of CP across different seeding rates.


Forage TDN seemed to be maintained at different seeding rates, but surprisingly, oats saw a gradual increase with increasing seeding rates from 62.1% TDN for normal (N) seeding rate to 67.2% TDN at N150 seeding rate (Table 1). Similarly, an 8-way species also had more or less the same TDN for the different seeding rates. Other mixtures appeared to have similar TDN values for the different seeding rates. On a general note, the 55-60% TDN requirements of a dry gestating beef cow from mid to late pregnancy have been met by all monocrops (controls) and mixtures at different seeding rates.


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