Trial Location: Fairview Research Farm NW-5-82-3-W6 on RR #35, MD of Fairview
Research Coordinator: Dr. Akim Omokanye
From: Peace Country Beef & Forage Association 2015 Annual Report
Usually we think of cover crops in terms of reducing soil erosion and adding organic matter to the soil – but they can do much more. Cover crops add organic matter but the amount really varies depending upon the cover crop species and the conditions under which it is grown. Some cover crops fix nitrogen thereby improving soil fertility but many more require nitrogen to grow. Some cover crop species may be a non-host for a pest or may release materials that are toxic to the targeted pest. Cover crops can help to reduce compaction and improve soil structure. The addition of the plant top and, especially root matter, helps to improve water infiltration and holding capacity. It can also decrease soil bulk density. Deep rooted cover crops can help to decrease the impact of soil compaction.
Methods
Eight cover crops were seeded in small plots in two replications at Fairview Research Farm (NW5-82-3W6) on RR #35. The site used was seeded to alfalfa and had been hayed for more than 10 years. Prior to seeding, soil tests at 0-6” soil depth done at Exova Laboratory (Edmonton) showed an OM of 3.0 % and a pH of 6.9. The site was sprayed with Roundup the fall before and worked in the spring before seeding.
The crops were seeded on May 25 at the following rates: Red Proso millet - 22.0 lbs/acre, Pearl millet - 22.0, Forage sorghum (Canadian Forage Sorghum Hybrid 30, CFSH 30) - 22.0 lbs/acre, Sorghum Sudan grass - 22.0 lbs/acre, Hairy vetch - 17.5 lbs/acre, Phacelia - 4.5 lbs/acre, Buckwheat - 25 lbs/acre and Hybrid brassica - 3.2 lbs/acre. The cereals (proso millet, CFSH 30, Sudan grass and pearl millet) were sprayed with 2,4-D Ester 700 at the recommended rate and plant growth stages. Other crops were not sprayed.
All crops were harvested on August 15 and samples taken for forage quality analysis. Red proso millet was harvested at the mid-dough stage and pearl millet was at 50% flowering stage. Both CFSH 30 and sorghum Sudan grass did not flower at all, so they were both harvested at the late vegetative stage (pre-boot stage). Hairy vetch was harvested at the early-pod stage. Composite forage samples were taken per crop, dried and later shipped to Central Testing Laboratory Ltd., Winnipeg, Manitoba for feed quality analysis using standard laboratory procedures for wet chemistry.
Results
Protein: The forage crude protein (CP) content was generally above 13% for all crops. The CP content was highest for CFSH 30 (24% CP) , followed by hairy vetch (20% CP) and then hybrid brassica (18 % CP). All cover crop species tested here met the CP requirements of growing and finishing calves that require 12-13% CP as well as that of a mature beef cow, which requires 7-11% CP depending on its physiological state.
Forage Minerals (Table 1): Phacelia had the highest forage Ca content (2.98%), followed by hybrid brassica (2.33%), buckwheat (1.59%) and then hairy vetch (1.49%). The four cereal crops (proso millet, CFSH 30, Sudan grass and pearl millet) all had far less forage Ca content (0.29-0.70% Ca) than other crops. But all crops tested here far exceeded the Ca requirements of 0.31% Ca by growing and finishing calves, 0.18% Ca by a dry gestating cow and 0.42% Ca by a lactating cow.
The forage P varied from 0.17% for proso millet to 0.33% for hybrid brassica. Except for proso millet, all crops had adequate levels of P for growing and finishing calves (0.21%) and a dry gestating cow (0.16% P). But only hybrid brassica was able to meet the level of P needed by a lactating cow (0.26% P).
All crops tested here far exceeded the requirements of Mg and K by both young and mature beef cattle. Of the 8 crops tested here, only hybrid brassica had sufficient Na for both young and mature beef cattle.
Acid Detergent Fiber (ADF) (Table 1): The fibrous component of a plant represents the least digestible fiber portion of forage or other roughage. This highly indigestible part of forage includes lignin, cellulose, silica and insoluble forms of nitrogen but not hemicellulose. Forages with higher ADF are lower in digestible energy than forages with lower ADF. That means, as the ADF level increases, digestible energy levels decrease. Considering that lower ADF values are preferred, in this study, hybrid brassica had the lowest ADF value and this was 8.1 to 21.3% lower in ADF than other crops. This therefore shows the outstanding forage quality of hybrid brassica for beef cattle. It will be sufficed to say that when all 8 crops tested in this study are presented side by side to cows in a preference study, hybrid brassica would likely be preferred and consumed more than others because of its lower ADF value (18.0%). This would likely be followed by CFSH 30 (Forage sorghum), which had 26.1% ADF content.
Energy: The forage energy (total digestible nutrients, TDN) varied from 56.7% TDN for phacelia to 79.4% TDN for hybrid brassica. Only 2 (buckwheat and phacelia) of the 8 tested cover crops fell short of meeting a mature beef cow’s energy requirements, which is 7% at mid-pregnancy stage, 9 at late-pregnancy stage and 11% during lactation. The 6 other crops exceeded the TDN needed by a mature beef cow. For growing and finishing calves, all tested cover crops (except for buckwheat and phacelia) were also able to meet the energy requirements of these calves.
For other forms of energy measured (ME, NEG, NEL NEM & DE) (Table 1), hybrid brassica consistently had higher values than other cover crops tested. Looking at the ME values in the present study, all cover crops (except for phacelia) were well within the suggested daily ME requirements of 2.23 to 2.54 mcal/kg of a mature beef cow. A mature beef cow requires 0.97-1.10 Mcal/kg of NEM at the dry gestation stage and 1.19-1.28 Mcal/kg NEM during lactation. Therefore, all the 8 cover crops tested here met the NEM requirement of a mature beef cow. Also, all cover crops tested met the 0.53-1.37 Mcal/kg of NEG growing and finishing calves.
Summary: Though DM yield was not determined in this study, looking at the forage quality, it is evident that hybrid brassica generally performed better than other cover crops tested, particularly taking into consideration forage Ca, P, K, Na, ADF, TDN and other forms of energy. The superior quality of hybrid brassica is strongly reflected by the ADF content (18%), which is 8.1 to 21.3% lower than other cover crops tested here. Its protein content (18%) placed it in the top 3 and it far exceeded the protein requirements of young and mature beef and dairy cows. This therefore shows that feeding hybrid brassica to beef cattle will probably not require any supplementation at all. Overall, all cover crops tested here have got high feed values and are therefore suggested for inclusion in cocktail cover crop mixtures in the area.
Some notes on Hybrid brassica: Hybrid brassica is an early maturing hybrid brassica, a cross between a forage turnip and a forage rape, with 10-12 weeks crop duration. It has good frost tolerance and retains leaf and stem quality in frosty or cold conditions. Forage Brassicas are useful for extending the grazing season when other forages are less productive. Brassicas can provide higher crude protein and digestibility at half the cost of hay or conserved forages. Brassicas have extremely high yield potential when grown on high fertility soils and properly managed. Brassicas can produce as much as 40 tons (wet) per acre. Hybrid brassica can commonly provide valuable feed when other crops are less productive.