Department of Plant Science - Extension Bulletins - Forages Improve Efficiency of Prairie Cropping Systems

M. H. Entz, P.D. Ominski, R. Mohr, A. Schoofs, D. Forster,
W.J. Bullied, S. Shirtliffe, and K.C. Bamford
Dept. of Plant Science, University of Manitoba, Winnipeg, MB, R3T 2N2

This paper begins with a summary of rotational benefits of alfalfa in prairie cropping systems. In a recent survey of 253 prairie farmers, it was found that while farmers observe these benefits, very few make a special effort to capture them. The most effective way to spread the rotational benefits of forages to more cropland is to cycle forages through the rotation more quickly. This can be achieved by shortening forage stand length from the typical six to seven years to four or even three years. For example, in many cases, a three year stand will give the same weed suppression and nitrgon benefits as a six year stand. In one set of experiments, it was found that one-year forage hay and silage crops reduced weed populations to the same extent as herbicides used in cereal grain crops. Factors discouraging producers from shortening forage stand length include economics, and difficulties in forage stand establishment and termination. A three year study indicated that seeding forages using a no-till system increased establishment in dry years. A second three year study was conducted to investigate the influence of tillage system on forage stand termination. No-till alfalfa stand termination was found to enhance the weed suppression benefits of the stand, and to increase efficiency of alfalfa nitrogen by following crops. A no-till approach to both forage stand establishment and termination was shown to improve the economics of shorter forage stands. A different study showed that including short-term alfalfa stands significantly enhanced that rotation benefits of field pea crops sown several years after the alfalfa stand had been removed.

There is considerable interest in developing cropping systems that reduce the use of pesticides, protect the soil from erosion, improve soil quality, and reduce reliance on external inputs of non-renewable energy (Morrison and Kraft, 1994). Therefore, it is understandable that there is renewed interest in traditional practices such as the inclusion of perennial forage crops in crop rotations.

Benefits of incorporating alfalfa or alfalfa/grass mixtures into cropping systems include increased soil organic matter, improved soil physical properties (Blackwell et al., 1990), reduced soil erosion (Stinner and House, 1989), suppression of weeds (Harvey and McNevin, 1990), and disruption of plant disease cycles. Because of their ability to contribute nitrogen to the soil, forage legumes significantly reduce reliance on non-renewable energy to produce nitrogen fertilizer (Rice and Biederbeck, 1983). A summary of rotational benefits of alfalfa is given in Table 1.

One of the most important benefits of forages for farmers is higher yields of grain crops which follow forages in the rotation. Rotational yield benefits of forages have been investigated in small plot trials in western Canada for many decades. Results of these trials indicate that in wetter regions (i.e., Black and Gray soil zones), grain yields are enhanced when alfalfa or alfalfa/grass mixtures are included in the rotation (Ferguson and Gorby, 1971; Baddarudin and Meyer, 1990). However, in drier areas (i.e., Brown and Dark Brown soil zones), perennial forage crops dry the soil to the point where yields of following grain crops are often reduced (Zentner et al., 1990). Most previous studies on yield response to forages in rotations in the northern Great Plains have focussed on the nitrogen contribution by legumes (eg., Baddarudin and Meyer, 1990); however, other yield enhancing benefits such as improved soil physical properties (Blackwell et al., 1990) have also been implicated (Hoyt and Leitch, 1983).

One unique attribute of forages is their ability to suppress weeds. The frequent cutting and heavy growth of forages reduces both the vigour of weeds and the seed production. Even alfalfa seed crops have been found to decrease populations of annual weeds. It is important to remember that forages include any crop whose vegetation is eaten by livestock. This includes such things as alfalfa, timothy, wheat chaff, or weedy crops cut for greenfeed.

Approximately 15 million acres in the prairie provinces of Canada are seeded to introduced forage species (about 7.5 million acres each of seeded pastures and seeded hay fields) (Anon., 1993). Because this area represents only 15.9% of the total arable land base in the region (Anon., 1993), only a small proportion of land in the area can receive the benefits of forages at any one time. Two approaches to increase exposure of agricultural lands to the rotational benefits of forage crops are to increase total forage acreage, or cycle forages through rotations more quickly. This second strategy would likely involve reducing the number of years a forage crop is included in the rotation (i.e., reducing forage stand duration). Previous research has shown that the minimum alfalfa stand duration for optimum N accumulation (Heichel et al., 1984; Kelner, 1994) and weed suppression (Dryden et al., 1983) is two to three years, while the economic optimum alfalfa stand duration in Manitoba was found to be four or five years (Jeffrey et al., 1993).

Table 1. Influence of alfalfa on a number of different agronomic and environmental parameters.

Parameter	Nature of Alfalfa Influence	References
Soil nitrogen	Five year alfalfa stand provides significant N for two following crops. N benefit can last up to 7 years Release of N from legume residue slower when legume stand terminated using no-till. Annual alfalfa crops can contribute an average 50 kg ha^-1N to the soil. As high as 120 kg ha^-1.	Ferguson and Gorby (1971), Bowren and Cooke (1975), Bailey (1987). Hoyt and Leitch (1983), Mohr, Entz and Janzen (unpublished data) Bruuslema and Christie (1987), Kelner (1994).
Soil structure	Alfalfa roots perform " biological tillage", thereby improving soil environment for root growth of subsequent crops. On heavy clay soils, inclusion of alfalfa in rotation increases soil water infiltration. No-till alfalfa removal keeps pores intact.	Blackwell et al. (1990), Entz (1994) Meek et al. (1990), Cavers and Eilers, Dept. of Soil Sci, U of MB (1994)
Subsoil N	A four year alfalfa stand effectively extracted N to a depth of 260 cm on an Osbourne clay soil in Manitoba. Fallowing the year after after forage breaking increases subsoil N, thereby increasing the risk of groundwater contamination.	Entz and Vessey (unpublished) Campbell et al. (1994)
Weeds	Two or three years of forage in a six year rotation virtually eliminated wild oat in cereal crops. A survey of commercial fields in Manitoba indicated significantly fewer wild oat, green foxtail and Canada thistle plants in wheat following forage crops vs. wheat following annual crops. Eighty percent of producers in a MB/SK survey indicated fewer weeds in annual crops after forage-breaking compared with annual crops in an annual crop rotation. Good control of wild oat, green foxtail and Canada thistle was observed for a period of one (11% of respondents), two (50% of respondents), or more (33% of respondents) years.	Siemens (1963) Ominski et al. (1994) Entz et al. (1995)
Soil water status after alfalfa	Black and Gray soil zones: Soil water in 0 to 60 cm usually recharged in alfalfa rotation, but subsoil drier. Fallow not required for water recharge after forage-breaking. Removing alfalfa stands using no-till increases soil water recharge by up to 3 cm. Dark Brown soil zone: Including alfalfa in rotation results in moisture shortages in following year. Fallow required for water recharge after forage-breaking.	Hoyt and Leitch (1983), Entz (1994), Bullied and Entz (unpublished data) Brandt and Keys (1982)
Grain yield of following crops	Recent survey indicated that 71% of producers in MB and SK observe a yield benefit from including forages in their crop rotations. Yield benefit greatest in wetter areas and lowest in Brown soil zone. Yield benefits decrease sharply as alfalfa stand length increases beyond four years. Cumulative yield benefit occurs when legumes repeatedly included in cereal-based crop rotation. In dry years, grain yields greater when alfalfa removed using no-till vs. tilled system.	Entz et al. (1995) Poyser et al. (1957). Entz and Gulden (unpublished data)

Before effective and meaningful research and extension programs related to forage-based cropping systems can be developed, a more thorough understanding of the current "state of the art" of commercial forage management is required. A survey of 253 Manitoba and Saskatchewan producers known to have forages in their rotations was conducted in 1992. Results are summarized in Table 2. Results indicate that while producers observe rotational yield and weed control benefits from forages, few producers are managing forage stands for maximum rotational benefit. For example, most producers maintain forage stands for longer than necessary for maximum agronomic benefit. The strategy of most producers appears to be to maximize forage stand length, and only reestablish a new forage stand when the existing stand looses productivity (Table 2). Other observations from the survey indicate that producers use a great deal of tillage both in the stand establishment and stand termination phases of the forage production system.

Table 2. Summary of the current role of perennial forages in prairie crop rotations; Survey of 253 Manitoba and Saskatchewan producers (Entz et al. 1995).

Questions on Forage Crop Management	Percent Response by Producers	Comments
Main farm enterprise	Mixed (grain and livestock) - 62.8%; Dairy, Livestock only, Grain and forage seed - (10% each).	Mixed farms evenly distributed across survey area; forage seed concentrated in eastern MB and northeastern SK. Percent of tillable acres on survey farms dedicated to forages - 30%.
Rotational benefits: Grain yield following forages.	Higher yield after forages - 67.4%; Lower yields after forages - 9.3%; No change - 23.3%	Yield benefits of forages greatest in wetter areas and lowest in southern SK. In dry areas, as frequency of summerfallow after forage breaking increased, rotational yield benefits increased. Yield benefits lower when forage stands longer than 5 years.
Rotational benefits: Weed suppression by forages.	Fewer weeds after forage-breaking - 83.3% More weeds after forage-breaking - 7.9% No difference in weed populations - 8.8%	Producers noted weed suppression for one (11% of respondents), 2 (50% of respondents), or more (33% respondents) years after forage-breaking. Suppression noted for annual grasses, annual broadleaf weeds and Canada thistle.
Forage stand length	Average forage stand length 6.5 years. Forage stands longest in southern SK (>8 years), and shortest in south-central MB (4 to 5 years).	Current forage stand length much longer than required for rotational yield and weed control benefits, and slightly longer than economic optimum (which is 4 or 5 years, Jeffrey et al. 1993).
Why do farmers terminate forage stands?	Reduced yields - 58.1%; gophers - 18.7%; rotational considerations - 11.6%.	The strategy of most producers is to maximize forage stand life, and rotate forages only when necessary due to declining productivity.
How do producers terminate forage stands?	Tillage alone - 76.6%; tillage and herbicides - 22.1%; herbicides alone - 1.3%.	Over 20% of producers indicated fallowing land for one full year after forage stand termination. Producers who used both tillage and herbicides relied less heavily on fallow the year after forage stand termination (19 vs. 27% for those who used tillage alone).
Forage establishment: Seeding equipment	Press drill - 48.5%; Airseeders or hoedrills - 19.0%; Broadcast seeding - 18.6%.	Few producers are using seeding equipment which would be compatible with conservation tillage systems.
Forage establishment: Companion crops	Ninety percent of producers use companion crops. Wheat or barley - 42.8%; oats - 31.0%; canola - 12%.	The majority of producers use competitive companion crops such as cereals or canola. The use of these companion crops is known to reduce forage establishment and yield.

Two factors which are thought to discourage producers in western Canada from cycling forages through rotations more frequently are the difficulties of establishing (Kilcher and Heinrichs, 1960) and terminating (Bullied and Entz, 1994) perennial forage stands. Forage establishment can be improved by using the soil-and-water-conserving zero tillage seeding system (Allen and Entz, 1994), and by choosing less competitive companion crops (Klebesadel et al., 1959). Effectiveness of forage stand termination may be improved by substituting herbicides for some tillage operations (Bullied and Entz, 1994). Another point worth mentioning here is that although perennial forages are considered to be soil-improving crops (Morrison and Kraft, 1994), traditional forage stand establishment and termination techniques rely heavily on intensive tillage, which can lead to soil erosion both during the forage establishment phase (Sturgul et al., 1990), and after forage stand termination (Campbell et al., 1990).

The purpose of this paper is to review the rotational benefits associated with forage crops, and secondly, to discuss how producers can best capture these benefits.

Results presented in this paper are from crop management and rotation trials conducted in Manitoba between 1990 and 1996. Information on methods and site characterization is given in numerous publications cited in this paper.

Establishment is the most difficult phase of the forage production system. Forage seedlings are especially vulnerable to soil moisture deficits because the small seeds are sown near the soil surface (Sheaffer 1989). Conventional seedbed preparation techniques result in dry seedbeds and increase the risk of soil erosion (Sturgul et al. 1990). Using companion or "nurse" crops cuts down on soil erosion, but also reduces forage stand establishment and second year forage yields (Waddington and Bittman 1983).

A better approach may be to use the zero-tillage (ZT) system where forages are direct-seeded into annual crop stubble. Previous studies have indicated that forage establishment can be as high (Wolf et al. 1985) or higher (Stout et al. 1990) under ZT compared with conventional tillage (CT). Wolf and White (1992), on the other hand, concluded that previous crop residue had to be removed for successful alfalfa establishment under ZT. A seedling population density of 100 alfalfa plants m^-2 is considered adequate for maximum forage yield and quality (Meyer 1985).

A three year study in Manitoba (Allen and Entz 1994) indicated that under wet post-seeding conditions, alfalfa and meadow bromegrass performed as well under ZT than CT when seeded into pea or canola stubble, however when the previous crop was wheat, establishment of meadow bromegrass was significantly reduced under ZT while alfalfa was unaffected. However, under dry post-seeding conditions, establishment of both forage species was dramatically increased by ZT. Superior forage plant establishment under zero tillage was attributed to higher levels of water in the surface soil.

Establishment year, and year after establishment herbage yields were unaffected by tillage system or previous crop type (Allen and Entz 1994). These results indicate that ZT is a feasible alternative for establishing alfalfa and meadow bromegrass, even when the previous crop was a 4,000 kg ha^-1 wheat grain crop. The ZT system should provide many of the establishment year benefits of a companion crop (ie. protection from blowing soil, shading) with less competition for resources, especially water. In dry years, the ZT system would be expected to enhance forage establishment.

Current Practices Ninety-eight percent of producers currently use some tillage to terminate forage stands (Entz et al. 1995). Terminating forage stands using tillage is expensive (approximately $25/acre), requires large amounts of time and fossil fuel energy, dries the soil, and reduces many of the accumulated soil-improvement benefits associated with forage (especially when fields are tilled after the first cut and fallowed for the remainder of the growing season). In wet years, even intensive tillage does not always completely kill the stand.

Using Herbicides to Terminate Forage Stands An alternative method of stand termination is to use herbicides and direct-seed a grain crop into the suppressed alfalfa residue. Effective herbicidal control of alfalfa can be acheived for less than $20/acre (Button, 1991; Smith et al. 1992; Bullied and Entz 1994). Examples of herbicide treatments that have been found to provide adequate suppression of pure alfalfa stands are Roundup/2,4-D Amine (1 L/acre + 0.2 to 0.4 L/acre) (Button 1991; Bullied and Entz 1994), Lontrel/2,4-D Ester (0.15 L/acre + 40 mL/acre) (Button 1991), Roundup (2 L/acre) (Bullied and Entz 1994), and Roundup/Banvel (1 L/acre + 120 mL/acre (Button 1991). For grass/legume mixtures, higher rates of Roundup (eg. 2 L/acre) are required. The height of alfalfa regrowth and the stage of alfalfa plant development appear to affect herbicide efficacy. Control of alfalfa treated with Roundup/2,4-D tank mixtures was superior when the herbicide treatment was applied after 20 cm of regrowth compared with 5 to 10 cm of regrowth. Preharvest applications of Roundup at 2 litres/acre also provide adequate control of alfalfa.

Soil Water Conservation Research over three site-years in Manitoba indicated that alfalfa plots which were killed (after second cut in early September) with herbicides conserved from 1 to 3 cm more water in the 150 cm soil profile between stand termination and spring seeding than alfalfa that was killed using tillage (Bullied and Entz 1994). Greater soil water conservation was attributed to more effective snow trapping and reduced soil water evaporation between snow melt and spring seeding. Soil water content in the top 10 cm of soil was consistently higher in the herbicide treated plots.

Grain Yields of Following Crops Yields of wheat following chemically-killed vs. mechanically-killed alfalfa were measured in five field trials in Manitoba between 1992 and 1994. In most instances, there was no effect of either method or time of alfalfa stand termination on wheat yield, when the forage was killed the year prior to wheat cropping. However, when the stand was sprayed in spring immediately prior to wheat cropping, lower wheat yields were observed. Protein concentration of wheat seeds tended to be higher for the tilled vs. sprayed treatments. A second set of experiments was established in Minnedosa, MB to investigate the effects of supplemental N fertilizer on wheat grown after alfalfa. Results indicated that under dry conditions (yields in 25 to 35 bu/acre range), no additional N fertilizer was warranted on either herbicide-killed or tilled alfalfa. However under more favourable growing conditions (wheat yields in 35 to 50 bu/acre range) addition of 30 lb/acre of actual N appeared warranted.

Effect of Alfalfa Stand Termination System on Weed Populations Results of four separate field trials in Manitoba (Ominski, unpublished data) showed that by not tilling forage stands (i.e., removing forages using herbicides instead of tillage or herbicide/tillage combinations), populations of annual weeds were greatly reduced. In one trial, the density of green foxtail in the tilled alfalfa was 47.5 plants m^-2 compared with 4.7 plants m^-2 where alfalfa was sprayed the previous fall. Populations of lamb's quarter in the tilled and untilled plots were 65 and 11 plants m^-2, respectively. These results indicate that by not disturbing the soil, the weed control "life" of a forage stand may be extended.

Effect of Alfalfa Stand Termination System on Soil Nitrogen Status Soil nitrate-nitrogen was measured in plots where alfalfa were terminated chemically or mechanically at different times of year. At one site (sandy soil), method and timing of alfalfa termination had no effect on available N release (as estimated by summing plant N uptake at maturity and soil NO₃-N content to 60 cm in Sept., after spring wheat harvest). At a second site (heavy soil), early alfalfa stand termination (terminated after first cut) resulted in greater release of available N than herbicide treatments.

It was concluded from this study that termination of established alfalfa stands by herbicides alone resulted in improved synchrony between N availability (from legume residue) and N uptake by a subsequent crop of spring wheat.

In a field study at the University of Manitoba conducted between 1990 and 1995, it was found that rotational benefits of field peas (to following wheat crops) were greater where alfalfa had been previously included in the rotation (Table 3).

Table 3. Yield of a wheat test crop grown at Winnipeg MB in 1994 as influenced by previous crop type. Note: No N fertilizer added to any of these rotations over the six year study period. W-Wheat; P-Field Pea; B-Barley; A-Alfalfa.

Crop Rotation	Grain Yield of Wheat Test Crop(W) (bu/acre)	Nitrogen Uptake by Wheat Test Crop (lb/acre)
1. W-P-B-W-W-W	15.8	29.2
2. W-P-B-W-P-W	20.2	43.0
3. A-A-W-W-W-W	24.0	43.7
4. A-A-W-W-P-W	37.5	74.8
5. A-A-A-W-W-W	25.1	41.5
6. A-A-A-A-W-W	33.7	51.4
7. A-A-A-A-A-W	46.1	82.5

Results indicate that, as expected, including field pea in an annual crop rotation increased the yield and N uptake by the following wheat crop (eg. Rotation 2 vs. Rotation 1). What was unexpected was the observation that rotational yield benefits of field pea were much greater when alfalfa had been included in the rotation four years earlier (eg. Rotation 4 vs. Rotation 3 or 2). In fact, the yield and N uptake of the wheat test crop (W) in rotation 4 was similar to where wheat was seeded after a five year alfalfa stand (Rotation 7).

Project 4. Annual Forages, Including Chaff, Assist in Integrated Weed Management.

Field studies at the University of Manitoba have shown that including a one-year annual forage hay crop in a cropping system reduced the need for herbicides. For example, annual and biennial forages such as triticale silage, single year alfalfa crops and sweet clover reduced wild oat populations to the same extent as herbicides used in a grain crop. Collection of chaff was found to reduce the spread of wild oat and green foxtail seeds within a field, and resulted in some weed seed being removed from the field.

The research reported here was conducted by no fewer than 6 U of Manitoba graduate students from 1990 to the present. This type of detailed field agronomy research would not be possible without the hard work and dedication of these students. Thanks also to the many farmers who have helped in the research; by filling out a survey, making land available for field trials, or by taking an interest and giving feedback on the research program.

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