M.H. Entz, J. Bullied, C.L. Allen, and P.D. Ominski

Dept. of Plant Science

Faculty of Agricultural and Food Sciences

University of Manitoba

Winnipeg, MB

R3T 2N2

This article reviews some of the benefits of including forage crops in cereal-based crop rotations. Information sources include: 1) previous research on forage-based crop rotations in Prairie Canada and the northern U.S., 2) a 1992 survey of 250 farmers in Manitoba and Saskatchewan, and 3) on-going field research on forage-based crop rotations at the University of Manitoba. Observed benefits of short-term alfalfa stands include higher yields in following cereal crops, suppression of annual and perennial weeds, improved soil structure, and recovery of deep-leached nitrates. The yield enhancing effect of the forage on subsequent crops decreased with forage stands greater than five years. At one heavy clay site, wheat following alfalfa rooted deeper than wheat following barley. This observation suggests that alfalfa provided some "biological tillage".

This article also describes management approaches that would make it easier to get alfalfa into and out of annual crop rotations. Under dry spring conditions, alfalfa establishment was two times greater in zero tillage compared with the conventional tillage treatments, while under wet spring conditions forage establishment was similar under zero and conventional tillage. Terminating forages stands with herbicides rather than tillage increased over winter water conservation, and increased surface soil water the following spring.

Presented at the 1994 Manitoba – North Dakota Zero-Tillage Farmer’s Association Workshop "Residue Management for Profitable Farming". Jan. 31 and Feb. 1 and 2, 1994, Minot, North Dakota.

A forage is any plant whose vegetation is eaten by livestock. Traditional forage crops include alfalfa, alfalfa/grass mixtures, straight grass stands, and annual forages (oats, corn, millet, etc.). Other plant products that qualify as forage are chaff, straw, and weeds.

The textbooks tell us that including perennial forage crops such as alfalfa or alfalfa grass mixtures in rotation with annual crops will increase soil organic matter and soil aggregation, suppress weeds, reduce nitrogen fertilizer requirements in following grain crops, reduce energy required in crop production, and extract deep-leached nitrates. It is also known that deep-rooted, long-season forages like alfalfa will deplete soil water reserves.

In this section of the paper, we will consider some of these benefits more closely; to see if they are being realized on prairie farms. Information has been derived from 1) previous research in Prairie Canada and the northern Plains of the U.S., 2) a survey of 250 farmers in Manitoba and Saskatchewan, and 3) research on forage-based cropping systems currently underway at the University of Manitoba.

Results of Producer Survey Of the 250 farmers who completed the U of M survey, 71% indicated higher grain yields on forage-breaking than following another annual crop. Results indicated that the performance of grain crops following forages differed in the different climatic/soil zones surveyed. For example, including forages in the rotation increased the yield of following grain crops in Zone 4,5, and 6, however, grain yields were unchanged in Zone 2, and grain yields were lower following forages in Zone 1 and 3. Zone 1 has the greatest moisture limitation, and hence the results are not surprising.

Yield decreases following forages in Zone 3 were attributed to the low frequency of summerfallow in this region. While there may be enough moisture to secure grain crop established in this region, soil water reserves may not be enough to carry it through to maturity. While Zone 2 is drier then Zone 3, the frequency of summerfallow the year agter forage-breaking was found to be twice as high is Zone 2 than in Zone 3. Hence, yield depression following alfalfa were less frequent.

The percentage of producers indicating lower grain yields following forages increased with average forage stand length greater than five years. This trend clearly showed that when stands are left in for more than five years, fewer benefits will be derived.

Lower grain yield following forage stands older than five years was likely not due to excessive water depletion by the forage, since soil water depletion by forages occurs by the second or third year of the stand (Entz Et al. 1993). The negative effect of stand length may have been related to nutrient deficiencies. At any rate, this evidence suggests that many farmers are leaving forage stands in too long.

Research Results Research in northern Alberta indicated that yield benefits of alfalfa lasted up to seven years (Hoyt and Leitch 1983). These researchers also showed that alfalfa provided a greater yield boost to following crops than alsike clover or birdsfoot trefoil. A study in a low organic matter sol in Saskatchewan (Brandt 1981) showed that alfalfa had a cumulative beneficial effect on soil fertility and yields of wheat. That is, the yield benefit due to alfalfa increased every time alfalfa was indicated in the rotation.

Results of Producer Survey Eighty-four percent of respondents in the producer survey indicated fewer weeds in annual crops after forage-breaking compared with annual crops in an annual crop rotation. Fifty percent of respondents indicated that the weed suppressing effect of the forage crop lasted for two years, while 33% indicated that the effect lasted three years after forage breaking. Over all climatic/soil zones, 50% of respondents indicated the greatest reduction was for annual broadleaf weeds, and 15% indicated the greatest reduction for Canada thistle.

The type of weed species suppressed by the forage differed depending on climatic/soil zone. The greatest decrease in annual grass weeds was observed in Zone 6, the greatest decrease in annual broadleaf weeds was observed in Zone 1 and 3, while the greatest decrease in Canada thistle was observed in Zone 5.

Research Results Very little research has been conducted in the past 40 years on weed suppression by crop rotation (ie. since about the time that herbicides were developed). However, the "old" research clearly shows that short-term forage stands reduce populations of wild oats and perennial weeds (Siemens 1963). For example, research at Brandon, Manitoba in the 1930’s and 40’s showed that even a one-year annual forage crop in a three year cereal grain rotation was enough to keep wild oat populations under control.

A recent weed survey in southwestern Manitoba (Ominski; University of Manitoba, 1993, unpublished data) showed that wheat after alfalfa had 86% fewer green foxtail, 94% fewer wild oats, and 56% fewer wild mustard plants than wheat in an annual crop rotation. Using forages for weed suppression should reduce herbicides selection pressure on weed populations. This means a lower risk of developing herbicide resistant weeds.

On-Farm Observations In the "old" days, farmers used to cut their weedy crops and feed them to livestock. This is still being practiced today, especially by organic farmers. If you have a herbicide resistant weed patch in one of your fields, you may want to consider doing this. It’s called taking lemons and making lemonade.

Many farmers in drier areas of the prairie have mounted chaff catchers on their combines. However, these units do not only capture chaff, they also catch weed seeds. Therefore weeds seeds are removed from the land. The chaff is usually fed to cattle (sometimes it is ammoniated prior to feeding to increase the non-protein nitrogen level). Remember to compost the manure before spreading it back on the land. Composting kills the weed seeds.

Research Results The ability of forage legumes to add nitrogen to soil has been known for centuries. Research in Manitoba showed that five year alfalfa stand reduced the need for fertilizer N for two consecutive cereal crops (Bailey 1982). In northeastern Saskatchewan, Bowren and Cooke (1975) reported that the yield of wheat after soil incorporated alfalfa was equal to wheat fertilized with 76 lb/acre of N.

A study at Brandon, Manitoba (Ferguson and Gorby 1971) showed that a four year alfalfa stand provided almost as much N to the soil as a six year or an eight year alfalfa stand. In 1959, Gorby stated that "Maximum benefit from alfalfa and perennial grasses is obtained by leaving then in production for at least two years, exclusive of the seed-down and break-up seasons".

The research at Brandon also showed that a mixture of alfalfa and bromegrass provided the same amount of N as pure alfalfa (Ferguson and Gorby 1971).

There is interest by producers in growing "annual" alfalfa varieties. Research in Minnesota and Manitoba has shown that under favorable growing conditions, a one-year alfalfa crop (seeded in May, one cut in July, regrowth plowed-down in September) can supply enough nitrogen for at least one wheat crop.

The amount of N supplied by any alfalfa depends on the forage stand density and the cutting management. For example, sparse stands will not provide as much N as dense stands (Remember: You should aim for 100 alfalfa plants/m2 in the establishment year). Also, the more intensive the cutting regime, the more nitrogen will be removed from the land in the form of hay.

Research in the Red River Valley of Manitoba found that wheat grown after a two year alfalfa stand had roots to a depth of 3.5 feet, compared with 2.5 feet for wheat following barley and wheat. It appears that alfalfa provided some "biological tillage" which allowed wheat roots to extend to greater depths.

While forages are generally regarded as soil-improving crops, intensive tillage used to break the stand can expose soil to erosion. Results of the producers survey indicated that 30% of farmers summerfallow for a full year after forage-breaking. Therefore, about 1/3 of fields seeded to forages will be susceptible to erosion the year after forage-breaking.

Factors that contribute to nitrate leaching are summerfallow, over-fertilization with nitrogen, and improper manure disposal. Research in Minnesota found that one year of alfalfa or reed canarygrass was effective at significantly decreasing nitrate levels in the top four feet of contaminated soil, but that corn and soybean were not effective (Randall et al. 1992).

Entz et al. (1992) showed that a three year alfalfa stand is effective at significantly decreasing nitrate concentrations as deep as 210 cm (7 feet) in the soil profile.

Caution: Summerfallowing the year after forage-breaking can actually aggravate the nitrate leaching problem. Research at Lethbridge, Alberta (Johnston and Janzen 1992) found that subsoil nitrate levels were the highest in rotations where land was fallowed after alfalfa-breaking. Water-conserving management systems that reduce the reliance on summerfallow the year after forage-breaking should be adopted.

The major limitation to including perennial forages in short-term rotations in the drier areas of the North America plains is the lack of water. Because perennial forages have deep roots and grow well into September, soil water reserves will often be low the next year. This often forces farmers to summerfallow the year after forage-breaking. One way to overcome this water shortage problem is to break up perennial forage stands in "wet" years. This should give you a better chance of getting water recharge in to the soil. The problem is predicting when a wet year will occur.In terms of soil moisture management, annual forages provide more flexibility to farmers in drier areas.

In wetter areas in western Canada and eastern North Dakota, perennial forages such as alfalfa usually do not result in droughts the year after forage-breaking. Research in Manitoba and northern Alberta showed that while subsoil moisture may be lower after a three or four year forage stand, there is usually enough precipitation to recharge water in the top two feet.

Low cereal yields on forage-breaking are not necessarily due to soil water shortages. Low cereal yields can also be due to nutrient shortages.

Approximately 12% of the arable land in the Black and Grey soils zones of western Canada is seeded to tame forage crops at any one time. This acreage should be used as efficiently as possible.

Results of our producer survey indicated that the average length of alfalfa and alfalfa/grass stands in this region are six and eight, respectively. However, economic analysis has shown that shorter stands (two to four year stand lengths) are also profitable (Jeffrey et al. 1993). The advantage of shortening alfalfa stands from six to three years, is that the benefits associated with the forage could be "spread" across more acres without increasing the total forage acreage.

One very compelling argument for "spending" the benefits of forage around the farm is to slow the development of herbicide resistant weeds.

Many farmers are reluctant to shorten forage stand length because of the difficulty in establishing and removing forage crops from the rotation. Establishment is perhaps the most challenging phase of the forage production system. Because forage seeds are small, they must be seeded shallow. In conventionally-prepared seedbeds, the top 2 cm of soil is often dry.

Field experiments were conducted at Portage la Prairie, MB in 1990, 1991, and 1992 to compare establishment of alfalfa and meadow bromegrass under zero (ZT) and conventional tillage (CT) following three different annual crops. All forages were seeded using a Nobel hoe-drill. Detailed methods were desribed in a scientific paper (Allen and Entz 1994). Measurements included volumetric soil water, forage establishment and forage dry matter yield.

Field trials to assess ZT alfalfa establishment were conducted under wet post-seeding (1990 and 1991) and dry post-seeding (1992) conditions. Under wet conditions (3 inches of rainfall 40 days after seeding), alfalfa establishment under ZT was somewhat lower on wheat stubble than on pea or canola stubble. However, establishment year alfalfa dry matter yields were unaffected by tillage system or previous crop type. Under dry conditions (less than ½ inch of rainfall 40 days after seeding), establishment of alfalfa following wheat was significantly higher under ZT compared with CT. Superior establishment of under ZT in 1992 was attributed to higher levels of surface soil water.

The majority of prairie farmers (98%) currently use some tillage to terminate forage stands (Mupondwa et al. 1993). However, tillage is expensive, 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 a wet year, even intensive tillage may not even be enough to completely kill the stand. The difficulty in removing forage stands using tillage is underscored by the fact that approximately 30% of prairie farmers still summerfallow the year after forage breaking (Mudondwa et al. 1993). An alternative approach is to spray the forage with a herbicide and direct-seed a grain crop into the suppressed residue.

Field experiments were established in a number of locations in central and western Manitoba (Bullied, U of M, unpublished data) to investigate the feasibility of 1) removing alfalfa using herbicides instead of tillage, and 2) direct-seeding cereal crops into suppressed forage residue. Herbicides included Roundup, Lontrel, Banvel and 2,4-D, 2, 4-D alone and in combination. Herbicides were applied to alfalfa regrowth (approx. 10 inches in height) either in the fall (mid-Sept.) or in spring (late-May). A tillage control was included in each experiment.

In general, herbicides were as effective, and in some instances more effective, than tillage in removing or terminating alfalfa, fall applied treatments usually provided a more effective kill. Over four sit-years of trials, our best results have been achieved by using roundup (1 L/acre) in combination with broadleaf herbicides (either banvel, lontrel, 2,4-D, or combination of 2 broadleaf herbicides plus roundup) applied in mid-September on 8 to 10 inches of alfalfa regrowth.The herbicide-killed alfalfa conserved more water than tilled alfalfa (about 1 to 3 inches of additional water in the herbicide-killed treatments). Greater water conservation in the herbicide-killed treatments were due to more snow-trapping and less soil water evaporation between snow melt and spring seeding.

In one study where alfalfa was terminated in mid-September, Roblin wheat yielded 60 bu/acre in the herbicide removal treatment and 46 bu/acre in the tillage removal treatment. Both treatments received an in-crop application of banvel.

Herbicide Recommendations for Forage Stand Removal: Available from Manitoba Agriculture Soils and Crop Branch (Box 2000, Carman, MB, R0J 0J0, (204) 745-2040) or the Zero-Tillage booth.

The authors would like to acknowledge the assistance of Mr. Keith Bamford. Financial assistance from The Potash and Phosphate Institute of Canada, the Foundation for Agronomic Research, the Canada-Manitoba Environmental Sustainability Initiative, the Manitoba Forage Council, and Manitoba Agriculture (Soils and Crops Branch) is also gratefully acknowledged. We are also grateful to the Manitoba Weed Supervisors Association for assistance in the 1993 weed survey. Finally, I would like to thank the Manitoba-North Dakota Zero Tillage Farmer’s Association for travel assistance and for the interest in our research program.