There is a lot known about forages in the northern plains, but little of this relates to zero tillage cropping systems. Farmers often view forages as separate from annual cropping although this does not have to be so. Generally, farmers in the northern plains recognize the benefits of forages in rotations, in particular better yields and weed control.1 But perennial stands are often kept longer than is needed to replenish soil with N. Annual and perennial forage crops improve many soil and weed factors and are probably an under-used tool for our region. Forages add diversity and intensity to crop rotations which benefit zero tillage more than conventional tillage systems.

Most forage producers agree that annual crop yields are higher when planted after a perennial forage crop than after an annual crop. Research shows yield benefits from forages can last 9 years.

Even on a farm where there are no livestock, forages could be beneficially included in zero till rotations. There is a market for the forage and the soil and nutrient benefits for the subsequent annual crops are significant. In a Manitoba study, zero till field pea yields improved when grown in an alfalfa-alfalfa-wheat-wheat-pea rotation compared to when they were grown in a wheat-pea-barley-wheat-pea rotation.2 The alfalfa was removed with herbicides. The year after the peas were grown, wheat yielded 500 kg/ha (7.5 bu/ac) more in the alfalfa rotation compared to the no alfalfa rotation.

The yield advantage of having forages in the rotation occurs for several reasons.

DEEP WATER USE

Deep-rooted alfalfa is one of the best ways to manage salinity. However, if the soil is too salty for alfalfa, then more salt tolerant grasses may have to be used.

Alfalfa can also retrieve deep-leached nutrients. A new stand can retrieve nutrients from 120 cm (48") and by the third year, nutrients can be retrieved from 210 cm (84").2

AlfalfaÌs deep roots effectively allow more water to infiltrate and increase the soil's ability to store water. This is because alfalfa root pores are continuous to the surface and they resist collapse. The pores can remain open for many years.

This"biological tillage" improves the root growth of subsequent crops, increasing their use of subsoil water and nutrients, as their roots are easily able to follow the old alfalfa root channels.

FORAGES REDUCE WEEDS

In general, fewer weeds occur in crops following forages as compared to following grain crops. However, weed reduction from short-term perennial stands will only be achieved by killing stands with herbicides - not by tillage (Figure 1). This is partly because tillage promotes germination of many weeds, particularly wild mustard, lamb's quarters and red root pigweed. Weed seeds left on the surface can be eaten by beetles and other small creatures which thrive in alfalfa and low disturbance zero till soils.

FORAGES CHANGE WEED POPULATIONS

Forages reduce some weeds more than others. Wild oats and green foxtail are greatly reduced by having alfalfa in the rotation (Figure 2).3 The effect is large enough that wild oat numbers in following crops may not require controlling. Often, wheat crops grown after alfalfa have almost no wild oats. Small-seed broadleaf weeds are less affected by having alfalfa as the previous crop.

Alfalfa is especially good at reducing Canada thistle. Roots of Canada thistle can be reduced by 60% as the alfalfa out-competes thistles for water and light. Control is helped by repeated cutting.

While alfalfa will reduce Canada thistle populations, it may allow dandelions to increase. Dandelions can be suppressed by killing the alfalfa stand before it gets gappy and over-run. Reducing alfalfa stand length to less than 4 years and fertilizing stands with adequate P, K, and S also reduces dandelion invasion.

The shift in weed composition by growing alfalfa reduces the risk of selecting for herbicide resistant weeds. For example, crops sown on wheat stubble must compete with weeds like wild oats, green foxtail and wild mustard (Table 1). However, crops sown in herbicide-killed alfalfa have to compete with wild buckwheat, wild mustard, lamb's quarters and dandelion.

Cutting sweet clover and cereal crops for feed effectively reduces annual weeds, especially wild oats.4 Avoiding an in-crop herbicide in these forage crops helps in rotating herbicides. Similar to perennial systems, annual forages are better at suppressing weeds when used in conjunction with zero tillage rather than with conventional tillage.

NITROGEN FROM ALFALFA

A three year stand of alfalfa is probably optimal for maximum N fixation. After this, the N simply cycles with little more being added to the soil. Pure alfalfa and alfalfa/grass mixtures will give equal N benefits, provided alfalfa is at least 50% of the mix.

Typically, 250 kg/ha (223 lb/ac) of N is released to the soil in the first two years after stand termination. However, this is affected by the size of the stand, and the soil's moisture and temperature when it is killed. One year of non-dormant ÎNitroÌ alfalfa yielding 3.8-6.3 t/ha (1.5-2.5 t/acre) of hay has added 120 kg/ha (107 lb/acre) of N to the soil.5 About half of this N was available to the following crop. Alfalfa residues typically supply most of the N required for two following crops.

When soils are cultivated in warm and wet conditions, a lot of N is released in the first season, leaving less N for following crops. If the stand is killed with herbicides rather than tillage, then N release will be slower giving more N to following crops for up to 5 years. This slower N release is better timed to the needs of subsequent crops, much like a split N application. This also improves N use efficiency.6

In a dry year, total N release from killed alfalfa may be greater in zero tillage as there is more moisture in the surface soil to help mineralize the N.

Another reason to avoid tillage when removing alfalfa, particularly in sandy soils, is that tilling increases nitrate levels below the root zone of annual crops. This nitrate can then leach into the groundwater.

If alfalfa is terminated with herbicides just before planting a spring crop, then N availability to this crop will be lower than if the alfalfa was sprayed in late-summer of the previous year. Some applied N fertilizer may be needed for new legume crops sown into freshly killed alfalfa. When alfalfa is sprayed in late-summer of the previous year, little or no extra N, above "starter-N", is needed for the cereal crop.

When changing from forages to grain crops, a soil test is useful! Forage hay crops remove 2-3 times more P, K and S than grain crops. Crop failures after Îforage-breakingÌ are often blamed on dried-out soil, when a lack of nutrients is a more likely explanation.

FORAGE ESTABLISHMENT

Establishing a forage stand is the most challenging phase in forage production. A no-till seedbed is better than a conventional one for establishing forages, as it is firm and moist, and the small forage seeds can be planted shallow.

A Manitoba study showed that in a dry spring, establishment of alfalfa and meadow bromegrass can be more successful under no-till compared with tilled soil.7 In this study, the moist zero tilled soil helped the crop survive a 30 day drought after seeding.

Work in North Dakota also shows the best alfalfa stands are produced by no-till systems.8 Early season alfalfa establishment under no-till is better than later-season establishment. With late-seeding, tilled seedbeds work better probably due to more weeds under zero till at this time.

Many farmers lack specialized forage seeding equipment so they often have to adapt their other equipment. With such a small seed, good depth control is vital. Disc seeders give the most precise depth control and can be adapted to seed forages. Baling the cereal straw before seeding improves crop establishment.8 Some farmers save time by broadcasting the seed and harrowing afterwards. Farmers in moist areas of Uruguay regularly broadcast forage legumes (clovers) and drill the forage grasses along with the cereal companion crop.

COMPANION CROPS

Even though 85-90% of producers use a companion crop to establish forages, companion crops do reduce stand establishment. Zero till establishment techniques give many of the benefits of a companion crop, like shading and reduced soil temperature. This occurs without their being competition with the forage seedlings.8

Without a companion crop, it is possible to take two hay cuts in the year of establishment. In some years, a third cut can be taken in mid-late October. Alfalfa stands are much more hardy in the first year of establishment, therefore a late-season third hay cut in the establishment year is possible.

TERMINATING ALFALFA IN A ZERO TILL SYSTEM

Direct seeding annual crops into chemically killed perennial forages works well if the stand is less than 4 years old. This keeps dandelions in check and reduces holes made by gophers. Alfalfa can be killed with glyphosate alone but control is improved by adding 2,4-D, or dicamba, at recommended rates. Extra glyphosate may be needed if the stand is grassy.

The alfalfa should be at least 20 cm (8") tall and close to flowering at the time of spraying. This improves the kill, much like pre-harvest RoundupÆ controls Canada thistle and quackgrass. Pre-harvest Roundup on hay crops allows an extra cut to be taken in the year the stand is killed. This greatly improves the economics of short term forage stands.

INTEGRATING GRAZING AND NO-TILL SYSTEMS

Integrated farming systems elsewhere in the world often have 1-2 years of forage then 1-2 years of grain crops. Farmers in New Zealand, Uruguay and Australia commonly use this "ley-farming" system. Ley farming is a system of alternating between legume-based pastures and grain crops. This provides more organic N to the grain crops.

Integrating these systems is not popular in the northern plains. However, some farmers have reduced their costs, improved animal performance and made their soils more productive by integrating grazing and annual cropping. This system is most effective under zero-tillage!

Adopting these management practices could improve beef production on marginal soils, and at a lower cost than grain-fed cattle. This will also recycle nutrients while maintaining the other rotational benefits of forages. However, soil compaction on heavy wet soils, and erosion on sandy soils, can sometimes reduce the systems attractiveness.

In North America, grazing and zero till tend to be integrated where alfalfa and alfalfa/grass hay crops are rotated with annual crops. However, other than sending cattle out to clean up crop residues after grain harvest, there are few operations where pastures and grain crops are rotated on the same piece of land. In some cases, marginal lands could support both annual crops and forage crops if zero till is used to minimize soil erosion, salinity problems and leave rocks in the ground.

Alternative grazing systems are viable. However, current grazing systems require minimal management, so there needs to be a clear economic benefit to encourage changing to a new system.

Management systems involving high-producing legume and grass species, regular fertilizer and rotational grazing would make pastures more economical on higher quality land.

" We're seeding more alfalfa on our farm. We don't raise any cattle but I can still sell the alfalfa to someone who does. Farmers are so focused on production that we don't look at marketing. We're going to have to develop markets - work at adding value to what we're raising. We're so used to just taking our production to the elevator or our calves to market in the fall and giving up ownership for what they're willing to pay us. That's the thing that has got to change"

Darrel Oech Beach, North Dakota

Prepared from information provided by:

Martin Entz,

Department of Plant Science

University of Manitoba, Winnipeg, Manitoba R3T 2W2

Telephone (204) 474-6077 Fax (204) 261-5732

Email "entz@bldgagric.lan1.umanitoba.ca"

References:

1. Entz MH et al (1995). J. Prod. Agric. 8:521
2. Entz MH (1996). U of Manitoba (unpublished)
3. Ominski P and Entz (1994). U of Manitoba
4. Schoofs A (1997). U of Manitoba (M.Sc. Thesis)
5. Kelner DJ and Vessey (1995). Can. J. Plant Sci 75:655
6. Mohr R (1996). U of Manitoba (Ph.D. Thesis)
7. Allen CL and Entz (1994). Can. J. Plant Sci. 74:521

Meyer D (1996). North Dakota State U Research