Agronomy Library > Soil Conservation

No-Till Alfalfa in Rotation - What the research shows
Author: Ron Heller
Date Created: March 10, 2006
Last Reviewed: January 30, 2007

Since glyphosate herbicide [1] has effectively replaced tillage to terminate perennial forages, farmers are more able to capture the value of alfalfa in rotation while taking advantage of the efficiencies associated with reduced tillage. Four beneficial spin-offs will generally occur if everything goes as planned – soil nitrogen (N) will increase, weed pressures will decrease, cereal crops will thrive, and soil erosion will be avoided.

In a summary [2] dated May 2003, researchers for Agriculture and Agri-Food Canada in Lethbridge reported on experiments with methods and timing of alfalfa termination, looking closely at the affects on subsequent irrigated barley and wheat crops. They concluded that:

To obtain optimum yield from cereal crops grown after alfalfa, [herbicide] treatments for the termination of alfalfa should be initiated in fall.
Decomposing alfalfa residues seemed to provide sufficient N for optimum cereal yield after fall termination of alfalfa.
To conserve soil from erosion, alfalfa residues should not be harvested after glyphosate application (fall termination).
These points of discussion support what more Alberta farmers are beginning to realize, as the adoption of cropping systems based on reduced tillage expands across the prairies. Many innovative growers have recognized that their no-till experience with annual cropping can be applied quite successfully to extended crop rotations with perennial forages. A new practice called sod seeding [3] , is actually replacing traditional tillage [4] .

Statistical analyses for weeds, available N, and yield were part of this 3-year study of three different termination treatments [5] . Each was compared for late summer, early fall, or spring timing, with the overall effects of every treatment evaluated for weed density (in-crop abundance and one year after wheat and barley), soil moisture (amounts and depth year to year), crop-available N (post seeding), and VAM [6] colonization (% of root).

The project’s plot seeder was equipped with no-till disc openers at 9 inch row spacing.

As an agronomist with a passion for soil conservation and economic value, I find the results of this research interesting. I would like to summarize some of the unmistakeable reduced tillage links found in the statements of the researchers’ report [7] .

Summary of RT Links [8] :

- there were sufficient weeds in all treatments that tillage or herbicide were required before seeding.

- Pre-seed burnoff to get an early jump on weeds is a fundamental direct seeding principle. Sod seeding may provide enhanced weed control due to a depleted weed seed bank in the soil, mulch barrier, and lower soil disturbance.

- The different yield response [to treatment time] may be due to an earlier seeding date… 

-  Early seeding is an inherent benefit of direct seeding that provides timeliness to capture soil moisture and maturity days. According to the results in this study, yield potential may have been compromised when the spring glyphosate treatment was delayed until alfalfa was >10cm tall thereby delaying seeding another 2 weeks after treatment.

- When time of treatment affected moisture content, the [spring] treatment resulted in the lowest [soil] moisture content. 

-  Soil moisture conservation, especially in dryland/rain-fed situations, has been a major reason for reducing tillage, almost inseparable from the desire to avoid erosion. Even under irrigation, soil moisture at depth can impact yield. In sod seeding, a fall termination begins saving soil moisture sooner than waiting for next spring when regrowth (green-up) must be allowed. H2O is the most essential nutrient for crop growth!

- The no-tillage plots where alfalfa had been terminated in [spring] consistently had the lowest total available N content. 

-  Nutrient cycling in undisturbed soil and direct seeded crops remains a little-known area for research study. Credit must be given to the pioneers of this study who chose to look at factors beyond yield in order to better understand crop response under no-till/sod conditions.

With reduced tillage and direct seeding methods (perennial forage termination and sod seeding being the ultimate no-till challenge) many factors combine for success or failure. Background offered in this report refers to other research and issues such as the lack of effective herbicides to control volunteer alfalfa, affects of allelopathic agents and auto toxicity of alfalfa, corn after alfalfa, the effects of tillage on VAM, and the mycorrhizal association on grain quality. These, and other soil-related aspects, must be continually evaluated to come up with the best methods for practical and profitable crop production.

The link to crop nutrient cycling provides a strong connection for reduced tillage and sustainable farming. Alfalfa in rotation, as a forage legume, potentially supplies intrinsic nitrogen while direct seeding assures efficient access to it.

The Alberta Reduced Tillage LINKAGES program attempts to create networking and knowledge for sustainable cropping systems. More information about perennial forage, crop rotations, and direct seeding can be accessed on line at www.reducedtillage.ca



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[1] Glyphosate is the chemical name of the active ingredient found in several registered herbicides (ie: Roundup™, Vantage™, Touchdown™, Glyfos™, etc.)

[2] Title: Method and time of alfalfa termination affects cereal growth and weed population J.R. Moyer et al.; (LRC Contribution no.387-02104).

[3] The term sod seeding refers to the practice of seeding directly into pasture or hayland without tillage, and preferably after the forage has been terminated with glyphosate. All sod is not equal however, and a pure alfalfa stand differs greatly from a field with grassy forage species. That distinction is important when considering methods and timing for effective termination and subsequent direct seeding crop rotations.

[4] As used here, tillage refers to perennial forage removal by plowing, discing cultivating, harrowing, etc.

[5] Treatment abbreviations: No – herbicide only; Minimum – herbicide + cultivation (noble blade); Conventional – intensive tillage with plow and tandem disc.

[6] Vesicular arbuscular mycorrhizal fungi – VAM interactions include plant growth and nutrient uptake.

[7] Canadian Journal of Plant Science 83: p.969-976

[8] Italized text from Report / followed by associated comments (R. Heller, reduced tillage agronomist).