Abstract
A three year study was conducted in the irrigated Sonoran Desert to compare the effect of different weed management methods in seedling alfalfa ( Medicago sativa L.) on crop stand and yield. Treatments included; grazing with sheep ( Ovis aries ) when the crop was ready for the first harvest, a combination of preemergence and postemergence herbicides, postemergence herbicides only, and an untreated control where weeds were harvested with the hay. Weed management practice did not affect alfalfa yield in the first season, although the herbicide treatments reduced total forage (alfalfa plus weeds) yield compared with the grazed treatments and the untreated control. Crop density was not different between treatments. Herbicide treatments lowered forage yields at the first harvest by eliminating of weeds and because of crop injury in 2 of the 3 yr. At the third and subsequent harvests, there were no differences in forage yield for treatments. Plots were weed free after the second harvest. Lamb grazing selectivity in weedy seedling alfalfa was also quantified by analyzing esophageal extrusa. The lambs were selecting the weeds over the alfalfa as grazing progressed. This preference was consistent between lambs and plots, although there were year differences. Forage quality of the winter annual broadleaf weeds present in this study was comparable with the alfalfa. We concluded that grazing lambs are a good weed control method in seedling alfalfa during the winter grazing season in the irrigated Sonoran Desert. Research Question Weeds in seedling alfalfa have been reported to reduce hay yields, reduce alfalfa stand, lower hay quality, and provide unpalatable feed to livestock. Every winter in the desert Southwest, lambs graze fall planted alfalfa for weed control. Not all growers, however, use sheep grazing and a great deal of controversy exists regarding this practice. The objectives of this study were (i) to compare weed management practices in seedling alfalfa for their ability to control weeds and to determine their effect on long term alfalfa stand and yield, and (ii) to quantify lamb grazing selectivity of available forage on weedy seedling alfalfa. The chemical composition of the various winter annual weeds infesting seedling alfalfa was also quantified. Weed management practice included; sheep grazing in lieu of the first harvest, two herbicide regimes, and an untreated control. Literature Summary Weeds are reputed to reduce forage yields in alfalfa when they are not controlled while the crop is in the seedling growth stage. Weeds are also assumed to have a deleterious effect on forage quality and alfalfa stand. By contrast, other authors praised the competitive ability of alfalfa and it's resilience from weed competition early in the crop life. Sheep grazing may represent an alternative to herbicide use because sheep can eat weeds without ill effects either to themselves or to the crop. The selection of forage species by grazing lambs is a complex phenomenon affected by a number of variables. The selection of one forage species over another by a free ranging grazing lamb may be affected by climate (weather affects forage growth), individual animal preferences, physical characteristics of the forage, chemical characteristics of the plant, forage height, stemminess, and leafiness. Study Description This experiment was repeated for 3 yr at the University of California Desert Research and Extension Center at Holtville. In each year, the crop was sown in October. Herbicide treatments were made in one regimen at planting, followed by postemergence treatments when the crop was in the three‐ to four‐trifoliate leaf stage, and only postemergence in the second regimen. Sheep grazing commenced in early Spring (January to March) when the crop was ready for the first normal harvest. Data collected included forage yield at most harvests for the first season of the crop and for the first harvest of the second season of the crop each year of the study. Alfalfa and weeds, when present, were separated and weighed at each harvest. Crop and weed density (stand) were determined at the first and second harvest, and at the first harvest of the second season. For the last two years of the experiment, a lamb grazing selectivity trial on weedy alfalfa pasture was conducted. Three lambs were fitted with esophageal Full scientific article from which this summary was written begins on page 123 of this issue. canulas in order to collect forage as it was consumed, which was used to determine grazing preferences. Lambs grazed for 10‐plus d until forage was depleted. Esophageal extrusa samples were separated by hand for broadleaf weeds, grasses, and alfalfa. Representative weeds were cut and analyzed for feeding quality. Applied Question How did the four treatments compare for their ability to control weeds? This vaned by year. Herbicide treatments reduced weeds the most at the first harvest. Results were mixed at the second harvest. Few to no weeds were present in the third or later harvests. What effect did weed control treatment have on forage yield and stand over the duration of the experiment? Overall alfalfa yields for the first season were not different between the four treatments. Total forage yield was higher for the grazed and mowed treatments than for the herbicide treatments because of the contribution of weeds. At the first and second harvests, weed control treatment had a decided effect on both forage yield and weed content in the forage. Herbicide treatment reduced total forage yield at the first harvest because of the lack of weeds in the hay and because of injury to the crop from the herbicide. At the second harvest, the herbicide treated plots had higher yields than the grazed or mowed plots. Additionally, the herbicide treated plots had fewer weeds than the other treatments. At the third harvest, and for all subsequent harvests up to the first harvest of the second season, there were no further differences in yield between treatments. There was no effect of treatment on crop stand at any harvest throughout the duration of this experiment. On weedy seedling alfalfa fields in the irrigated Sonoran Desert, what is the forage preference of grazing lambs? Contrary to popular belief, grazing lambs preferentially grazed winter annual broadleaf weeds over available alfalfa forage. Lambs did not eat alfalfa in the proportions in which it was originally available until 8.5 d of grazing. Even after 10 d of grazing, the lambs were still actively selecting for the weeds even though weed forage had decreased substantially. What is the forage value of winter annual broadleaf weeds? As with any forage, cutting date and physiological maturity are extremely important to any feed analysis. For the weeds under consideration in this study and at the time at which we cut these weeds, winter annual broadleaf weeds were quite high in forage quality for grazing lambs while the winter annual grasses had less feed value. The nutritive value, considering only CP, ADF, and NDF, of the broadleaf annuals compared favorably with alfalfa. However, such other factors as inadequate windrow drying during the desert winter and consequent mold damage might make these weeds objectionable in alfalfa hay bales. Recommendations Under the conditions of this experiment, weed control practice in seedling alfalfa was transitory, lasting for the first and second harvest. Grazing sheep or not treating represent alternatives to herbicide use in seedling alfalfa without deleterious effects on long term yield and crop stand. The winter annual broadleaf weeds studied under the conditions of this experiment are not detrimental to alfalfa hay quality. Grazing lambs had a great degree of preference for weeds in seedling alfalfa and would probably therefore serve as an effective nonherbicide weed control method.
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Claims 20
Claim · model-written summary
Weed management did not change first-season alfalfa yield.
- Taxon
- alfalfa
Medicago sativae0 - Treatment
- Weed management practicee0
- Outcome
- alfalfa yielde0
- Direction
- did not affecte0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Weed management practice did not affect alfalfa yield in the first season”
Claim · model-written summary
Herbicide treatments reduced total forage yield relative to grazed and untreated treatments.
- Taxon
- alfalfaMedicago sativae0
- Treatment
- herbicide treatmentse0
- Outcome
- total forage (alfalfa plus weeds) yielde0
- Direction
- reducede0
- Comparator
- the grazed treatments and the untreated controle0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“the herbicide treatments reduced total forage (alfalfa plus weeds) yield compared with the grazed treatments and the untreated control”
Claim · model-written summary
Crop density did not differ among treatments.
- Taxon
- alfalfaMedicago sativae1
- Treatment
- treatmentse0
- Outcome
- Crop densitye0
- Direction
- was not differente0
- Comparator
- treatmentse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Crop density was not different between treatments.”
e1“weed management methods in seedling alfalfa ( Medicago sativa L.)”
Claim · model-written summary
Herbicides lowered first-harvest forage yield through weed elimination and crop injury in two of three years.
- Taxon
- alfalfaMedicago sativae1
- Treatment
- Herbicide treatmentse0
- Outcome
- forage yieldse0
- Direction
- lowerede0
- Qualifier
- 2 of the 3 yre0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Herbicide treatments lowered forage yields at the first harvest by eliminating of weeds and because of crop injury in 2 of the 3 yr.”
e1“weed management methods in seedling alfalfa ( Medicago sativa L.)”
Claim · model-written summary
Forage yield did not differ among treatments from the third harvest onward.
- Taxon
- alfalfaMedicago sativae1
- Treatment
- treatmentse0
- Outcome
- forage yielde0
- Direction
- no differencese0
- Comparator
- treatmentse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“At the third and subsequent harvests, there were no differences in forage yield for treatments.”
e1“weed management methods in seedling alfalfa ( Medicago sativa L.)”
Claim · model-written summary
Plots were weed free after the second harvest.
- Taxon
- alfalfaMedicago sativae1
- Organ / stage
- second harveste0
- Outcome
- Plots were weed freee0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Plots were weed free after the second harvest.”
e1“weed management methods in seedling alfalfa ( Medicago sativa L.)”
Claim · model-written summary
Lambs selected weeds over alfalfa as grazing progressed.
- Taxon
- alfalfaMedicago sativae0
- Interactor
- weedse0weed
- Outcome
- lambs were selecting the weeds over the alfalfae0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The lambs were selecting the weeds over the alfalfa as grazing progressed.”
Claim · model-written summary
Lamb preference varied between years but was consistent across lambs and plots.
- Taxon
- alfalfaMedicago sativae1
- Outcome
- preference was consistent between lambs and plotse0
- Qualifier
- there were year differencese0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“This preference was consistent between lambs and plots, although there were year differences.”
e1“weeds over the alfalfa”
Claim · model-written summary
Winter annual broadleaf weed forage quality was comparable to alfalfa.
- Taxon
- alfalfaMedicago sativae0
- Interactor
- winter annual broadleaf weedse0weed
- Outcome
- Forage quality of the winter annual broadleaf weedse0
- Comparator
- alfalfae0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Forage quality of the winter annual broadleaf weeds present in this study was comparable with the alfalfa.”
Claim · model-written summary
Herbicides reduced weeds most at the first harvest.
- Taxon
- alfalfaMedicago sativae1
- Organ / stage
- first harveste0
- Treatment
- Herbicide treatmentse0
- Interactor
- weedse0weed
- Outcome
- weedse0
- Direction
- reducede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Herbicide treatments reduced weeds the most at the first harvest.”
e1“weed management methods in seedling alfalfa ( Medicago sativa L.)”
Claim · model-written summary
Herbicide plots yielded more than grazed or mowed plots at the second harvest.
- Taxon
- alfalfaMedicago sativae1
- Treatment
- herbicide treated plotse0
- Outcome
- yieldse0
- Direction
- highere0
- Comparator
- grazed or mowed plotse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“At the second harvest, the herbicide treated plots had higher yields than the grazed or mowed plots.”
e1“weed management methods in seedling alfalfa ( Medicago sativa L.)”
Claim · model-written summary
Herbicide plots had fewer weeds than other treatments at the second harvest.
- Taxon
- alfalfaMedicago sativae1
- Treatment
- herbicide treated plotse0
- Interactor
- weedse0weed
- Outcome
- weedse0
- Direction
- fewere0
- Comparator
- other treatmentse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Additionally, the herbicide treated plots had fewer weeds than the other treatments.”
e1“weed management methods in seedling alfalfa ( Medicago sativa L.)”
Claim · model-written summary
Grazing lambs selected winter annual broadleaf weeds over alfalfa forage.
- Taxon
- alfalfaMedicago sativae0
- Interactor
- winter annual broadleaf weedse0weed
- Outcome
- grazing lambs preferentially grazed winter annual broadleaf weedse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“grazing lambs preferentially grazed winter annual broadleaf weeds over available alfalfa forage.”
Claim · model-written summary
Lambs did not eat alfalfa in its available proportion until 8.5 days of grazing.
- Taxon
- alfalfaMedicago sativae0
- Outcome
- did not eat alfalfa in the proportions in which it was originally availablee0
- Value
- 8.5 de0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Lambs did not eat alfalfa in the proportions in which it was originally available until 8.5 d of grazing.”
Claim · model-written summary
Lambs still selected weeds after ten days of grazing despite declining weed forage.
- Taxon
- alfalfaMedicago sativae1
- Interactor
- weedse0weed
- Outcome
- lambs were still actively selecting for the weedse0
- Value
- 10 de0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Even after 10 d of grazing, the lambs were still actively selecting for the weeds even though weed forage had decreased substantially.”
e1“weed management methods in seedling alfalfa ( Medicago sativa L.)”
Claim · model-written summary
Winter annual broadleaf weeds had high forage quality for lambs.
- Taxon
- alfalfaMedicago sativae1
- Interactor
- winter annual broadleaf weedse0weed
- Outcome
- forage quality for grazing lambse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“winter annual broadleaf weeds were quite high in forage quality for grazing lambs”
e1“weed management methods in seedling alfalfa ( Medicago sativa L.)”
Claim · model-written summary
Winter annual grasses had less feed value.
- Taxon
- alfalfaMedicago sativae1
- Interactor
- winter annual grassese0weed
- Outcome
- winter annual grasses had less feed valuee0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“winter annual grasses had less feed value”
e1“weed management methods in seedling alfalfa ( Medicago sativa L.)”
Claim · model-written summary
Broadleaf annual nutritive value in CP, ADF and NDF compared favorably with alfalfa.
- Taxon
- alfalfaMedicago sativae0
- Interactor
- broadleaf annualse0weed
- Outcome
- nutritive value, considering only CP, ADF, and NDF, of the broadleaf annualse0
- Comparator
- alfalfae0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The nutritive value, considering only CP, ADF, and NDF, of the broadleaf annuals compared favorably with alfalfa.”
Claim · model-written summary
Sheep grazing or no treatment can replace herbicides without harming long term alfalfa yield or stand.
- Taxon
- alfalfaMedicago sativae0
- Outcome
- alternatives to herbicide use in seedling alfalfae0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Grazing sheep or not treating represent alternatives to herbicide use in seedling alfalfa without deleterious effects on long term yield and crop stand.”
Claim · model-written summary
Lamb grazing would likely provide effective nonherbicide weed control.
- Taxon
- alfalfaMedicago sativae0
- Outcome
- effective nonherbicide weed control methode0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Grazing lambs had a great degree of preference for weeds in seedling alfalfa and would probably therefore serve as an effective nonherbicide weed control method.”
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