Biomass shifts and suppresses weed populations under CA. Michael Mulvaney
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A presentation from the WCCA 2011 event held in Brisbane, Australia.
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Biomass shifts and suppresses weed populations under CA. Michael Mulvaney
- 1. Biomass shifts and suppresses weed populations under conservation agriculture Michael J. Mulvaney, Virginia Tech, USA C. Wes Wood, Auburn University, USA Andrew J. Price, USDA ARS National Soil Dynamics Lab, USA SANREM CRSP is made possible by the United States Agency for International Development and the generous support of the American people through USAID Cooperative Agreement No. EPP-A-00-04-00013-00.
- 2. Introduction • Conservation agriculture: – ↓ Erosion – Improved soil structure – ↑ SOM – Soil temperature – ↑ Soil moisture moderation Kip Balkcom, 2008
- 3. CA for limited-input smallholders • #1 problem: Weed suppression
- 4. Solution? • High biomass cover crops (killed mulches) • Mulch Ted Kornecki, 2008
- 5. Hypothesis • Combine cover crops and mulches • Improve soil quality on productive field • Effects on: – Weeds, soil C, yields
- 6. Objective Quantify weed suppression of a summer cover crop and organic mulches under no-till collard (Brassica oleracea L.) production during conversion to CA: • Weed populations • SOC • Collard yield
- 7. Methods • Previous fallow (3 years) • 3 years: 2005–2008 • Central-Eastern AL, USA • 2x4 RCB: – 2 summer cover crops: • Forage soybean, weed fallow – 4 organic mulches: • Lespedeza, mimosa, oat straw, control • 6.7 Mg ha-1 yr-1
- 8. Cropping Schedule Rye Soybean Collards Rye or Control Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Mulch application
- 9. Methods • Weed coverage – Transects • 50 count transects • 2x per plot • Classified: – Broadleaves – Grasses – Sedges
- 10. Methods • C & N: – Dry combustion • Yield: – 65 DAP – 2.8 m2
- 11. Statistics • SAS: – Proc Means: Means and standard errors – Proc Glimmix: Model variable selection – 95% CL for treatment comparisons
- 12. Results — broadleaf coverage • Year 1: • Without mulch, broadleaf weeds problematic
- 13. Results — broadleaf coverage • Year 1: • Without mulch, broadleaf weeds problematic • Years 2 & 3: • Control effective without mulch
- 14. Results — grass coverage • Year 1: • Mulches don’t help • Year 2: • Weeds shift toward grasses • But mulching helps • Year 3: • Same as year 2?
- 15. Results — sedges • Summer cover crop x mulch interaction • Year 1: • Mulches don’t help • Years 2 & 3: • Reasonable control
- 17. SOC after 3 yrs A B BC CC
- 19. Yields • Collard Yields: – No treatment differences – Ave in SC (2001) 13,450 kg/ha – Ave: 17,900 kg/ha – Assuming 25% waste & 1.1 lbs/bunch: • ATL market, Nov. 18, 2009: – 25 lbs/ctn: US$12/ctn • US$14,222/ha – No premium assumed
- 20. Conclusions • Forage soybean does not effectively suppress weeds • Broadleaf and sedge control – suppressed under high biomass CA after 1st yr • Grass control – variable, increases in 2nd yr • Population shifts from broadleaves and sedges toward grasses • Conversion from fallow to CA increased SOC • Yield not affected by mulching or forage soybean
Notes de l'éditeur
- This effect was most apparent on broadleaf control (Figure 1). Mulching the first year was effective for suppression of broadleaf weeds. Suppression of broadleaf weeds during the first year appears to lessen broadleaf infestation during subsequent years, although mulching during 2007-8 did not have the same level of suppression compared to the non-mulched control. Since conservation tillage tends to shift weed populations away from broadleaves (Teasdale et al., 1991; El Titi, 2003), it is not surprising that broadleaf control can be enhanced with mulch application.
- This effect was most apparent on broadleaf control (Figure 1). Mulching the first year was effective for suppression of broadleaf weeds. Suppression of broadleaf weeds during the first year appears to lessen broadleaf infestation during subsequent years, although mulching during 2007-8 did not have the same level of suppression compared to the non-mulched control. Since conservation tillage tends to shift weed populations away from broadleaves (Teasdale et al., 1991; El Titi, 2003), it is not surprising that broadleaf control can be enhanced with mulch application.
- The population shift toward grasses under conservation tillage makes grass control more difficult (El Titi, 2003). During the first year of no-till, grass control was not effective using any of the mulches (Figure 2), but subsequent years showed much better grass suppression using mulches compared to the non-mulched control. Grass infestation was maintained below 10% by the application of any mulching material in 2007 (compared to 17% for the non-mulched control), and below 6% in 2008. The data show that mulching suppresses monocot weed populations in no-till systems if used for more than one year compared to the control, and may suggest that >2 years of no-till with high-biomass producing cover crops may be effective at reducing grassy weeds, although more data are needed to support this claim. In any case, the data show that grass populations under no-till are highly variable, with populations increasing dramatically during the second year of conversion from conventional tillage, but decreasing in the third year. Mowing grasses before seed heads become viable may reduce the grass populations to manageable levels during transition to conservation tillage.
- During the first year of transition from conventional to conservation tillage, yellow nutsedge (Cyperus esculentus L.) control was highly problematic, with total coverage ranging from 7-21% (Figure 3). However, subsequent years of high residue no-till improved sedge suppression, generally below 5% coverage, although there was not much difference between any of the mulching treatments and the control. It is interesting to note that sedge coverage was subject to a significant cover crop by mulch interaction (Table 1), resulting from increased sedge suppression by mimosa prunings after a forage soybean summer cover crop in 2006 and increased sedge suppression achieved in control plots when combined with forage soybean in 2007 and 2008 (Figure 3). Although it is unclear why this should be the case, it is apparent that sedge suppression is improved during subsequent years of high-biomass producing cover crops in combination with no-till, with or without the application of mulches. Yellow nutsedge was the only perennial weed species present after three years (Fig. 4).
- Spatial distribution of weeds: tends to be in-row, where row cleaners were used prior to transplant. Shows that no-till is effective for weed suppression. Will be interesting to see how manure injection will affect weed populations in the SESARE project.
- SOC did not differ by summer cover crops trts nor mulching trts, but was diff’t by depth.All trt’s, incl. control, significantly improved SOC in the 0-5 cm depth after 3 yrs. Any mulching trt tended to increase SOC compared to a no-mulch control in the 0-5 cm fraction.Mimosa and Lespedeza were significantly higher than the control at 0-5 cm.Only mimosa is significantly diff’t than initial C in the 5-10 cm depth.The results imply that conversion to no-till with the utilization high biomass winter cover crops had a greater impact on the improvement of SOC than did the inclusion of organic mulchesAssuming 58% of SOM is C, 2% SOC translates to almost 3.5% SOM! Not bad for an agriculturally productive soil in AL, where most soils are about 1%. (0.7% SOC is about 1.2% SOM, initial values.)
- SOC did not differ by summer cover crops trts nor mulching trts, but was diff’t by depth.All trt’s, incl. control, significantly improved SOC in the 0-5 cm depth after 3 yrs. Any mulching trt tended to increase SOC compared to a no-mulch control in the 0-5 cm fraction.Mimosa and Lespedeza were significantly higher than the control at 0-5 cm.Only mimosa is significantly diff’t than initial C in the 5-10 cm depth.The results imply that conversion to no-till with the utilization high biomass winter cover crops had a greater impact on the improvement of SOC than did the inclusion of organic mulches