Increased weed diversity, density and above-ground biomass in long-term organic crop rotations

Abstract While weed management is consistently a top priority among farmers, there is also growing concern for the conservation of biodiversity. Maintaining diverse weed communities below bioeconomic thresholds may provide ecosystem services for the crop and the surrounding ecosystem. This study was conducted to determine if weed diversity, density and biomass differ within and among organic and conventional crop rotations. In 2007 and 2008, we sampled weed communities in four long-term crop rotations near Mead, Nebraska using seedbank analyses (elutriation and greenhouse emergence) and above-ground biomass sampling. Two conventional crop rotations consisted of a corn (Zea mays) or sorghum (Sorghum bicolor)–soybean (Glycine max)–sorghum or corn–soybean sequence and a diversified corn or sorghum–sorghum or corn–soybean–wheat (Triticum aestivum) sequence. Two organic rotations consisted of an animal manure-based soybean–corn or sorghum–soybean–wheat sequence and a green manure-based alfalfa (Medicago sativa)–alfalfa–corn or sorghum–wheat sequence. Species diversity of the weed seedbank and the above-ground weed community, as determined by the Shannon diversity index, were greatest in the organic green manure rotation. Averaged across all sampling methods and years, the weed diversity index of the organic green manure rotation was 1.07, followed by the organic animal manure (0.78), diversified conventional (0.76) and conventional (0.66) rotations. The broadleaf weed seedbank density in the tillage layer of the organic animal manure rotation was 1.4×, 3.1× and 5.1× greater than the organic green manure, diversified conventional and conventional rotations, respectively. The grass weed seedbank density in the tillage layer of the organic green manure rotation was 2.0×, 6.1× and 6.4× greater than the organic animal manure, diversified conventional and conventional rotations, respectively. The above-ground weed biomass was generally greatest in the organic rotations. The broadleaf weed biomass in sorghum and wheat did not differ between organic and conventional rotations (CRs), but grass weed biomass was greater in organic compared to CRs for all crops. The above-ground weed biomass did not differ within CRs, and within organic rotations the grass weed biomass was generally greatest in the organic green manure rotation. The weed seedbank and above-ground weed communities that have accumulated in these rotations throughout the experiment suggest a need for greater management in long-term organic rotations that primarily include annual crops. However, results suggest that including a perennial forage crop in organic rotations may reduce broadleaf weed seedbank populations and increase weed diversity.

[1]  N. McRoberts.  Ecology and integrated farming systems: Ed. by D. M. Glen, M. P. Greaves and H. M. Anderson. ISBN 0 471 95534-5. (329 pp; £49.00) Chichester, UK, John Wiley & Sons , 1996 .

[2]  Louise E. Jackson,et al.  Ecology in agriculture , 1997 .

[3]  K. Hurle,et al.  Influence of farming system on weeds in thresh crops of a six-year crop rotation. , 2000 .

[4]  P. Risser.  Competitive relationships among herbaceous grassland plants , 1969, The Botanical Review.

[5]  J. Bakker,et al.  The Soil Seed Banks of North West Europe: Methodology, Density and Longevity , 1996 .

[6]  G. Hergert,et al.  Long-Term Effects of No-tillage in a Winter Wheat (Triticum aestivum)-Sorghum (Sorghum bicolor)-Fallow Rotation , 1988, Weed Science.

[7]  H. Coble,et al.  Initial Weed Densities Affect No-Tillage Weed Management with a Rye (Secale cereale) Cover Crop , 1997, Weed Technology.

[8]  A. Légére,et al.  Diversity and assembly of weed communities: contrasting responses across cropping systems , 2005 .

[9]  F. Chapin,et al.  EFFECTS OF BIODIVERSITY ON ECOSYSTEM FUNCTIONING: A CONSENSUS OF CURRENT KNOWLEDGE , 2005 .

[10]  P. B. Cavers.  Seed banks: Memory in soil , 1995 .

[11]  Daniel A. Ball,et al.  Weed Seedbank Response to Tillage, Herbicides, and Crop Rotation Sequence , 1992, Weed Science.

[12]  J. Cardina,et al.  Crop rotation and tillage system effects on weed seedbanks , 2002, Weed Science.

[13]  R. Aerts,et al.  Competition in heathland along an experimental gradient of nutrient availability , 1990 .

[14]  Geoffrey R. Squire,et al.  Community-scale seedbank response to less intense rotation and reduced herbicide input at three sites , 2000 .

[15]  H. Sjursen.  Change of the Weed Seed Bank during the First Complete Six-Course Crop Rotation after Conversion from Conventional to Organic Farming , 2001 .

[16]  P. Milberg,et al.  A Survey of Weeds in Organic Farming in Sweden , 2000 .

[17]  J. M. Anderson,et al.  Biodiversity and Ecosystem Function in Agricultural Systems , 1994 .

[18]  R. Norris,et al.  Cutting Interval and Irrigation Timing in Alfalfa: Yellow Foxtail Invasion and Economic Analysis , 1991 .

[19]  Colbach,et al.  Evaluating field-scale sampling methods for the estimation of mean plant densities of weeds , 2000 .

[20]  C. Daughtry,et al.  Weed Suppression by Live and Desiccated Hairy Vetch (Vicia villosa) , 1993, Weed Science.

[21]  Yongqing Ma.  Allelopathic studies of common wheat (Triticum aestivum L.) , 2005 .

[22]  L. K. Ward,et al.  The role of weeds in supporting biological diversity within crop fields , 2003 .

[23]  M. Palmer.  Does diversity beget diversity? A case study of crops and weeds , 1997 .

[24]  Robert L. Zimdahl,et al.  Weed-Crop Competition: A Review , 2004 .

[25]  P. Mineau,et al.  Conservation of biodiversity within Canadian agricultural landscapes: Integrating habitat for wildlife , 1996 .

[26]  R. Zimdahl.  Weed-Crop Competition , 2004 .

[27]  S. Clay,et al.  Weed Seedbanks and Corn Growth following Continuous Corn or Alfalfa , 1998 .

[28]  E. Regnier,et al.  Allelopathic Influence of Germinating Seeds and Seedlings of Cover Crops on Weed Species , 1996, Weed Science.

[29]  A. C. Grundy,et al.  Non‐chemical weed management in organic farming systems , 2001 .

[30]  H. Mooney,et al.  Biodiversity and Ecosystem Function , 1994, Praktische Zahnmedizin Odonto-Stomatologie Pratique Practical Dental Medicine.

[31]  Miguel A. Altieri,et al.  Biodiversity And Pest Management In Agroecosystems , 1994 .

[32]  K. Gross,et al.  Weed aboveground and seedbank community responses to agricultural management systems , 2001 .

[33]  M. Liebman,et al.  Integration of soil, crop and weed management in low-external-input farming systems , 2000 .

[34]  J. Mt. Pleasant,et al.  Incidence of Weed Seed in Cow (Bos sp.) Manure and its Importance as a Weed Source for Cropland , 1994, Weed Technology.

[35]  David Tilman,et al.  Secondary Succession and the Pattern of Plant Dominance Along Experimental Nitrogen Gradients , 1987 .

[36]  M. Liebman,et al.  Crop Rotation and Intercropping Strategies for Weed Management. , 1993, Ecological applications : a publication of the Ecological Society of America.

[37]  E. Mahn,et al.  Structural changes of weed communities and populations , 1984, Vegetatio.

[38]  S. Clay,et al.  Influence of crop rotation, tillage, and management inputs on weed seed production , 1999, Weed Science.

[39]  J. Posner,et al.  Organic and Conventional Production Systems in the Wisconsin Integrated Cropping Systems Trials: I. Productivity 1990–2002 , 2008 .

[40]  A. B. Hald,et al.  Weed vegetation (wild flora) of long established organic versus conventional cereal fields in Denmark , 1999 .

[41]  K. Gross,et al.  Weed seedbank and community shifts in a long-term cropping systems experiment , 2005, Weed Science.

[42]  P. Porter,et al.  Organic and Other Management Strategies with Two-and Four-Year Crop Rotations in Minnesota , 2003 .

[43]  S. Southway,et al.  Influence of autumn applied herbicides on summer and autumn food available to birds in winter wheat fields in southern England , 1999 .

[44]  David Tilman,et al.  Competition Among Grasses Along a Nitrogen Gradient: Initial Conditions and Mechanisms of Competition , 1993 .

[45]  A. G. Thomas,et al.  Weed communities associated with arable Saskatchewan farm management systems. , 2000 .

[46]  M. Cavigelli,et al.  Weed seedbank dynamics in three organic farming crop rotations , 2004 .

[47]  P. Bàrberi,et al.  Size and composition of the weed seedbank after 7 years of different cover‐crop‐maize management systems , 2004 .

[48]  L. Wiles,et al.  A New Soil Sampler and Elutriator for Collecting and Extracting Weed Seeds from Soil , 1996, Weed Technology.

[49]  F. Forcella,et al.  Implications of weed seedbank dynamics to weed management , 1997, Weed Science.

[50]  Dessaint,et al.  Influence of weed management strategies on soil seedbank diversity , 1998 .

[51]  L. Hume.  Long-term effects of 2, 4-D application on plants. I. Effects on the weed community in a wheat crop , 1987 .

[52]  D. Clements,et al.  Promotion of weed species diversity and reduction of weed seedbanks with conservation tillage and crop rotation , 2006, Weed Science.

[53]  Laurie E. Drinkwater,et al.  Cropping Systems Rsearch: Reconsidering Agricultural Experimental Approaches , 2002 .

[54]  D. D. Buhler.  Weed population responses to weed control practices. I. Seed bank, weed populations, and crop yields , 1999, Weed Science.

[55]  M. Liebman,et al.  Impact of composted swine manure and tillage on common waterhemp (Amaranthus rudis) competition with soybean , 2004, Weed Science.

[56]  M. Cavigelli,et al.  Long‐Term Agronomic Performance of Organic and Conventional Field Crops in the Mid‐Atlantic Region , 2008 .

[57]  R. Pearce,et al.  Growth Analysis of Weed and Crop Species with Reference to Seed Weight , 1993, Weed Science.

[58]  H. A. Roberts,et al.  CHANGES IN THE NUMBERS OF VIABLE WEED SEEDS IN SOIL UNDER DIFFERENT REGIMES , 1973 .

[59]  Paolo Bàrberi,et al.  Long‐term tillage and crop rotation effects on weed seedbank size and composition , 2001 .

[60]  N. Silvestri,et al.  Weed communities of winter wheat as influenced by input level and rotation , 1997 .

[61]  D. Dubois,et al.  Soil Fertility and Biodiversity in Organic Farming , 2002, Science.