Pest regulation: Use reduced tillage in arable fields

Supporting evidence from individual studies

1. A replicated, randomized, controlled study in 1997–2001 in a rainfed pea-wheat-barley field near Barcelona, Spain, found more weeds in plots with reduced tillage, compared to conventional tillage. Pest numbers: More weed biomass was found in plots with reduced tillage, compared to conventional tillage, in one of two comparisons (grasses: 27 vs 0 g/m²). Methods: Reduced tillage or conventional tillage was used on two plots each (30 x 45 m plots). A mouldboard plough was used for conventional tillage (25 cm depth). A chisel plough was used for reduced tillage (15 cm depth). A seed drill, fertilizer, and post-emergence herbicide were used on all plots. Weeds were sampled each year, when crops were harvested (June–July 1998–2001, 10 quadrats/plot, 0.25 m² quadrats).

   Study and other actions tested

   Referenced paper

   Mas M.T. & Verdú A.M.C. (2003) Tillage system effects on weed communities in a 4-year crop rotation under Mediterranean dryland conditions. Soil and Tillage Research, 74, 15-24.

2. A replicated, randomized, controlled study in 1998–2000 in an irrigated vegetable field in the Salinas Valley, California, USA, found similar numbers of crop pests and diseases in plots with reduced tillage, compared to conventional tillage. Pest numbers: Similar numbers of crop pests and diseases were found in plots with reduced tillage, compared to conventional tillage (Sclerotina minor: 0.3–1.8 vs 0.3–1.9% of plants had symptoms; big vein disease: 3.0–3.4 vs 2.7–3.6% of plants had symptoms; pea leafminers: 10–98 vs 8–84 insects/sticky card; 2.2–3.4 vs 2.2–3.6% corky root disease severity, on a scale from 1 to 12, on which 12 is the highest severity). Methods: There were four plots (0.52 ha), for each of four treatments (reduced tillage or conventional tillage, with or without added organic matter). In plots with added organic matter, compost was added two times/year, and a cover crop (Merced rye) was grown every autumn or winter. Lettuce or broccoli crops were grown in raised beds. Sprinklers and drip irrigation were used in all plots. Soils were disturbed to different depths (conventional tillage: disking to 50 cm depth, cultivating, sub-soiling, bed re-making, and bed-shaping; reduced tillage: cultivating to 20 cm depth, rolling, and bed-shaping).

   Study and other actions tested

   Referenced paper

   Jackson L.E., Ramirez I., Yokota R., Fennimore S.A., Koike S.T., Henderson D.M., Chaney W.E., Calderon F.J. & Klonsky K. (2004) On-farm assessment of organic matter and tillage management on vegetable yield, soil, weeds, pests, and economics in California. Agriculture, Ecosystems & Environment, 103, 443-463.

3. A replicated, randomized, controlled study in 2002–2003 in a rainfed wheat field in northwest Turkey found more weeds, but similar numbers of weed species, in plots with reduced tillage, compared to conventional tillage. Pest numbers: More weeds were found in plots with reduced tillage, compared to conventional tillage, in three of four comparisons (36–64 vs 29–49 plants/m²), but there were similar numbers of weed species (14–15 vs 11–13). Methods: Conventional tillage with a mouldboard plough, reduced tillage with a rototiller, or reduced tillage with a disc was used on three plots each (75 x 15 m plots). Fertilizer and herbicide were used on all plots. Weeds were measured in nine quadrats/plot (1 x 1 m quadrats, three times/growing season, before the herbicide was used).

   Study and other actions tested

   Referenced paper

   Ozpinar S. (2006) Effects of tillage systems on weed population and economics for winter wheat production under the Mediterranean dryland conditions. Soil and Tillage Research, 87, 1-8.

4. A replicated, controlled study in 1993–2006 in an irrigated tomato-corn field in Davis, California, USA, found similar numbers of natural enemies in soils with reduced tillage or conventional tillage. Natural enemy numbers: Similar numbers of predatory mites were found in soils with reduced tillage or conventional tillage (8–12 vs 5–7 individuals/100 g fresh soil). Methods: Conventional tillage or reduced tillage was used on six plots each (0.4 ha plots). Plots were tilled about five times/year (conventional) or two times/year (reduced; depth not reported). All plots were irrigated. Half of the plots were fertilized, and compost was added to the other half. Soil samples were collected eight times in March 2005–November 2006 (three samples/plot). Mites were sampled with soil cores (5 cm diameter, 10 cm depth).

   Study and other actions tested

   Referenced paper

   Sanchez-Moreno S., Nicola N.L., Ferris H. & Zalom F.G. (2009) Effects of agricultural management on nematode-mite assemblages: soil food web indices as predictors of mite community composition. Applied Soil Ecology, 41, 107-117.

5. A replicated, randomized, controlled study in 2005–2007 in a rainfed field in the central Bekaa Valley, Lebanon, found more weeds in plots with reduced tillage, compared to conventional tillage. Pest numbers: More weeds were found in plots with reduced tillage, compared to conventional tillage (density: 113 vs 44 weeds/m²; dry weight: 61 vs 34 g/m²). Methods: Reduced tillage or conventional tillage was used in four plots each (14 x 6 m), in October. Conventional plots were ploughed (25–30 cm depth) and then shallowly disc cultivated. Reduced plots were shallowly disc cultivated (10 cm depth). Barley, chickpeas, and safflower were planted in November. Barley and safflower were fertilized (60–100 kg N/ha). Weed density and dry weight were measured on 30 March. Herbicide was used on all plots after sowing the seeds in November 2005. Herbicide was also used, and all plots were hand weeded, after the weed measurements in 2006.

   Study and other actions tested

   Referenced paper

   Yau S.K., Sidahmed M. & Haidar M. (2010) Conservation versus conventional tillage on performance of three different crops. Agronomy Journal, 102, 269-276.

6. A replicated, randomized, controlled study in 1985–2008 in a rainfed wheat-vetch field near Madrid, Spain, found more weed species in plots with reduced tillage, compared to conventional tillage. Pest numbers: More weed species were found in plots with reduced tillage, compared to conventional tillage (8.3 vs 7.3 species), but no differences in the evenness or diversity of weed communities were found (reported as Pielou’s index and Shannon’s index). Methods: Conventional tillage or reduced tillage was used on four plots each (20 x 40 m). A mouldboard plough and a cultivator were used for conventional tillage (depths not reported). A cultivator and/or a chisel plough were used for reduced tillage (depths not reported). Wheat and vetch were grown in rotation. Post-emergence herbicide was used on all plots, when the wheat was tillering. All plots were fertilized. Weeds were sampled when the wheat was tillering or the vetch stems were elongating (February–April 1986–2008, 5–20 samples/plot, 30 x 33 cm sampling areas).

   Study and other actions tested

   Referenced paper

   Plaza E.H., Kozak M., Navarrete L. & Gonzalez-Andujar J.L. (2011) Tillage system did not affect weed diversity in a 23-year experiment in Mediterranean dryland. Agriculture, Ecosystems & Environment, 140, 102-105.

7. A replicated, controlled study in 1991–2009 in a rainfed faba bean field in Sicily, Italy, found similar numbers of pests in plots with reduced tillage, compared to conventional tillage. Pest numbers: Similar numbers of Orobanche crenata root parasites were found in plots with reduced tillage, compared to conventional tillage (10 broomrapes/m²), and the root parasites were similar in weight (1.50 vs 1.59 g). Similar amounts of weed biomass (1.3 Mg/ha) and weed species (16–19 species) were found in plots with reduced tillage or conventional tillage. Methods: Reduced tillage or conventional tillage was used on two plots each (18.5 x 20 m plots). A mouldboard plough (30 cm depth; in summer) and a harrow (depth not reported; before sowing) were used for conventional tillage. A chisel plough (40 cm depth), a mouldboard plough (15 cm depth, in 1991–1998), and a harrow (depth not reported; before sowing) were used for reduced tillage. In all plots, a hoe was used to control weeds (depth not reported; 1–2 times/year). Faba beans were grown in rotation with durum wheat. During durum wheat growth, herbicide was used in all plots. All plots were fertilized (46 kg P₂O₅/ha). Root parasites and weeds were measured in three samples/faba bean plot (four rows/sample, 3 m rows).

   Study and other actions tested

   Referenced paper

   Giambalvo D., Ruisi P., Saia S., Di M.G., Frenda A.S. & Amato G. (2012) Faba bean grain yield, N2 fixation, and weed infestation in a long-term tillage experiment under rainfed Mediterranean conditions. Plant and Soil, 360, 215-227.

8. A replicated, randomized, controlled study in 2009–2011 in two irrigated pepper fields in central Italy found more weeds in plots with reduced tillage, compared to conventional tillage. Pest numbers: More weeds were found in plots with reduced tillage, compared to conventional tillage, in four of eight comparisons (94–152 vs 73–122 plants/m²). More weed biomass was found in plots with reduced tillage, compared to conventional tillage, in three of eight comparisons (31–58 vs 25–36 g dry matter/m²). Methods: A mouldboard plough (30 cm depth) was used on all plots in autumn, before winter cover crops were planted. Cover crops were mown or chopped in spring, before tillage. Conventional tillage or reduced tillage was used on 12 plots each (6 x 12 m plots), in May 2010–2011. A mouldboard plough and a disc (two passes) were used for conventional tillage (which incorporated the cover crop residues into the soil to a depth of 30 cm). A rotary hoe was used for reduced tillage (which incorporated the cover crop residues into the soil to a depth of 10 cm). Pepper seedlings were transplanted into the plots in May, and fruits were harvested twice/year in August–October 2010–2011. Weeds were sampled 30 days after transplanting (six samples/plot). All plots were fertilized before the cover crops, but not after. All plots were irrigated.

   Study and other actions tested

   Referenced paper

   Radicetti E., Mancinelli R. & Campiglia E. (2013) Influence of winter cover crop residue management on weeds and yield in pepper (Capsicum annuum L.) in a Mediterranean environment. Crop Protection, 52, 64-71.

9. A replicated, randomized, controlled study in 1994–2009 in a rainfed pea-cereal field near Madrid, Spain, found more weeds in plots with reduced tillage, compared to conventional tillage. Pest numbers: More weeds were found in plots with reduced tillage, compared to conventional tillage, in two of four comparisons (11.2–15.4 vs 8.8–12.4 plants/m²). Similar numbers of weed species were found in plots with reduced tillage or conventional tillage (data reported as an index of species richness). Methods: Reduced tillage or conventional tillage was used on four plots each (each with three 10 x 25 m sub-plots, with different pea-cereal rotations), in October or November. A mouldboard plough was used for conventional tillage (30 cm depth). A chisel plough was used for reduced tillage (10 cm depth). The peas were not fertilized. Weeds were identified and counted in four quadrats/sub-plot (0.125 m² quadrats).

   Study and other actions tested

   Referenced paper

   Santín-Montanyá M.I., Zambrana E., Fernández-Getino A.P. & Tenorio J.L. (2014) Dry pea (Pisum sativum L.) yielding and weed infestation response, under different tillage conditions. Crop Protection, 65, 122-128.

10. A replicated, randomized, controlled study in 1999–2011 in an irrigated tomato-cotton field in the San Joaquin Valley, California, USA, found that tillage had inconsistent effects on weed numbers, but different weed species were found in plots with reduced tillage, compared to conventional tillage. Pest numbers: Fewer weeds were found in plots with reduced tillage, compared to conventional tillage, in two of six comparisons (in June 2011: 61–126 vs 158–190 plants/m²), but more weeds were found in one of six comparisons (in tomatoes, in January 2003: 48 vs 45 plants/m²). Different communities of weeds were found in plots with reduced tillage, compared to conventional tillage, in one of two comparisons (in plots with winter cover crops; data reported as distance in ordination space). Methods: Reduced tillage or conventional tillage was used on 16 plots each, in 1999–2011. The plots (9 x 82 m) had six raised beds each. Winter cover crops (triticale, rye, and vetch) were planted on half of the plots, in October 1999–2010, and crop residues were chopped in March. Different numbers of tillage practices were used for conventional tillage (19–23 tractor passes, including disc and chisel ploughing) and reduced tillage (11–12 tractor passes, not including disc and chisel ploughing). All plots were fertilized (conventional tillage: 89.2 kg/ha dry fertilizer, 111.5 kg/ha urea; reduced tillage: 124.9 kg/ha urea). Weeds were counted in January 2003 (1 m² quadrats, four quadrats/plot), as well as March 2006 and June 2011 (0.25 m² quadrats, two quadrats/plot). Soil cores were collected in June 2011 (8.25 cm diameter, 0–10 cm depth). Seeds from these soil cores were germinated, and weed species were counted.

    Study and other actions tested

    Referenced paper

    Shrestha A., Mitchell J.P. & Hembree K.J. (2015) Weed seedbank characterization in long-term cotton–tomato rotations in California. Agronomy Journal, 107, 597-604.