On-farm assessment of organic matter and tillage management on vegetable yield, soil, weeds, pests, and economics in California

https://doi.org/10.1016/j.agee.2003.11.013Get rights and content

Abstract

In intensive vegetable production, low organic matter (OM) inputs and leaching of nitrate (NO3-N) decrease soil quality with time. Four management regimes were compared for their effects on soils and on production issues in a cooperative research project with a commercial vegetable grower in the Salinas Valley, California, USA, on an 8.3 ha field: minimum tillage with OM (+OM) inputs; minimum tillage with no OM (−OM) inputs; conventional tillage +OM inputs; and conventional tillage −OM inputs. Minimum tillage retained the same raised beds for the 2-year study (four crop cycles), and tilled to approximately 20 cm depth. Conventional tillage used many passes for surface and subsoil tillage, and disturbed the soil to approximately 50 cm depth. In +OM, compost was added two times per year, with a rye (Secale cereale) cover crop in the fall or winter, whereas −OM treatments followed the typical practice of only incorporating crop residues. Addition of cover crops and compost increased microbial biomass C (MBC) and N (MBN), reduced bulk density, and decreased the NO3-N pools in the 0–90 cm profile, so that leaching potential was lower compared to −OM treatments. Tillage practices had generally similar effects on soils except that surface soil moisture and NO3-N in the deep profile were consistently lower with minimum tillage. Minimum tillage tended to decrease lettuce (Lactuca sativa) and broccoli (Brassica oleracea) yields, but was not associated with increased pest problems. Weed density of shepherd’s purse (Capsella bursa-pastoris) and burning nettle (Urtica urens) were occasionally lower in the +OM treatments. Disease and pest severity on lettuce was slight in all treatments, but for one date, corky root disease (caused by Rhizomonas suberifaciens) was lower in the +OM treatments. The Pea Leafminer, Liriomyza huidobrensis, was unaffected by management treatments. Economic analysis of the three lettuce crops showed that net financial returns were highest with minimum tillage −OM inputs, despite lower yields. Various tradeoffs suggest that farmers should alternate between conventional and minimum tillage, with frequent additions of OM, to enhance several aspects of soil quality, and reduce disease and yield problems that can occur with continuous minimum tillage.

Introduction

Participatory research with farmers on commercial fields provides a unique opportunity to study the diverse impacts of management practices on yield, pests, environmental quality, and economics. Since research is performed in situ, findings are representative of typical ecological responses by the populations and communities of organisms within the actual agroecosystem, as compared to research station experiments that often cannot replicate the abiotic and biotic environment of real farms (Witcombe, 1999, Wander and Drinkwater, 2000). Also, the results of on-farm research can be valuable to farmers who are stakeholders in the design and management of experiments (Goma et al., 2001). This is especially true if treatments are conducted at the scale of operations used on the farms.

Ideally, farmer participatory research employs a systems approach that addresses and integrates several aspects of production, biology, economics, social and sustainability issues. In terms of ecology, this might involve investigation of the autecology of organisms, population and community dynamics, and/or biogeochemical flows, e.g., of nutrients and water, as well as the aspects of human ecology that affect decision-making and resource use. From an agronomic perspective, this emphasizes the evaluation of management practices to increase yield and economic gain, and with efficient use of resources.

Trade-offs exist between the benefits and drawbacks of management practices designed to increase soil quality, which concerns the effects of soil management on agricultural productivity, and on the characteristics of soils that contribute to environmental quality (Karlen et al., 1997, Liebig and Doran, 1999). For example, reduced tillage is known to increase soil organic matter (SOM) (Silgram and Shepherd, 1999), but can decrease the productivity of some crops (Carter, 1991, Sims et al., 1998), as well as increase the incidence of some diseases (Jackson et al., 2002). Cover crops decrease the leaching of nitrate (NO3-N) below the root zone (McCracken et al., 1994) and can increase N availability and crop yield (Paustian et al., 1992), but a drawback of certain cover crops is as alternate hosts for diseases that can then infect the subsequent cash crop (Koike et al., 1996). Higher financial costs from deeper tillage can be compensated by higher yields and net returns (Popp et al., 2001, Wesley et al., 2001), although higher fuel use contributes to greenhouse gas production (Robertson et al., 2000). Systems research attempts to account for these varied outcomes.

Intensive production for crops such as lettuce, broccoli, and celery (Apium sp.) occurs in the Salinas Valley of coastal California, USA, which is a major supplier of these vegetables nationwide. The mild climate and the high inputs of irrigation and fertilizers allow the production of two or three crops per year. Large NO3-N leaching and denitrification losses occur in these cropping systems (Jackson et al., 1994, Ryden and Lund, 1980), and NO3-N exceeds the public health standard (10 mg N l−1) in nearly half of the wells in the upper aquifer. Very little OM is returned to the soil after vegetable harvest, but use of cover crops and compost has recently increased. Tillage occurs frequently, ranging from single passes with cultivators for weed control, to disking, subsoiling, and leveling a field between crops.

The impact of reduced tillage and increased OM inputs on vegetable production and soils was evaluated in a participatory on-farm experiment with a Salinas Valley grower, using management regimes that were viable possibilities for farmers, with the use of large plots to represent operations at the farm-scale. Conventional tillage (subsoiling, disking, and surface mulching) was compared with minimum tillage that disked the surface layer of semi-permanent beds, and shanked the furrows. Organic matter was added as both cover crops and compost, with the purpose of incorporating both readily labile and more resistant sources of C. Cover crops increase the active fraction of the SOM for a few weeks to months after incorporation (Crozier et al., 1998, Jackson, 2000, Schutter and Dick, 2002). Manure and compost may contribute more C to slow versus active pools of SOM, partly depending on compost maturity (Paustian et al., 1992, Drinkwater et al., 1998). The objectives of the 2-year experiment (four crop phases) were to compare the effects of alternative tillage and OM management by: (1) monitoring changes in crop yield and nutrient uptake, soil microbial biomass, and N availability; (2) documenting effects on weeds, pathogens, and insect pests; and (3) evaluating the total costs and net returns as a means of assessing the economic viability of adopting practices conducive to increasing soil quality.

Section snippets

Soils and management practices

The field trial was established in April 1998 on an 8.3 ha site in the Salinas Valley of California. The Salinas silt loam is a fine-loamy, mixed, thermic Pachic Haploxerolls (FAO Haplic Phaeozems) (Table 1). The coastal Mediterranean-type climate has mild, rainy winters, and foggy, cool, rain-free summers. Rainfall was 44.35 cm from 4 April 1998 through 31 March 1999 and 34.93 cm from 1 April 1999 through 26 April 2000. The field was in long-term use for irrigated cool-season vegetable (e.g.,

Soil organic matter and bulk density

In this silt loam soil, total C and N concentrations (g kg−1) in the surface 0–15 cm layer were higher after 2 years of addition of cover crops and compost, compared to non-amended soils (Table 3). Tillage treatment did not have a significant effect on either total C or N concentrations, nor were there significant tillage×OM interactions. The addition of organic amendments caused a decrease in bulk density in the surface (0–6 cm) layer, but not at the lower depth (47–53 cm) (Table 3). No effects

Discussion

Managing a cropping system to promote soil quality has implications for crop yield and economic returns. Addition of cover crops and compost increased soil MBC, and reduced the potential for NO3-N leaching loss. These inputs were occasionally associated with lower weed density and corky root disease, which has previously been shown to be suppressed by a rye cover crop (vanBruggen et al., 1990). Although OM inputs often resulted in higher marketable lettuce yields, this did not necessarily

Conclusions

Addition of cover crops and compost, and a combination of minimum and conventional tillage methods appear to be the most attractive management option to farmers for coping with various production, economic, and soil quality tradeoffs. Although OM inputs increased some attributes of soil quality (higher MBC and MBN in the surface layer, lower bulk density in the surface layer, and less propensity for NO3-N to leach below the rootzone), and resulted in some production benefits (reduction in

Acknowledgements

We thank Tanimura and Antle, Inc. for their donations of time, labor, and materials, and for their excellent cooperation and attention to experimental details. Many people helped with the project, especially Martin Burger, Amy Clymo, Paula Ellison, Hung Kieu, and Kerri Steenwerth. Funding came from the USDA Western Regional Sustainable Agriculture Research and Education Program (95-COOP-1-2414), the Kearney Foundation of Soil Science, and the California Integrated Waste Management Board.

References (60)

  • Bergmann, W., 1992. Nutritional Disorders of Plants. Jena, Gustav Fisher Verlag, Germany, p....
  • K.F Bronson et al.

    Nitrogen response in cotton as affected by tillage system and irrigation level

    Soil Sci. Soc. Am. J.

    (2001)
  • C.A Campbell et al.

    Tillage—fertilizer changes: effect on some soil quality attributes under long-term crop rotations in a thin Black Chernozem

    Can. J. Soil Sci.

    (2001)
  • M.S Clark et al.

    Changes in soil chemical properties resulting from organic and low-input farming practices

    Agron. J.

    (1998)
  • C.R Crozier et al.

    Tracing nitrogen movement in corn production systems in the North Carolina Piedmont; a nitrogen-15 study

    Agron. J.

    (1998)
  • T.H Dao

    Tillage and crop residue effects on carbon dioxide evolution and carbon storage in a Paleustoll

    Soil Sci. Soc. Am. J.

    (1998)
  • L.E Drinkwater et al.

    Fundamental differences between conventional and organic tomato agroecosystems in California

    Ecol. Appl.

    (1995)
  • L.E Drinkwater et al.

    Legume-based cropping systems have reduced carbon and nitrogen losses

    Nature

    (1998)
  • J.B Dumas

    Sur les procédés de l’analyse organique

    Ann. Chim.

    (1981)
  • S.A Fennimore et al.

    Organic amendment and tillage effects on vegetable field weed emergence and seedbanks

    Weed Technol.

    (2003)
  • W.J Gale et al.

    Carbon dynamics of surface residue- and root-derived organic matter under simulated no-till

    Soil Sci. Soc. Am. J.

    (2000)
  • M Gallardo et al.

    Production and water use in lettuces under variable water supply

    Irrig. Sci.

    (1996)
  • Gee, G.W., Bauder, J.W., 1986. Particle-size analysis. In: Klute, A. (Ed.), Methods of Soil Analysis. Part 1. Physical...
  • H.C Goma et al.

    Participatory studies for agro-ecosystem evaluation

    Agric. Ecosyst. Environ.

    (2001)
  • D.M Granatstein et al.

    Long-term tillage and rotation effects on soil microbial biomass, carbon and nitrogen

    Biol. Fert. Soils

    (1987)
  • D.A Horneck et al.

    Methods of soil analysis used in the soil testing laboratory at Oregon State University

    Agric. Exp. Stn. S.M.

    (1989)
  • L.E Jackson et al.

    Crop nitrogen utilization and soil nitrate loss in a lettuce field

    Fert. Res.

    (1994)
  • L.E Jackson

    Fates and losses of nitrogen from a nitrogen-15-labeled cover crop in an intensively managed vegetable system

    Soil Sci. Soc. Am. J.

    (2000)
  • L.E Jackson et al.

    Minimum tillage practices affect disease and yield of lettuce

    Calif. Agric.

    (2002)
  • Janitzky, P., 1986. Cation exchange capacity. In: Singer, M.J., Janitzky, P. (Eds.), Field and Laboratory Procedures...
  • Cited by (67)

    • Winter cover crops and no-till promote soil macrofauna communities in irrigated, Mediterranean cropland in California, USA

      2021, Applied Soil Ecology
      Citation Excerpt :

      Together, reduced tillage and cover cropping may have a synergistic effect on soil biological communities, since soil organisms would be expected to thrive with more abundant food resources and reduced disturbance (Lavelle et al., 2001). In the highly productive, irrigated cropping systems of California, USA, intensive agricultural practices that rely on tillage and chemical inputs have generated concerns of declining soil and environmental quality (Jackson et al., 2004; Mitchell et al., 2000). Recent initiatives to implement conservation agriculture practices such as winter cover cropping and reduced tillage may have large impacts on soil biological communities, macrofauna in particular.

    • Cover cropping frequency is the main driver of soil microbial changes during six years of organic vegetable production

      2017, Soil Biology and Biochemistry
      Citation Excerpt :

      4) To our knowledge, our study is the first, field-based experiment in California to evaluate the effects of compost made only from yard-waste (i.e., municipal solid waste) in tillage-intensive systems. Compost in previous vegetable studies in California was made primarily from animals manure (Fennimore and Jackson, 2003; Jackson et al., 2004), or a mixture of household organic and green waste (Suddick and Six, 2013). The C:N ratios of compost in those studies was considerably lower (i.e., 10–17) than the compost in our study (22), and unfortunately the compost application rates, on an oven-dry basis, were not reported.

    View all citing articles on Scopus
    View full text