Minimum Tillage, Cover Crops and Compost
Louise Jackson, Irenee Ramirez, Ron Yokota, Steve Fennimore, Steve Koike, Bill Chaney, Karen Klonsky

Management practices for increasing soil quality and their effects on production issues were tested in irrigated, intensive vegetable production in a cooperative research project with a commercial grower, Tanimura and Antle, Inc., in the Salinas Valley. Four management treatments were carried out on an 8.3 ha field:
  • Minimum tillage with organic matter (OM) inputs
  • Minimum tillage with no OM inputs
  • Conventional tillage with OM inputs
  • Conventional tillage with no OM inputs
Minimum tillage ('Sundance System', Sundance Farms of Coolidge, AZ) retained the same raised beds for the two-year study, 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 treatments with OM inputs (+OM), compost was added two times per year, with a rye cover crop in the fall or winter, whereas -OM treatments followed the typical practice of only incorporating crop residues.

The results of comparing +OM and -OM treatments showed that cover crops and compost:
  • Increased total soil C and N, and soil microbial biomass C and N
  • Reduced bulk density
  • Decreased the nitrate (NO3--N) pools in the 0-90 cm profile, so that leaching potential was lower
  • Increased yields of vegetables
  • Decreased the weed density of shepherd's purse (Capsella bursa-pastoris) and burning nettle (Urtica urens) on some dates
  • Decreased corky root disease (caused by Rhizomonas suberifaciens) of lettuce on one sampling date
The results of minimum vs. conventional tillage were generally similar, except that:
  • Surface soil moisture (0-15 cm deep) was lower with minimum tillage.
  • NO3--N in the deep profile (15-90 cm deep) was lower with minimum tillage.
  • Yields were sometimes lower with minimum tillage, but this was not associated with increased pest problems.
The highest yielding treatment, conventional tillage +OM inputs, had:
  • Acceptable net returns despite the costs associated with cover crops, compost, and fuel and labor for conventional tillage.
  • Lower economic profitability for lettuce compared to broccoli grown with this regime.
  • mprovements in some attributes of soil quality, including higher soil C and microbial biomass, lower nitrate leaching potential and less severity of weeds and disease, compared to the typical practice in the area, conventional tillage -OM inputs.

References

 

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