Conservation tillage is usually defined as a management practice that maintains at least 30 percent of the soil surface with plant residue cover and reduces soil disturbance. On a national scale, conservation tillage is used on 41 percent of all land and conservation and reduced tillage combined farm 63 percent of all cropland (Conservation Information Technology Center, 2007). However, in California's Central Valley, conservation tillage practices are used on less than two percent of annual crop acreage (Mitchell et al. 2007).
In 2003, the plots in the corn-tomato rotation were divided in half, and conservation and standard tillage were applied to one half of the main plots. New conservation tillage operations and equipment were developed, including a modified Orthman 1tRIPr, which strip-tilled the bed center, applied fertilizer and herbicide and swept crop residue from the furrows before tomato transplanting (see Equipment Development). The yields for the tomato and corn crops were significantly higher under standard tillage as compared to conservation tillage, over the period from 2003-2007 (see tillage data here). Corn yields were only slightly higher, while tomato yields were higher by a larger margin under standard tillage.
Researchers at Russell Ranch found that conservation tillage can be used successfully with sub-surface drip irrigation to control weed densities (Sutton et al. 2006). Sub-surface drip practically eliminates the need for herbicides; since no surface water is applied, few weeds germinate. In 2003, treatments with furrow irrigation, standard tillage and herbicides did not have significantly different yields than treatments with drip irrigation and conservation tillage, with or without herbicides. In 2004, drip irrigation resulted in significantly higher yields than furrow irrigation; using herbicides resulted in significantly higher yields than not using herbicides. Furrow irrigated treatments without herbicides resulted in lower tomato yields in both years. These findings suggest that conservation tillage, when paired with sub-surface drip, could reduce the need for herbicides in reduced tillage systems.
Additional information on conservation tillage in California
The University of California and National Resources Conservation Service (NRCS) Tillage Workgroup has tracked a steady and dramatic increase in interest in conservation tillage (CT) alternatives over the past eight years. The Workgroup itself has grown from a handful of founding members, including Russell Ranch researchers, to well over 600 affiliates today. In recent years, successful CT innovations have been documented in dairy forage, tomato with cover crop and cotton systems in the Central Valley with the greatest and most widespread adoption activity currently underway in San Joaquin Valley dairies. Up-to-date information on CT in California is available at the UC/NRCS CT Workgroup's Web site.