Strip-tillage in California’s Central Valley
click image to zoomJeff MitchellFigure 7. Strip-tilled forage corn stand, Frank Gwerder Dairy, Modesto, California, 2007. At ten San Joaquin Valley farms in 2007, we compared stand establishment following strip-tillage with plant stands achieved with traditional tillage (fig. 7). Forage corn producers using strip-tillage tend to seek populations of between 28,000 and 36,000 plants per acre. While there were slight differences in stands achieved in strip-tilled fields relative to traditional tilled fields, particularly at a site in Turlock where strip-tilling was done before pre-irrigating and at a site in Hanford where a higher seeding rate was used in the traditional till field, generally adequate stands have been achieved using strip-till.
Early season weed control is critical for successful strip-till production because the entire soil surface is not tilled. Weeds and weed seeds in the inter-row spaces that would otherwise be buried in a conventional broadcast tillage are not disturbed or displaced in a strip-tillage system, causing increased weed densities early in the season. However, buried weed seeds are also not brought to the surface strip-till. To date, weed management in San Joaquin Valley triple-crop systems has generally been accomplished by use of Roundup Ready corn varieties and by in-season application of glyphosate. Data from our experiments at 8 locations in the San Joaquin Valley in 2007 indicated that fewer weeds emerged in the strip-till than in the traditional tillage plots at several locations. All of these locations had Roundup Ready varieties of corn and glyphosate was applied once after corn emergence. The higher weed densities in strip-tillage plots were noticed in fields where the glyphosate application was delayed. Most of the weed population at these sites was comprised of volunteer cereals from preceding rotations and pigweeds (Amaranthus spp.). Preventing weed competition during the first few weeks of corn establishment is very important to avoid yield losses. In the current strip-till systems in the San Joaquin Valley, the norm is one application of glyphosate after corn planting. Thus, proper timing of this erbicide application is very important. Studies should be conducted to ascertain the effect of the timing of glyphosate application on forage yield under strip-tillage systems. Also, the use of preemergence herbicides and alternative weed management strategies also should be explored.
Over time, with less deep tillage in a strip-till system and as more residues cover the soil, fewer surface weeds may emerge in strip-tillage systems than emerge under traditional tillage. But the primary means for weed control in strip-till systems in these dairies are timely glyphosate applications with Roundup Ready corn and cultivation when weeds are small.
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