On-Farm Comparison of Three Methods of Reduced Tillage
Louise Jackson, Irenee Ramirez, Israel Morales, Steve Koike
Minimum tillage to retain semi-permanent, raised beds for multiple crop seasons is done by some growers in the Salinas Valley to decrease time, fuel and labor costs that accrue from disking and re-shaping beds between each crop. The effects of shallow vs. deep minimum tillage were tested on a growers' field for a three-year period (Jackson et al., 2002, California Agriculture).
Shallow minimum tillage refers to operations such as the 'Sundance System' that utilize disks and lister bottoms to incorporate crop residues and cultivate the tops and sides of the beds in a single pass. This method tills shallowly (approximately 20 cm) so that it can be used with subsurface drip irrigation.
Deep minimum tillage, in contrast, is intended to retain semi-permanent beds but also reduce soil compaction. A four-step minimum tillage set of operations (totaling 1.5-2 hours per acre) was designed by American Farms in Chualar, CA to till to approximate 40 cm deep, and consists of the following passes:
- Minimum-till chisel to simultaneously chisel the furrows to approximately to 40 cm depth with a narrow shank, and disk hill the beds.
- 'Sundance System' to till the surface layer.
- Minimum-till ripper that utilizes angled, broad shanks with floating wings to break the compacted layer at depth in the beds.
- Surface rototill/mulcher to smooth the surface and prepare a seedbed.
A comparison of shallow ('Sundance System') and deep minimum tillage showed that:
- Lettuce yield was higher with deep minimum tillage.
- Lettuce drop disease (Sclerotinia minor) decreased over a period of several years with deep minimum tillage.
- Higher soil microbial biomass and total SOM tended to occur in the surface layer of soil with continuous shallow minimum tillage.
- Periodic deep minimum tillage (i.e., chiseling and ripping) is recommended for long-term retention of semi-permanent, raised beds in lettuce production
Jackson, L.E., I. Ramirez, I. Morales, and S.T. Koike. 2002. Minimum tillage
practices affect disease and yield of lettuce. California Agriculture 56:35-39.