The fundamental motivator for growers to reduce tillage, say researchers at the University of California, is simple economics.
"California growers are investigating a range of minimum tillage options primarily to reduce production costs," says Jeff Mitchell, a weed scientist at the University of California at Davis. "Reducing production costs has become a compelling a critical goal of growers throughout this region of California, which has historically been an area of phenomenal productivity."
Mitchell, who spoke June 25 at the Southern Conservation Tillage Conference for Sustainable Agriculture at Auburn University, says, preplant tillage operations typically account for 18 to 24 percent of overall production costs for annual crops grown in the West Side region of the San Joaquin Valley. An average of nine to 11 tillage-related passes are routine during the fall-spring period, according to his calculations. "These passes represent not only considerable energy, equipment and labor costs, but recent research indicates that tillage reduces soil organic matter and emits considerable dust as well," he says.
In 1999, Mitchell was among a large group of California researchers, farmers, private industry members and government representatives involved in the initiation of a four-year study comparing yields in a cotton-tomato rotation under both conservation and conventional tillage systems, with and without the benefit of winter cover crops.
What the study found is that it is possible to maintain crop yields under conservation tillage systems if some equipment modifications are made.
In 2001, tomato plots in the study, under normal tillage conditions, yielded 63.4 tons per acre with a cover crop and 60.1 tons per acre under without a cover crop. In the comparable conventional tillage research plots, the tomatoes yielded 60.5 tons per acre with a cover crop and 64.4 tons per acre without a cover crop.
"Data from our 2001 tomato harvest indicates that yields in the conservation tillage systems were similar to those in the standard till plots with an elimination of six tillage operations following last year’s cotton crop," Mitchell says.
In comparison, cotton yields in the 2001 study ranged from 2.8 bales per acre with conventional tillage and a cover crop to 3.6 bales per acre with conventional tillage and no winter cover crop. Under the conservation tillage system, the cotton crop yielded 3.0 bales per acre with a cover crop and 3.2 bales per acre without a cover crop.
Mitchell says, "2001 cotton yields were reduced by as much as 18 percent in the conservation tillage and cover crop system, relative to the standard tillage control system. However, there was an elimination of eight or nine tillage operations in the conservation tillage system, which may significantly reduce input expenses."
Also fueling the renewed interest in conservation tillage systems is a desire among growers to reduce soil compaction, the erosion of organic matter, the carbon emissions related to intensive tillage operations, and overall inputs.
"Escalating diesel fuel costs have resulted in sharp declines in net farm income and threaten the long term economic viability in many Central Valley crop production regions," Mitchell says. "A medium-sized row crop farm of 4,000 acres in this region may have weekly diesel fuel costs of upwards of $12,000."
He adds, "Although the term conservation tillage denotes a range of crop production alternatives that typically leave a minimum of 30 percent of the soil surface covered by residues from previous crops, the development and adoption of these systems for California’s very diverse cropping systems is likely to spawn many tillage system variants that do not fully reflect the classic model systems that have been developed in other regions."