Simultaneous Diffusion of Herbicide Resistant Cotton and Conservation Tillage

This study addresses three primary research questions. First, does diffusion of herbicide-resistant (HR) cotton seed varieties encourage diffusion of conservation tillage? Second, does diffusion of conservation tillage practices encourage diffusion of HR cotton? Third, what other economic, institutional, or agronomic factors explain diffusion of each technology? Conservation tillage practices preserve at least 30% of residue from the previous crop on fields. Conservation tillage involves less intensive field tillage and fewer passes across the field. Specific practices include mulch till (where soil is disturbed prior to planting), ridge till (where residue is left between tilled ridges) and no-till (where no tillage is carried out). Conservation tillage can reduce soil erosion and attendant water pollution. By reducing erosion, it can maintain the long-term productivity of soils. It can also increase soil carbon sequestration (Sandretto & Payne, 2006). Conservation tillage can form part of conservation plans that growers are required to adopt on highly erodible land (HEL) (Claassen, 2006). Under law, growers are required to adopt conservation compliance plans on HEL to be eligible for some farm program benefits. Traditionally, intensive tillage has been the main means of weed control (Carpenter & Gianessi, 1999). In the 1970s, the introduction of post-emergence herbicides provided growers with more weed control options throughout the growing season. The introduction of HR seed varieties in the mid 1990s, primarily Roundup® Ready glyphosate-resistant seed varieties, allowed growers to spray glyphosate over the top of crops, killing weeds without causing crop damage. Glyphosate is a broad-spectrum herbicide with a relatively long window of effectiveness during the growing season. The rapid adoption of HR cotton and soybean varieties has been attributed to the greater flexibility in weed management they afford growers (Carpenter & Gianessi, 1999; Marra, Piggott, & Carlson, 2004). Amid controversies about the environmental impacts of transgenic crop varieties and widespread use of glyphosate, there is also the possibility that transgenic, HR seed varieties and conservation tillage are complementary. This suggests that adoption of HR seed could have environmental benefits of reducing soil erosion, water pollution, and carbon emissions. This latter effect could come both from soil carbon sequestration and from the fact that conservation tillage (especially no-till) entails less fuel for tilling passes across the field (Brookes & Barfoot, 2006). Some studies have explicitly considered how adoption of HR seeds and conservation-tillage practices complement each other. Fulton and Keyowski (1999) introduce a theoretical model illustrating how the returns to adopting HR canola increase with relative reliance on conservation tillage methods. Carpenter and Gianessi (1999) discuss complementarities between HR seed varieties and conservation tillage in soybean production. Ward, Flanders, Isengildina, and White (2002) applied data-envelopment analysis to data from Georgia cotton growers to evaluate the allocative and technical efficiency of production with transgenic seed varieties and conservation tillage. They concluded that “Roundup Ready technology is better utilized with conservation tillage than with conventional tillage” (p. 12). These studies focus on how adoption of one technology affects incentives to adopt the other. George B. Frisvold University of Arizona