In the United States, chile peppers (domesticated species within the Capsicum genus) are primarily produced in California, New Mexico, Arizona, and Texas [U.S. Department of Agriculture, National Agricultural Statistics Service (USDA-NASS), 2020]. Among these states, the economic and cultural impact of chile pepper is perhaps most significant in New Mexico. In a typical year, chile pepper acreage in New Mexico is ≈45% of the U.S. total for this crop, and chile peppers harvested in New Mexico are ≈33% of those harvested in the United States (USDA-NASS, 2020). In 2019, chile peppers were planted on 9100 acres in New Mexico and provided over $50 million in cash receipts to farmers in this state (USDA-NASS, 2020). New Mexico chile peppers are grown with irrigation for green fruit and for red fruit. Red fruit are mature green fruit. Green and red fruit are both sold to processors and fresh markets. Chile peppers grown for processing were valued at $41.4 million in 2019, and chile peppers for fresh market were valued at $8.6 million in 2019 (USDA-NASS, 2020). New Mexico’s contribution chile pepper production in the nation reflects, in part, an accumulation of expertise and infrastructure following four centuries of chile pepper cultivation in this state (Bosland, 2015).
Chile pepper production in New Mexico has long relied on human labor for weeding. Labor has become increasingly expensive and is now recognized as a significant threat to the sustainability of chile pepper production in New Mexico (Gandonou and Waliczek, 2013; Hawkes et al., 2008). The need for hand hoeing is caused, in part, by the inability of chile pepper plants to establish competitive advantages over weeds (Amador-Ramirez, 2002), and the long growing seasons for this crop in New Mexico (Bosland and Walker, 2014). New Mexico farmers typically seed chile pepper in March through April, the crop stand is thinned in May through June, and green fruit are generally harvested in August through September. Red fruit are often harvested in October. Throughout this growing season, weeds emerge. If not controlled, weeds reduce yield (Schroeder, 1992, 1993), reduce harvest efficiency (Schroeder, 1993; Schutte and Cunningham, 2015), and potentially harbor pathogens that are injurious to chile pepper crops (Sanogo et al., 2009, 2013). Herbicides for chile pepper in New Mexico include bensulide, carfentrazone-ethyl, clethodim, clomazone, glyphosate, halosulfuron-methyl, imazosulfuron, napropamide, paraquat, pelargonic acid, pendimethalin, pyraflufen-ethyl, sethoxydim, s-metolachlor, and trifluralin. Although these herbicides are effective on many of the weed species that occur in chile pepper fields in New Mexico, weeds that emerge after crop emergence frequently escape chemical control. Weeds between chile pepper rows can be controlled with cultivation; however, cultivation does not affect weeds near or within crop rows. Weeds in crop rows can generally be suppressed with synthetic or natural mulches (Chen et al., 2017); however, mulches are not often used in chile pepper production in New Mexico.
Like all agricultural soils, soils in chile pepper fields contain reservoirs of viable weed seeds (herein called “seedbanks”) that enable local persistence of weed populations. High seedbank densities generally increase herbicide dose requirements and frequencies (Dieleman et al., 1999; Hartzler and Roth, 1993; Schutte and Cunningham, 2015), decrease efficacies of mechanical interventions such as cultivation (Davis and Williams, 2007; Dieleman et al., 1999), and increase hand hoeing requirements (Riemens et al., 2007; Schutte and Cunningham, 2015). Recognizing the impacts of seedbank density on weed control outcomes, comprehensive weed management plans feature tactics that aim to reduce the number weed seeds in soil (Swanton et al., 2008).
A method for seedbank reduction that uses commonplace crop production technology is the false seedbed (Cloutier et al., 2007). False seedbeds occur before cash crop planting by first stimulating weed seed germination through tillage and, if necessary, irrigation. Subsequent weed seedlings are then eliminated with shallow tillage. False seedbeds are like stale seedbeds except that stale seedbeds do not use tillage to eliminate weed seedlings that emerge before cash crop planting (Cloutier et al., 2007). By removing germinable weed seeds from upper soil layers, false and stale seedbeds can improve subsequent crop production in several ways: reducing weed densities (Shem-Tov et al., 2006), reducing labor requirements for weeding (Shem-Tov et al., 2006), reducing weed biomass at crop harvest (Caldwell and Mohler, 2001; Lonsbary et al., 2003), increasing crop yield (Johnson and Mullinix, 1995; Johnson and Mullinix, 1998), and increasing profitability (Islam et al., 2009; Lonsbary et al., 2003).
Many weed species in chile pepper feature annual life cycles (Lee and Schroeder, 1995). Because annual weed species are dependent upon seeds for year-to-year persistence, methods for seedbank reduction may improve weed management programs for chile pepper. To our knowledge, false seedbeds have not been systematically evaluated for chile pepper production in New Mexico. The primary objective for this study was to compare economic costs of false seedbed implementation against possible economic benefits derived from reductions in labor requirements for weeding. To accomplish this objective, we determined the false seedbed effects on weed densities, labor requirements for weeding, and fruit yields for chile pepper.
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False seedbed effects on soil fertility just before chile pepper seeding. Soil samples were taken by collecting 30 cores [1 inch (2.5 cm) diameter, 10 cm (3.9 inches) depth] in a W-shaped pattern across an experimental unit. Cores from each experimental unit were pooled, mixed, and analyzed by a commercial laboratory (A&L Plains Agricultural Laboratories, Lubbock, TX). Fields differed between experimental runs and were located at the New Mexico State University, Leyendecker Plant Science Research Center, Las Cruces, NM (lat. 32.19°N, long. 106.74°W). Data are means of four replications, unless noted otherwise. Within a column, means were not significantly different based on analysis of variance (α = 0.05).