Environmental quality and public health concerns about the use of chemicals in conventional agriculture have driven a large increase in demand for organic food (Dorais, 2007). Acreage of certified organic farm land in vegetable production in the United States has increased by 62% between 1995 and 2008 [U.S. Department of Agriculture (USDA), 2010]. Although growers have obtained higher prices and seen growth in demand for organic products, many farmers are reluctant to convert to organic agriculture because of perceived risks of lower yields and challenges in managing pests (Beveridge and Naylor, 1999; Hanson et al., 2004; Oberholtzer et al., 2005). Weed control, especially management of perennial weeds, is often cited by farmers as a barrier to transition to organic production (Turner et al., 2007; Verschwele and Häusler, 2004). During the mandated 3-year-transition period from conventional to organic agriculture in the United States, many farmers adopt biological, cultural, and mechanical techniques that aid in building soil fertility and suppressing weeds with the potential to enhance yields in the first organic year (Hanson et al., 2004).
Compost applications during transition to organic vegetable production and after transition have helped to improve soil OM and microbial biomass, alter nematode communities, and increase the concentration of plant available macro- and micronutrients (Baysal et al., 2008; Briar et al., 2011; Martini et al., 2004; Smukler et al., 2008). Improvements in soil quality as a result of organic material addition are often associated with improvements in vegetable yield (Briar et al., 2011; Russo and Taylor, 2006). However, the cropping system used during transition can interact with compost application to affect yield and soil fertility. Intensive vegetable production in high tunnels resulted in higher tomato yields in the first organic year than other transition strategies including tilled fallow, hay, and field vegetable production (Briar et al., 2011). Weed suppression and grain yields in the first certified organic year can be affected by the species of cover crop used during 3 years of transition (Smith et al., 2011). Transitional strategies of different agronomic crop rotations affected weed seedbank density and soil aggregate size in the first year of certified organic production (Corbin et al., 2010). Weed populations and soil fertility during organic transition are affected by transition cropping systems and can subsequently affect yield in the first certified organic year. Multifunction cropping systems can be used to address multiple management issues that constrain production, but the relative importance of individual issues in affecting yields is not clearly understood (Larkin et al., 2011). Previous research on organic transition strategies has not simultaneously compared the differences in weed suppression, soil fertility, and organic vegetable production in different systems.
This research was conducted to assess the effectiveness of strategies for simultaneously suppressing weeds, enhancing soil fertility, and improving organic vegetable yields during transition to organic agriculture in Ohio. Five transition strategies were implemented to mirror current farmer and researcher practices such as growing vegetables, tilled fallow, and mowing, with novel strategies such as prairie biomass production and summer annual smother crops. The objective of this study was to evaluate soil quality, response of annual and perennial weed populations, and compare yields in tomato and potato production in the first certifiable organic year after 3 years of transition strategies and compost application. We hypothesize that weed competition and soil quality will be affected by 3 years of transition strategy and compost application. Further, we hypothesize that transition strategy and compost application as well as resulting weed populations and soil fertility will affect tomato and potato yields.
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