The practice of applying mulches for the production of vegetables dates back thousands of years (Coolong, 2012; Rowe-Dutton, 1957). A primary purpose for using mulches is for weed suppression in the crop to be grown. Mulches typically function by blocking light or creating environmental conditions that can prevent germination or suppress weed growth shortly after germination. However, numerous other benefits are often obtained including increased earliness, moisture conservation, temperature regulation of the root zone and aboveground growing environment, reduced nutrient leaching, altered insect and disease pressures, and in some instances, reduced soil compaction or improved soil organic matter (Diaz-Perez, 2010; Lamont, 1993, 2005; Ngouajio and McGiffen, 2004). Currently, polyethylene (plastic) film-mulches are the primary mulch used in vegetable production for in-row weed control; however, weed control between rows can be a significant challenge for some producers. Weeds can hinder access for crop maintenance and harvesting activities affecting yields (Law et al., 2006). Weed control is especially challenging for organic growers. In a national survey of organic growers, weed control was ranked as their number one research priority (Walz, 1999).
Using hay and wheat straw mulches between rows of plastic is a chemical-free weed control option that adds organic matter to the soil and can control weeds on the edges of plastic mulch beds where control by other methods may be difficult. Organic mulches between rows can also reduce soil splash during rains (Stall, 2008). The weed control effectiveness may also be dependent on the quantity of mulch used. Schonbeck (1996) considered 7 to 10 tons/acre of hay or wheat straw to be sufficient for weed control, while 4 to 5 tons/acre were not. However, rye (Secale cereale)-based mulches applied at a rate of 2.3 tons/acre were adequate for controlling weeds in summer-grown cabbage (Brassica oleracea var. capitata) in Poland, suggesting that local environmental factors will likely have an impact on the effectiveness of varying rates of organic mulches (Zaniewicz-Bajkowska, 2009).
Incorporating cultivation along with mulching can be important for achieving effective weed control. Law et al. (2006) reported that when organic mulches were applied early in the growing season without any prior mechanical cultivation, weed control was inadequate, resulting in low crop productivity. However, when mulches were applied after shallow cultivation of plots, adequate weed control was obtained throughout the harvesting season. According to Schonbeck (1996), many growers cultivate for several weeks after planting, and then apply mulches for effective weed control for the remaining part of the season.
Although hay and wheat straw mulches have many benefits, growers should be aware that mulch quality can also impact weed control effectiveness and introducing weed seeds can be a concern with organic-based hay and wheat straw mulches (Relf and McDaniel, 2004; Stall, 2008). Organic mulches tend to be more expensive in terms of materials and high application costs, especially for large-scale operations (Schonbeck, 2009). An alternative to the use of new hay or wheat straw for mulching that can cut costs substantially is to use old or spoiled hay that is no longer good for animal feed (Stout, 2011). Using round bales for mulching can also reduce the labor requirements considerably because there is more hay in each bale than in square bales. It is also notable that round bales can be handled mechanically and unrolled to peel off layers that are appropriate for mulching between rows of plastic. Tractor three-point-hitch-mounted bale unrollers that clamp on the center axis of round bales are used to lift and move large bales around and unroll them for feeding livestock. These implements carry the bale on the centerline of the tractor, so they cannot be used to unroll bales between rows of plastic because there is typically not enough space to drive the tractor between the rows. The objective of this study was to document the effects of modifying a traditional bale unroller such that the unroller could be offset a sufficient distance for the tractor to straddle the row of plastic and unroll the bale in the space between adjacent rows of plastic as well as test the efficacy of the modified unroller with several types of organic mulches for between-row weed control.
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