Organic weed management of vegetable crops typically includes a combination of crop rotation, tillage, hand weeding, mowing, and mulching with plastic films (Baker and Mohler, 2015; Kasirajan and Ngouajio, 2012; Wang et al., 2008). However, considerable research has been performed to develop new weed control tactics for organic growers, including flame weeding (Melander et al., 2005), laser weeding (Mathiassen et al., 2006), steam and hot water or oil treatments (Kristoffersen et al., 2008; Zhang et al., 2012), electric current treatments (Sahin and Yalınkılıc, 2017), abrasive weeding (Wortman, 2014), biobased herbicides (Baker and Mohler, 2015), cover crop mulching (Crawford et al., 2018), and biobased and biodegradable mulches (Kasirajan and Ngouajio, 2012). The efficacy of each method varies with soil conditions, weather, crop type, growth stage, and weed species present. As a result, successful ecological weed management on a given farm often requires a diverse and adaptive suite of tactics (Liebman et al., 1997).
Plastic mulch films provide excellent weed control for organic vegetable bed-tops, but weeds that escape and grow through the crop planting hole can reduce yields by up to 44%; therefore, they must be managed (Wortman, 2015). Abrasive weeding is a physical weed management tactic that shreds newly emerged weed seedlings with grits propelled by compressed air (Forcella, 2009). It has been used to successfully manage weeds in the crop planting hole of plastic and bioplastic mulch film, with negligible damage to the crop or mulch (Braun et al., 2019). Any small, gritty material can be used for abrasive weeding, and many have been tested, including granulated corn (Zea mays) gluten meal, corn cob grit, soybean (Glycine max) meal, greensand fertilizer, and walnut (Juglans sp.) shell grit (Wortman, 2014). Abrasive weeding with organic fertilizers as abrasive grits can increase crop growth, yield, and profitability due to the increased plant available N following mineralization of organic N from the abrasive grits (Braun et al., 2019; Carlson et al., 2020). In-season delivery of N fertilizer via abrasive grits could shift the balance of crop–weed competition by improving the synchrony of soil N availability and peak crop demand (Liebman and Davis, 2000; Wortman et al., 2011).
Nitrogen requirements are significant for most vegetable crops, yet plant available N is often limiting in organic production due to poor synchrony between N mineralization and crop uptake requirements (Mikkelsen and Hartz, 2008; Noll et al., 2020). Net N mineralization from organic fertilizers is driven by the N content and chemical composition (e.g., carbon-to-N ratio) of the organic fertilizer and the mineralization (or immobilization) rate of the soil (Flavel and Murphy, 2006; Kumar and Goh, 2003; Stadler et al., 2006). Therefore, it is possible to leverage the nutrient composition of organic fertilizer abrasive grits to more precisely manage soil N availability in organic vegetables while concurrently providing physical control of weeds in the crop planting hole of plasticulture systems.
The goal of this study was to explore the possibility of manipulating soil N availability and crop responses through the use of organic fertilizer abrasive grits with variable N contents. The specific objectives were to quantify weed biomass, potential plant available N uptake, and yield of organic ‘Carmen’ sweet red pepper (Capsicum annuum) and organic ‘Gypsy’ broccoli (Brassica oleracea var. italica) in response to variable abrasive grit fertilizer analyses, application rates, and background soil fertility.
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