Many vegetable growers prefer to stagger harvest over the growing season. In the northeastern United States, however, the growing season is too short to follow early-harvested cool-season crops with a second vegetable crop, but long enough that summer weeds can be problematic in fallow fields. Cover cropping can provide effective weed control, but the practice must be simple to implement. In the northeastern United States, there are few options available fitting the requirement for a rapid-growing summer cover crop. The short growing season, disease resistance, and low cost of buckwheat make it an ideal option for weed control (Björkman et al., 2008; Clark, 2007; Magdoff and van Es, 2000; Sarrantonio, 1994).
Vegetable growers considering implementation of buckwheat as part of their weed management and soil conservation practices are confronted with several questions. First, is no-tillage (NT) planting effective and if not, how much tillage is necessary? Second, how long after incorporating the crop residue must one wait to sow buckwheat? Third, what are the early- and late-season limits for seeding buckwheat? Fourth, what is the dry matter yield of the buckwheat cover crop? The current research addresses these questions and offers production advice on the implementation of buckwheat as a cover crop option in vegetable production.
Growers need inexpensive, simple, and effective methods for using cover crops for soil conservation and weed management. Traditionally, growers are advised to wait 2 weeks before planting a cover crop following vegetable harvest (Magdoff and van Es, 2000). Björkman (2010) recommended sowing buckwheat, to be harvested for grain, in early July in the northeastern United States. We sought to determine whether the buckwheat cover crop could be planted less than 2 weeks following pea harvest to test whether a quicker planting of the cover crop might suppress weeds even better. We also examined different planting treatments to evaluate the extent to which tillage might be reduced. Finally, we varied the date of buckwheat planting to determine when during the summer a successful stand can be established.
The incorporation of fresh organic matter can result in the presence of phytotoxins or increased microbial activity detrimental to germinating seeds and young seedlings (Cochran et al., 1977). The emergence of sweet corn (Zea mays) and lambsquarters (Chenopodium album) are negatively affected by crimson clover (Trifolium incarnatum) residue (Dyck and Liebman, 1994). Phytotoxins and microbes and/or their by-products may result in seedling mortality or loss of vigor. Therefore, planting a cover crop immediately after incorporating fresh crop residue is not recommended, and a 2-week wait is the common recommendation (Magdoff and van Es, 2000). However, that recommendation precludes many cover crops and severely reduces the possibility of double-cropping vegetables. It would, therefore, be valuable to identify alternative options to the conventional recommendations. The ultimate goal of reducing wait time is a better use of cover crops in vegetable systems, and better soil health by reducing the time that soil is bare while growing conditions are good, particularly in wet temperate climates like the Great Lakes region and much of the Atlantic Coast. Our results indicate that the 2-week wait can be reduced under certain conditions and that 1 week may in fact be optimal.
Incorporated residue of succulent vegetables in the warm growing season can decompose more quickly than more mature plant tissue, or than during the cooler months (Parr and Papendick, 1978). Vegetable crop residue may be high in nitrogen (N) and low in phenolics immediately following incorporation. Incorporated pea residue, in particular, contributes to high soil carbon (C) and N levels as well as increased overall microbial biomass and microbial enzymatic activity (Fauci and Dick, 1994). In young pea residue, the C to N ratio (C/N) is less than 20 (Copas, 2010), which represents a N content that permits substantially higher decomposition rates than when C/N is greater than 20 (Nicolardot et al., 2001). High-N residues decompose faster than low-N residues (Bruun et al., 2006; Lupwayi et al., 2004; Nicolardot et al., 2001; Sarrantonio, 2003). Legume residue with a C/N less than 20 can provide net N mineralization within 10–20 d, whereas the equivalent amount of N in more mature residue (C/N = 25–50) can take many months to be available (Bruun et al., 2006; Sarrantonio, 2003). In fact, soil microbial activity can peak in the first week after incorporation of green pea residue (Lupwayi et al., 2004). Furthermore, buckwheat is less affected by N tie-up than most other cover crops, and may grow even when N availability is reduced by freshly incorporated residue (Stone, 1906). Nevertheless, the buckwheat seed could be sensitive to soilborne pathogens stimulated by the crop residue (Björkman, 2001).
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