Evaluation of Cool-season Vegetable Rotations in Organic Production

Abstract

<jats:p>Certified organic production is challenging in the southeastern United States due to high weed, insect, and disease pressure. Maintaining and building soil organic carbon in midscale organic production systems can also be difficult due to the warm, moist conditions that promote decomposition. Focusing on cool-season cash crops paired with warm-season cover crops may help alleviate these production problems. This 3-year study (2011–13) evaluated two vegetable rotations of cool-season crops with cover crops for their productivity, disease management, and soil building potential in Watkinsville, GA. In the first rotation, cool-season cash crops included onion (<jats:italic>Allium cepa</jats:italic>), strawberry (<jats:italic>Fragaria</jats:italic> ×<jats:italic>ananassa</jats:italic>), and potato (<jats:italic>Solanum tuberosum</jats:italic>). These crops were rotated with green bean (<jats:italic>Phaseolus vulgaris</jats:italic>), oats/austrian winter pea (<jats:italic>Avena sativa</jats:italic>/<jats:italic>Pisum sativum</jats:italic> ssp. <jats:italic>arvense</jats:italic>), southernpea (<jats:italic>Vigna unguiculata</jats:italic>), and sunn hemp (<jats:italic>Crotalaria juncea</jats:italic>). In the second rotation, cool-season cash crops included onion, broccoli (<jats:italic>Brassica oleracea</jats:italic> Italica group), lettuce (<jats:italic>Lactuca sativa</jats:italic>), and carrot (<jats:italic>Daucus carota</jats:italic> ssp. <jats:italic>sativus</jats:italic>). These were rotated with millet (<jats:italic>Urochloa ramosa</jats:italic>), sunn hemp, egyptian wheat/iron clay pea (<jats:italic>Sorghum</jats:italic> sp./<jats:italic>Vigna unguiculata</jats:italic>), and sorghum × sudangrass (<jats:italic>Sorghum bicolor</jats:italic> × <jats:italic>S. bicolor</jats:italic> var. <jats:italic>sudanese</jats:italic>)/iron clay pea. Onion yields in both rotations were at least 80% of average yields in Georgia. Lettuce yields were at least double the average yields in Georgia and were comparable to national averages in the 2nd and 3rd years of the study. Strawberry yields in these rotations were lower than Georgia averages in all 3 years with a trend of lower yields over the course of the study. By contrast, potato, although lower than average yields in Georgia increased each year of the study. Broccoli yields in the first year were substantially lower than average Georgia yields, but were comparable to average yields in the 2nd year. Carrot remained less than half of average Georgia yields. Green bean were half of average Georgia yields in the 2nd year and were comparable to average yields in the 3rd year. As expected from what is observed in cool-season organic vegetable production in Georgia, disease pressure was low. Cover crops maintained soil organic carbon (C) with a small increase in active C; however, there was a net loss of potentially mineralizable nitrogen (PMN). Active C averaged across both rotations at the beginning of the study at 464 mg·kg<jats:sup>−1</jats:sup> and averaged 572 mg·kg<jats:sup>−1</jats:sup> at the end of the study. On the basis of this study, using cover crops can maintain soil carbon without the addition of carbon sources such as compost. Finally, longer term work needs to be done to assess soil management strategies.</jats:p>

Winter Broccoli and Cauliflower under Organic High Tunnels in a Humid, Subtropical Climate

“…Differences among planting dates and cultivar type did not appear to have a major or consistent influence on the average marketable yield of fall/winter broccoli grown under our high tunnel system, although the cultivar 'Imperial' was slightly quicker to mature (1 week) compared with 'Belstar' and 'Fiesta'. In addition, all planting dates and cultivars demonstrated a high percentage of marketability, and our yields were equal or greater than another organic open field broccoli study conducted at the same location in Georgia (Boyhan et al, 2016). There were no indications of damage to the either broccoli or cauliflower heads grown under the high tunnels because of cold temperatures during the experimental timeframe, although some leaf tissue showed signs of frost damage later in the season.…”

An Extension Specialist's Reflections from the Field: Discovering Ag of the Middle in the Shift from Direct Sale to Wholesale Vegetable Production

“…Here, we examine one field study of a simplified crop rotation (reported in full in Boyhan et al. ) to suggest that this shift may also allow small‐acreage producers to maintain their commitment to “sustainable” agriculture by identifying crop rotations that maintain or build soil health while resulting in harvests that are potentially profitable. However, crop rotations that can serve wholesale markets while maintaining production values (organic, building soil health) are not a one‐size‐fits‐all prospect.…”

“…Each rotation included three blocks (e.g., ABC , BCA , and CAB) of four replicates, grown in a continuous three‐year cycle, with 12 plots per rotation and 24 plots total (Boyhan et al. ).…”

“…Economic analysis indicated that both rotations were potentially profitable (Table ) (Boyhan et al. ; Tshikala et al. ) .…”

“…Boyhan et al. 's () cool season vegetable rotation study encountered challenges with short planting windows, but also demonstrated that summer cover cropping is a viable economic option for a mid‐acreage farm with sufficient equipment to properly manage a summer cover crop. Our ongoing collaboration in this area includes a large‐scale, multi‐institutional study of cover crops on soil and water quality and economic feasibility; it also incorporates ethnographic and community‐based social marketing approaches to address key social, organizational, and policy barriers to cover crop adoption.…”