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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 (Allium cepa), strawberry (Fragaria ×ananassa), and potato (Solanum tuberosum). These crops were rotated with green bean (Phaseolus vulgaris), oats/austrian winter pea (Avena sativa/Pisum sativum ssp. arvense), southernpea (Vigna unguiculata), and sunn hemp (Crotalaria juncea). In the second rotation, cool-season cash crops included onion, broccoli (Brassica oleracea Italica group), lettuce (Lactuca sativa), and carrot (Daucus carota ssp. sativus). These were rotated with millet (Urochloa ramosa), sunn hemp, egyptian wheat/iron clay pea (Sorghum sp./Vigna unguiculata), and sorghum × sudangrass (Sorghum bicolor × S. bicolor var. sudanese)/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⁻¹ and averaged 572 mg·kg⁻¹ 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.

Abstract

Seeds from ‘Bartlett’ and ‘Winter Nelis’ and ovules from seedless ‘Bartlett’ pears were collected periodically between 25 days after full bloom and harvest. Extracts were analyzed for hormones by combined gas chromatography-mass spectrometry, using the technique of selected ion current monitoring. Levels of 6 gibberellins were low in all samples prior to appreciable embryo growth (25 days after full bloom). Content of gibberellins A₁₇, A₂₅, A₄₅ and a presumed 3β-hydroxy gibberellin A₄₅ rose dramatically during rapid embryo growth between 65 and 85 days after full bloom, while the gibberellin content of embryoless ovules of ‘Bartlett’ did not change during this period. Two unidentified gibberellin-like compounds, one isomeric with gibberellin A₂₅ and the other corresponding to a hydroxy gibberellin A₄₅, were detected 85 days after full bloom. Abscisic acid content was also maximal between 65 and 106 days, ovules of seedless ‘Bartlett’ exhibiting considerably higher concentration than seeds of either cultivar. Levels of 5 abscisic acid metabolites varied with seed type and sampling period. Phaseic acid levels remained low in ‘Bartlett’ seeds and ovules during all developmental stages but increased in ‘Winter Nelis’ seeds at 122 days. Concentration of cis, Trans-dihydrophaseic acid, although low, rose as ‘Winter Nelis’ seeds matured while ovules of seedless ‘Bartlett’ showed no such increase. Levels of 2 metabolites, tentatively identified as trans, trans-dihydrophaseic acid and a hydroxylated derivative of dihydrophaseic acid, varied only slightly with development. A third metabolite, characterized as a keto derivative of dihydrophaseic acid or a hydroxy-derivative of phaseic acid, was present in large quantities in unfertilized ovules during the early period of fruit growth, but increased in seeds only after 65 days. The possible roles of these compounds are discussed in relation to seed, fruit, and flower development.

Abstract

Concentrations of abscisic acid (ABA), dihydrophaseic acid (DPA), and their metabolites were measured in mature pear seeds, using gas-liquid chromatography (GLC). ABA content of Pyrus communis L. cv. Bartlett seeds fell during imbibition, but was not affected by temperature (4 vs. 21°C) or time (0 to 4 weeks) of stratification in a moist medium. Levels of DPA and 3 of its metabolites were not correlated with dormancy. The amount of chilling required to break dormancy was not correlated with ABA or DPA content in imbibed, non-stratified seeds of 6 Pyrus species.