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  • Author or Editor: James Duthie x
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In each of seven field experiments, density of watermelon (cultivar Sugar Baby) plants was varied over the range 1000-9000 plants/ha by varying the distance between plants in single-row, replicate plots. Per unit area, reproductive biomass and marketable yield each increased linearly with density. An upper limit on these response variables at high density was not detected in any experiment. The rate of increase per 1000 plants/ha ranged from 1.1 to 3.2 Mg·ha-1, for reproductive biomass, and from 0.5 to 1.1 Mg·ha-1, for marketable yield. The linear effect of density explained >90% of the increase in reproductive biomass in most experiments. The effect on marketable yield was more variable because the marketable fraction of reproductive biomass often was highly variable. In most experiments, the marketable fraction did not vary systematically with density. The linear rate of change in the marketable fraction with density did not exceed 3% per 1000 plants/ha on average in any experiment. Intraspecific competition intensified rapidly as density was increased in some experiments. Intensity of competition appeared to vary among environments.

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We conducted several experiments to determine the best system for production of spring cabbage (Brassica oleracea L. Capitata group) with conservation tillage (CT) in the southern plains of the United States. Rye (Secale cereale L.) was selected as the best cover crop to cover the soil in a short time. Raised beds were formed in the fall and planted with rye. With most studies, the rye was allowed to remain on the soil surface rather than being tilled into the soil. Planting densities, rates of nitrogen fertilizer, and herbicide materials were evaluated to determine the best system for cabbage production. In each study, various cover crop practices were compared with bare soil production systems. Soil erosion was reduced by the use of rye cover crops. Cabbage was produced in the CT system, but cabbage yields were higher in bare soil plots than in the rye-covered plots. We are also in the process of developing a system of CT that involves permanent bermudagrass [Cynodon dactylon (L.) Pers.] pastures and watermelon [Citrullus lanatus (Thunb.) Matsum. & Nakai]. This system allows both crops to be grown simultaneously on the same land.

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