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  • Author or Editor: C. Summers x
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Abstract

Watermelon [Citrullus lanatus (Thunberg) Matsumura and Nakai], cultivars ‘Allsweet’, ‘Charleston Gray’, ‘Crimson Sweet’, and ‘Iopride’ were grown from transplants at Ames, Iowa, harvested at 4-day intervals for a total of 11 harvests. Carbohydrates from fruit juice extracts were determined by high-pressure liquid chromatography, and flesh color was determined by using a colorimeter. The reducing sugars, fructose and glucose, generally increased in concentration from 20 to about 36 days after anthesis and thereafter declined in each of the 4 cultivars. Sucrose was measurable in the fruit tissue 20 days after anthesis and thereafter increased. Total sugar concentration increased from 20–60 days after anthesis, with its most rapid increase occurring between 20 and 36 days. For the 4 cultivars sampled, relative sweetness index and total sugar concentration values were similar. Results confirm that ‘Charleston Gray’ develops its maximum red flesh color before reaching maximum sweetness. Such a developmental pattern may have a negative affect on per capita consumption when fruits are harvested on the basis of flesh color rather than edible quality.

Open Access

Abstract

Watermelon [Citrullus lanatus (Thunberg) Matsumura and Nakai] juice samples of ‘Allsweet’ and ‘Crimson Sweet’ were stored at 0° and −30°C. Concentrations of fructose, glucose, and sucrose were determined by using HPLC over a period of 44 days at 2- to 7-day intervals. Changes in sugar concentrations suggest that sucrose is hydrolyzed to fructose and glucose within a period of 10 days for samples stored at 0°. A 19.6% decrease in total sugar concentration was observed after 37 days storage. A 17.8% sugar loss also was observed in samples stored at −30° for 37 days.

Open Access

Observations that tomato transplants died or were severely stunted when set into unincorporated sorghum-sudan hybrid surface mulch led us to further investigate the potential allelopathic impacts of this warm-season cover crop in a series of field experiments. Survival and dry weights of tomato, lettuce, and broccoli transplants were determined in fallow, incorporated sorghum-sudan-, and unincorporated sorghum-sudan-mulched soils. All three species transplanted into plots in which the sorghum-sudan had been cut and left on the soil surface had a significantly lower dry weight than plants transplanted into fallow soil or into soil where the sorghum-sudan had been incorporated. Additionally, fewer transplants survived in the mulch treatment. The surface mulch plots also significantly reduced weed biomass nearly 10-fold. We believe that a water-soluble compound that is leached out of the sorghum-sudan hybrid is toxic to all three of the plants tested. Further laboratory and greenhouse tests are under way to determine the exact nature of the toxic substance.

Free access

Improving soil quality and suppressing weeds are two challenges facing strawberry growers. Cover crops, such as perennial ryegrass (Lolium perenne) and sorghum-sudangrass (Sorghum sudanense), have been used in rotation with strawberry in the Midwest. The objective of the field study was to investigate the effects of various cover crops on soil quality and weed populations for strawberry production. The experiment was established in 1996 at the Iowa State Univ. Horticulture Station, Ames, in plots that previously were planted continuously in strawberry for 10 years. Nine treatments were arranged in a randomized complete-block design with three replications. Treatments included cover crops of Indian grass (Sorghastrum avenaceum), switchgrass (Panicum virgatum), big bluestem (Andropogon gerardii), black-eyed susan (Rudbeckia hirta), marigold (Tagetes erecta `Crackerjack'), sorghum-sudangrass, perennial ryegrass, strawberry (Fragaria ×ananassa `Honeoye'), and bare soil (control). Data from 1998 showed that both annual and perennial cover crops were established more readily (higher treatment-plant populations and less weed populations) than in 1997. Water infiltration rates were highest in bare soil plots and lowest in P. virgatum plots. Bare soil plots and S. sudanense plots had the lowest percent soil moisture.

Free access

Velvetbean (Mucuna deeringiana L.) was used in crop rotation to determine the influence on southern root-knot nematode (Meloidogyne incognita) in sustainable vegetable production. Replicated trials were conducted at four locations. Two cover crop treatments, crimson clover and subterranean clover, were used in the sustainable plots and rye was the plow-down cover crop for the conventional plots. Selected as the vegetable crops were tomato, pepper, and eggplant. Following the final harvest, velvetbean was planted into the sustainable plots and disked under after 90 days. Results from soil samples before and after velvetbean, indicated the sustainable plots had substantially reduced nematode densities, while most conventional plots showed increases. A correlation between location, treatment, root-gall indexes and nematode density occurred in all crops for 1992. In 1993 there was only a correlation between root-gall index and nematode density in pepper. However, root-gall indexes were significant for location and treatment in all crops.

Free access