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Delbert D. Hemphill Jr.

Agricultural plastics area significant contributor to solid waste disposal problems, particularly in areas with heavy use of plastic-covered greenhouses or mulch films. Field-burning and landfilling are no longer viable options for disposal in many areas. Reuse and reduced weight of films are two methods to reduce the amount of material requiring disposal. Recycling, incineration, and on-site degradation appear to be the most-promising technologies for disposal. Each technology has its drawbacks. These include dirt and pesticide residues on mulch films, the presence of stabilizers and photoactivators, possible limitations to recycling mixtures of types of plastics, and high costs for recycling and incineration facilities. This is an active area of research for many members of the American Society for Plasticulture.

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John Z. Burket, Delbert D. Hemphill and Richard P. Dick

Cover crops hold potential to improve soil quality, to recover residual fertilizer N in the soil after a summer crop that otherwise might leach to the groundwater, and to be a source of N for subsequently planted vegetable crops. The objective of this 5-year study was to determine the N uptake by winter cover crops and its effect on summer vegetable productivity. Winter cover crops [red clover (Trifolium pratense L.), cereal rye (Secale cereale L. var. Wheeler), a cereal rye/Austrian winter pea (Pisum sativum L.) mix, or a winter fallow control] were in a rotation with alternate years of sweet corn (Zea mays L. cv. Jubilee) and broccoli (Brassica oleracea L. Botrytis Group cv. Gem). The subplots were N rate (zero, intermediate, and as recommended for vegetable crop). Summer relay plantings of red clover or cereal rye were also used to gain early establishment of the cover crop. Cereal rye cover crops recovered residual fertilizer N at an average of 40 kg·ha-1 following the recommended N rates, but after 5 years of cropping, there was no evidence that the N conserved by the cereal rye cover crop would permit a reduction in inorganic N inputs to maintain yields. Intermediate rates of N applied to summer crops in combination with winter cover crops containing legumes produced vegetable yields similar to those with recommended rates of N in combination with winter fallow or cereal rye cover crops. There was a consistent trend (P < 0.12) for cereal rye cover crops to cause a small decrease in broccoli yields as compared to winter fallow.

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Michael J. Lamb, George H. Clough and Delbert D. Hemphill

The effects of supplemental Ca and varying NO3:N H4 ratios on transplant growth and NH4-N utilization were studied using watermelon (Citrullus vulgaris L. `Crimson Sweet') seeded in plastic multicell trays. The growing media consisted of a commercial peat mix amended with CaCO3 (10% w/v). Fertigation with five NO3:N H4 ratios and five levels of supplemental Ca (4, 8, 12, 16 mmol.) was applied daily in factorial combinations. The highest NO3:N H4 ratio produced greatest shoot dry weight, shoot N, and shoot NO3-N and K concentrations. Increasing NH4 and Ca decreased media pH and increased EC. After 21 days, supplemental Ca decreased shoot N and dry weight, but after 28 days had no effect. Additional Ca increased shoot Ca but decreased Mg and K. Supplemental Ca and N ratio interacted to affect leaf area. Pretransplant N ratio and supplemental Ca effects on seedling field performance, flowering, and yield were evaluated.