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Robert Wiedenfeld

Onion production requires N fertilization, yet use efficiency of applied N is low. Improvements may be possible with a better understanding of plant growth and nutrient requirements over time. Onion growth and nutrient uptake was extremely slow during the winter months following planting, then increased substantially in the spring. Onion leaf N concentrations declined with age, while bulb N concentrations fluctuated with growing conditions but showed no longterm trend. Responses to N application were due primarily to timing and less to rate applied. Nitrogen uptake increased in some cases very quickly following N application, and in other situations was still evident after 6½ months. Yield increases, however, occurred only for preplant and winter fertilizer applications, not for spring application. Yield responses to both timing and rate varied by cultivar, with the later maturing cultivar doing best at the highest rate of preplant and the higher 2 rates of the winter applied N fertilizer.

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Robert Stubblefield and Robert Wiedenfeld

A field study was conducted in south Texas in the spring 1990 to determine the effects of ground cover, planting method and drip irrigation rates on cantaloupe growth, yield and quality. Transplanting vs. direct seeding enhanced early vine growth with earlier yields, although direct seeding later caught up resulting in comparable final cumulative yields. Black polyethylene mulch also improved earliness but at the loser irrigation rate total yields were reduced due to deflection of rainfall by the mulch. Irrigation at .1, .3, .5, .7 and .9 times pan evaporation had little effect on final cumulative yields with exception to the .1 and .3 rates. Melon sugar content was highest for transplants with direct seeded melons becoming comparable only at mid to final harvest. The combined practices of transplanting and black polyethylene mulch resulted in a 14 day earliness advantage over the treatments that were direct seeded on bare soil although final yields were unaffected. No appreciable increase in soil salinity were found as a result of drip irrigation usage.

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Robert Wiedenfeld and Robert Stubblefield

Plastic mulch ground cover and drip irrigation have produced substantial increases in yield and earliness of melons. However, such practices affect water movement, and nutrient and salt distribution in the soil. Salt levels in the soil after a melon crop using drip or flood irrigation increased in bare soil but decreased where plastic mulch had been used. Apparently capillary rise of water in response to surface evaporation brought salts up into the root zone. Very little of the applied N was detectable at the end of the study. However, enhanced early vine growth due to N application where drip irrigated but not where flood irrigated indicated that flood irrigation may have caused earlier N losses. Yield responses to N regardless of irrigation method indicated that early availability may have been most important. Yield increases were found for drip vs flood irrigation, and for plastic mulch vs bare soil, both of which may have been earliness effects; but the later treatments did not get the chance to catch up due to the occurrence of vine decline.

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Robert Wiedenfeld, Eden Hinojosa and Robert Stubblefield

A study was conducted in subtropical south Texas in 1989 to determine the effects of planting method, polyethylene mulch, and rate of drip irrigation on cantaloupe growth, yield and quality. Irrigation at .25, .50, .75, 1.0, or 1.25 times pan evaporation had little effect on soil moisture or yield, with all water application levels keeping the soil close to field capacity. Transplanting vs. direct seeding enhanced early vine growth and caused earlier yield, although direct seeded plants later caught up and had final cumulative yields slightly higher than the transplants. Black polyethylene mulch also improved earliness and reduced the number of culls compared to bare soil, but at the lowest watering level total yields were reduced by the mulch due to deflection of the rainfall received. The combined practices of transplanting and polyethylene mulch caused approximately a 9 day earliness advantage over the treatment that was direct seeded on bare soil although final yield was unaffected. Soil salinity buildup may cause problems which would affect the position of the drip line and the frequency and amount of water applied.

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Robert Wiedenfeld, Eden Hinojosa and Robert Stubblefield

A study was conducted in subtropical south Texas in 1989 to determine the effects of planting method, polyethylene mulch, and rate of drip irrigation on cantaloupe growth, yield and quality. Irrigation at .25, .50, .75, 1.0, or 1.25 times pan evaporation had little effect on soil moisture or yield, with all water application levels keeping the soil close to field capacity. Transplanting vs. direct seeding enhanced early vine growth and caused earlier yield, although direct seeded plants later caught up and had final cumulative yields slightly higher than the transplants. Black polyethylene mulch also improved earliness and reduced the number of culls compared to bare soil, but at the lowest watering level total yields were reduced by the mulch due to deflection of the rainfall received. The combined practices of transplanting and polyethylene mulch caused approximately a 9 day earliness advantage over the treatment that was direct seeded on bare soil although final yield was unaffected. Soil salinity buildup may cause problems which would affect the position of the drip line and the frequency and amount of water applied.

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Robert Wiedenfeld, B. Scully, Marvin Miller, Jonathan Edelson and Jiandong Wang

Purple blotch (Alternari a porri) and thrips (Thrips tabaci) can seriously reduce yields of short day onions in South Texas. The level of injury caused by these organisms is influenced by the concentration of nitrogen in leaf tissue. Lower levels of tissue nitrogen increase susceptibility to A. porri but decrease susceptibility to thrips. The purpose of this study was to evaluate the effect of tissue N levels on joint susceptibility of 4 onion cultivars to A. porri and thrips. Foliage was fertilized at 0, 4, 8, 12 or 16 lbs N/ac/wk for 6 weeks. Nitrogen concentrations in onion leaves varied over time and by leaf age, but showed very little effect due to foliar fertilization. Significant differences in thrips were noted among cultivars, but not among leaf N concentrations with cultivars. Purple blotch outbreak occurred late in the growing season and was not related to leaf N levels. Total N uptake failed to respond to foliar fertilization, therefore overall use efficiency of the foliar N applied averaged only about 10% relative to the amount taken up in the check plots.

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L. Brandenberger, M. Baker, D. Bender, F. Dainello, R. Earhart, J. Parsons, R. Roberts, N. Roe, L. Stein, M. Valdez, K. White and R. Wiedenfeld

During the past several years, watermelon trials have been performed in the state, but not as a coordinated effort. Extensive planning in 1997 led to the establishment of a statewide watermelon trial during the 1998 growing season. The trial was performed in five major production areas of the state including: The Winter Garden (Carrizo Springs); South Plains (Lubbock); East Texas (Overton); Cross Timbers (Stephenville); and the Lower Rio Grande Valley (Weslaco). Twenty seedless and 25 seeded hybrids were evaluated at each location. Drip irrigation with black plastic mulch on free-standing soil beds was used to grow entries in each area trial and yield data was recorded in a similar manner for each site. Results were reported in a statewide extension newsletter. Future plans include a continuation of the trial in the hope that multiple-year data will provide a basis for valid variety recommendations for watermelon producers in all areas of the state.