In a vegetable nutrition experiment, fertilizers were applied in such a way as to make possible a study of the effects of three levels each of nitrogen, phosphorus, and potassium on the yield and food value of carrots. The levels of each nutrient applied were: nitrogen 50, 100, and 150 pounds; phosphoric acid 100, 200, and 300 pounds; and potash 50, 100, and 150 pounds per acre. The experiment was arranged in a 3 X 3 X 3 design with second order interactions confounded with blocks. Under the conditions of the experiment it was found that applications of nitrogen caused a very highly significant, positive, linear response for root yield; that applications of phosphorus had no primary effect on yield; and that applications of potassium caused a highly significant, positive, linear and quadratic response for root yield. Nitrogen applications caused a very highly significant, positive, linear trend for crude protein content, and a negative trend of similar significance for crude ash content. No effect was observed on dry weight, total available carbohydrate or total carotenoid contents. Phosphorus applications had no primary effect on those food value factors assayed. Potassium applications caused a significant, negative, linear trend for dry weight, and a highly significant, positive, linear trend and a significant, positive, quadratic trend for ash content. No primary effect was observed on total available carbohydrate, crude protein, or total carotenoid contents. Five significant interactions were found. These were: quadratic phosphorus X linear potassium, for total yield; linear nitrogen X linear phosphorus and linear phosphorus X quadratic potassium, for total available carbohydrates; quadratic phosphorus X quadratic potassium, for crude protein; and quadratic nitrogen X linear phosphorus for crude ash content. The experimental design adopted, and the statistical analysis used, proved satisfactory for the evaluation of primary and second order interaction effects. Significance of pairs of adjusted means for root yield, calculated as a part of the statistical analysis, has been summarized by means of the tri-cyclograph. / Land and Food Systems, Faculty of / Graduate

Olpidium was correlated with the frequency of precipitation greater than one half inch but was not correlated with root temperature, CO₂ or 0₂ concentration, saturated hydraulic conductivity, the height of the carrot beds, marketable yield or cull rate. Olpidium isolates with and without TNV did not produce lesions on carrot roots under greenhouse conditions. TNV was detected in both brown and white roots but only from problem fields. Carrot rootlets rub-inoculated with TNV failed to produce necrotic symptoms. Olpidium and TNV were found in onion, lettuce, celery and some weed species common to PRD problem fields. However, no root tip browning was observed in any of these hosts. Fast growing Pythium species were recovered equally frequently in brown and symptomless rootlets and from problem and non-problem soils. Most weeds, celery, onion and lettuce also had a high incidence of fast growing Pythium. The highly pathogenic, slow growing Pythium sulcatum was recovered only from problem soil. The recovery rate from symptomless roots was very low compared to brown roots. P. sulcatum was not isolated from celery or any of the weed species common in problem soil. Lettuce and onion were found to support low levels of infection. Evidence suggests that P. sulcatum is a primary incitant. PRD losses can be kept to a minimum and marketable yields increased by using tolerant varieties, such as HiPak; raised beds, if there is a readily available supply of irrigation water; precision seeding at 1 1/4 inches; and a crop rotation of onions preceding carrots. Matric potential was controlled in small containers separated from osmotic solutions of polyethylene glycol (PEG) 6000 by Pellicon ultrafiltration membranes (nominal molecular weight cutoff:500, Millipore Corp.). Matric potentials could be maintained for periods of 3-5 weeks before microbial breakdown of membranes occurred. Flow rate for the membranes was 1.0 cm³ cm⁻² day⁻¹ for a water potential difference across the membrane of 0.2 bar. Water potential measured with tensiometers or thermocouple psychrometers in a cylindrical container (4.3 cm diam. x 10 cm) with a membrane acrosss the bottom, remained relatively constant under conditions of soil surface evaporation but decreased rapidly when young plants were grown in the system. Soil cells (5.5 x 2.0 x 10 cm with one 43 mm diameter membrane in each side), containing two young carrots, and emersed in a -0.2 and -2.0 bar PEG solution had an average matric potential of -0.4 and -2.5 bars respectively over a three week period. The carrots transpired 7.8 and 3.9 ml/day at osmotic potentials of -0.2 and -2.0 bars respectively which suggests that sufficient water was passing through the membrane to meet the needs of a growing carrot. / Land and Food Systems, Faculty of / Graduate

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Thesis (Ph. D.)--University of Missouri-Columbia, 2000. / Typescript. Vita. Includes bibliographical references. Also available on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 2000. / Typescript. Vita. Includes bibliographical references. Also available on the Internet.