Graduate Thesis Or Dissertation
 

Interaction of crop plant population with weed competition in corn (Zea mays L.), bush snap beans (Phaseolus vulgaris L.), and onion (Allium cepa L.) at differing stages of development

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  • Yield reductions due to competition of weeds with crop plants can be extremely important. Early weed competition can be as important in reducing crop yield as weed competition for the entire season. The objectives of this study were (1) to determine the weed control achieved by narrow row-cropping patterns, (2) to measure the competitive effect achieved with narrow row-cropping patterns, with low photosynthetic capacity crop plants or with high photosynthetic capacity plants, in competition with high photosynthetic capacity weeds, (3) to determine at what time weed control becomes important and (4) to determine if the time at which competition begins could be determined by change in weight, sugar content, and/or nitrogen content of the commercial crop. Also, two greenhouse studies were made to evaluate the differential uptake of nitrogen by two competiting species, corn (Zea mays L.) and pigweed (Amaranthus rectroflexus L.), and to evaluate the effect of competition for soil and light between two broadleaf species, snap beans and pigweed. Yields of bush snap beans (Phaseolus vulgaris L.), corn (Zea mays L.), and onion (Allium cepa L.) were all decreased significantly by the presence of weed competition throughout the entire growing season. Reduction in total area occupied by an individual crop plant resulted in decreased effects on vegetative and reproductive parts due to weed competition and increased the effect of crop plant-to-plant competition. Early weed control was important in all crops. In 1969, yield reductions in corn and beans allowed, to compete with weeds for a period of five to six weeks after crop emergence were equal to those from plots with weed competition for the entire season. In 1970, corn required two weeks of cultivation after emergence and snap beans required three weeks of cultivation after emergence to decrease losses due to weed competition. Weed weight yields were significantly reduced in snap beans at the 5 x 5 inch spacing when compared to the 15 x 5 and 35 x 5 inch spacings. As measured by leaf fresh weight, competition was determined to begin between snap beans and redroot pigweed at 36 to 44 days after crop emergence at crop plant spacings of 35 x 5 and 15 x 5 inches. Significant weed competition did not develop after 51 days at crop plant spacings of 5 x 5 inches. Competition between corn and redroot developed 41 days after emergence for all plant spacings. This study indicated the time at which competition between crop and weeds could be determined by leaf fresh weight measurements or by measuring the leaf area of the crop plants. At a fertilizer rate of 77-101-64 pounds of N-P-K per acre, corn made greater gains in total green weight than did pigweed in the greenhouse. However, with the further addition of 300 pounds of ammonium nitrate per acre, pigweed continued to make gains while corn growth was unaffected. At all fertility rates, pigweed had higher levels of total leaf nitrogen than corn. When snap beans had emerged and become established before the emergence of pigweed, the total green and dry weight of pigweed was significantly reduced if growing in full competition or in competition for soil factors only.
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