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Phosphorus Effects on Competitive Interactions of Smooth Pigweed (Amaranthus hybridus) and Common Purslane (Portulaca oleracea) with Lettuce (Lactuca sativa)

Bielinski M. Santos, Joan A. Dusky, William M. Stall, Donn G. Shilling and Thomas A. Bewick
Weed Science
Vol. 46, No. 3 (May - Jun., 1998), pp. 307-312
Stable URL: http://www.jstor.org/stable/4045866
Page Count: 6
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Phosphorus Effects on Competitive Interactions of Smooth Pigweed (Amaranthus hybridus) and Common Purslane (Portulaca oleracea) with Lettuce (Lactuca sativa)
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Abstract

Replacement series studies were conducted under controlled conditions to determine the effect of phosphorus (P) rates and population densities on the competitiveness of smooth pigweed and common purslane with lettuce. Densities were 2, 4, and 8 plants per 113 cm², whereas P rates were 0, 0.4, and 0.8 g P L⁻¹ soil. A P-deficient Histosol (0.3 mg water-extractable P L⁻¹ soil) was used. High P fertility enhanced the competitive ability of lettuce in smooth pigweed-lettuce mixtures. Smooth pigweed was not responsive to P rates. However, luxurious P consumption by smooth pigweed occurred, reducing the amount of the nutrient available for lettuce absorption. In common purslane-lettuce mixtures, the weed was responsive to P rates, increasing its competitive ability, whereas no increase in lettuce competitive ability was observed. Both weed species were more competitive than lettuce. Competition for P appears to be the main mechanism of common purslane interference on lettuce grown in low-P organic soils. Alternative fertilization strategies (i.e., banded applications) may reduce the effect of smooth pigweed on lettuce.

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