Abstract

The study of competitive ability between crops and weeds is relevant for the adoption of more sustainable control methods, with lower costs for producers and less environmental impact. In this context, the objective of this work was to evaluate the competitive ability of quinoa genotypes (Q 1303, Q 1324, and Q 1331) in association with the weeds Euphorbia heterophylla and Urochloa plantaginea in different plant proportions within the association. The experiment was conducted in a randomized block design with four repetitions. The treatments were distributed in proportions (100:0, 75:25, 50:50, 25:75, and 0:100%) of crop and/or weed plants corresponding to 20:0, 15:5, 10:10, 5:15, and 0:20 plants per pot. The competitiveness of the species was analyzed through diagrams applied to substitution experiments and through relative competitiveness indices. Fifty days after species emergence, measurements were made on tillering of U. plantaginea, number of leaves of quinoa and/or Euphorbia, plant height, stem diameter, chlorophyll index, gas exchange, leaf area, dry mass of the aerial part, as well as the measurement of nitrogen and phosphorus concentrations in the crop leaves. Heavy interspecific competition occurred between quinoa genotypes the weeds, with mutual harm to the species involved in the community. U. plantaginea proved to be more aggressive to quinoa compared to E. heterophylla. The quinoa genotypes showed similar competitive abilities, with emphasis on Q1303, which showed greater tolerance to association with U. plantaginea. The most detrimental competition for quinoa was interspecific, indicating the need for control of E. heterophylla and U. plantaginea even at low infestation levels.

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