Competition of Amaranthus species with dry bean plants

Abstract

Weeds compete with field crops mainly for water, light and nutrients, and this competition is among other factors, a function of the occurrence of weed density, and the intrinsic competitive ability of each vegetal species. The objective of this research was to evaluate the competitive ability of five weed species of the Amaranthus L. genus (A. deflexus, A. hybridus, A. retroflexus, A. spinosus and A. viridis) with dry bean plants (Phaseolus vulgaris L. - 'Carioca Precoce' cultivar), using the replacement series design. A fixed total density equivalent to 80 plants m-2 was used in pots of 2.8 L capacity varying the proportions between the species in coexistence. To install the experiment, Amaranthus seedlings were transplanted to the pots at the phenological stage of completely expanded cotyledon leaves, while the crop was seeded. A factorial scheme (5 x 5) was used to carry out the experiment, consisting of five species of Amaranthus (pigweeds) and five species proportions (beans:pigweeds): 4:0, 3:1, 2:2, 1:3 and 0:4. Randomized blocks with four replicates were installed and the experiment was repeated twice. Dry bean plants were more competitive than each one of the five Amaranthus species when the species proportion was equivalent. A. deflexus and A. viridis were the weed species which phenology were less affected by the competition with dry bean; the intraspecific competition was more damaging for dry bean plants, suggesting that the damages caused by the weeds are more related to high density of infestation than to the intrinsic competitive ability of the species.

Phytosociological Survey of Weeds in Cultivars of Common Beans With Different Types of Growth in the North of Minas Gerais

“…Although it has a C4 photosynthetic metabolism and has higher lighting demands, this species has shown to be very competitive with beans at this development stage. The species from the Amaranthus genus can cause great losses because they have a high initial growth vigor, efficient root system and seed dormancy, and they can also host plant pathogens (Carvalho and Christoffoleti, 2008). Barroso et al (2010), in a study that assessed competitiveness of several species of weeds on beans, in two sowing periods, saw that A. viridis showed to be the most aggressive among all, causing harm in the growth and development of beans, with reductions that reached 80% in the final productivity of the crop.…”

Habilidade competitiva relativa de milhã em convivência com arroz irrigado e soja

“…Embora a cultura apresente maior habilidade competitiva, os danos ocasionados pelas plantas daninhas ocorrem, pois se relacionaram à maior população (Vilá et al, 2004;Carvalho & Christoffoleti, Pesq. agropec.…”

“…Índices de competitividade entre arroz irrigado ou soja e milhã (Digitaria ciliaris), expressos por competitividade relativa (CR) e coeficientes de agrupamento relativo (K) e de competitividade (C). Carvalho & Christoffoleti (2008), o que sugere que os danos causados pelas plantas daninhas relacionaram-se mais estreitamente com as altas populações de ocorrência do que com a habilidade competitiva intrínseca das espécies. As PRT de AF e MMSPA apresentaram diferenças significativas e foram inferiores a 1, que corresponde a linhas côncavas e mostra que a competição entre a cultura da soja e a milhã ocorreu pelos mesmos recursos do meio (Radosevich, 1987;Roush et al, 1989;Cousens, 1991).…”

“…Verificaram-se resultados semelhantes para a cultura do feijão em competição com papuã (Passini et al, 2003) ou com diferentes espécies de caruru (Amaranthus deflexus, A. hybridus, A. retroflexus, A. spinosus e A. viridis) (Carvalho & Christoffoleti, 2008). No entanto, a planta daninha pode mostrar-se mais competitiva do que a cultura, conforme foi observado em nabo forrageiro, em competição com soja .…”

Produção e partição de matéria seca de cultivares de feijão em competição com plantas daninhas

“…Esses autores verificaram que o feijoeiro possui maior habilidade competitiva do que esta espécie e que a competição interespecífica pode ser considerada desprezível. Carvalho & Christoffoleti (2008) verificaram que a competição entre o feijoeiro e diversas espécies do gênero Amaranthus foi prejudicial para a cultura e as plantas daninhas, porém de forma mais pronunciada para as espécies infestantes. No entanto, conforme Teixeira et al (2009), o feijoeiro apresenta baixa capacidade competitiva e está enquadrado no grupo de culturas agrícolas que menos sombreiam o solo, o que expõe a cultura a intensa interferência de plantas daninhas.…”