Observações sôbre o efeito da luz no crescimento da tiririca, Cyperus rotundus L.

English. The effect of shading induced by Jack bean plants on the growing of nutsedge was investigated. Three treatments were included: a) shading without root competition; b) shading plus competition of the root systems; c) competition of roots without shading. The control contained only nutsedge plants. Of the two factors involved in the association of the species, shading proved to be the most important in determining the inhibition in the growth of nutsedge. The effect of artificial shading on the developmental pattern of the nutsedge plants was also studied. The more intense the shade, the greater the decreasing in the growth rate of the nutsedge plants. Under conditions of 92.5% of shading the growth was inhibited in about 60% when compared with the control plants. The compensation point of light, determined colorimetrically, showed that the point of equilibrium between the photosynthetic and respiratory processes was attained in the range of 800 to 1,000 lux of light intensities. By considering that a 2.5-months-old Jack bean culture only allows 1 to 1.5% of the incident light to reach the soil surface, it can be assumed that the infestation of nutsedge should be lowered by the shading effect induced by the Jack bean plants.

Portuguese. Foram estudados: os efeitos do sombreamento de tiririca (Cyperus rotundusL.), no campo, com plantas de Canavalia ensiformisD.C.; a ação de luz artificial; o ponto de compensação de luz. o sombreamento reduziu drasticamente a multiplicação dos tubérculos. Plantas mantidas com luminosidade artificial de 15% da radiação solar tiveram o desenvolvimento subterrâneo muito prejudicado. A capacidade vegetativa da tiririca mostrou-se reprimida sòmente com redução acentuada da luminosidade.