Competição entre cana-de-açúcar e plantas daninhas na fase inicial de crescimento vegetativo

Abstract

Weeds are a main biotic factors that cause reduction in productivity of sugar-cane. Its control carried out mainly by the use of herbicides, raises the production cost, and environmental pollution. One alternative is the use of varieties tolerant to this factor. Therefore, the objective of this study was to evaluate the initial growth, nutrition and water use in plants of four varieties of sugar-cane subject to competition with two weed species. Were utilized four varieties of sugar-cane (RB867515, RB931011, RB92579 e RB98710) subjected to competition with two weed species (Digitaria horizontalis e Euphorbia heterophylla) under the completely randomized design in factorial 4 (varieties) x 3 (levels of competition) with the addition of more than 2 treatments (weeds isolated), with 5 replicates. Evaluated on a weekly growth of four varieties of cane sugar (plant height, stem diameter, leaf number and leaf area), SPAD index in the variety of weed and, moreover, every other day by weighing vessel, quantifying the amount of water used by plants and calculated the Efficiency of Use of Water (EUA) and Transpiration Coefficient (CT). At the end of the experiment after 74 days under competition, the experiment was collected. At this point it was determined the concentration of chlorophyll a, b, total and carotenoids, dry biomass production, levels of N, P, K and Na. Generally, the weed species that caused the greatest reductions in the growth of varieties of sugar-cane was D. horizontalis. The variety of sugar-cane RB98710 was more susceptible to competition. In relation to content of photosynthetic pigments, it was observed that both varieties of sugar-cane, as the weed species have suffered significant reductions in levels of these pigments, when subjected to competition, whether determined by SPAD readings, or by extraction of chlorophyll, where the D. horizontalis also caused more pronounced reductions. The varieties of sugar cane suffered significant reductions in N, P and K, and the variety RB98710 that had lower nutrient reductions, while RB931011 was the most likely. Among the weeds, E. heterophylla expressed higher levels of N and P, while D. horizontalis surpassed in the K and Na. The varieties of sugar-cane showed greater efficiency in water use, while the weeds were high transpiration coefficient, which qualifies them as potentially harmful in the competition for water.