Desenvolvimento e produtividade de mandioca cultivada em diferentes sistemas de plantio e intervalos entre capinas

Abstract

Competition exerted by weeds is one of the main limitations when producing cassava, therefore, the use of no-till systems, with the conservation of straw on the soil, shows to be an alternative to reduce the establishment weeds, however this system may interfere in the development of cassava roots. The main goal with this work was to measure the influence of different farming systems and the levels of weed control on the productivity of cassava. A field experiment in randomized blocks subdivided into plots with four replicates was developed. Two different farming systems were used in the plots (no-till and conventional) and in the subplots the weed control levels were allocated, with weed control happening every 30, 60, 90 and 120 days after planting (DAP). Two control-plots were also cultivated during the whole development cycle of cassava, one with daily weed control and one without weed control. The evaluated variables were plant height, stem diameter, final plant stand, shoot fresh mass, starch content, harvest index, number, length and diameter of roots, noncommercial root yield, commercial root yield and total yield. Phytosociological analyzes were carried out in the weed community, in which the number of weeds (Mi ha-1), shoot dry mass (Kg ha-1), frequency, relative frequency, density, relative density, relative dominance, importance value index and relative importance were evaluated. The increase in the interval between weed controls decreased the height and the diameter of the stem, as well as the fresh shoot mass, starch content, number, length and diameter of roots and the total cassava productivity. The productivity of the crop was lower in the no-till farming system. Weed control performed every 30 days and the daily weed control provided the highest productivity of the crop. Increasing the interval between weed controls, generally, increased the number and the shoot dry mass of weeds. In the phytosociological survey, 33 species distributed in 16 botanical families were quantified. The species, Spermacoce latifolia, Sida rhombifolia, Avena sativa, Lolium multiflorum and Maranta sobolifera, presented high relative importance. Strategies should be developed for the effective control of these weeds when present in cassava fields in order to avoid high yield losses.