Plantas daninhas na silvicultura de Eucalyptus grandis x Eucalyptus urophylla: biomassa e nutrientes

Abstract

The determination of the period of coexistence of weeds with the eucalyptus stand helps in the integrated management of weed competition, acting as an efficient tool that reduces the use of herbicides and the economic and environmental costs. Therefore, the objectives of the present study are to determine the period of coexistence of a hybrid of Eucalyptus grandis x Eucalyptus urophylla with weeds, evaluating the impact on biomass production, concentrations and stock of macro and micronutrients. The experiment was carried out in Bioma Pampa, in the municipality of Candiota - RS, and followed the design of Random Blocks, with three replications. For eucalyptus, treatments consist of increasing periods of coexistence or control with weeds. For the weeds, the treatments considered were the stages of their development, which were divided into 3 stages (1, 2 and 3) respectively. The total biomass of eucalyptus in the coexistence treatment was 53.7 Mg ha-1 and in the weed control treatment until 168 days it was 81.4 Mg ha-1. This reduction was in the order of 34%. It is recommended that from the 56th to the 140th day, the critical period for preventing interference (PCPI), the eucalyptus grows free from coexistence with weeds. The total interference prevention period (PTPI) was 140 days. The maintenance of weeds for 378 days promoted a significant reduction in the production of total biomass and wood. The highest nutrient utilization efficiency (EUN) was observed in wood. The total amount of weed biomass during the 3 stages was 35.2 Mg ha-1, following the order of the different species: Eragrostis pilosa (29.9 %) > Baccharis coridifolia (18.1 %) > Paspalum sp. (9.8%) > Senecio sp. (8.0 %) > Aspilia montevidensis (7.7 %) > Lolium multiflorum (7.0 %) > Sporobolus sp. (6.1 %) > Erianthus angustifolius (5.5 %) > Conyza bonariensis (4.0 %) > Cynodon dactylon (3.9 %). The third development period differed statistically from the other periods and represented 63% and 60% of the total macro and micronutrients allocated to the biomass. Statistical analyzes show that weed biomass production has a seasonal behavior, with phase 3 of development accounting for more than half (54.8%) of all quantified biomass, followed by phase 2 (30.6%) and 1 (14.6%).