Ecophysiological modeling of the critical age of weed competition control in tropical Eucalyptus plantations

The critical age of weed competition control is important to implement management strategies, minimizing productivity losses and reduce forest formation costs. The study aimed to determine the critical age of control and quantify productivity losses to the detriment of interference caused by weeds. Seven experiments were conducted between 2016 and 2017 in the Brazilian states, Maranhão, Pará, and Tocantins. The experimental design used was in randomized blocks, with 8 treatments, and 4 replications. The plots consisted of 150 trees (10 x 15) each, with the useful plot consisting of 104 plants (8 x 13), simple border and population density of 900 to 1010 trees per hectare. The treatments included both weed-free and weedy environments, with specific control periods assigned to each treatment. The treatment codes used were as follows: A.00 = (weedy from 0 to 6 years), A.01 = (weed-free from 0 to 1 year), A.02 = (weed-free from 0 to 2 years), A.01.35 = (weed-free from 0 to 1 and 3 to 5 years), A.16 = (weed-free from 1 to 6 years), A.26 = (weed-free from 2 to 6 years), A.06 = (weed-free from 0 to 6 years) and; F.02 (weed-free in 1.5 m range in the planting row from 0 to 2 years). Annual measurements were taken at 12, 24, 36, 48, 60 and 72 months after planting, measuring the variables total height (m), crown depth (m) and breast height circumference (mm). Through these variables, the total volume with bark (V, m³ ha-1) and the mean annual increment with bark (MAI, m³ ha-1 y-1) were calculated. The critical age of control ranged from 2.1 to 3.2 years. At 72 months, the impact of living with weeds resulted in an average V reduction of 30.5 m³ ha-1 (15.5%), with a potential loss up to 40.8 m³ ha-1 (21%). For the MAI, an average reduction of 5.1 m³ ha-1 y-1 (15.4%) and a potential loss of 6.8 m³ ha-1 y-1 (20.9%) were observed. The control of the weeds in tropical Eucalyptus plantations is economically viable up to 24 months.