Seletividade de herbicidas e adubação nitrogenada no cultivo de palma forrageira (nopalea cochenillifera) (L.) salm – dick cv miúda.

Abstract

The research aimed to evaluate the selectivity of herbicides and the effect of nitrogen fertilization on the cultivation of forage cactus (N. cochenillifera) cv Miúda. Two studies were conducted: the first to evaluate the selectivity of herbicides and weed control efficacy, and the second to assess nitrogen fertilization. The first study was divided into two experiments: the first for herbicide selectivity evaluation and the second for weed control efficacy assessment. The second study involved one experiment to evaluate nitrogen fertilization. The first experiment, assessing herbicide selectivity, was conducted in a completely randomized design with a 5 x 5 factorial scheme and four replications, totaling 100 experimental plots. The first factor comprised (isoxaflutole 262.5 g a.i. ha-1, flumioxazin 62.5 g a.i. ha-1, imazapic 147 g a.i. ha-1, sulfentrazone 400 g a.i. ha-1, and control without herbicide), and the second factor comprised application times (0, 30, 60, 90, 120) days after planting. Evaluated variables included herbicide phytotoxicity, number of cladodes per plant, plant height and width, cladode area index, photochemical efficiency of photosystem II (Fv/Fm), and green and dry mass productivity of the aerial part and root dry mass. Evaluations occurred at 15 and 60 days after herbicide application, except for productivity variables, which were assessed at harvest, 300 days after planting. The second experiment, assessing weed control efficacy, was conducted in a completely randomized design with five treatments and four replications. Treatments included the four herbicides plus the control from the first experiment. Weed control percentage was evaluated based on the emergence flux in the control treatment, with assessments at 30, 60, and 90 days after herbicide application. The nitrogen fertilization experiment was conducted in a randomized block design. Treatments included nitrogen doses (0, 25, 50, 100, 200, 400 kg ha- 1) with four replications, totaling 24 plots. Evaluations occurred 720 days after planting and assessed green and dry mass productivity of the aerial part, number of cladodes per plant and per hectare, plant height and width, cladode area index, and economic nitrogen dose. In the first study (experiment 1), all variables were influenced by herbicides. Phytotoxicity and plant height showed significant interaction at both 15 and 60 days after application (DAA). Cladode area index and Fv/Fm showed interaction only in the first evaluation, affected by isoxaflutole and flumioxazin, but plants recovered by 60 DAA. Number of cladodes per plant was affected by herbicides only at 15 DAA, with significance for application times at 60 DAA, indicating plant recovery. Plant width was not affected by herbicides but was significant for application times. Isoxaflutole and flumioxazin caused injuries and reduced number of cladodes, cladode area index, and photosynthesis, but did not affect productivity. Imazapic and sulfentrazone did not affect productivity or morphology of forage cactus cv Miúda, regardless of application time. All herbicides were effective in weed control and selective for forage cactus cv Miúda, with isoxaflutole and flumioxazin recommended at planting for safety. In the fertilization experiment, all variables were influenced by nitrogen doses, showing significant quadratic response (p<0.01). Estimated maximum green and dry mass productivity were 308.84 and 31.29 t ha-1, respectively, associated with 214.17 and 251 kg ha-1 of N, representing 45.32% and 67.42% increases over no fertilization. Number of cladodes per plant and per hectare showed significant quadratic response (p<0.01) with maximum estimated values of 48.62 and 2,035,100.43 cladodes, respectively. Maximum estimated plant height and width were 95.98 and 65 cm at 212 and 200 kg ha-1 of N, respectively. Cladode area index reached a maximum of 3.88 m2 m-2 at 221 kg ha-1 of N, a 55.20% increase without N. Forage cactus (N. cochenillifera) cv Miúda responds well to nitrogen fertilization, significantly enhancing growth and productivity.

Keywords: cactus, xerophyte, forage plants, chemical control, mineral nutrition.