Effects of gibberellic acid on Tifton 85 bermudagrass (Cynodon spp.) in constructed wetland systems

This study aimed to evaluate 1) the influence of gibberellic acid (GA(3)) in the development of Tifton 85 bermudagrass grown in constructed wetland systems (CWs) and 2) the plant's capacity to remove nutrients and sodium from synthetic municipal wastewater (SMW). The experiment was carried out in Viçosa, Minas Gerais, Brazil, and consisted of foliar applications of GA(3) set in randomized blocks design, with four replicates and 6 treatments as following: NC (control with plants); 0 μM GA(3); N1: 5 μM GA(3); N2: 25 μM GA(3); N3: 50 and N4: 100 μM GA(3) per CWs, NC* (control with no plants): 0 μM GA(3). The study was conducted over two crop cycles in the spring 2016. The parameters used to evaluate the performance of the Tifton 85 bermudagrass were its plant height, productivity, chlorophyll measurement, number of internodes, nutrients and Na removals. Chemical analyses of the effluents were conducted. In response to the application of GA(3), the increase in height of Tifton 85 bermudagrass in the first crop cycle was higher than the increase in height in the second crop cycle. The decrease in plant growth in response to GA(3) in the second crop cycle may be linked to the age of the plant tissue and climatic conditions. The greater growth of the plants cultivated in the CWs allows a more efficient removal of pollutants, using simple management and low cost. The results suggest that applying 50 μM of GA(3) to the development of Tifton 85 bermudagrass provides higher dry matter yield and removal of nitrogen, phosphorus, and sodium for the first crop cycle in CWs. However, in the second crop cycle, the application of GA(3) had no effect on dry matter production and nutrient removal by Tifton 85 bermudagrass in CWs.