Transporte de agrotóxicos e uso de água em diferentes manejos de irrigação de arroz

Abstract

The flooded rice production system is a heavily user of chemicals and water for irrigation. Due to flooding water can runoff from the fields or been lost throughout percolation. Along with this water, pesticides can be transported, contaminating the surface and ground water. So, the proper irrigation management is an important practice in the prevention of environmental impact, both by reducing pesticide transport and the amount of water used for irrigation. Therefore, this dissertation had four objectives of: 1) review on literature the state of the art on pesticide transport to the environment (Chapter I), 2) evaluate the effect of water management systems on water and pesticides runoff (Chapter II), 3) evaluate the effect of irrigation on imazethapyr and imazapic leaching (Chapter III), 4) evaluate the effect of irrigation management on rice yield, water use efficiency (Chapter IV). The intermittent and flush irrigation, respectively, provides a reduction of 53 and 95% of the runoff, 46 and 60% mass of pesticide transported to the environment and increase of 15 and 40% in the efficiency of water use, due to an economy of 23 and 43% in the volume of water used in irrigation. That economy is partly attributed to increased storage of rainwater, with 492 and 299 mm for flush and intermittent irrigation managements, respectively. Irrigation promotes herbicide leaching, but the difference between treatments is only observed in the topsoil (0-5cm), where the flush irrigation promoted greater aerobic degradation. Regarding to rice yield, there was no significant difference between continuous and intermittent flooding, but was found a reduction in grain yield on plants submitted to flush irrigation, possibly by the occurrence of water stress, reflecting on plant height, delaying in rice growing season duration and lower number of spikelets per panicle.