Environmental profile of rice production in Southern Brazil: A comparison between irrigated and subsurface drip irrigated cropping systems

摘要

Agricultural activities in 2005 accounted for 10-12% of the total global anthropogenic emissions of greenhouse gases (GHGs) and the majority of N2O and half of CH4 emissions. Therefore, mitigating GHG emissions in agriculture is fundamental to reduce its share of responsibility for the global climate change. Rice (paddy) is the second most important commodity worldwide, and rice cropping fields significantly contribute to climate change since they are a considerable source of methane. In this study, improvements were made to several stages of the life cycle of the rice production system in Southern Brazil with the aim of mitigating environmental impacts, namely: 1) Cultivation, 2) Power generation, 3) Drying, 4) Milling, 5) Packaging, and 6) Transportation. This study was carried out from June 2012 to August 2013. The functional units adopted were 1 ha, 1000 kg of rice at the farm gate and 1000 kg of packed rice (5-kg net weight packs), available at retail. The system boundary covered field operations, including transportation after harvest, fertilizer production, power generation, packaging and transportation to the retailer. The results showed that the new rice production system (subsurface drip irrigated rice crop, among others improvements) significantly mitigates environmental impacts, particularly due to reduced water consumption (approximately 2800 m(3) t(-1) packed rice at retail) and primary energy demand (approximately 6300 MJ t(-1) packed rice at retail) as well as GWP (approximately 1200 kg CO2- eq t(-1) packed rice at retail), besides the benefit of increased yield (1150 kg rice at farm gate ha(-1)). The new irrigation system accounted for most of these benefits. The entire rice production chain was improved, from farm to transportation and distribution to retail stores. The results indicated that changing the irrigation from the flooded system to the SSDI system was responsible for most savings, i.e. 50% less water consumption, 90% less electric power consumption, 30% less eutrophication, 66% less acidification, 66% lower GWP, not to mention 15% higher yield. The power plant based on rice husk combustion accounted for 498 MJ electric power exported to the grid and 129 kg silica produced from rice husk. The drying stage was responsible for using 254 MJ renewable energy from waste, thus saving 177 kg of firewood and recovering 16 kg of rice. (C) 2016 Elsevier Ltd. All rights reserved.