بررسی چرخه حیات (lca) نظام تولید ذرت در شرایط آب و هوایی مشهد

چرخه حیات (lca) رویکردی برای ارزیابی اثرات زیست محیطی تولید محصول یا انجام یک فعالیت است که بر اساس دو شاخص میزان مصرف منابع و انتشار انواع آلاینده ها به محیط زیست محاسبه می گردد. بدین منظور، این مطالعه با هدف تعیین اثرات زیست محیطی نظام تولید ذرت در شرایط آب و هوایی مشهد با استفاده از lca انجام شد. بمنظور تجزیه و تحلیل اثرات زیست محیطی، از روش 14040iso به ازای یک واحد کارکردی معادل با یک تن دانه استفاده شد. بدین ترتیب، میزان نهاده های ورودی (از جمله سوخت های فسیلی و کودهای معدنی)، تولید و نقل و انتقال نهاده های کشاورزی (نظیر تولید کودهای شیمیایی) و عملیات بکارگرفته شده در مزرعه (شامل شخم و برداشت) به ازای یک واحد کارکردی تعیین گردید. در گام اول، ممیزی چرخه حیات (lci)، میزان مصرف نهاده ها و انتشار آلاینده ها به ازای یک واحد کارکردی تعیین شد. در مرحله بعد، ارزیابی تاثیر چرخه حیات (lcia) انجام گرفت و بر اساس شاخص هایی اطلاعات مرحله قبل در شش گروه تاثیر شامل تخلیه منابع (نظیر مصرف سوخت های فسیلی و کودهای معدنی فسفر و پتاسیم)، تغییر کاربری اراضی، تغییر اقلیم (گرمایش جهانی)، سمیّت (جوامع انسانی، بوم نظام های خشکی و آبی)، اسیدی شدن اراضی و اوتریفیکاسیون (بوم نظام های خشکی و آبی) دسته بندی شدند. در نهایت، بعد از نرمال سازی و وزنی سازی داده ها شاخص زیست محیطی (ecox)که نشاندهنده سهم نظام مورد مطالعه در میزان مصرف نهاده ها و انتشار آلاینده ها می باشد، محاسبه گردید. محاسبه شاخص زیست محیطی نشان داد که بیشترین سهم نظام تولیدی ذرت به ترتیب برای گروه های موثر اسیدی شدن (2.59) و تغییر اقلیم (0.61) حاصل شد. بدین ترتیب، با توجه به نتایج و بمنظور کاهش اثرات زیست محیطی نظام تولید ذرت چنین بنظر می رسد که می توان از روش های مختلف مدیریت نظام زراعی همچون کاربرد نهاده های آلی، تناوب، گیاهان تثبیت کننده نیتروژن و خاکورزی حداقل بر مبنای بهره گیری از اصول کم نهاده برای کاهش این اثرات زیست محیطی بهره جست.

Study of Life Cycle Assessment (LCA) for Corn Production System under Mashhad Climatic Conditions

Introduction;Life Cycle Assessment (LCA) is an appropriate technique for evaluating the potential effect of agriculture through assesses of material and energy flow throughout a product 's life cycle that take measures for improving environmental performance and to make modifications to a crop system. Life cycle assessment (LCA) is a methodology for assessing the environmental impacts associated with a product, process or activity, by identifying, quantifying and evaluating the resources consumed, and all emissions and wastes released into the environment. Due to enhancing utilization of synthetic and chemical inputs in agriculture fields and its consequent environmental impacts, LCA seems to be an appropriate technique to quantify. This study examined the environmental impacts for corn production under Mashhad climatic conditions by using LCA methodology. The analysis considered the entire system, which was required to produce one ton of corn grain.;Materials and Methods;For this purpose a functional unit was assumed based on ISO 14040 methods. It included the extraction of raw materials (e.g. fossil fuels and minerals), the production and transportation of farming inputs (e.g. fertilizers) and all agricultural operations in the field (e.g. tillage and harvest). In a first step, all emissions and the consumption of resources connected to the different processes were listed in a Life Cycle Inventory (LCI) and related to a common unit, which is one ton of grain. Next a Life Cycle Impact Assessment (LCIA) was done, in which the inventory data were aggregated into indicators for environmental effects, which included resource depletion, land use, climate change (global warming), toxicity (human, terrestrial and aquatic toxicities), acidification and eutrophication (terrestrial and aquatic ecosystems). After normalization and weighting of the indicator values it was possible to calculate summarizing indicators for resource depletion and environmental impacts (EcoX).;Results and Discussion;The global warming potential (GWP) is used to express the contribution that gaseous emissions from production systems make to the environmental impact of climate change and global warming. Terrestrial eutrophication is caused by atmospheric deposition of nutrients on natural land agroecoecosystems. Aquatic eutrophication potential is mainly determined by the nitrate leaching and phosphorus. Acidification potential enhances with increased nitrogen fertilizer application and air emissions of SO2, NOx and NH3. EcoX indicated that the highest environmental impacts were observed in acidification (2.59) and climate change (0.61) categories. The study reveals that despite the technological improvements in its manufacture and use during the last years, greater production intensity increases emissions of pollutants (such as N2O, NOx, NH3 and PO4P) contributing to the greenhouse effect, acidification, and eutrophication. Fertilizers containing heavy metals (including Cd, Zn, Co, Se and Hg) also have a toxic effect.;Conclusion;LCA can be undertaken to account for all greenhouse gases (GHGs) emitted for crop production system so that mitigation approaches focus on the primary sources of GHG emissions. Diesel production and consumption used in field operations demonstrated to be the main source of environmental impacts in the different agricultural management techniques for all impact categories, except for eutrophication. Intensive application of chemical fertilizers led to adverse impact on resource uses efficiency into consideration, enhance environmental impact. Therefore, one of the appropriate strategies to mitigate the environmental effect of agricultural production is achieving suitable yield per unit of area by improving resource use efficiency. It seems that management systems based on low input system including organic fertilizers and minimum tillage could be regarded as alternative management strategies to reduce problematic environmental impacts. Rather than chemical fertilizers, organic amendments have been suggested as a method for ‘low input agriculture’ to achieve sustainability in dry land agriculture. The most important goal of any life cycle study is, of course, to improve and optimize the system.;Acknowledgement;This research was funded by Vice Chancellor for Research of Ferdowsi University of Mashhad, which is hereby acknowledged.