Environmental impact of rice production based on nitrogen fertilizer use

Abstract

While essential to food production, nitrogen (N) fertilizers in agricultural ecosystems are also important sources of environmental pollution nationally and globally. The environmental impact of three N fertilization levels (30, 60, and 90kgha-1) plus a non-N control (0kgha-1) in growing three rice cultivars (cv. Hashemi, cv. Alikazemi, and cv. Khazar) were assessed for 2years in northern Iran, with the methodology of the life cycle assessment (LCA). The impact categories evaluated in this study were global warming, acidification, terrestrial eutrophication, and depletion of fossil, phosphate, and potassium resources. Over cultivars, no use of N fertilizer provided the lowest grain yield (2194kgha-1), whereas the N rates of 60 and 90kgha-1 increased grain yield by 52.9 and 66.9%, respectively. Over N rates, cv. Khazar produced the highest grain yield (3415kgha-1) and cv. Hashemi the lowest (2663kgha-1). On-farm (foreground) emissions were higher than off-farm (background) emissions in most impact categories. The maximum value of environmental index (1.33) was observed for cv. Hashemi with 90kgNha-1, while the minimum value (0.38) was observed for cv. Khazar without N fertilization. Moreover, cv. Khazar showed the lowest resource depletion index (0.44) with 90kgNha-1, whereas cv. Hashemi with no use of N showed the maximum value (0.96). Over cultivars, high N rates imposed drastic impact to the categories acidification and terrestrial eutrophication. However, selection of high-yielding cultivars significantly alleviated the impact to most categories. Fertilization that enables optimal yields, in accordance with the nutrient requirements of crops, ensures the most efficient land use and sustainable rice production.