No abstract

Trifluralin [2,6-dinitro-N,N-dipropyl-4-(trifluoromethyl)benzenamine] ranks among the most commonly used herbicides in the United States. The compound persists under most environmental conditions, yet it is rapidly transformed under certain anaerobic conditions. In this study, the fate of trifluralin in anoxic environments and the contribution of Fe(II) to its anaerobic degradation have been investigated. Trifluralin was rapidly degraded under anaerobic conditions in a range of soils representing typical agricultural usage in the Midwest. The presence of nitrate or oxygen suppressed trifluralin degradation. Degradation rate increased under iron-reducing conditions, and the addition of trifluralin appeared to promote reoxidation of extractable Fe 2+ . Transformation of trifluralin under iron-reducing conditions apparently involved the soil solid phase and was not limited by bioavailability. In a soil-free aqueous system, no reaction of trifluralin with dissolved Fe 2+ was detected in the presence or absence of kaolinite clay under anoxic conditions. Reduced but not oxidized or reoxidized forms of purified ferruginous smectite (sample Swa-1) catalyzed rapid transformation (72% of applied in 30 h) of trifluralin to polar products with a concomitant reoxidation of structural Fe in the clay. Results indicate that, as for other nitroaromatics, trifluralin is subject to reaction with Fe(II) associated with the minerals in anoxic environments.

Modern agriculture contributes significantly to greenhouse gas emissions in several ways. From the perspective of sustainability assessment, it is not enough to evaluate mitigation measures that rely only on emissions reductions. In this article, we use the method of decoupling analysis to construct a decoupling index based on carbon footprint and crop yield and evaluate the relationship between crop production and greenhouse gas emissions using the most modern grain production base in China as a case study. The results indicate that a weak but variable decoupling trend occurred from 2001 to 2015 and that each branch achieved on average a weak decoupling across the study period. In addition, rice production constituted 80% of the regional carbon footprint in a crop's life cycle. The results of our analysis of rice production show that weak decoupling was the most common outcome but was not consistent because a weak coupling occurred in 2015. Each branch on average achieved a weak decoupling except for the SH branch. Our research indicates that high agricultural material inputs with low utilization efficiency contributed to the poor relationship between crop production and greenhouse gas emissions in the study area. Fertilizer, especially N fertilizer, was an important contributor to the total greenhouse gas emissions of crop production. As a supplement to carbon footprint assessment, this decoupling analysis helps local decision-makers diagnose the level of green growth, identify key options to mitigate greenhouse gas emissions from agriculture, and adopt more targeted interventions towards sustainable agriculture.