资源环境科技发展态势分析平台

Enhanced efficiency fertilizers (EEFs) are used to minimize gaseous losses of applied nitrogen (N). Higher N retention resulting in increased uptake by plants is intended to offset the additional cost of these EEFs. Pacific Northwest Douglas-fir forests are N limited and assumed to have high N retention rates. Assuming N retention rates are high can lead to the over application of fertilizers which is both economically inefficient and detrimental to ecosystem health. We tested the hypothesis that EEF-fertilized plots have the highest ecosystem N recovery rates by tracing four urea-based fertilizers for four weeks after application in five commercially managed Douglas-fir forests in Oregon and Washington. Three EEFs, Environmentally Smart Nitrogen (ESN), N-(n-butyl) (NBPT), and Arborite coated urea fertilizer (CUF), were tested along with unformulated urea granules. These three particular EEFs are designed to reduce volatile losses of ammonia (NH3(gas)). Fertilizers were enriched with N-15, which facilitates the tracing of N as it moves between ecosystem pools. Retention rates were calculated for the forest floor and mineral soil to a depth of 20 cm. Retention rates were not significantly improved with the use of EEFs. On average, 30.2% of the applied N was lost from the system after four weeks. The lack of improvement in N retention with EEFs suggests that volatilization may not be a substantial loss pathway at these sites and therefore the application of these higher cost EEFs is not warranted.