Abstract
Nitrogen (N) fertilization can greatly improve plant productivity but needs to be carefully managed to avoid harmful environmental impacts. Nutrient management guidelines aimed at reducing harmful forms of N loss such as nitrous oxide (N2O) emissions and nitrate (NO3-) leaching have been tailored for many cropping systems. The developing bioenergy industry is likely to make use of novel cropping systems, such as polycultures of perennial species, for which we have limited nutrient management experience. We studied how a switchgrass (Panicum virgatum) monoculture, a 5-species native grass mixture and an 18-species restored prairie responded to annual fertilizer applications of 56 kg N ha-1 in a field-scale agronomic trial in south-central Wisconsin over a 2-year period. We observed greater fertilizer-induced N2O emissions and sub-rooting zone NO3- concentrations in the switchgrass monoculture than in either polyculture. Fertilization increased aboveground net primary productivity in the polycultures, but not in the switchgrass monoculture. Switchgrass was generally more productive, while the two polycultures did not differ from each other in productivity or N loss. Our results highlight differences between polycultures and a switchgrass monoculture in responding to N fertilization.
Highlights
Nitrogen (N) pollution from agricultural systems has local, regional, and global environmental impacts
Crop type and fertilizer effects on total N2O emissions were significant in both years (Fig 1A and 1B)
In 2011, N2O emissions from all crop types were approximately 3 times greater from the fertilized plots when compared to the unfertilized plots (Fig 1A)
Summary
Nitrogen (N) pollution from agricultural systems has local, regional, and global environmental impacts. Ammonia volatilization contributes to acid precipitation, while nitrous oxide (N2O) is the single greatest ongoing source of ozone depletion [4] and an extremely potent greenhouse gas [5]. These forms of N pollution are commonly linked to excessive or misapplied N fertilizer [6,7]. Nutrient application guidelines and best management practices have been developed for many major cropping systems These guidelines rely on knowledge about a cropping system and its performance under diverse conditions; such knowledge may PLOS ONE | DOI:10.1371/journal.pone.0151919 March 18, 2016
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