| Buffers are strips of vegetation adjacent to agricultural production that serve to protect natural resources from pollutant loading. To date, there has been limited research on buffer efficiency and capacity in irrigated pasture. The overall objective of this study was to use stable N isotopes to quantify the effectiveness of vegetative buffers for attenuating N in runoff from irrigated pasture.; There are two main stable N isotope methods: The delta15N method is good for semi-quantitative estimates of N flow in undisturbed ecosystems; however, if background variability cannot be accounted for and/or if fractionating processes have a large effect on the isotopic signature of the N to be traced, delta 15N will not work as a tracer. In contrast, the 15N-enriched method can be used as a tracer to test hypotheses and quantify N-cycling through the landscape, regardless of background variability in delta15N.; The first field study used 98 atom % 15N-enriched KNO 3 to quantify buffer efficiency. More 15N was lost from the non-buffered treatments than from the buffered treatments (8 or 16m), with the majority of the impact occurring in the first four weeks after 15N application. For the remainder of the study, however, there was a steady release of 15N from the buffers into runoff, suggesting that for buffers to be sustainable there is a need to manage buffer vegetation to maximize N retention.; The second study examined the effects of regular cutting on vegetative buffer uptake of NO3--15N. Over the irrigation season, cut buffers sequestered 2.3 times the 15N of uncut buffers related to an increase in above-ground biomass following cutting. Examining the corresponding impact of regular cutting on both surface runoff and subsurface water quality illustrated that cutting also significantly decreased soluble 15N concentrations. However, the dominant influence on runoff water quality from irrigated pasture remains irrigation rate: reducing the irrigation rate by 75% resulted in a 50% decrease in total runoff losses and a 7-fold decrease in runoff 15N concentration.; This study clearly demonstrates that buffers are a useful tool in irrigated pasture and that their function can and should be optimized through proper resource management. |
