Quantifying the Impact of Regular Cutting on Vegetative Buffer Efficacy for Nitrogen-15 Sequestration
2005
Bedard-Haughn, A. | Tate, K. W. | van Kessel, C.
This study used the stable ¹⁵N isotope to quantitatively examine the effects of cutting on vegetative buffer uptake of NO₃ ⁻–N based on the theory that regular cutting would increase N demand and sequestration by encouraging new plant growth. During the summer of 2002, 10 buffer plots were established within a flood-irrigated pasture. In 2003, ¹⁵N-labeled KNO₃ was applied to the pasture area at a rate of 5 kg N ha⁻¹ and 99.7 atom % ¹⁵N. One-half of the buffer plots were trimmed monthly. In the buffers, the cutting effect was not significant in the first few weeks following ¹⁵N application, with both the cut and uncut buffers sequestering ¹⁵N. Over the irrigation season, however, cut buffers sequestered 2.3 times the ¹⁵N of uncut buffers, corresponding to an increase in aboveground biomass following cutting. Cutting and removing vegetation allowed the standing biomass to take advantage of soil ¹⁵N as it was released by microbial mineralization. In contrast, the uncut buffers showed very little change in ¹⁵N sequestration or biomass, suggesting senescence and a corresponding decrease in N demand. Overall, cutting significantly improved ¹⁵N attenuation from both surface and subsurface water. However, the effect was temporally related, and only became significant 21 to 42 d after ¹⁵N application. The dominant influence on runoff water quality from irrigated pasture remains irrigation rate, as reducing the rate by 75% relative to the typical rate resulted in a 50% decrease in total runoff losses and a sevenfold decrease in ¹⁵N concentration.
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