Bedard-Haughn A, Tate K W, van Kessel C
Department of Plant Sciences, University of California, Davis, CA 95616, USA.
J Environ Qual. 2005 Aug 9;34(5):1651-64. doi: 10.2134/jeq2005.0033. Print 2005 Sep-Oct.
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.
本研究基于定期刈割会通过促进新的植物生长来增加氮需求和固存这一理论，使用稳定的15N同位素定量研究刈割对营养缓冲带吸收NO3(-)-N的影响。2002年夏季，在一个漫灌牧场内设立了10个缓冲小区。2003年，以5 kg N ha(-1)的施用量和99.7原子%的15N向牧场区域施用15N标记的KNO3。一半的缓冲小区每月进行修剪。在缓冲带中，施用15N后的最初几周内，刈割效应不显著，刈割和未刈割的缓冲带都在固存15N。然而，在灌溉季节，刈割缓冲带固存的15N是未刈割缓冲带的2.3倍，这与刈割后地上生物量的增加相对应。刈割和去除植被使现存生物量能够利用微生物矿化释放的土壤15N。相比之下，未刈割的缓冲带在15N固存或生物量方面变化很小，表明存在衰老现象且氮需求相应降低。总体而言，刈割显著改善了地表水和地下水对15N的截留。然而，这种效应与时间有关，仅在施用15N后21至42天变得显著。灌溉牧场对径流水质的主要影响因素仍然是灌溉速率，因为相对于典型速率将灌溉速率降低75%导致总径流损失减少50%，15N浓度降低7倍。
