Abstract Temporal and spatial measurements of soil organic carbon (C) under grazed pastures are needed to quantify the effects of different grazing management regimes on C stocks. We examined soil organic C stocks under permanent pastures at the Ballantrae Hill Country Research Station in southern Hawke's Bay, New Zealand. Soils were sampled to three depths (0–75, 75–150, 150–300 mm) in 2003 and to the two upper depths in 2014, in three farmlets under different annual phosphorus (P) fertiliser inputs and stocked with sheep to maintain similar grazing pressure (i.e., stock units per unit of pasture production) across farmlets since 1975. The farmlets examined were NF = no annual P applied, LF = 125 kg single superphosphate (SSP) ha−1, and HF = 375 kg SSP ha−1, on an annual basis since 1980. The permanent sites included three slope classes [low slope (LS; 1–12○), medium slope (MS; 13–25○), high slope (HS; >25○)], on three different aspect locations grouped relative to the true north [east (E; 35–155○), southwest (SW; 275–35○), northwest (NW: 155–275○)]. A year-by-farmlet interaction trend on soil C stocks in the upper depth (0–75 mm) was associated with linear numerical differences in soil C stocks in 2003 (30.9, 32.5 and 35.1 Mg C ha−1 on the NF, LF, and HF farmlets, respectively) but not in 2014. This trend was not seen in the deeper soil layers (75–150 and 150–300 mm). In contrast, slope and aspect had major effects on soil C stocks. Overall, soil samples collected on the steepest slope class (>25○) resulted in higher soil bulk densities (BD) and carbon-to‑nitrogen (C:N) ratios, and lower N and C concentration, and soil C stocks at all soil depths, compared with samples collected at the other two slope classes. Soil samples collected on the NW-facing slopes resulted in higher BD, and lower N and C concentration, and soil C stocks at all soil depths, compared with samples collected at the other two aspect locations. Both of these topographic features need to be considered in soil sampling regimes of hill grazing lands to obtain an accurate estimate of organic C stocks. Data from this long-term study provide science, policy and industry with invaluable insights on soil organic C stocks in grazing hill-country soils and highlight the value of long-term structured experiments for monitoring soil C stocks. Implications Sequestering of organic carbon (C) in soil offers an option for offsetting C in atmospheric emissions. We examined soil C accumulation under a long-term phosphorus (P) application and sheep stocking regime grazing experiment. The hill country experiment has been running since 1975, with three distinct farmlets that received either no P, an intermediate amount or an amount that exceeds annual maintenance. Farmlet per se had a minimal impact on soil C accumulation, but slopes and aspects had a substantial impact and need to be considered in the design of soil sampling regimes that monitor soil organic carbon over space and time.

中文翻译：

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磷肥和羊放养对比下山地牧场土壤有机碳储量及地形特征

摘要 需要对放牧牧场下的土壤有机碳 (C) 进行时空测量，以量化不同放牧管理制度对 C 库的影响。我们在新西兰霍克湾南部的 Ballantrae Hill 乡村研究站检查了永久牧场下的土壤有机碳库。2003 年在三个深度（0-75、75-150、150-300 毫米）和 2014 年对两个以上深度的土壤进行了采样，在不同年磷（P）肥料输入下的三个农场中，并放养羊以保持相似自 1975 年以来农场的放牧压力（即每单位牧草产量的库存单位）。检查的农场是 NF = 未施用年度磷，LF = 125 kg 单一过磷酸钙 (SSP) ha−1，HF = 375 kg SSP ha− 1，自 1980 年以来每年一次。永久站点包括三个坡度等级 [低坡度 (LS; 1-12○)、中坡度 (MS; 13-25○)、高坡度 (HS; >25○)]，在三个不同的方面位置相对于真北 [东 (E; 35–155○), 西南 (SW; 275–35○), 西北 (NW: 155–275○)]。上部深度（0-75 毫米）土壤碳库的逐年交互趋势与 2003 年土壤碳库的线性数值差异有关（NF、LF 上的 30.9、32.5 和 35.1 Mg C ha−1）和 HF 农场），但在 2014 年没有。这种趋势在较深的土壤层（75-150 和 150-300 毫米）中没有出现。相比之下，坡度和坡向对土壤碳库有主要影响。总体而言，在最陡坡等级 (>25○) 上收集的土壤样品导致土壤体积密度 (BD) 和碳氮 (C:N) 比率较高，以及 N 和 C 浓度较低，和在所有土壤深度的土壤 C 库，与在其他两个坡度等级收集的样品相比。与在其他两个方面位置收集的样品相比，在面向 NW 的斜坡上收集的土壤样品导致更高的 BD、更低的 N 和 C 浓度以及所有土壤深度的土壤 C 库。在山地牧场的土壤采样制度中需要考虑这两种地形特征，以获得有机碳库的准确估计。这项长期研究的数据为科学、政策和行业提供了关于放牧山地土壤中土壤有机碳库的宝贵见解，并突出了监测土壤碳库的长期结构化实验的价值。影响 土壤中有机碳 (C) 的封存为抵消大气排放中的 C 提供了一种选择。我们研究了长期施用磷 (P) 和绵羊放养制度放牧实验下的土壤碳积累。山地试验自 1975 年以来一直在运行，三个不同的农场要么没有收到磷，要么收到中等数量的磷，要么收到超过年度维护量的磷。农田本身对土壤碳积累的影响很小，但坡度和坡度有很大的影响，需要在设计土壤取样制度时加以考虑，以监测土壤有机碳随空间和时间的变化。