ABSTRACT

Soil organic carbon (SOC) was studied at 0–45 cm depth after 28 years of cropping with arable and mixed dairy rotations on a soil with an initial SOC level of 2.6% at 0–30 cm. Measurements included both carbon concentration (SOC%) and soil bulk density (BD). Gross C input was calculated from yields. Averaged over all systems, topsoil SOC% declined significantly (−0.20% at 0–15 cm, p = 0.04, −0.39% at 15–30 cm, p = 0.05), but changed little at 30–45 cm (+0.11%, p = 0.15). Declines in topsoil SOC% tended to be greater in arable systems than in mixed dairy systems. Changes in BD were negatively related to those in SOC%, emphasizing the need to measure both when assessing SOC stocks. The overall SOC mass at 0–45 cm declined significantly from 98 to 89 Mg ha⁻¹, representing a loss of 0.3% yr⁻¹ of the initial SOC. Variability within systems was high, but arable cropping showed tendencies of high SOC losses, whilst SOC stocks appeared to be little changed in conventional mixed dairy with 50% ley and organic mixed dairy with 75% ley. The changes were related to the level of C input. Mean C input was 22% higher in mixed dairy than in arable systems.

摘要

在 0-30 厘米处初始 SOC 水平为 2.6% 的土壤上进行 28 年的耕作和混合奶牛轮作后，在 0-45 厘米深度研究了土壤有机碳 (SOC)。测量包括碳浓度 (SOC%) 和土壤容重 (BD)。总 C 输入是根据产量计算的。在所有系统中平均，表土 SOC% 显着下降（0-15 cm 时为 -0.20%，p  = 0.04，15-30 cm 时为 -0.39%，p  = 0.05），但在 30-45 cm 处变化不大（+0.11% , p  = 0.15)。耕地系统中表土 SOC% 的下降往往大于混合奶牛系统。BD 的变化与 SOC% 的变化呈负相关，强调在评估 SOC 库存时需要同时测量两者。0–45 cm 处的总 SOC 质量从 98 到 89 Mg ha 显着下降^-1，表示初始 SOC 每年损失 0.3% ^-1。系统内的变异性很大，但耕作显示出 SOC 损失高的趋势，而 SOC 库存似乎在 50% 的传统混合奶制品和 75% 的有机混合奶制品中几乎没有变化。这些变化与 C 输入的水平有关。混合奶制品的平均碳输入量比耕地系统高 22%。