Abstract: The soil physical and chemical properties of alfalfa with various geographical distributions were investigated. The results showed that the content of soil organic carbon (SOC) was higher in irrigated area than in arid area. The biggest difference value of SOC contents among different soil layers was up to 3.41 g·kg^-1 that was found in 90～100 cm soil layers. The change of SOC contents in the 0～100 cm soil layers of irrigated area was 6.81～12.49 g·kg^-1 and average value was 9.25 g·kg^-1, that was 22% higher compared with arid area. The contents of total soil nitrogen (TSN) in arid area increased with soil depth decreasing, the change values of TSN contents were between (0.44±0.04) g·kg^-1 and (1.03±0.01) g·kg^-1. The contents of TSN in 0～30 cm soil layers were relatively stable, whereas the TSN contents decreased sharply in 30～60 cm soil layers then TSN contents were relatively stable again, and maintained at (0.66±0.01) g·kg^-1 scope in 70～100 cm soil layers. The fractal dimension of soil in irrigated alfalfa was lower than that of arid area alfalfa, and significantly increased in the range of 0～40 cm with the soil depth increasing (P<0.05). The fractal dimension of 0～20 cm soil layer was less than that of 20～40 cm soil layers. The soil aggregates of >5 mm was the most contents under dry sieving conditions, followed by 5～2 mm soil aggregates, 0.5～0.25 mm aggregates was the least one. These results showed that the SOC and TSN contents of alfalfa differed from different irrigation levels. The soil aggregate structure of irrigated alfalfa was better than that of arid area that was more suitable for alfalfa cropping. However, the water content of arid area in 0～30 cm soil layer was similar to that of irrigated alfalfa indicating that continuous cropping alfalfa had strong drought resistance.

Key words: Alfalfa soil, Nitrogen, Organic carbon, Fractal dimension, Irrigated area, Arid area

摘要： 为研究连作模式下不同气候区苜蓿（Medicago sativa L.）土壤理化指标地域分布的差异性，对甘肃省灌区和旱作区连作苜蓿土壤的全氮（TSN）、有机碳（SOC）及土壤团粒结构等指标进行研究。结果表明：灌区SOC含量均高于旱作区，90～100 cm土层差值最大，达3.41 g·kg^-1；0～100 cm土层灌区SOC含量为6.81~12.49 g·kg^-1，均值为9.25 g·kg^-1，比旱作区高22%。旱作区TSN含量随土壤深度增加而减小，含量为（1.03±0.01）~（0.44±0.04） g·kg^-1；0～30 cm土层灌区TSN含量相对较稳定，30～60 cm土层则急剧下降，70～100 cm内又较为稳定，TSN含量维持在（0.66±0.01） g·kg^-1。灌区苜蓿土壤的分形维数均低于旱作的，0～40 cm土层内随土壤深度增加而增大（P<0.05），随着土壤深度的增加>0.25 mm土壤团粒质量在干筛和湿筛处理下均呈现降低趋势；0～20 cm土层的土壤分形维数小于20～40 cm的，在干筛条件下，>5 mm的土壤团聚体含量最高，5～2 mm的次之，0.5～0.25 mm的最少。因此，苜蓿土壤SOC和TSN含量随着灌溉水平的差异表现出显著变化，且灌区苜蓿土壤团粒结构优于旱作区更适合苜蓿耕作，但旱区苜蓿土壤0～30 cm土层保水性等同于灌区的，说明连作苜蓿具有较强的抗旱性。

关键词: 苜蓿土壤, 全氮, 有机碳, 分形维数, 灌区, 旱作区