土壤团聚体微生物量对紫花苜蓿种植年限的响应

Microbial biomass in soil aggregates in response to different alfalfa planting years

摘要:

为了探索苜蓿种植对半干旱黄土丘陵区土壤质量的影响,采用野外调查和室内分析相结合的方法,选取农田(CK)和不同种植年限(3,7,12,18 a)紫花苜蓿地0~20,20~40 cm土层土壤为研究对象,对不同种植年限紫花苜蓿地土壤团聚体微生物量碳(MBC)、微生物量氮(MBN)分布特征进行了研究。结果表明:土壤团聚体有机碳、MBC和MBN均在1~0.25 mm粒级团聚体中分布最多,其含量变化分别为6.25~10.37、111.25~343.96和19.04~56.40 mg/kg。当农田更替为苜蓿草地后,随种植年限延长至12 a,各粒级土壤团聚体MBC、MBN含量递增趋势明显,在0~20 cm土层,12a与CK相比分别增加56.21%~65.08%和43.85%~91.72%;0~20 cm土层MBC、MBN均高于20~40 cm土层;＞0.25 mm各粒级土壤团聚体MBC/MBN均大于＜0.25 mm小团聚体。表明种植紫花苜蓿能改善土壤质量,但种植年限超过12 a,土壤会发生一定程度退化。

Abstract:

This study aimed to explore the effects of alfalfa planting on soil quality in semi-arid Loess Hilly region.Alfalfa paddocks in Loess Hilly region with different growing years (3,7,12,and 18 years) were selected,with a nearby paddock with no alfalfa planting history as the control.The distribution characteristics of microbial biomass carbon (MBC) and microbial biomass nitrogen (MBN) in soil aggregates from the top 40 cm soil layer were studied.Our results showed that soil total organic carbon,MBC and MBN were most abundant in aggregates with 0.25~1 mm particle size,ranging from 6.25~10.37 g/kg,111.25~343.96 mg/kg and 19.04~56.40 mg/kg,respectively.When the farmland was replaced by alfalfa,MBC and MBN contents in aggregates with different particle sizes all increased significantly with the planting years up to 12 years.Compared with the control,MBC and MBN contents from the top 20 cm soil layer at the paddock with 12 years of alfalfa planting increased by 56?65% and 44?92%,respectively;which were also greater than those from the 20~40 cm soil layer.The ratio of MBC:MBN in aggregates with ＞0.25 mm particle size was higher than that in aggregates with ＜0.25 mm particle size.Our results showed that soil quality could be significantly improved through alfalfa planting with a planting years of ≤12,followed by a decline if alfalfa growing years were beyond that.