Data from: Earthworm activity and availability for meadow birds is restricted in intensively managed grasslands

1. Earthworms are an important prey for the endangered meadow birds of
north-west Europe. Although intensive grassland management with high
manure inputs generally promotes earthworm abundance, it may reduce the
effective food availability for meadow birds through desiccation of the
topsoil, which causes earthworms to remain deeper in the soil. 2. We
studied the response of Red Worm Lumbricus rubellus, a detritivore, and
Grey Worm Aporrectodea caliginosa, a geophage, to soil moisture profiles
in the field and under experimental conditions. Surfacing earthworms were
counted weekly in eight intensively managed grasslands (treated with high
inputs of slurry by slit injection) with variable groundwater tables in
the Netherlands. At each count, soil penetration resistance, soil moisture
tension and groundwater level were measured, while air temperature and
humidity were obtained from a nearby weather station. The response to
variation in the vertical distribution of soil moisture was also
experimentally studied in the two earthworm species. 3. In the field,
earthworms’ surfacing activity at night was negatively associated with
soil moisture tension and positively by relative air humidity.
Surprisingly, there was no effect of groundwater level; an important
management variable in meadow bird conservation. Under experimental
conditions, both L. rubellus and A. caliginosa moved to deeper soil layers
(>20 cm) in drier soil moisture treatments, avoiding the upper
layer when moisture levels dropped below 30%. 4. Synthesis and
applications. We propose that in intensively managed grasslands with
slurry application, topsoil desiccation reduces earthworm availability for
meadow birds. This can be counteracted by keeping soil moisture tensions
of the top soil above -15 kPa. We suggest that the late raising of
groundwater tables in spring and the disturbance of the soil by slit
injection of slurry increase topsoil desiccation. This decreases earthworm
availability when it matters most for breeding meadow birds. Meadow bird
conservation will benefit from revised manure application strategies that
promote earthworm activity near or at the soil surface.

1. 蚯蚓是欧洲西北部濒危草地鸟类的重要捕食猎物。尽管采用高粪肥投入的集约化草地管理通常可提升蚯蚓种群丰度，但该管理方式可通过表层土壤干燥化，迫使蚯蚓滞留于土壤深层，进而降低草地鸟类可获取的有效食物资源。
2. 本研究针对两种蚯蚓——腐食性动物（detritivore）赤爱胜蚓（Lumbricus rubellus）与食土性动物（geophage）灰远盲蚓（Aporrectodea caliginosa），探究其在野外与实验条件下对土壤水分剖面的响应。研究人员在荷兰8处地下水位各异的集约化管理草地（采用条带注入（slit injection）法施加高剂量粪液（slurry））中，每周计数出土蚯蚓的数量。每次计数时，均测定土壤穿透阻力（soil penetration resistance）、土壤水分张力（soil moisture tension）与地下水位，并从邻近气象站获取气温与相对湿度数据。此外，研究还通过实验探究了两种蚯蚓对土壤水分垂直分布变化的响应。
3. 野外观测结果显示，蚯蚓夜间出土活动与土壤水分张力呈负相关，与空气相对湿度呈正相关。令人意外的是，地下水位并未对其产生影响——而地下水位本是草地鸟类保护中的关键管理变量。在实验条件下，当进行土壤水分干燥处理时，赤爱胜蚓与灰远盲蚓均会迁移至20cm以下的深层土壤；当土壤水分含量降至30%以下时，二者均会主动避开表层土壤。
4. 结论与应用。本研究提出：在施加粪液的集约化管理草地中，表层土壤干燥化会降低草地鸟类可获取的蚯蚓资源。该负面影响可通过将表层土壤水分张力维持在-15kPa以上予以抵消。研究同时指出，春季推迟抬高地下水位，以及采用条带注入粪液造成的土壤扰动，均会加剧表层土壤干燥化，进而在草地鸟类繁殖的关键时期降低其可获取的蚯蚓资源。若能通过修订粪肥施用策略，促进蚯蚓在土壤表层或近表层活动，将对草地鸟类的保护工作大有裨益。