Water and phosphorus (P) are two critical resources for high nature value farming in semi-dry mountains.
ey are major drivers of grassland productivity but can negatively aect plant diversity. Soil moisture
is known to aect soil microbial activity and plant P nutrition but the eects of irrigation on soil P
status, soil microbial P and plant P nutrition in semi-natural grasslands remain largely unexplored, which
impedes the optimization of fertilization. e aim of this study was to assess the mid-term eects of
irrigation on P availability in the soil, the size of the soil microbial P pool and plant P nutrition in semi-dry
mountain grasslands. At the end of a ve-year irrigation-fertilization factorial experiment on eleven seminatural
grasslands of an inner-alpine valley, soil P availability and herbage P content did not signicantly
dier between the irrigated and the not irrigated treatments. Fertilization increased herbage P content
from 2.2 to 3.1 mg P kg-1 dry mass (P<0.001). e size of the microbial P pool remained unaected by
irrigation and fertilization. We conclude that for semi-natural mountain grasslands, no correction factor
for irrigated compared to not irrigated meadows is necessary to estimate the P fertilization requirement
per unit of herbage yield.