Eects of irrigation on phosphorus in soil, soil microbes and plants of semi-natural grasslands

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 a€ect plant diversity. Soil moisture is known to a€ect soil microbial activity and plant P nutrition but the e€ects 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 e€ects 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 signicantly di€er 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 una€ected 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.