Effects of NPK fertilisation in arid southern Mongolian desert steppes

Few studies have been performed on the importance of nutrient availability for plant productivity at <200 mm annual precipitation and available meta-analyses have produced contradicting results. Here, we present data from a 3-year experiment on the effects of NPK-fertilisation under ambient precipitation in dry Central Asian steppes. The study site had an annual mean precipitation of ca. 160 mm and represented an intensively grazed montane desert steppe. One year of NPK-fertilisation at levels equivalent to 10 and 20 gN/m² (100 and 200 kg/ha) increased above-ground mean standing crop in a moist year to 1130 and 1490 kg dry mass/ha, respectively, compared to the 615 kg/ha from the control. The absolute increase was smaller in subsequent drier years, but the crop again more than doubled under fertilisation. The effects were most pronounced for the main fodder plants Agropyron cristatum and Allium polyrrhizum, which benefited from fertilisation more than other less palatable species. Both species also showed increased levels of foliar N. Fertilisation enhanced flowering activity on the community level, and soil analyses revealed that nutrients accumulate in the soil. Effects are therefore expected to be long lasting. Our results imply that nutrient shortage may co-limit plant growth at well below 200 mm annual precipitation. Considering that predominantly nomadic land use is known to result in nutrient withdrawal, our data raise concerns of a largely unnoticed potential pathway to pasture degradation.