hawkweed

The rate of spread of mouse-ear hawkweed (Hieracium pilosella) patches, the effect of hawkweed on soil properties, and the nutrient content of hawkweed biomass was investigated on grazed unfertilised land on Glencairn Station (altitude 440 m, mean annual rainfall 500-600 mm) in the Mackenzie basin, southern South Island, New Zealand. Pallic soils (Typic Ustochrepts) under hawkweed patches and under surrounding herbfield were analysed for exchangeable cations, organic C and total N. Total nutrients in hawkweed and herbfield biomass were measured.

Changes in soil chemistry in relation to hawkweed (Hieracium pilosella) presence were determined at a site receiving less than 600 mm rainfall where hawkweed was colonising Pallic Soils (yellow-grey earths). pH was significantly lower (by 0.5 units) and organic carbon values were significantly higher (0.7% absolute, 40% relative) within hawkweed patches than in adjacent soil, but there was no significant difference in total nitrogen.