COMPARATIVE NUTRIENT RESPONSES BY PINUS-RADIATA, TRIFOLIUM-REPENS, DACTYLIS-GLOMERATA, AND HIERACIUM-PILOSELLA ON A MACKENZIE BASIN OUTWASHPLAIN SOIL

The nutrient responses by a pine (Pinus radiata), a pasture grass (coc ksfoot, Dactylis glomerata), a pasture legume (white clover, Trifolium repens), and a hawkweed (mouse-ear hawkweed, Hieracium pilosella), we re compared in a pot trial using a Mackenzie Basin outwash plain soil. Responses to nitrogen (N) and phosphorus (P) were tested alone and in combination, whereas responses to sulphur (S), potassium (K), magnesi um (Mg), micronutrients, and lime were tested only in the presence of both N and P. All species responded to N and P, and to S and lime in t he presence of N and P, but none responded to K, Mg, or micronutrients . N was the major deficient nutrient for the non-legume species, with grass and hawkweed responding by 700% in the presence of added P, wher eas pine showed a much smaller (56%) response. Clover showed the great est response to P. Hawkweed showed the smallest response to P, but the greatest responses to S and lime. While pine responded to the same nu trients as the herbaceous species, it is suggested that the responses by pine occurred before mycorrhizae formation, and may be more pertine nt to seedlings establishing from seed in the absence of mycorrhizae, than to plants with well-developed mycorrhizal root systems. The respo nses by pine to N, P, S, and lime reported here therefore need to be c onfirmed with plants which possess mycorrhizal root systems at the tim e of fertiliser application. The comparative nutrient responses by mou se-ear hawkweed are discussed. It is suggested that hawkweed is effici ent at absorbing P, an attribute that would be of competitive advantag e in soils with low P availability and which may have contributed to i ts widespread invasion of the tussock grasslands.