Comparative nutrient responses by Pinus radiata, Trifolium repens, Dactylis glomerata, and Hieracium pilosella on a Mackenzie Basin outwash plain soil

The nutrient responses by a pine (Pinus radiata), a pasture grass (cocksfoot, Dactylis glomerata), a pasture legume (white clover, Trifolium repens), and a hawkweed (mouse-ear hawkweed, Hieracium pilosella), were 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), magnesium (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 the 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, whereas pine showed a much smaller (56%) response. Clover showed the greatest response to P. Hawkweed showed the smallest response to P, but the greatest responses to S and lime. While pine responded to the same nutrients as the herbaceous species, it is suggested that the responses by pine occurred before mycorrhizae formation, and may be more pertinent to seedlings establishing from seed in the absence of mycorrhizae, than to plants with well-developed mycorrhizal root systems. The responses by pine to N, P, S, and lime reported here therefore need to be confirmed with plants which possess mycorrhizal root systems at the time of fertiliser application. The comparative nutrient responses by mouse-ear hawkweed are discussed. It is suggested that hawkweed is efficient at absorbing P, an attribute that would be of competitive advantage in soils with low P availability and which may have contributed to its widespread invasion of the tussock grasslands.