Subtropical grasses in Bay of Plenty dairy pastures.

摘要

Data was collected for Bay Milk Products Ltd, using a standard rate of growth technique, in 9 farms during 1989-95. Each farm had up to 3 cage sites which were placed so as to represent the major soil/pasture differences within a farm. Herbage samples were split into Lolium perenne, other grasses, weeds, Trifolium spp. and dead material. Samples were analysed to assess the effects of C4 grasses on total pasture and L. perenne growth rates. In most years C4 grasses were prominent and summer growth rates were at their maximum, but there was no evidence that L. perenne growth rates were penalized by the C4 grass component in the same or subsequent years because L. perenne growth rates were both consistent between years and varied independently of theother grass component. It is suggested that C4 grasses are widespread in the Bay of Plenty dairy pasture ecosystem, and that they make a significant contribution to pasture production. Because C4 grasses can be readily introduced to new sites by seed spread by grazing animals, in water courses and in late hay crops, and because some seeds persist for many years in the seed bank, C4 species are likely to become increasingly common. The temporal problems associated with monitoring the spread of C4 grasses are highlighted. Their contribution to yield depends upon seasonal conditions and therefore displays high within-year and between-year variability. Several suggestions are made on how to reduce the C4 grass component of the pastures and practical management strategies to prevent the natural seed output of C4 grasses are presented. However, it should be recognized that agronomically useful types could form a useful component of the sward in years when climatic conditions during the summer period are conducive to their vigorous growth.