Effects of grass suppression on legume abundance during two contrasting seasons on a summer-dry hill country site

The low level of legumes in New Zealand hill pastoral systems is a recognized problem that is likely to affect sustainability. The relative importance of the factors that cause low legume abundance has not been sufficiently tested, especially on dry hill country. This paper reports the effects of grass suppression in two contrasting years in a summer-dry hill country site on the east coast of the North Island. Suppressing grass with haloxyfop herbicide (Gallant) in late autumn increased legume abundance by > 25% in both years, but the response patterns were strongly influenced by soil moisture status. Moist late spring and summer conditions produced 34% more legume growth in both ± herbicide treatments. Residual effects of grass suppression favoured white clover over subterranean clover growth under moist seasonal conditions. The control of grass growth in these hill swards improved legume abundance, but the overriding factor affecting legume content in the pasture was the level of soil moisture. Key words: grass suppression, haloxyfop herbicide, hill country, legume abundance, soil moisture, subterranean clover, summer-dry, white clover