Effects of soil fertility on the persistence of dryland cocksfoot and tall fescue pastures

Abstract

The persistence of pastures sown with tall fescue, cocksfoot or mixtures of the two species was evaluated by tiller core measurements on 106 paddocks that had been sown in 1989 or 1991 on dryland east coast sheep/beef farms. In both North and South Island paddocks, cocksfoot was the dominant grass in mixtures of tall fescue and cocksfoot. Tall fescue presence was usually much lower than that of ryegrass and other unsown grasses, regardless of sowing mixture. High levels of cocksfoot were associated with low levels of ryegress, browntop and other perennial grasses. North Island paddocks had higher P levels (Olsen P=25) than South Island paddocks (Olsen P=21) but had lower levels of clover (32%) and higher levels of browntop (26%) than South Island paddocks (52% clover, 13% browntop). In North Island paddocks sown with cocksfoot, there were weak, negative associations of white clover with fertiliser N inputs (r = -0.45) and soil P levels (r = - 0.41). These effects of P and N on clover appeared to be owing to increased cocksfoot dominance at high fertility. In the North Island, the best white clover presence was found in pastures that were low in cocksfoot but high in ryegrass, browntop and other unsown perennial grasses. In the South Island there was no significant association of clover with soil test levels or fertiliser history. Comparison of 1996 measurements made on North Island paddocks with 1991 measurements on the same paddocks indicated that establishment effects could have long-term effects on the persistence of tall fescue and cocksfoot. Inclusion of cocksfoot in the seed mix reduced tall fescue persistence. High levels of perennial ryegrass at establishment were also associated with poor tall fescue persistence. These effects appeared to be more important than soil fertility constraints in reducing tall fescue persistence. The presence of other vigorous grasses, such as ryegrass, during establishment may also reduce or delay cocksfoot dominance and thus improve white clover persistence. Keywords: cocksfoot, dryland, pasture persistence, soil fertility, tall fescue