Caucasian clover performance in a year of severe drought

Abstract

In a year of spring-summer drought on a sandy volcanic ash soil, ryegrass/caucasian clover (RG/ CC) and RG/white clover (RG/WC) pastures had similar rapid increases in pasture growth rates during September. Growth rates peaked around 25 October (65-70 kg DM/ha/day) for RG/CC and around 14 October (50-60 kg DM/ha/day) for RG/ WC. As drought intensified the declines in pasture growth rates were similar, but delayed by up to 3 weeks for RG/CC. Both pastures reached minimum summer growth rates of <10 kg DM/ha/day at the beginning of February (4% soil moisture). Spring/ autumn application of nematicide increased pasture growth. WC was almost completely lost from RG/ WC pasture and was largely replaced by summer grass. Drought did not affect CC plant survival, but some leaf wilting and brown-off occurred in February. Autumn pasture recovery was similar except that the recovery of RG/CC pasture in the absence of nematicide application was delayed and significantly reduced. The absence of clover and replacement by summer grass reduced autumn response to nematicide by RG/WC. On treated RG/ CC plots there was a 96% reduction in root galling by the root knot nematode (Meloidogyne hapla) and reduced populations of grass grub (Costelytra zealandica) and clover root weevil (Sitona lepidus) in autumn. This led to a 107% increase in fine root mass/unit mass of CC rhizome material, compared with untreated CC. These pests depend on, or are favoured by, pasture clover, so that higher populations were retained by the presence of clover in RG/CC compared with the RG/WC pasture. CC can be considered as a drought-persistent rather than a drought-resistant plant. Keywords: caucasian clover, drought, persistence, pests, production, ryegrass, Trifolium ambiguum, Trifolium repens