The effect of novel endophytes and nitrogen on pasture production and composition: A dissertation submitted in partial fulfilment of the requirements for the Degree of Bachelor of Agricultural Science with Honours

A trial was conducted on an irrigated site at Lincoln University, Canterbury to analyse the effects of new novel endophyte strains in perennial ryegrass cultivars and nitrogen on pasture production and composition. Novel endophyte strains were AR1 and AR37 (control: nil endophyte) with ryegrass cultivars Samson (diploid) and Aberdart·(diploid, expressing a high water soluble carbohydrate trait). Combinations of novel endophyte and ryegrass cultivar were tested (ALE, AAR1, SLE, SAR1, SAR37). Two nitrogen fertiliser regimes were applied to plots, low N (0 kg N/ha/year) and high N (160 kg N/ha/year). Total dry matter production during the trial period (February to September 2008) was highest in SLE with 3661 kg DM/ha and lowest in ALE with 3249 kg DM/ha. No significant differences in total or seasonal pasture production were found between endophyte x ryegrass cultivar treatments (p>0.05). There was a trend to low clover content in SAR37 (mean, 7.0%), however this was not significantly lower than AR1 or low endophyte treatments (p>0.05). SAR37 and AAR1 produced the lowest clover plant densities (172 and 183 plants/m² respectively; p=0.023) and clover growing point densities (612 and 798 GP/m² respectively; p=0.017) in autumn. Tiller density was higher in endophyte infected treatments in autumn with 10840, 7064 and 8157 tillers/m² in AAR1, SAR1 and SAR37 respectively. A negative relationship between tiller density and white clover plant density was found in autumn (R²=0.47), and produced an apparent tiller density threshold of around 6000 tillers/m² below which clover density was reduced to below 400 plants/m². Nitrogen fertiliser (160 kg N/ha/year) reduced clover content from 23 (no-N) to 7% in April, 7 to 2% in June and 23 to 7% in September. No evidence of interactions between endophyte, cultivar and nitrogen were found in any season (p>0.05). There was no evidence of difference in clover content due to more selection by sheep in some endophyte plots than others, thus diet selection was eliminated as a determining factor of low clover content. Instead, higher tiller density in endophyte infected pastures appears to suppress clover plant density. Therefore, an increased competitive advantage of endophyte infected ryegrass is suggested as the main factor causing reduced clover content in pastures, however, there is more research required in this area before conclusions can be made.