The effect of ryegrass cultivar, endophyte strain and nitrogen fertiliser on pasture production, persistence and composition: A dissertation submitted in partial fulfilment of the requirements for the degree of Bachelor of Agricultural Science with Honours at Lincoln University

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New perennial ryegrass cultivars, improved endophyte strain and increased use of nitrogen fertiliser are three technological changes available to New Zealand pastoral farmers. Understanding their interactive effects is a priority as it is likely that in the future these will be used together. Previous studies have noted interactions between these three factors determined above and have concerns for the effect that they have on endophyte concentration in pastures. A study was conducted at the Iversen Field Research Area, Lincoln University, Canterbury, New Zealand to determine the difference in response to nitrogen fertiliser of perennial ryegrass cultivars varying in endophyte strain. Three replicated blocks were planted in a factorial combination of cultivar and endophyte with cultivars chosen to represent a comparison of standard diploid grasses with new cultivar development. Nitrogen was applied at 0 and 160 kg/N/ha. Endophyte score, Argentine stem weevil damage and pasture measurements were collected to determine the difference in response to nitrogen fertiliser. There were several key results of this trial. There was no effect of ploidy or hybrid cultivar and endophyte strain (AR1, AR37, HE) on endophyte concentration. The percentage Argentine stem weevil damage was lower in plants infected with AR1 (AR1, 18% tiller damage, Nil, 26.2% tiller damage) but was not affected by cultivar or any other interactions. All perennial ryegrasses infected with AR1 and AR37 had less clover than nil endophyte in April 2007 but in June 2007, the effect was only significant in 'Aberdart'. There were relative small effects of endophyte strain (AR1, AR37, HE) on pasture growth in January and April and in June, there, was an endophyte x cultivar interaction. There were more tillers in 'Aberdart' than any other cultivar; however, it also had the lowest tiller mass (g DM). Application of nitrogen in 'Aberdart' caused a (25%) increase in the tiller number and in 'Samson' caused a (29%) increase in tiller mass. There was an endophyte x cultivar interaction in 'Quartet' where plants infected with ARI produced more tillers/m2 than endophyte free grass .. These results may have implications for pastoral farmers. In the first field based study of the interactive effects of endophyte strain, cultivar and nitrogen there is limited evidence of reduced endophyte concentration, but there is a need to monitor over the next 2-3 to detect any further differences that may emerge. The change in clover content is important and while endophyte may increase persistence it may decrease clover and hence the feeding value of pastures. Pastures in the North Island are exposed to a wider range of insect pests than those in Canterbury. Therefore endophyte concentration might be more important in these areas of the country with these results having a more pronounced affect than in Canterbury.