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The objective of this study was to quantify the farm gate nitrogen (N) offset potential of perennial ryegrass (Lolium perenne L.; PRG) white clover (Trifolium repens L.; WC) swards by comparing the herbage and milk production from dairy farmlets that were simulations of full farming systems. A study was established where 120 cows were randomly assigned to 4 farmlets of 10.9 ha (stocking rate: 2.75 cow/ha), composed of 20 paddocks each. Cows were fed 526 kg of DM of concentrate on average each year. The 4 grazing treatments were PRG-only at 150 or 250 kg of N/ha and PRG-WC at 150 or 250 kg of N/ha. Cows remained in their treatment group for an entire grazing season and were re-randomized as they calved across treatments each year. As cows calved in the spring as standard practice in Ireland, they were rotationally grazed from early February both day and night (weather permitting) to mid-November, to a target postgrazing sward height of 4.0 cm. Mean sward WC content was 18.1% and 15.4% for the 150 and 250 kg of N/ha PRG-WC treatments, respectively over the 3-yr period. When WC was included, lowering the N rate did not reduce pregrazing yield, pregrazing height, or herbage removed, but those factors decreased significantly when WC was absent. Total annual herbage DM production was 13,771, 15,242, 14,721, and 15,667 kg of DM/ha for PRG-only swards receiving 150 or 250 kg of N/ha and PRG-WC swards receiving 150 or 250 kg of N/ha, respectively. In addition, when WC was present, compressed postgrazing sward heights were lower (4.10 vs. 4.21 cm) and herbage allowance (approximately 17 kg/cow feed allocation per cow per day) higher than the high-N control (+ 0.7 kg of DM/cow per day). There was a significant increase in milk production, both per cow and per hectare, when WC was included in PRG swards. Over the 3-yr study, cows grazing PRG-WC had greater milk (+304 kg) and milk solids (+31 kg of fat + protein) yields than cows grazing PRG-only swards. This significant increase in milk production suggests that the inclusion of WC in grazing systems can be effectively used to increase milk production per cow and per hectare and help offset nitrogen use. This result shows the potential to increase farm gate N use efficiency and reduce the N surplus compared with PRG-dominant sward grazing systems receiving 250 kg of N/ha, without negatively affecting milk solids yield or herbage production, thus increasing farm profit by €478/ha. [ABSTRACT FROM AUTHOR]

Official National List (NL) testing of perennial ryegrasses commenced in Ireland at the start of the 1970s with Northern Ireland (NI) having one site as part of the UK NL testing network, and the Republic of Ireland (ROI) using 5 sites. The different testing strategies adopted to achieve sufficient precision for regional Recommended Listing in ROI from a multi-site system and from a single-site system in NI were considered, including the test protocols, use of sequential sowings, timeframes and 'merit scores'. The precision with which varieties can be discriminated for yield potential was shown to decline at lower trial plot yields. Furthermore, reducing the number of data sets used for decision making was shown to increase the 'breeder's risk' of having an improved variety incorrectly rejected but not the 'tester's risk'' of erroneously recommending a variety that was not a clear improvement, because statistical analysis expanded confidence limits. These variety lists initially assessed only yield and persistency, giving a progressive improvement in recommended varieties and despite high genotype-x-environment interaction effects was most clearly evident in spring productivity improvements. The lists have been highly influential in both jurisdictions as almost all agricultural grass seed sales were recommended in ROI or NI, but the overuse of late maturing varieties in the ROI market and declining reseeding levels across Ireland indicated the current limits of this influence. This, and increasing requirements from Irish farmers for improvement in the nutritive value of varieties to support greater dependence on grass for animal production, has led to increased testing for digestibility and other quality parameters. While there is valid scientific evidence that shows that improvements in perennial ryegrass varieties has increased milk and meat production, more detailed information is required to satisfy the specific needs of local farmers. Consequently, a research initiative has been instigated to develop an index that will incorporate all the yield, persistence and quality performances of each recommended variety into a ranking score for a specific herd management system. This guidance should simplify recommendations and better quantify variety improvements in financial terms. It is envisaged that this will encourage an increase in the renewal of Irish pastures, promote selection of varieties based on enterprise-specific value and will continue to enhance the profitability and sustainability of grass-dependent Irish farming as has been achieved since recommended lists were first introduced in Ireland. [ABSTRACT FROM AUTHOR]