Variation in spring temperatures, grass production and response to nitrogen over twenty years in the uplands

Large between-year variation was observed in spring air and soil temperatures at Pant-y-dwr Hill Centre (305 m altitude) from 1967 to 1984 and at Bronydd Mawr Research Centre (330 m) from 1985 to 1986 in Powys. The mean date of attaining T-sum 200°C accumulated air temperature was 13 March (range 9 February to 23 April) and that of soil temperature at 100 mm depth permanently above 5 5°C was 9 April (range 7 March to 4 May). Net herbage accumulation and response to applied N from Aberystwyth S23 perennial ryegrass (Lolium perenne L.) swards during April were also highly variable and were correlated with the date of reaching target soil temperatures of above 5 5°C for 5 consecutive days ( r =−0·68, P < 0·001 for net herbage accumulation and r =−0·70, P < 0·001 for response to N).
The use of early flowering varieties of perennial ryegrass gave a significant increase of herbage growth in spring compared with late varieties. From 1979 to 1980 net herbage accumulation during April from the early variety Frances was 94% more than from Perma (late) and 55% more than from Talbot (intermediate) varieties. Under conservation management more winter hardy and persistent varieties of Italian and hybrid ryegrasses ( L. multiflorum L. and L. multiflorum X L. perenne ) gave higher quantities of firstcut silage crops in early June than RvP Italian ryegrass.
After the severe winters of 1978–79 and 1985–86, subsequent spring production from a wide range of ryegrasses was shown to be affected by sward survival, highlighting the value of winter hardy varieties when resowing in the uplands