The effects of defoliation regime on seasonal and total yields of spring- and autumnsown material of three populations Festuca arundinacea(syn. 1 and syn. 2 from North Africa and the British cultivar S. 170) were examined at Cambridge from the period June 1963 to April 1965.
A micro-plot technique was used in which defoliation treatments were defined by vertical height above soil level. The vertical growth intervals between successive defoliations were, for the summer cutting regimes 7.5–25 cm and 2.5–12.5 cm, and for the winter regimes 7.5–20 cm, 2.5–20 cm, 7.5–12.5 cm, and 2.5–7.5 cm.
In summer 1963 mean yields of all populations were very similar, being equivalent to approximately 12000 kg/ha. Mean population yields for the following three 6-month periods were equivalent to (in kg/ha): syn. 11519, 14740, 3385; syn. 2 2194,17669, 5523; S. 170 1656, 19832,3696.
Variety x treatment interactions were found in every season. In particular, S. 170 winter production was reduced by severe defoliations in the preceding summer, and syn. 1 and syn. 2 summer production by severe defoliations in the preceding winter. It is suggested that such interactions may have been responsible for conflicting assessments of the relative potential production of these populations.
Syn. 1 appeared to offer no advantage over S. 170, and syn. 2 only to outyield S. 170 where spring sowing was followed by infrequent or lax defoliations in all seasons. Agronomic implications are discussed.