Influence of soil mulching on winter chilling of kiwifruit

The influence of soil temperature during winter and early spring on subsequ ent budbreak and flowering of kiwifruit vines (Actinidia deliciosa (A. Chev .) C.F. Liang et A.R. Ferguson 'Hayward') was studied at three sites during a 2-year period. Soil under kiwifruit vines was mulched for 28-day periods by laying sheets of clear polythene under vines. Mulching in June or July increased soil temperatures at 0.1 m depth by 1-2 degrees C compared to con trol vines, whereas mulching in August and September elevated soil temperat ures by 3-6 degrees C. Increases in soil temperature were directly proporti onal to the amount of solar radiation incident on the orchard (r(2) = 0.97) . Mulching did not substantially alter the time of budbreak, the amount of budbreak, the rate of shoot growth, the number of flowers per shoot, or the number of flowers per winter bud. However, in one season the proportion of shoots that produced flowers was reduced when vines at the warmest site we re mulched during late winter (August), but increased when vines at another warm site were mulched during early spring (September). These data suggest that the performance of kiwifruit vines is not very sensitive to soil temp erature.