No abstract

Blackcurrant bushes (cv. Magnus) planted on a free-draining Lismore stony silt loam were used to study the yield responses to four irrigation regimes, using one unirrigated and three irrigated treatments.Irrigation treatments were applied each time gravimetric soil samples (0-150 mm deep) taken 300mmfrom the hedgerow fell to 10, 15,or20%soil moisture (s.m.) content.In the first two years, the 15 and 20% s.m. treatments produced yields 150-220% higher than both the unirrigated and infrequently irrigated 10% s.m. treatments. As the unirrigated and 10% s.m. treatment bushes developed with time, the annual yield differences decreased to a level where, by the fifth harvest, the 15 and 20% s.m. treatment yields respectively were only 15% and 37% higher than the unirrigated treatment yield.Average berry weight increased with irrigation frequency during the first three seasons. However, differences in berry weight decreased gradually with time and by the 1986/87 season showed no significant differences between treatments.No consistent trend was obvious from the sugar levels recorded during the trial period. Generally sugar levels were not significantly different in wet seasons but in drier seasons, irrigation tended to reduce total soluble solid levels by around 1-1.5% compared to the unirrigated treatmentThe 15 and 20% s.m. treatments required on average 5 and 14 irrigations per season respectively to maintain their particular soil moisture level. Received 15 March 1988; accepted 18 August 1988Because of the poor performance of the treatments irrigated below 15 % soil moisture and the excessively high number of irrigations required to maintain soil moisture levels above 20% it seems unlikely that the optimum regime will be outside the 15 to 20% soil moisture range.