The Response of Black Currants to Different Soil Moisture Conditions and Two Levels of Nitrogenous Fertilizer

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Abstract
Two-year-old black currant bushes (cv. Amos Black), planted in November 1956 on a freely drained fine sandy loam soil, were used to study growth and crop responses to three watering treatments and two levels of nitrogen fertilizer, using six replications of plots containing 12 bushes each. In each unit plot half the bushes were left unpruned. Water was applied in treatments (a) and (b) when soil moisture tensiometers set 1 ft (0.3 m) deep indicated tensions of 20 cm Hg and 50 cm Hg respectively. In the third treatment (c) the bushes were not watered. The nitrogen fertilizer rates were 70 lb/acre (78 kg/ha) and 140 lb/acre (157 kg/ha). Irrigation increased shoot growth even in relatively wet seasons, and the crop increases achieved by irrigation became progressively larger each year irrespective of the level of cropping of the unwatered bushes, which reached 6.5 tons/acre (14.6 tons/ha) in 1961. The average yield increase was about 60% from the unpruned and 50% from the pruned bushes. In the last year of the experiment the crop yield response to irrigation was 124% on the unpruned and 80% on the pruned bushes. These increases were mainly the result of increased shoot growth, but irrigation also increased berry production per strig (raceme) and berry size. Although pruning reduced the response to irrigation, it showed advantages, compared with no pruning, in the form of more even ripening of berries, easier picking and larger berries, and, in the normal course of events, it would prolong the life of a uniform cropping plantation. There was no difference between the effects of nitrogen treatments on the growth or cropping of watered or unwatered bushes. The higher rate of nitrogen application increased leaf nitrogen but depressed leaf phosphorus, the latter effect being more marked in the irrigated bushes.

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