| Summary: | The present study was carried out in summer 1970, when a rainy July following upon a dry June caused abundant detrimental late tillering among spring cereals in large parts of South Finland, and in part also in Central and North Finland. In four irrigation experiments, established in the clay area of South Finland, the irrigation performed in the middle of June (2 x 30 mm) increased the yield of two rowed barley by 1750 kg/ha on an average or by 71 % (variation range 49—104 %). In addition irrigation improved the quality of barley significantly by preventing detrimental late tillering. The irrigated evenly ripened barley was at harvesting time on an average 12.3 per cent units drier, with a hectolitre weight that was 3,6 kg higher when compared to the non-irrigated green grained barley. Analyses of the sheaves collected from the fields indicated that irrigated barley when compared to non-irrigated barley contained: a) equally many individuals per square meter, b) 14% less ears per individual, c) 83 % more grains per ear, d) 9 % heavier grains; in fact the total result was a 70 % higher grain yield. Causes of late tillering and the significance of irrigation in preventing this detrimental phenomenon are discussed. It is further established that in years when no late tillering occurs, irrigation affects the grain yield components in ways that differ from those established in the present study.
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