The aim of the studies conducted in the years 2000-2002 in Kruszyn Krajeński, in the vicinity of Bydgoszcz, was determining the changes in morphological features (the weight and length) of root system and grain yield of oat (Avena sativa L. ‘Dragon’) as a result of giving up many-year sprinkling irrigation and nitrogen fertilization on a very light soil. There was observed an after-effect of sprinkling irrigation on a decrease in the root weight and length as well as a decrease in grain yield in the first two years since the treatment had been stopped. The yield of the experimental objects became even only in the third growing season. However, no negative after-effect of nitrogen fertilization on the oat features was observed. Earlier sprinkling irrigation and the lack of fertilization promoted rooting in the soil profile. It was observed at the same time that the lack of irrigation broadened the grain yield to root weight ratio and grain yield to rooting degree ratio. A lower rooting degree goes together with the relatively higher grain yield.

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