RESULTS OF 11-YEAR N-FERTILISER TRIAL IN A SOUR CHERRY ORCHARD

From 1989 to 1999 the experiment was carried out on an alluvial loamy soil in Warsaw-Wilanów, Central Poland. ´Schattenmorelle´ cherry trees self-rooted and on Prunus avium seedling stocks were spaced 5 × 3 m. With narrow (1 m) herbicide strips, 4 N-fertiliser treatments, including an unfertilised check, were applied. Another unfertilised check was established with wide (3 m) herbicide strips. In the first 4 years no differences were noted due to the treatments and leaf N concentration was high, ranging from 2.54 to 2.73% d.m. Starting from the 5^th year (1995) leaf N concentration of unfertilised trees was lower, compared with those fertilised with 60 kg N/ha over the whole surface, varying in successive years from 2.06 to 2.39%. Tree growth was increased only by fertilisation over the whole orchard floor, in the periods 1993-1994 and 1995-1996. Yield increment due to this fertilisation was significant in the biennial periods 1994-1995 and 1996-1997 but not in the last (1998-1999) period. The increase of yield was mainly due to a larger tree size. A slight improvement of cropping was also noted due to wider, relative to narrow, herbicide strips, without N fertilisation. Fertilisation limited to herbicide strips only or fertilisation applied only in the first 3 years after planting was ineffective. Leaf N of 2.30% d.m. may be considered as critical for sour cherries; however, for reliable diagnosis N analyses should be made annually.