YIELDS OF CROP DRY-MATTER AND NITROGEN IN LONG-TERM BARLEY ROTATION TRIALS AT 2 SITES IN NORTHERN SYRIA

Trials were established at two sites in 1982 to compare six 2-course rotations, in which barley alternated with feed legumes (pure or mixed with barley), fallow or barley, in partial factorial combination with different N and P fertilizer regimes. This paper summarizes data from the second to the seventh cropping seasons. Barley yielded most after fallow and more after legumes than after barley; but, on the basis of total dry matter production over both courses, barley-legume rotations outyielded barley-fallow and barley-barley rotations. In terms of net nitrogen offtake, which may be taken as a rough measure of feed value, barley-legumes surpassed the other rotations by c. 100% at both sites, whether the comparison was made on values obtained from plots with or without added fertilizer. Of the legumes, Lathyrus sativus was slightly more productive than Vicia sativa, and this carried over into the rotational yield of both dry matter and nitrogen. Rotations involving pure legumes were slightly more productive than those involving legume/barley mixtures. Yields of all crops and rotations varied greatly from year to year depending on rainfall. Those of the barley-fallow rotation were much less Variable than those of the barley-barley rotation at the wetter site (323 +/- 103 mm), with the barley-legume rotation intermediate; but variability was much greater at the drier site (250 +/- 79 mm), with much less difference between rotations. Nevertheless, fertilizer use and rotations including legumes gave a significant yield advantage under the driest conditions.