MODELING THE EFFECTS OF ELYMUS-REPENS (L) GOULD COMPETITION ON YIELD OF CEREALS, PEAS AND OILSEED RAPE

Effects of Elymus repens (L.) Gould competition on yield of winter rye (Secale cereale L.), winter wheat (Triticum aestivum L.), spring barl ey (Hordeum vulgare L.), peas (Pisum sativum L.), and spring oilseed r ape (Brassica napus L.) were studied in field trials conducted on the same location through 3 years. The competitiveness of the five crops a gainst E. repens could be ranked as follows, with the most competitive crop mentioned first: rye>wheat, barley much greater than rape, peas. Yield losses ranged from 8% in rye to around 35% in peas and rape at a density level of 100 primary shoots m-2 in spring. The different pre vailing climatic conditions in the growing seasons had no effect on th e yield-density relationships in rye, peas, and barley, whereas signif icant interactions were found in wheat and rape. The cumulative emerge nce patterns of primary shoots were described in the spring-sown crops , and models were derived to simulate the sensitivity of competition p arameters to the actual time of shoot recording. The importance of cho osing the right time for shoot emergence counts in relation to thresho ld recommendations and other aspects is discussed.