G. Delchev*

Department of Plant Production, Faculty of Agriculture, Trakia University, 6000, Stara Zagora, Bulgaria

Abstract. During 2010 – 2012 a field experiment was conducted. Eight hybrids of winter oilseed canola (Brassica napus L.) were investigated: 2 ClearField hybrids – PT200CL and Sunset; 1 ClearField Maximus hybrid – PX100CL; 4 conventional hybrids – PT205, Rohan, Exagon and Nelson; 1 conventional Maximus hybrid – PR44D06. On fields with damaged by frost winter canola in spring were sown and investigated: 2 conventional hybrids spring oilseed canola – Zhura and Williams; 1 cultivar of durum wheat (Triticum durum Desf.) – Elbrus; 3 hybrids oil-bearing sunflower (Helianthus annuus L.): 1 conventional hybrid – Arena, 1 ClearField hybrid – Allego and 1 ExpressSun hybrid – P64LE20; 2 hybrids grain maize (Zea mays L.): 1 cool resistance conventional hybrid – Novatop and 1 Duo System hybrid – Blason duo; 1 hybrid grain sorghum (Sorghum bicolor Moench.) – Alise.

Seed yield of spring oilseed canola hybrids Zhura and Williams with optimal sowing densities are lower than the yields of winter hybrids Exagon and Nelson with minimum sowing densities. Changes in the seed yield of oilseed canola due to changes in number of seeds per pod, seed weight per pod and 1000 seeds weight. After plowing of fields with damaged by frost winter canola hybrids spring durum wheat should not be planted. Changes in the grain yield of durum wheat are due to changes in number of grains per spike, grain weight per spike, and 1000 grains weight. After plowing canola crops it is appropriate to sow imitolerant or tribenulon-methyl tolerant sunflower hybrids instead of conventional sunflower hybrids. Changes in the seed yield of oil-bearing sunflower are due to changes in number of seeds per head, seed weight per head and 1000 seeds weight. After plowing of canola, more weeded fields should be sown with cycloxydim tolerance maize hybrids and less weeded fields – with conventional maize hybrids. Changes in the grain yield of maize are due to changes in number of grains per cob, grain weight per cob, and 1000 grains weight. Grain sorghum grown by Concept technology is a suitable crop for sowing on fields after damaged by frost winter canola. Changes in the grain yield of sorghum are due to changes in number of grains per panicle, grain weight per panicle, and 1000 grains weight.