M. Nankova1*, A. Ivanova1, N. Tsenov2

1Dobrudzha Agricultural Institute, 9520 General Toshevo, Bulgaria 2Agronom I Holding, 9300 Dobrich, Bulgaria

Abstract. Under conditions of Haplic Chernozems, the dynamics and the intensity of dry matter increase in the spikes of the common winter wheat cultivars Pryaspa, Enola, Iveta, Bolyarka and Dragana were followed in the trial field of Dobrudzha Agricultural Institute, General Toshevo during 2009 – 2011. The investigation was carried out during stages 57-59, 69, 73, 83 and 94-95 according to Zadoks in a stationary field trial designed by the split plot method. The cultivars were grown after 4 previous crops – pea, oilseed rape, sunflower and grain maize at four levels of nutrition regime formed after main mineral fertilization. The nitrogen fertilization norms after oilseed rape, sunflower and grain maize were 60, 120 and 180 kg/ha, and after pea – 30, 60 and 90 kg/ha, respectively. The phosphorus and potassium fertilization was applied as a background, with 60 kg/ha. Each of the previous crops had a check variant without mineral fertilization. The dynamics of spike increase was influenced most by the meteorological conditions of the investigated years. The strength of effect of this factor increased in the course of vegetation. Mineral fertilization and the type of cultivar were next in significance. The role of the previous crop in the course of vegetation was low, being statistically significant only at the final stage. Similar tendency was observed in the daily rate of spike increase, but at the beginning of heading the cultivar had a better expressed effect in comparison to mineral fertilization. The intensity of spike increase was highest after nitrogen fertilization with 120 and 180 kg/ha. The cultivars had higher daily rate of spike increase during inter-stage periods 73–69 and 83–73 according to Zadoks. The spikes of cultivar Dragana increased with the highest mean daily rate from heading to maturity (16.126 kg/da/day). Depending on the type of previous crop, the mean values of daily intensity varied from 13.418 kg/da/day (maize) to 15.106 kg/da/day (pea). The differentiation with regard to the meteorological conditions of the year was very well expressed; the spikes increased with highest rate in 2011 – 20772 kg/da/day, averaged for heading-maturity. High values were determined of the correlations between the dry matter formed in the spikes during the separate stages of development and the rate and intensity of dry matter accumulation.