M. Nankova*, A. Atanasov
Dobrudzha Agricultural Institute, 9520 General Toshevo, Bulgaria
(Manuscript received 28 June 2018; accepted for publication 5 September 2018)

Abstract. During2014–2017,theinfluenceofsomemainagronomyfactorsonthesizeoftheresultantagronomiceffectfromtheirapplicationtocontemporary common winter wheat cultivars was investigated. The study was carried out in the experimental field (Haplic Chernozems soil type) of Dobrudzha Agricultural Institute – General Toshevo. The trial was designed by the split plot method, in four replications, on harvest area of 12m2. Cultivars Sadovo 1, Pryaspa, Kami, Kalina, Kiara, Kossara and Katarjina were grown after winter oilseed rape, spring pea, sunflower and grain maize at four levels of nutrition regime. The nutrition regime was differentiated depending on the previous crop. After spring pea, 30, 60 and 90 kg N/ha were used, and after the rest of the previous crops – 60, 120 and 180 kg N/ha. With the exception of the check variant all fertilizer variants were against background fertilization with 60 kg P2O5/ha and 60 kg K2O/ha. The positive reaction from the complex interaction of the tested agronomy factors was best expressed in 2015 – 2409.2 kg/ha, while during the extremely unfavorable year 2016, the effect was only 628.2 kg/ha. The independent and combined action of the mineral fertilization and the year conditions had determining influence on the size of the agronomic effect (AE). The positive effect from the mineral fertilization on the values of AE was accompanied by slight differentiation between the tested fertilization norms. Within this study, the highest mean value of AE was determined after fertilization with N180P60K60 – 2274.2 kg/ha. The variation in the mean size of AE depending on the type of previous crop was high – from 900.6 kg/ha (pea) to 2031.2 kg/ha (oilseed rape). The applied agronomy practices caused differentiation in the mean values of AE according to the type of cultivar. The cultivars Kiara (1796.1 kg/ha) and Kalina (1704.5 kg/ha) were with the highest size of AE. They exceeded the AE values of the two standard cultivars Sadovo 1 and Pryaspa by 30.26% and 23.62%, respectively. Averaged for the research, it was found that AE was in positive statistically significant correlation with grain yield and its physical properties.