N. Nankov, G. Milev, A. Ivanova, I. Iliev, M. Nankova*

Dobrudzha Agricultural Institute, 9520 General Toshevo, Bulgaria

Abstract. The investigations on the long-term growing of wheat without rotation as well as its two-field rotation with maize in Dobrudzha Agricultural Institute date back to 1957. In a stationary field trial carried out during 2011 – 2013, cultivar Enola was grown at planting density 500 germinating seeds/m2. Four levels of nutrition regime were tested, which were formed by systematic introduction of the following fertilizer norms: N0P0K0, N60P50K30, N120P100K60 and N180P150K90. The long-term growing of wheat in two-field crop rotation increased the productivity of the crop with 16.8 % in comparison to its cultivation without rotation. The yield from cultivar Enola under long-term non-rotation growing was influenced to a much higher degree by the meteorological conditions of the year (1.6 times) as compared to two-field rotation with maize. The systematic mineral fertilization increased wheat productivity under the two forms of rotation. Under two-field crop rotation, the increase of yield according to the non-rotation growing was with 20.9%. Averaged for the investigated period, wheat had higher productivity after mineral fertilization with N120P100K60 (N:P:K=1:0.8:0.5). The intensive nitrogen fertilization, even when preserving the ratio with the other main macro elements, led to lower productivity, especially of the wheat grown without rotation. The factor determining wheat productivity under two-field rotation was mineral fertilization; its strength of effect was 1.9 times higher than its effect on long-term growing without rotation. The meteorological conditions during wheat growing influenced the physical indices of grain, and were especially well expressed on test weight. Under low nutrition regime (the check variant and N60P50K30), the grain in the monoculture was smaller in comparison to the two-field crop rotation. Under the higher levels of fertilization and in the monoculture a tendency was observed toward larger grain. The test weight in both crop rotations decreased with the higher fertilization norms. No significant correlations were found between productivity and the physical properties of grain under both types of growing. Under long-term growing of wheat in two-field rotation, there was a high positive correlation between absolute and test weight of grain.