Scientific Papers Series A. Agronomy

spring vegetation. SWA varies between 85-
90% of FC.
Figure 12. Cases with minimal air temperature below-
15oC for more than 3 days during the dormancy
Figure 15. Deviation of rainfall sum during the period
October-March
Figure 13. Beginning of the late vegetative stage at the
date of air temperature proof rising above 5 o C
On the all over the arable land the SWA are
decrease, except the western part of Thracian
Lowland (Figure 17). The biggest decreasing in
the northern part of Danubian Plain and the rest
part of Thracian Lowland (stations Haskovo,
Chirpan and Sliven), where are observed
statistical significance difference between
SWA during two periods of investigation.
In the early stages of spring vegetation soil
water supply is usually sufficient, but in the
process of developing their consumption
increases.
Figure 14. Rainfall sum for the period October-March
Probability of happen of such precipitations in
these areas varies between 27% in the region of
Silistra and Shabla (in extreme eastern districts)
and 72% in the region of Veliko Tarnovo,
Targovishte (67%) and Rouse (63%). Approve
the tendency of increasing of the winter
rainfalls as show the deviations for two periods
of investigation. They are not statistical
significant (Figure 15).
In early spring growing season in Northwestern
Bulgaria, part of the Central Danube Plain and
Dobrudja region in Northern Bulgaria SWA are
between 90 and 95% of the FC (Figure 16). In
Southeast Bulgaria (Haskovo, Sliven and
Karnobat) precipitations for the period from
October to March are no sufficient to
compensate the water deficit in the soil in early
Figure 16. SWA in the beginning of wheat’s spring
vegetation for the top 100 cm
Figure 17. Deviation of SWA in the beginning of
wheat’s spring vegetation for the top 100 cm
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