5 Irrigation and Drainage in Polish Agriculture …
93
It was stressed, that on average, the soil quality in Poland can be assessed as
respectively low. There is 27% of arable soils belonging to good or very good (classes
I–III), while poorest soils (classes V–VI) occupy more than 33% of the arable land.
Soil quality classification for grasslands receives even lowest merit: soils of classes
I–III account for only about 14%, soils of class IV—for 39%, while soils of class
V–VI are most common, covering as much as 46% of total grassland area [4].
5.1.3 Agro-Climatic Conditions
Poland lies in the moderate transitional climate zone. There are noticed impacts
of a dry continental climate from the east and a mild oceanic climate from the
western side. They bring about considerable variability in long-term weather trends
but also short term ones (days, weeks) [6]. The average annual air temperature value
is +7.5 °C and it ranges from slightly above 5 °C in the north-eastern part of the
country and mountain areas to about 9°C in the south-western part [7]. Average, longterm annual precipitation (1961–2015) is equal to 605 mm and in the vegetation
season (April–September) reaches 388 mm. The average of 210 days is noticed
for the growing period, during which potential evapotranspiration over most of the
country exceeds precipitation, taking effect in continuous water deficit on light soils,
in particular, that are attributable to rather low water-holding capacity. The driest
regions of Poland, however, involve the whole central region, but also north-western
and mid-eastern parts. It is a fact, they have yet been most threatened by frequent
and severe droughts, associated by the annual rainfall amount not reaching 300 mm.
Low precipitation and high potential evapotranspiration influence water quantity and
generate water management problems in these regions [2]. Only in the mountain zone
and the sea coast average precipitation is high enough to satisfy the requirements of
agricultural plants. Moreover, there have been such occurrences in Poland, locally
and periodically, when excessive rainfall water contributed to extensive waterlogging
and flooding of soils.
5.1.4 Agricultural Water Resources
The average annual precipitation of 605 mm gives the volume of 192 km
3 of water
in one year. At the same time, estimated annual runoff becomes about 62 km
3 /yr
with a variability ranging from 38 to 90 km
3 /yr, and in the end, the available water
resources (assumed to be equal to 40% of mean runoff) amount to 26 km
3 /yr. It
should also be stressed, that there are over 8000 lakes with an area of over 1 ha
and the total capacity of 17 km
3 , while the capacity of artificial reservoirs amounts
to 4.5 km
3 . There exist 4700 fish ponds, covering the total area of 45000 ha, and
providing the capacity of 0.5 km
3 . When it comes to groundwater, the renewable
resources in usable layers have gone to the level of 11 km
3 . To sum up, natural water
93
It was stressed, that on average, the soil quality in Poland can be assessed as
respectively low. There is 27% of arable soils belonging to good or very good (classes
I–III), while poorest soils (classes V–VI) occupy more than 33% of the arable land.
Soil quality classification for grasslands receives even lowest merit: soils of classes
I–III account for only about 14%, soils of class IV—for 39%, while soils of class
V–VI are most common, covering as much as 46% of total grassland area [4].
5.1.3 Agro-Climatic Conditions
Poland lies in the moderate transitional climate zone. There are noticed impacts
of a dry continental climate from the east and a mild oceanic climate from the
western side. They bring about considerable variability in long-term weather trends
but also short term ones (days, weeks) [6]. The average annual air temperature value
is +7.5 °C and it ranges from slightly above 5 °C in the north-eastern part of the
country and mountain areas to about 9°C in the south-western part [7]. Average, longterm annual precipitation (1961–2015) is equal to 605 mm and in the vegetation
season (April–September) reaches 388 mm. The average of 210 days is noticed
for the growing period, during which potential evapotranspiration over most of the
country exceeds precipitation, taking effect in continuous water deficit on light soils,
in particular, that are attributable to rather low water-holding capacity. The driest
regions of Poland, however, involve the whole central region, but also north-western
and mid-eastern parts. It is a fact, they have yet been most threatened by frequent
and severe droughts, associated by the annual rainfall amount not reaching 300 mm.
Low precipitation and high potential evapotranspiration influence water quantity and
generate water management problems in these regions [2]. Only in the mountain zone
and the sea coast average precipitation is high enough to satisfy the requirements of
agricultural plants. Moreover, there have been such occurrences in Poland, locally
and periodically, when excessive rainfall water contributed to extensive waterlogging
and flooding of soils.
5.1.4 Agricultural Water Resources
The average annual precipitation of 605 mm gives the volume of 192 km
3 of water
in one year. At the same time, estimated annual runoff becomes about 62 km
3 /yr
with a variability ranging from 38 to 90 km
3 /yr, and in the end, the available water
resources (assumed to be equal to 40% of mean runoff) amount to 26 km
3 /yr. It
should also be stressed, that there are over 8000 lakes with an area of over 1 ha
and the total capacity of 17 km
3 , while the capacity of artificial reservoirs amounts
to 4.5 km
3 . There exist 4700 fish ponds, covering the total area of 45000 ha, and
providing the capacity of 0.5 km
3 . When it comes to groundwater, the renewable
resources in usable layers have gone to the level of 11 km
3 . To sum up, natural water