Currently, three basic types of irrigation systems are used in agriculture:
- surface irrigation (flooding or underseepage),
- sprinklers, water cannons, micro-sprinklers.
- drip irrigation with drip lines or directly under the plant.
There are also subsurface drip systems, still rarely used in Poland. The choice of irrigation system depends primarily on the crop. Row crops, such as berry bushes and fruit trees, are most often irrigated with drip lines or directly with drippers under the plant. Crops such as potatoes are often irrigated with sprinklers and water cannons, either stationary or mobile. Catch crops such as cereals are irrigated by regulating the availability of capillary and surface water, i.e. by surface irrigation, usually combined with a properly executed water reclamation. Each of the above-mentioned types of irrigation carries different investment and operating costs and has different water losses. For example, losses in sprinkler and irrigation systems can be as high as 50% or more:
Istnieją również podpowierzchniowe systemy kropelkowe, rzadko jeszcze wykorzystywane w Polsce. Wybór systemu nawodnieniowego zależy przede wszystkim od rośliny uprawnej. Uprawy rzędowe, jak krzewy jagodowe i drzewa owocowe, najczęściej nawadnia się przy pomocy linii kroplujących lub bezpośrednio kroplownikami pod roślinę. Uprawy takie jak np. ziemniaki często nawadnia się deszczowniami i armatkami wodnymi, stacjonarnymi lub mobilnymi. Uprawy łanowe jak zboża, nawadnia się przez regulację dostępności wody kapilarnej i powierzchniowej tj. przez nawodnienia powierzchniowe, najczęściej połączone z właściwie przeprowadzoną regulacją melioracji wodnych. Każdy z wymienionych rodzajów nawodnień niesie ze sobą inne koszty inwestycyjne i operacyjne oraz charakteryzuje się różnymi stratami wody. Na przykład straty w systemach deszczujących i zraszających mogą dochodzić nawet do 50% i więcej:
|Source of water losses||Scope of losses||Typical value of losses|
|Evaporation to air||0-10%||<3%|
|Blow by wind||0-20%||<5%|
|Irrigation of side areas||0-5%||<2%|
The research shows that drip systems have the lowest losses: drip lines and under-plant drippers.
The decision to irrigate basically comes down to two simple questions – when to irrigate and how much to irrigate?
Farms that are not equipped with soil moisture sensors placed in the root zone of the plants are reliant on estimates, or calculations, to determine the irrigation rate and time. Soil moisture clearly indicates the water content of the root zone. Knowing the classification of the soil in question (sand, clay, loess, loam), it is possible to estimate how much water is available for plants at any given time. In irrigation practice, irrigation should be controlled so that the amount of water exceeds the moisture content characteristic of 35% of the effective water capacity (field water capacity), i.e., for example, for loose sand, the moisture content should be at least between 7% and 5%. The estimation method is subject to a large error and one never knows how much water is actually available to the plants. The first of the estimation methods, the organoleptic method, relies on the human senses, where the choice of when to irrigate is based on an assessment of soil moisture determined by touch, or based on a visual assessment of the condition of the crop – both methods are imperfect. The tactile soil moisture assessment method only assesses the moisture content of the surface soil layer, which is unrepresentative of the entire soil profile. Even a significant rainfall – of the order of 20 mm – after a drought, is only able to wet the topsoil when the soil underneath is still dry. A visual assessment of the deteriorating plant condition is then far too late, because by that time the crop has already suffered water stress and this has already affected development and yield. Based on organoleptic methods, it is not possible to determine how much water should be supplied to the plants. The most common practice is to water until the water stops soaking in, i.e. until the full water capacity of the soil is reached. This is a detrimental practice because much of this water will run off into the soil, taking easily soluble components with it, contaminating ground and surface water. The next estimation method is to determine irrigation needs based on evapotranspiration, i.e. evaporation from the plant surface (respiration) and the soil surface. The method is based on counting evaporation on the basis of meteorological measurements: temperature, sunshine, wind speed, air humidity and atmospheric pressure once the development stage of the plant is reached. This method can be used to determine relatively accurately the daily water consumption of plants and therefore the theoretical irrigation rate, but it does not take into account water losses through soakage into the soil and horizontal flow below the soil surface, as well as runoff along the soil surface. It also does not take into account the current state of soil hydration in relation to the field water capacity of the soil and the preference of the plant. It is therefore unknown whether the plant is still subject to water stress despite irrigation. The optimal solution is to use systems based on both actual soil moisture data and actual weather data – with reference to the current needs of the plant.