Commission Decision (EU) 2018/813Show full title

3.8. Irrigation U.K.

This section is relevant for all farms using irrigation, and especially for farms located in areas of water scarcity. It relates to efficient irrigation techniques that minimise water use and/or maximise water use efficiency (WUE(1)).

3.8.1. Agronomic methods for optimising irrigation demand U.K.

BEMP is to optimise irrigation demand by the following measures:

• Soil management: soil physicochemical properties highly influence water requirements and irrigation scheduling. Key soil parameters include depth, moisture holding capacity and infiltration rate. Soil moisture holding capacity depends on texture and organic matter content, which can be increased by appropriate crop rotations and through the addition of organic matter amendments, manures, etc. The effective soil depth is increased by penetrating the compacted soil layers with planting pits, thus offering the roots of the plants accessibility to a larger volume of soil water. The evaporation rate of water from soil can be reduced by applying reduced tillage (e.g. inter-row tillage) or by organic or plastic mulching.

• Selection of crop species and varieties according to water use efficiency (WUE): selection of genotypes resistant to water stress or salinity, and better suitable to water deficit irrigation.

• Determination of crop water requirements: precise calculation of crop water requirements based on crop evapotranspiration (ET), in relation to plant growth stage and weather conditions.

• Assessment of water quality: the physical and chemical parameters of the water should be monitored in order to ensure high-quality water available for the plants. In terms of the physical parameters, water should be delivered at ambient temperature and sufficiently clean (e.g. particles and/or suspended solids can cause blockages in the irrigation equipment). In terms of the chemical parameters, a high soluble salt concentration is responsible for clogging the irrigation distribution equipment and may require extra amounts of water to avoid salt accumulation in the root zone. Additionally, a high concentration of some elements, e.g. sulphur (S) and chlorine (Cl), can cause toxicity problems to the plants and should thus be carefully monitored.

• Precise irrigation scheduling to match crop ET with water supply. This can be implemented using the water balance method(2) and/or soil moisture sensors(3).

Applicability U.K.

This BEMP is broadly applicable to all farms using irrigation and especially for farms located in arid areas. Some measures may require investment and operational costs which may be a barrier for small farms. However, these costs may be outbalanced by the savings resulting from the reduced use of water, and, in some cases, by increased profits due to higher yields.

Associated environmental performance indicators and benchmarks of excellence U.K.

Environmental performance indicators	Benchmarks of excellence
(i81) WUE, expressed as kg/m3 (i82) Percentage change in irrigation demand (%)	N/A

3.8.2. Optimisation of irrigation delivery U.K.

BEMP is to select the most efficient irrigation system that optimises the irrigation delivery in the cultivated area:

• Drip irrigation for intensive cropping systems (row crops).

• Low-pressure sprinkler for row crops and fruit trees, with water sprayed under the crop canopy. When designing such a system, the operating pressure, the nozzle type and diameter, the spacing layout and the wind speed need to be carefully examined to achieve high uniformity of irrigation.

Applicability U.K.

This BEMP is broadly applicable to both arid and humid areas, to most soil types and mainly for crops planted in rows, e.g. alfalfa, cotton, corn.

Drip irrigation on clay soils must be applied slowly in order to avoid surface water ponding and run-off. On sandy soils, higher emitter discharge rates are needed to ensure adequate lateral wetting of the soil. For crops planted on slopes, the target is to minimise changes in emitter discharge rates as a result of land elevation changes.

In low-pressure sprinkler systems, the operating pressure should be adjusted to achieve the appropriate irrigation rate based on the soil's physical characteristics. For crops planted on slopes, low-pressure sprinklers can be used provided that the lateral pipes supplying water to the sprinklers are laid out along the land contour whenever possible, so that pressure is minimised and sprinklers provide a uniform irrigation.

Associated environmental performance indicators and benchmarks of excellence U.K.

a Irrigation efficiency represents the applied water that is actually available to the plants. This indicator is calculated by multiplying the conveyance efficiency, which is the efficiency of the transfer of water to the field, e.g. through canals, by the field application efficiency.
Environmental performance indicators	Benchmarks of excellence
(i83) Drip irrigation installed (Y/N) (i84) Low pressure sprinklers installed (Y/N) (i85) Irrigation efficiencya at crop level (%)	N/A

3.8.3. Management of irrigation systems U.K.

BEMP is to efficiently operate and control irrigation systems, to avoid water losses and high run-off rates, and to avoid over- and/or under-irrigation incidents. Water meters are important to determine the exact amount of water used for irrigation and to detect water losses. Diversion ditches can collect run-off from sloping surfaces to minimise damage to crops.

Applicability U.K.

This BEMP is broadly applicable to all farms using irrigation and especially for farms located in arid areas.

Associated environmental performance indicators and benchmarks of excellence U.K.

Environmental performance indicators	Benchmarks of excellence
(i86) Irrigation efficiency at farm level (%)	N/A

3.8.4. Efficient and controlled irrigation strategies U.K.

Optimal irrigation can be achieved with appropriate strategies aimed at avoiding over-irrigation or water deficit.

In regions where water resources are very limited, BEMP is the application of water deficit irrigation: in this strategy, the crop is exposed, during some growth stages or during the whole growing season, to a specific level of water stress that results in limited or no yield reduction.

An example of deficit irrigation is Partial Root Drying (PRD): it consists of alternately watering one side or the other of crops planted in a row, so that only parts of the roots are exposed to water stress.

Applicability U.K.

Deficit irrigation is specifically applicable in very arid areas where it makes sense for a farmer to maximise the net income per unit of water used rather than per unit of land. However, it cannot be used over extended time periods.

Before its application, it is essential to assess the impact of specific deficit irrigation strategies by running multi-year open-field experiments for each given crop in relevant agro-climatic zones.

Associated environmental performance indicators and benchmarks of excellence U.K.

Environmental performance indicators	Benchmarks of excellence
(i81) WUE, expressed as kg/m3	N/A

(1)

WUE is defined as crop yield (e.g. kg) per volume unit (e.g. m³) of irrigation water applied. Practices that improve the yield per ‘water drop’ improve the WUE. Thus, WUE is enhanced by increasing crop production and/or reducing seasonal water application. In order to ensure high crop yields, the capture and storage of rainfall in the soil and the ability of the crop to utilise soil moisture must be maximised, whilst the severity of water deficits during key stages of crop development should be minimised.

(2)

The water balance method consists of three basic steps: (i) estimating the available water (AW) in the root zone from soil texture and rooting depth, (ii) selecting the allowable water deficit (AWD) depending on crop species, growth stage, soil water capacity and the irrigation system's pumping capacity and (iii) estimating the crop evapotranspiration (ET). With this method, irrigation is applied whenever the ET exceeds the AWD.

(3)

Soil moisture sensors are used to set the frequency and the amount of irrigation. The amount is calculated through the changes of the soil moisture content between two irrigation events, assuming that evapotranspiration (ET) between the two equals the soil moisture change between the two occasions. Alternatively, it is calculated by measuring the soil tension before application of irrigation and using the allowable water deficit (AWD) to estimate the amount of water to be supplied.