Kiwi Irrigation - Water Needs of Kiwi Farms in Southern France

Kiwifruit is a water-demanding plant, typically requiring between 800 and 1200 mm of water per year. A steady and sufficient water supply is essential, as kiwifruit is sensitive to both drought and overwatering. Water requirements can reach 1000 mm per month from mid-May to mid-October, but should be regulated according to soil type and its water-holding capacity.

Kiwis require regular irrigation, which can reach 2,000 m³/ha. Controlled irrigation is necessary to avoid staining the fruit, especially if irrigation is applied to the foliage. The kiwi's leaves, which are very wide and have a thin epidermis, cause significant evapotranspiration, even at night, making the trees susceptible to water stress. The plant also has a high humidity requirement.

Understanding Kiwi Water Needs

• Drip irrigation is very efficient, allowing precise water delivery directly to the root zone.
• Micro-sprinklers provide good coverage and are suitable for large orchards.
• Under-canopy sprinkling is recommended for uniform irrigation of the soil, respecting the anatomy of the kiwi root system.

Kulker recommends installing self-regulating micro-jets with a flow rate of 35 l/h, installed on the trellis wires. Micro-jets provide a controlled wet radius, increase humidity, and lower temperatures in the plot. In addition, they save up to 16% water and 24% energy compared to sprinkling. A 130-micron filter is essential to protect the micro-jets from clogging.

Irrigation strategies for optimal production

• Avoid overwatering, which can cause waterlogging and wilting. Kiwis are susceptible to root asphyxiation and waterlogging.
• Use monitoring tools such as tensiometers or probes to measure soil moisture.
• Adapt irrigation to climatic conditions and the plant's stage of development.
• Maintain regular watering, especially during the growing season.

Water inputs must be sufficient and timely for high yields and quality fruit. Irrigation is generally appropriate from May to the end of September, but may be necessary earlier to combat frost and at the end of the season, before harvest.

Irrigation monitoring tools

• Hydraulic sensors such as flow meters and pressure gauges are useful for monitoring the irrigation system.
• Connected weather stations help anticipate water needs.
• Software platforms can centralize and analyze data to optimize irrigation.
• Rain gauges are used to measure water inputs from irrigation or rain.
• TDR probes are used to measure soil moisture.

Irrigation and T-bar

• T-bar driving is a common method in the Southwest of France.
• The T-bar helps optimize sun exposure and air circulation.
• Irrigation management is made easier with this method.

To get down to business: Signs of water deficiency, signs of excess water, tools and reference values

Visible signs of water deficiency:

• Kiwis under water stress may have blue-green foliage.
• Other signs of water deficiency include reduced shoot growth, wilting, small fruit size, sunburn on fruit, and reduced yield for the current and next season.
• Wilting leaves are a visible sign of water deficiency.
• If the soil becomes too dry, the fruit may fall.
• Water stress can cause an immediate halt in fruit growth, especially during the first 6 weeks after flowering.
• Leaves may dry out and fruit may wilt, which can weaken the kiwi plant.

Visible signs of excess water:

• Overwatering can lead to root asphyxiation, as roots lack oxygen when the soil is saturated with water. The symptoms of root asphyxiation are similar to those of drought.
• Leaves may dry out and wilt, and eventually drop, resulting in delayed maturity. It is important not to confuse these symptoms with a lack of water and to add water.
• Overwatering can cause root rot.
• Necrotic spots may appear on the leaves, surrounded by a yellow halo.
• Plants may show signs of decline, leading to the death of the tree.
• Partial browning of the absorbing roots may be observed.
• Reduced growth of terminal stems with chlorotic or undersized leaves may indicate a problem with overwatering.
• Branches and fruits may wilt due to dehydration.
• In the most severe cases, entire orchards can dry out and die within weeks.
• Excess humidity can promote the development of fungal diseases.

Soil moisture measuring tools:

• Tensiometers: These tools measure water tension in the soil, indicating water availability for plants. Tensiometers help track soil moisture and optimize irrigation.
• Capacitive probes: These probes continuously measure soil moisture. They allow you to track changes in moisture over time and better understand your kiwis' water consumption. The data can be posted online and viewed by anyone. Capacitive probes allow you to continuously monitor soil moisture.
• TDR (Time Domain Reflectometry) probes: These probes measure soil moisture by sending electromagnetic pulses.
• Bouyoucos Gessetto probes: These are used to measure the soil's matrix potential and are connected to central units that transmit the data to a computer platform to define irrigation advice. The probes are positioned at different depths (20, 40 and 60 cm) and distances from the row to define the soil unit explored by the roots.
• It is important to use a rain gauge to check the actual millimeters of water delivered.

Hydraulic sensors:

• Flow meters: These are used to monitor the flow of water in the irrigation system, ensuring that the correct amount of water is being delivered.
• Pressure gauges: These monitor the pressure in irrigation lines, helping to detect potential pressure problems that could affect watering efficiency.

Weather sensors:

• Connected weather stations: These stations measure climate parameters (temperature, humidity, precipitation, etc.) and help anticipate crop water needs. They are essential for efficient irrigation management, as they help adjust watering based on actual weather conditions.
• The use of a minimum and maximum thermometer is recommended for daily data recording, as well as the use of a rain gauge.

Other tracking tools:

• Scholander Pressure Camera: This tool is used to measure the water potential of the tree.
• Management software: Software platforms allow data from different sensors to be centralized and analyzed in order to optimize irrigation.
• Evapotranspiration (ETP): ETP is a measure of the amount of water lost through soil evaporation and plant transpiration. It is used to assess crop water needs and adjust irrigation.
• To calculate water requirements, the following formula is used: ETc = ETo x Kc , where ETc is the crop evapotranspiration, ETo is the reference evapotranspiration (dependent on climatic conditions) and Kc is the crop coefficient (representing the development of the crop). In one study, the Kc used was 0.82.
• Water conductivity and temperature probes for monitoring irrigation water quality.
• Rain gauge to measure rainfall and adjust irrigation.

Reference values:

• Water flow rate for irrigation: A water flow rate of 30 to 40 m³/h is generally required for irrigation of kiwis.
• Water flow rate for antifreeze: A minimum flow rate of 40 m³/h is required for an antifreeze sprinkler system. The pressure must be 5 to 6 bars at the pump outlet to obtain 3.5 bars at the sprinklers.
• Antifreeze spraying should start between 0 and 0.5°C.
• Water requirements: Kiwis need approximately 1500 m³/ha available from March 15 and 3500 to 4000 m³/ha from May to October.
• For frost protection down to -3°C, a minimum water flow rate of 3 mm/h is required. An increase in flow rate of 0.5 mm/h should be allowed for each additional degree below -3°C.
• Kiwis need regular irrigation of up to 2000 m³/ha and a requirement of up to 1000 mm/month from mid-May to mid-October.
• A sprinkler system must guarantee a minimum uniformity coefficient (CU) of 80% for optimal protection against frost.

Conclusion and perspectives

To efficiently irrigate a hectare of kiwifruit, use a micro-sprinkler system, carefully monitor soil moisture, and adapt irrigation to the climate and plant development stages. Irrigation is essential for producing high-quality kiwifruit, so precise and tailored management is essential.