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It is important that any intensive pear orchard has a secure supply of good quality irrigation water. Water plays a key role in all stages in the growth and development of pear trees.
Irrigation management in an intensive pear orchard should aim to achieve the full production potential with the most efficient use of irrigation water. This means selecting the most suitable irrigation system, understanding tree water use, scheduling and monitoring irrigation using the most appropriate techniques.
There is a vast amount of pre-existing information about irrigation in orchards and this page is only designed to provide a brief overview and direction to further information.
Selecting an irrigation system
Irrigation monitoring and scheduling
Water quality
Maintenance of irrigation systems
Further information
References
Selecting an irrigation system
The suitability of an irrigation system will depend on factors such as soil type, crop type, planting density, water quality and supply, irrigation equipment availability and economic factors such as capital and operating costs.
In frost prone areas it is important to also consider the effectiveness of the irrigation system for frost protection.
There are many irrigation systems available for use in orchards and each have their own advantages and disadvantages. For high density orchards the most favoured systems are mini-sprinkler or drip irrigation.
It is important that irrigation systems are designed by someone who is familiar with the irrigation method and orchard conditions.
See further information for more detailed explanations of irrigation systems.
Figure 1: Mini-sprinkler irrigation
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Irrigation monitoring and scheduling
Irrigation scheduling is the process through which an irrigator determines the volume and frequency of water to be applied to their orchard.
The aim of an irrigation scheduling plan is to calculate tree water use and determine the length of time it will take for trees to deplete soil moisture between irrigations. This means understanding climatic conditions (evaporation), soil moisture and tree water use at different growth stages.
In general terms, irrigation scheduling has been largely based on soil moisture. Calculations for scheduling irrigations have been based on
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Readily Available Water (RAW)- using the size of the wetting pattern, the root zone depth and water holding capacity of the soil and
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Tree Water Use - using Pan Evaporation, Crop Factors (which relate tree water use at a particular stage of growth to the amount of pan Evaporation) and the planting square (Boland et al. 2002).
Monitoring of soil moisture to determine if irrigation amounts are accurate is often done through soil moisture monitoring devices that measure soil suction (eg. tensiometers, gypsum blocks) or soil moisture content (eg. EnviroScan®). The positioning of these devices in an orchard needs to be carefully selected in order to allow for soil and crop variations.
In more recent years investigations into precision irrigation have looked at incorporating adjustments for tree canopy cover to determine water use (Goodwin et al. 2005) and the use of tools that directly measure plant water stress such as pressure bombs.
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Scheduling for Regulated Deficit Irrigation (RDI)
Regulated Deficit Irrigation (RDI) looks to restrict water during periods of slow fruit growth and rapid shoot growth to save water as well as reduce vegetative vigour.
In the most basic terms RDI scheduling involves applying less water at the same frequency during the period of vigorous shoot growth. During this period fruit growth is slow and less sensitive to water. In pears this is generally from the start of November until 6-8 weeks before harvest (see Figure 2). See further information for more details of scheduling for RDI.
Figure 2: Pear fruit growth (Boland et al. 2002)
RDI has been widely investigated and used in moderate to low density orchards and has proven to be a useful tool. In intensive pear orchards, potentially on less vigorous rootstocks) the risk of water shortage inducing heavy stress (with reduction of fruit quality and flowering capacity for the next year) is higher (Sansavini et al. 2008). This means that any irrigation management strategy will need to be adjusted to suit.
Growers should consult an irrigation expert for further assistance with irrigation scheduling and monitoring in their orchards.
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Water Quality
It is important that water intended for irrigation is tested as poor water quality can impact on plant health and productivity as well as irrigation equipment.
Salinity
Salinity is a measure of the amount of dissolved salts in the water. High salinity levels make it difficult for cells to absorb water and dehydration can occur.
The level of dissolved salts can be measured through weighing the amount of dissolved solids per litre of water (mg/L). This is referred to as the total dissolved solids (TDS). Electrical conductivity (EC) of water is also a measure of the salinity level.
The most desirable level of salinity for pears on loamy soils is <700 EC (TDS 500). However actual irrigation salinity thresholds willl be site specific, varying with climate, soil conditions and cultural practices.
See further information for more about salinity
pH
Acidity or alkalinity will not necessarily rule out water use for irrigation. It may however influence the choice of fertilisers for fertigation and pesticide activity in spray tanks. Acid and alkaline waters can also affect irrigation equipment.
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Maintenance of irrigation systems
It is important that regular monitoring of the irrigation system is undertaken to ensure that the correct amount of water is consistently delivered across the orchard. Growers need to check flow rates and pressure regularly and ensure that the system does not have blockages, broken pipes and emitters or missing emitters. See further information for details on maintaining irrigation systems.
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Further Information
The following resources may be useful for growers. However they are intended as an information source only. Any specific chemical or other management recommendations may be outdated or irrelevant for Australian conditions and growers should seek local advice.
Please note: By electing to visit sites linking from this page you will be leaving the intensivepear.com website.
Australian Resoures
Selecting irrigation systems
Irrigation monitoring and scheduling
Water quality
Maintenance of irrigation systems
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References
Boland, A., Ziehrl A. and Beaumont, J. (2002). Guide to Best Practice in Water Management - Orchard Crops, Knoxfield : Department of Natural Resources and Environment
Goodwin, I., Whitfield, D.M. and Connor, D.J. (2006). 'Effects of tree size on water use of peach (Prunus persica L. Batsch).' Irrigation Science 24:59-68
Sansavini S, Ancarini, V. and Neri, D. (2008). 'Overview of intensive pear culture: Planting density, rootstocks, orchard management, soil-water relations and fruit quality.' Acta horticulturae 800: 35-50.
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Orchard Management 
