Application Guidance: Irrigation Decision Support Systems
Decision support for irrigation can come from various sources within the field or using aerial imagery. Determining which metrics matter for each grower depends upon their needs, budget, and crop. To make IDSS selection easier for growers, the Product Evaluation Hub has identified three categories of IDSS for use in the cultivation of specialty crops in California: (1) soil-based, (2) canopy-based, and (3) remote-sensing-based. Within these groups, various key data parameters are available to growers.
- Soil-based
- Volumetric Water Content
- Measure of the amount of water stored within soil, given as the ratio of water volume to total soil volume.
- Assists in determining how much water is needed to replenish the soil and monitoring soil water content during signs of plant stress.
- Soil Water Potential
- Measure of how much pressure (kPa or bars) is required to move water within the soil.
- An indication of how readily available water is to a plant.
- Soil Salinity
- Measure of bulk salt content in the soil solution
- Affects plant water uptake, soil structure, and availability of nutrients.
- Monitor and prevent salt accumulation and ensure balanced fertilizer application.
- Soil Temperature
- Influences water absorption, evaporation, root growth, and microbial activity.
- Predict drought and plant stress conditions and irrigate at soil temperatures efficient for absorption.
- Volumetric Water Content
- Canopy-based
- Evapotranspiration
- Measure of water used and lost by the plant through transpiration and evaporation from plant and soil surfaces.
- Optimize irrigation schedules to meet crop water needs and replace losses from evapotranspiration
- Precipitation
- Impacts soil moisture levels, crop water needs, and irrigation scheduling.
- Reduce or delay irrigation based on recent rainfall, use rainfall predictions for irrigation planning, and aid in drought and flood management.
- Canopy Temperature
- Measuring the temperature of crop leaf and stem surfaces can help detect plant water stress and give insight into evapotranspiration rates.
- Growing Degree Days
- Measure of heat accumulation used in predicting crop growth stages and development.
- Optimize irrigation schedules by aligning water application with varying crop water needs during different developmental stages.
- Leaf Wetness
- Measure of moisture presence on leaf surfaces to assist in scheduling irrigation for a time of day when leaves will dry more quickly and reducing over-irrigation if leaves are still wet.
- Normalized Difference Vegetation Index (NDVI)
- Measures the amount of red light and near-infrared light reflected by crops to give a vegetation index.
- Allows for application of different irrigation levels based on variations in plant density and health.
- Evapotranspiration
- Remote-sensing based
- Colorized NDVI
- Values from NDVI data are assigned colors on a gradient to create a map that helps visualize high and low plant growth.
- Thermal Imagery
- Detects temperature variations in crops and soil.
- Gives real-time monitoring of potential water stress and soil moisture levels.
- Water Stress Maps
- Identify regions where crops are experiencing stress from water deficiency and over-irrigation.
- Color Infrared Maps
- Measures near-infrared, red, and green light reflectance to create a map that depicts vegetation health, moisture stress, and over/under irrigated zones.
- Colorized NDVI
It is possible to integrate all three of these categories in an IDSS. Several California IDSS providers offer even more integration options, such as monitoring of well depth and water valve control. Unique to some providers are different ways of calculating derived measurements, such as Actual Evapotranspiration (ETa), as well as the various modeling algorithms that go into making crop predictions and irrigation recommendations.
For an extensive overview of various IDSS available in California, including those not yet evaluated, see Jha et al. 2022.