Implementation of new irrigation system technologies and strategies is continuously on tree nut growers’ minds. Irrigation systems of the future will need to be nimble and flexible to deal with variability in the orchard for maximum water use efficiency.
Growers may look at water use as it relates to rate and timing, but there is another important aspect to consider when designing an irrigation system in an orchard, known as spatiotemporal variability.
Spatiotemporal variability may be caused by variation in soil physical and hydraulic properties, which affects soil water infiltration rates. Soils that have high spatiotemporal variability are said to be more heterogeneous, while those with low spatiotemporal variability are said to be more homogenous. Heterogeneous soils have areas of varying infiltration rates or soil water holding capacity.
It is the responsibility of the grower and/or irrigation system designer to account for spatiotemporal variability in order to meet engineering and horticultural requirements as well as maintain economic viability of an orchard, according to UC experts. They recommend that this variability be considered in future almond irrigation system designs as well as irrigating by tree variety and managing irrigation to optimize the orchard’s ability to provide agroecosystem services (e.g., improved soil health and water quality).
Account for Spatiotemporal Variability
Water stress in an orchard is not always due to low available water. Spatiotemporal variability and varying infiltration rates can also cause too much water to be present in certain parts of an orchard. UC Davis Associate Professor of Agricultural Water Management and Irrigation Engineering Isaya Kisekka explained reasoning for this issue in an Almond Board of California webinar in which he referenced research at CAPEX ranch in the Central Valley.
Kisekka explained why trees in a row were experiencing dieback when other trees on the same irrigation lateral appeared healthy. “The biggest problem is this particular ranch has low infiltration rates in some areas because the water, especially the surface water that they get, has very low electrical conductivity,” he said, “and from soil physics, we know that can create sodicity problems which result in low infiltration and drainage problems.”
How do growers and/or irrigation system designers design a system to address these problems? The answer, according to Kisekka, is a flexible system that accounts for soil type, infiltration rates and soil water holding capacity among other factors. Most importantly, irrigation zones need to be established based on where these characteristics differ in an orchard.
In a Kings County Farm Bureau webinar, grower Dino Giacomazzi of Giacomazzi Almond Company Inc., explained how he first approached variability when planting his almond orchards. “We went through a very extensive process of research, looking at every technology available,” he said. “We mapped all of our fields by soil type and designed irrigation sets based on the soil type. We engineered our systems so that our lateral pipelines and drip hoses followed the soil type contours.”
Giacomazzi said that the system was designed for short, high-frequency irrigation or long, low-frequency irrigation based on soil type. “After many years of implementing variable rate irrigation, we discovered that higher frequency irrigation worked well for all soil types,” he said. “We don’t tend to use the soil type zones anymore, but we do use our dual laterals to irrigate pollinators differently than Nonpareil going into harvest.”
Irrigate by Variety
Along with spatiotemporal variability, the different horticultural characteristics (crop water use, biomass accumulation, canopy structure, etc.) of varieties like Nonpareil, Butte and Aldrich affect overall water use efficiency in orchards. Kisekka recommends growers and/or irrigation system designers consider designing future systems based on varieties in rows to maximize this efficiency and improve production.
“It will be easiest if irrigation system designers can already design a system that allows a grower to control each of these rows or these different varieties independently,” he said, citing research on site-specific irrigation by variety that looked at the potential benefits to water use efficiency.
Kisekka noted that varieties like Nonpareil, Butte and Aldrich reach hull split at different times. “If all the trees receive full irrigation before hull split and then we start cutting back, there could be opportunities here to achieve some water savings and improve our irrigation water use efficiency,” he said. “The other benefit is to allow us to continue to irrigate the variety that has not yet reached its optimum harvesting time.”
In order to irrigate in this fashion, a flexible system is required. A system that would allow growers to continue irrigating Nonpareil trees during drying and before harvest of pollinators, according to Kisekka, is ideal.
Giacomazzi explained how his system for almonds is set up by variety to separately irrigate his Nonpareil and Monterey trees. “In our newer systems, we designed them for higher frequency irrigation and included separate laterals for Nonpareil & pollinators,” he said. “Rather than having lots of little valves like we have in our variable rate systems, we have gone to bigger sets, less hardware, more acres irrigated per hour. Our goal is to irrigate as many trees as possible as many times as possible in a single day.”
Kisekka also stressed the need for the growers and irrigation system designers to consider other factors besides production within the agroecosystem when designing irrigation systems, such as water quality, soil health, reduction in greenhouse gas emissions and carbon sequestration.
“For example, we need to design systems that can provide water to both the tree as well as the cover crops in some areas where cover crops are proved to be viable,” he said, “because these cover crops have many benefits. They can improve soil health and they can also improve bee habitat, which is important for pollination.”
Kisekka recommends dual purpose irrigation systems with microsprinklers or a combination of drip and microsprinklers that can reach not only the primary crop but also the cover crop. Microsprinklers can also be used to aid in carbon sequestration of wood chips from whole orchard recycling by breaking the chips down, and recent UC Davis research has found that a 58% increase in total soil carbon is possible from chip incorporation in almond orchards.
Another area Kisekka said to consider is agricultural managed aquifer recharge, which concerns water quality and quantity and its success is closely tied to efficient fertigation during the season. “This goes to, again, thinking about a dual-purpose irrigation system,” he said. “So, you design irrigation systems that would meet crop ET but also can allow flooding of the orchard to recharge groundwater if flood waters exist.”