Irrigation Practices

System Efficiency

Changing from an irrigation system with lower potential application efficiency to a system with higher potential for application efficiency.

Irrigation System Change Quick Facts

• Not all applied water reaches the root zone of the plants. Part of the water is lost by evaporation during and following the irrigation. The remaining part is stored in the root zone and eventually used by the plants. Only part of the water is used efficiently; the rest is lost for the crops on the fields that were to be irrigated.
• Different irrigation systems are associated with different field application efficiencies. The potential field application efficiency of surface (border, furrow, basin flood), sprinkler, and drip irrigation is about 60%, 75%, and 90%, respectively.
• With good design and maintenance, these values represent the typical efficiency that each system can reach. With poor design or inadequate maintenance (e.g., not checking a drip system for emitter plugging or rodent damage), any irrigation system will operate below its full potential efficiency.
• Low-volume irrigation systems such as drip and micro-sprinkler are typically regarded as more efficient than high-volume systems.
• Improving field application efficiency does not always result in less water use overall; with more efficient systems, crops may consume more water while producing better yields.

Distribution Uniformity

Improving management and maintenance to improve distribution uniformity through attention to equipment failures or correcting system design deficiencies. Irrigation efficiency overall, which includes distribution uniformity, can be improved with maintenance and improved irrigation scheduling.

Reducing Non-Beneficial ET

Reducing Non-Beneficial ET Quick Facts

• Evaporation from irrigation application with sprinkler systems can be reduced by improving irrigation scheduling according to weather conditions, operating at the correct design pressure, maintaining valves and correcting leaks, and using technologies to improve irrigation scheduling (i.e. soil moisture, plant moisture, or ET based). Evaporation from wetted soil can be addressed with irrigation scheduling and frequency.
• Evapotranspiration from weeds is usually associated with irrigation systems delivering water broadly, such as surface or sprinkler methods. Broad applications of fertilizer can also contribute.
• Amending salinity-affected soils with gypsum and/or acids can improve their soil water infiltration characteristics and reduce the surface wetting of soils, thus reducing evaporation losses.
• Subsurface drip achieved with either buried drip lines or by watering stakes is an effective way to reduce evaporation losses and will help limit the growth of summer weeds. These systems pose an additional cost for installation and maintenance. In areas having marginal quality irrigation water, these systems can complicate salinity management because salts will accumulate in the soil above the emitters; precipitation can then push these salts down into the active rootzone, leading to spikes in crop stress.
• Non-beneficial ET can also be caused by excess vegetative crop growth that does not contribute to yield. Excess vegetative growth is usually the result of irrigation and nitrogen fertilization regimes that promote vegetative instead of reproductive growth, either through improper rates or timing.
• While these best practices are not novel, concerted efforts to implement them can result in significant reductions in non-beneficial consumptive use, on the order of 5 to 15%.

Recycled Water

Using municipal or winery waste waters as an irrigation source.

Irrigation with Recycled Water Quick Facts

• Recycled waters from municipalities and wineries can be useful as an irrigation water supply for crops, and is often underutilized.
• The quality of the recycled water will be the primary constraint on its use for salt-sensitive crops such as wine grapes. High levels of ions such as chloride can be toxic to sensitive crops, thus the composition and risks of the recycled water need to be assessed thoroughly before using it as an irrigation source. Further treating the recycled waters to improve their quality for irrigation may be cost prohibitive.
• Crops that are more tolerant of salts such as grass forages, alfalfa and pistachios may be more suited than winegrapes to utilize recycled waters on a long-term basis.
• Winegrapes have a unique susceptibility to high salt levels in the irrigation water in that this can result in high salt uptake in the fruit which in turn leads to wine having an undesirable salt taint. Thus the use of recycled waters with wine grapes intended to produce high quality wines needs to be approached with caution and an understanding of the potential risks to the crop.

Irrigation Efficiency Ranges

Potential ranges of irrigation efficiency (%) for typical irrigation methods and varying levels of irrigation management (adapted from UC ANR Publication 8571, Table 3):

• 1 Irrigation systems often less than ten years old, frequent maintenance of irrigation systems, and use of ETc, soil, or plant water status monitoring to guide irrigation scheduling.
• 2 Irrigation systems often older than ten years, less frequent maintenance of irrigation systems, and minimal use of ETc, soil, or plant water status to guide irrigation scheduling.
• 3 Irrigation systems 20 years or older, very little or no maintenance of systems, and no use of ETc, soil moisture, or plant water status monitoring to guide irrigation scheduling.
• 4 Linear move or center pivot systems that use drop tubes and low-pressure bubblers to deliver water directly into furrows and minimize wind drip and canopy interference. Furrows are typically blocked with furrow dikes every two to four yards to control where water infiltrates.

Irrigation Practices — Summary