The Cost of Inefficient Irrigation

According to the Merriam-Webster dictionary, the simplest definition of “Irrigation” is the “watering of land by artificial [nonnatural] means to foster plant growth.” This would imply that any water applied to a crop and not taken up by the plant can be classified as inefficient irrigation.

Among the many factors that affect the overall irrigation efficiency (IE), one of the most commonly used parameters is distribution uniformity (DU), which can broadly be described as a percentage of how evenly water is applied to the cropped landscape. Generally, higher DU values mean the water is evenly distributed, reducing dry spots and ponding areas. More specific scientific terms such as low quarter DU and Christiansen’s Coefficient of Uniformity, which indicate more details about the spatial distribution of the wetting patterns of the applied water, are readily available in the literature.

However, we will adhere to the term DU as the main focus of this article is to focus on the impact of DU on our water, soil and air resources with an emphasis on addressing the environmental challenges faced by growers in California’s San Joaquin Valley (SJV), commonly referred to as the “food basket of the world.” A combination of fertile soil, diverse crop production systems and innovative irrigation technologies are some of the factors that make the SJV a critical agricultural hub.

In addition to optimizing IE in terms of the economic returns measured as crop yield divided by the amount of water applied, growers are also cognizant of how DU affects environmental concerns, such as soil fertility, waterlogging, soil salinization and erosion, nutrient leaching and runoff, and greenhouse gas emissions, among other social and economic factors.

“DU is a pivotal factor in determining the environmental sustainability of irrigation practices.”

The uneven application of water due to low DU can harm soil health as over-irrigated areas may experience waterlogging, which depletes oxygen levels in the soil and hampers root growth and the survival of aerobic microbes essential for converting nutrients for plant uptake. Waterlogging can also accelerate the breakdown of organic matter, reducing soil fertility over time. Conversely, drier patches of bare land due to under irrigation can become prone to accelerated soil erosion and compaction, making them unfavorable for seed emergence and plant growth.

Ultimately, poor DU can further exacerbate the problem of soil salinization, as salts are left on the soil’s surface following evaporation of any capillary water from within the soil profile. Furthermore, when too much water is applied unevenly in areas with insufficient drainage, fields become inaccessible for agronomic and cultural practices associated with pest management and harvesting.

The environmental consequences of nutrient leaching, particularly nitrates and runoff associated with the loss of phosphates, are closely tied to irrigation practices. These nutrients are transported to nearby rivers, lakes and groundwater systems, contributing to water pollution and eutrophication, which is the excessive growth of algae and aquatic plants due to nutrient enrichment, that depletes oxygen levels in water bodies and disrupts aquatic ecosystems.

Inefficient irrigation practices can also contribute to GHG emissions. For example, over-irrigation in low-DU systems increases the energy required to pump and distribute water, particularly in pressurized irrigation systems like sprinklers and drip irrigation. The additional energy demand often relies on fossil fuels, leading to higher carbon dioxide emissions. Furthermore, waterlogged soils in over-irrigated areas become anaerobic, creating conditions that favor the production of methane and nitrous oxide — potent GHGs. The environmental impacts of poor DU extend beyond the confines of agricultural fields. Water wasted due to uneven distribution often diverts resources away from natural ecosystems, such as wetlands, rivers, and lakes. These ecosystems provide critical services, including habitat for wildlife, water purification, and flood regulation. Reduced water availability can lead to the degradation of these ecosystems, threatening biodiversity and disrupting the delicate balance of natural processes.

Based on the significant environmental implications of DU outlined above, adopting strategies that enhance IE is imperative. More importantly, from economic and social viewpoints, adopting a proactive preventative approach is necessary instead of detection and remediation. Some of the practices briefly outlined here for further consideration include upgrading irrigation infrastructure, regular maintenance of existing equipment, adoption of innovative soil and crop management practices, routine monitoring and reassessment of soil moisture technology, and continuous periodic grower education and training. Modernizing irrigation systems with advanced technologies, such as precision sprinklers and drip emitters, can improve DU and reduce water waste. Well-maintained irrigation systems prevent leaks, clogs, and other issues compromising DU. Ensuring that all personnel associated with irrigation and agronomic practices understand basic soil properties related to water movement and crop water requirements will go a long way toward optimizing the DU of irrigation systems. This can be further enhanced with state-of-the-art tools, such as soil moisture sensors, aerial imaging and artificial intelligence (AI) to assess water distribution, which can help identify and address areas with poor DU. Finally, providing farmers with the knowledge and skills to implement the Best Available Conservation Management Practices in irrigation is crucial for achieving sustainable outcomes.

DU is a pivotal factor in determining the environmental sustainability of irrigation practices. For example, poor DU wastes water and energy and can contribute to soil degradation, water pollution, GHG emissions and biodiversity loss, among other challenges not discussed in this paper. Conversely, improving DU offers a pathway to more efficient and sustainable agriculture, benefiting the environment and society. As the global population continues to grow and climate change intensifies water scarcity, optimizing DU should be a central focus of efforts to ensure the long-term viability of agriculture and the health of our planet.

Dave Goorahoo, PhD, and Florence Cassel, PhD