Arid regions can produce ideal conditions for growing turfgrass. However, the tradeoff is that these regions don’t receive enough precipitation, so turf managers rely on irrigation to keep turf alive. Issues with irrigation water quality can lead to problems in the soil, making it challenging to maintain healthy turfgrass landscapes.
The chemical makeup of irrigation water is highly dependent upon the soils and bedrock mineralogy of the surrounding region. In the southeast, where the soils are acidic and highly-weathered, the irrigation water is typically acidic and low in soluble salts. In arid regions, irrigation water takes on the properties of the surrounding soils and bedrock and is typically high in pH while containing higher concentrations of salts. When irrigating turfgrass, the dissolved mineral salts in that irrigation water are redistributed from the water table into the plant root zone. As plants take up water and evaporation dries the soil out, salts from the irrigation water are concentrated in the soil and can cause specific problems for plant growth and soil management.
Salinity refers to the overall concentration or level of dissolved salt. Salinity can be measured in irrigation water directly but can also be measured in the soil through what is called a “saturated paste extraction.”
Turfgrass roots take up water through concentration gradients between the soil and the root cells. Under normal conditions, the established gradient is such that water moves from the soil into the plant roots. When soils are high in salinity, it affects this concentration gradient and makes it more difficult for turfgrass to take up water. The plants experience the symptoms of drought, even though water may be plentiful in the soil. This issue is sometimes referred to as “physiological drought.” Different turfgrass species have different levels of tolerance to saline soil conditions. Within a given turfgrass species, some cultivars may be bred to have greater salinity tolerance.
The solution for managing salinity is leaching or applying an excess of irrigation so that the soils produce drainage that reduces the salts left in the soil. There are multiple methods to calculate how much water one needs to apply to produce leaching. Many great resources are also available to help turf managers understand how to monitor and manage soil salinity – consult your local university extension office or agronomist network to find resources applicable to your region.
Wetting agents can be a valuable tool to manage soil salinity. Wetting agents can promote better penetration and distribution of water in the soil, which could make leaching efforts more effective in removing salts.
Sodicity refers to the concentration or level of sodium relative to other positively charged ions or cations (calcium and magnesium). Sodicity can be measured in the irrigation water directly or in the soil through the same saturated paste extraction used to measure salinity.
When soils are irrigated with water containing high sodium levels, soil structure is compromised, and the soils become extremely difficult to manage. Soil aggregates are dispersed or “deflocculated,” which causes large open channels and pores to break down into smaller, disconnected pores. The soils take on water much more slowly and are more susceptible to runoff and erosion.
At the University of California, Riverside, test plots in a salinity study showed the detrimental effects of high levels of sodium in water on turf grass.
The solution for managing sodic soils is to apply calcium, usually in the form of gypsum. Calcium (Ca2+) is divalent, meaning it has a “2+” charge. Sodium (Na+) is monovalent, meaning it has a “1+” charge. When calcium is applied to a sodic soil, the 2+ charge has a greater affinity to adhere to the negatively-charged exchange sites, allowing it to displace and remove sodium. After applying the gypsum, the soil must be leached to remove the sodium from the system.
Researchers and turf managers from arid regions have led the way in researching and defining best practices for the management of saline and sodic conditions. As population and urbanization increases, we will likely see an increase in the amount of irrigated turfgrass in the USA. At the same time, we’re seeing more extreme weather events and periodic droughts that put pressure on the water supply. These changes could mean that water quality issues that were once restricted to arid regions could become more prevalent in other regions. That means we’ll have to apply existing principles in new environments to manage irrigation water and soil problems successfully.
Arid regions present unique challenges for turf irrigation water management. This golf course in Hawaii uses water from a high-salinity source, so reverse osmosis is used to remove salts to avoid issues with turf performance.
The foundation of managing any problem starts with diagnosing and understanding it. Before jumping to solutions – including management practices or products – it is helpful to define the problem with irrigation water and soil testing. Those results should be related to observable effects on the turfgrass tracked over time. With this foundation, management practices can be evaluated in the proper context and adjusted to provide meaningful results.
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