How surfactants influence soil water availability and plant response

Wetting agents are widely used in turf management to improve water movement through soil and help manage water-repellent soils and localized dry spot.

Research at Lancaster University has looked more closely at what happens within the soil–plant system when a surfactant is applied.

PhD researcher Vasileios Giannakopoulos investigated the effects of surfactant-treated sandy soil on soil water availability, plant-water relations and growth. The experimental work used barley and corn rather than turfgrass, so the findings should not be interpreted as direct turf performance data. They do, however, provide useful insight into the processes that may help explain how wetting agents influence plant response to water availability.

Greater soil water availability

Laboratory testing found that water was more available in surfactant-treated sandy soil at equivalent soil moisture levels.

Samples of sandy soil were treated either with water or with water containing a surfactant. Soil water availability was then measured across a range of moisture levels using thermocouple psychrometers.

The results indicate that surfactants can alter the relationship between the amount of water present in the soil and how readily that water is available to plants.

Preparation of sample for measurements inside these chambers, i.e. psychrometers.

Effect on plant water use

A separate glasshouse experiment examined barley grown in either surfactant-treated or untreated sandy soil.

Under well-watered conditions and elevated evaporative demand, transpiration was approximately 13% higher in plants grown in the surfactant-treated soil.

Measurements also indicated greater stomatal opening, suggesting that the treated plants were able to maintain greater water use under the conditions of the experiment.

Whole Plant gas exchange chamber (excluding roots).

Response to drying soil

The researchers then repeated the experiment under mild soil drying.

Barley grown in surfactant-treated soil maintained a higher leaf-water status than untreated plants under low evaporative demand.

This suggests that the surfactant treatment helped reduce plant water stress under these specific experimental conditions.

Measurements of how open the plant’s stomata are (stomatal conductance).

Effect on biomass

Further experiments investigated plant growth.

Barley and corn were grown for three weeks in sandy soil, with half of the plants receiving the surfactant treatment and the remainder serving as untreated controls. Nutrition and irrigation were kept consistent between treatments.

At harvest, shoot dry biomass was approximately 20% greater in the surfactant-treated plants.

The experiment was conducted under well-watered conditions, so the result should be considered separately from the drought-response work.

What could this mean for turf management?

The research provides additional insight into why surfactants can influence more than the distribution of water within the soil.

By changing soil water availability, surfactants may also affect the way plant roots access water and how plants respond as soils begin to dry.

Further research in turfgrass and under field conditions is required before the physiological responses observed in barley and corn can be translated directly into turf-management recommendations.

For turf professionals, the work adds to the understanding of the soil–water–plant interactions that underpin effective wetting-agent programmes.

Measurements of leaf-water status using a pressure chamber.