Barley straw is the dry, fibrous stalk remaining after the grain has been harvested. This agricultural byproduct has a long history of use in farming practices. Its use for improving water quality began in the United Kingdom in the early 1990s, where it was deployed in water features to manage unwanted growth.
Defining Barley Straw and Its Structure
Barley straw is structurally distinct from barley hay, which is the entire plant cut green and dried for high-nutrient animal feed. Straw is the hollow, golden-yellow stalk left over after the grain head is removed, making it a material with very low nutritional value. This composition means barley straw contains a high proportion of cellulose and lignin, the tough structural components of the plant cell walls.
The high cellulose content and low levels of nitrogen and phosphorus differentiate straw from hay, which is rich in protein and nutrients. Compared to other cereal straws, barley straw is often described as softer and more pliable. This specific chemical makeup allows barley straw to function effectively in water treatment applications.
The Chemical Mechanism of Algae Suppression
The ability of barley straw to suppress algae growth relies entirely on a process of slow, aerobic decomposition within the water. When the straw is submerged and oxygen is present, fungi and other microbes colonize the material and begin to break down its structural components. This microbial action generates humic substances, which are complex organic molecules that become dissolved in the water.
These dissolved organic compounds are the precursors to the anti-algal effect. In the presence of sunlight, these humic substances act as photocatalysts, driving a reaction with dissolved oxygen in the water. This continuous chemical process leads to the slow, steady generation of trace amounts of hydrogen peroxide.
The low, sustained concentration of hydrogen peroxide is the primary compound that inhibits the growth of new algae cells. This effect is considered algistatic, meaning it prevents or slows future algae growth, rather than algicidal, which would kill existing algae. Warmer water (above 68°F) speeds up microbial decomposition, making the straw effective in one to two weeks, while colder water (below 50°F) can take six to eight weeks.
Proper Deployment in Ponds and Waterways
Effective algae suppression requires the barley straw to be deployed correctly. It is recommended to place the straw loosely within a mesh bag, netting, or cage rather than using tightly packed bales. Breaking up the straw maximizes the surface area exposed to the water and ensures sufficient oxygen flow throughout the material.
The most successful deployment involves floating the straw near the surface of the water, ideally in the upper three to four feet of the water column. This placement ensures the straw is exposed to the highest levels of dissolved oxygen and sunlight, both necessary for the chemical reaction that generates hydrogen peroxide. Anchoring the net or bag near an area of water movement, such as a fountain or inlet, also helps to distribute the active compounds throughout the water body.
Application is most effective when performed in early spring, before the onset of the seasonal algae bloom. For larger water bodies, an application rate of approximately 90 to 450 pounds of straw per surface acre is a common recommendation, with higher rates used for water with heavy algae problems or high turbidity. The straw remains effective for four to six months, after which it must be replaced to maintain continuous algae control.
Alternative Agricultural and Horticultural Uses
Beyond its unique function in aquatic environments, barley straw is valued in various agricultural and horticultural applications. A primary use is as a protective mulch in garden beds and cultivated areas. When spread over the soil, the straw layer helps to suppress the growth of weeds by blocking sunlight.
The dense, fibrous material also acts as an excellent insulator, helping to retain soil moisture by reducing evaporation and moderating soil temperature fluctuations. In livestock operations, barley straw is often used as comfortable animal bedding. Its softer texture is sometimes preferred for delicate or young animals, though its low nutritional content means it is not a suitable primary feed source.