Kelp, better known as seaweed, has been used as a fertilizer on turf for many years. It is also the most universally recognized natural biostimulant and is the most widely used biostimulant in both agriculture and turfgrass management (Hattori, 1999). It contains many important plant growth regulators, such as auxins, cytokinins and gibberellins. It also contains micronutrients to enhance a plant's ability to resist pest and disease attack (Hattori, 1999).

Blunden (1991) reported that seaweed also contains betaines, substances that behave like cytokinins in most species of marine algae used in the manufacture of seaweed extracts.

Limited research has been carried out on seaweed extract application using a foliar nutrient program, which is commonly practiced within the turfgrass industry. The objectives of this research were to study the effects of pure seaweed extract on turfgrass growth, nutrition and stress tolerance.

Materials and methods

The research was conducted on a USGA golf green from July 2005 to October 2005 at University College Dublin, Ireland. In July, an experiment was initiated using a seaweed extract biostimulant (supplied by Maxicrop) applied biweekly at 2 milliliters (ml) per square meter onto treatment plots measuring 1.5 square feet. Foliar fertilizer was applied at either the recommended nutrient rates of 37, 2.61 and 40.67 kilos [nitrogen (N), phosphorous oxide and potassium oxide] per hectare respectively (for a quick conversion from kilos per hectare to pounds per acre, multiply by 0.9 or at two-thirds the recommended rate).

The foliar fertilizer program used was from a recommended nutrient program for a USGA golf green in Ireland. The nutrients were applied using a hand-held sprayer. The seaweed extract was mixed with water to give a seaweed application volume of 50 milliliters per square meter at each biostimulant application. Control treatments were also used, which only received the two separate nutrient rates. The experiment was set up as a completely randomized design with four replications.

The green was mowed daily at a height ranging between 0.145 inches and 0.156 inches. Irrigation was applied as needed.

Clippings dry weight, tissue and rootzone nitrate nitrogen, phosphorus, potassium and grass color were determined monthly from mid-August until mid-October. Leaf proline (Bates et al., 1973), soil organic matter (ASTM D 2974-87) and root mass (Doak et al., 2005) were measured in October. The results were analyzed as a factorial experiment (nutrient rate and biostimulant) using SAS, PROC MIXED as repeated measures ANOVA (SAS Institute, Cary, N.C.).

Results

Figure 1: Turfgrass Dry Weight

The seaweed extract significantly enhanced grass dry weight compared to the control treatment on the first measurement date, while the opposite occurred on the last measurement date (Figure 1).

On the second measurement date, no significant difference in grass dry weight was detected between biostimulant treatments. The use of biostimulants appeared to have a limited impact on grass growth, particularly as temperatures decline in the autumn.

Tissue nitrogen was significantly higher on both the first and second measurement dates compared to the last measurement date for both seaweed and control treatments. The seaweed significantly enhanced leaf tissue nitrogen compared to the control in August only. It is probable that as ambient and rootzone temperatures decreased during late summer/early fall, the beneficial effect of seaweed extract on nitrogen uptake decreased.

The seaweed treatment significantly elevated leaf tissue phosphorus levels compared to the control treatment on the first measurement date, but the opposite occurred on the second one. On the final measurement date, no significant difference in leaf tissue phosphorus occurred. Leaf tissue phosphorus concentration was significantly lower on the first measurement date compared to the last two dates for both seaweed and control treatments.

The seaweed extract decreased tissue potassium concentrations compared to the control in August with no significant differences in leaf tissue potassium being found on subsequent measurement dates. On the first measurement date, leaf tissue potassium was lower than the following two measurement dates for the seaweed treatment.