DR. Paul Research Update
Seaweed applications spur plant growth in New Zealand trials

By Paul Hepperly

May 10, 2004: Seaweed is a rich source of trace minerals, vitamins and plant hormones that has been widely used by organic farmers to promote crop growth; yet, many farmers are not fully aware of this resource and its potential benefits on their farms.

Researchers in New Zealand tested soil, foliar, and combined soil plus foliar applications of seaweed for their effects on kiwifruit growth. Organic-research.com recently published a full report of this thee-year analysis of seaweed impact on kiwifruit production (Perham, J. 2003. Ocean Brew Seaweed Kiwi Efficacy Trials. www.organic-research.com).

Seaweed applications increased kiwifruit firmness and storage life while reducing fruit rot up to 50 percent. Positive effects on fruit quality were found from both soil and foliar applications and the combined applications added to the benefits. The kiwi vines killed by wind were reduced by 44 percent when using the combined seaweed applications. The fruit calcium level was increased by seaweed about 10 percent while fruit nitrogen was about 20 percent less than the non-treated fruit.

These changes in nutrient composition were associated with reduced kiwifruit pitting. Fruit pitting in kiwi is a physiological disease associated with low calcium and high nitrogen levels.

Fruit weight when seaweed was used increased up to 11 percent, but the number of 22 count marketable fruit increased a whopping 71 percent.

Many seaweed providers are using sustainable harvest techniques to ensure the long-term viability of this wild natural resource. Foliar application is a technique that can result in great benefits from often relatively small natural inputs.

The New Zealand kiwifruit results illustrate how small foliar applications applied as tonics can have large impacts on crop quality and growth in some environments. Besides the direct impact on kiwifruit production, seaweed applied to soil increased earthworm numbers up to 150 percent over the control, indicating positive environmental impact.

Dr. Paul Hepperly is New Farm Research & Training Manager at The Rodale Institute. He grew up on a farm in northwestern Illinois and has 30 years of research experience in tropical and temperate agricultural systems.