May 2008, Vol. 20, No.5


Testing Tidal Energy

A proprietary turbine-generator unit (TGU) designed to harness the energy-producing power of tidal and ocean currents is being tested off the coast of Eastport, Maine.

Early last December, Ocean Renewable Power Co. (ORPC; Fall River, Mass.) launched Energy Tide 1, a barge specially retrofitted to accommodate the TGU and testing assembly, and began a series of preliminary tests to help determine design capabilities, efficiency, and performance of the prototype TGU.

ORPC is dedicated to producing emission-free electricity from the energy resources of the oceans, according to a company news release. ORPC is developing proprietary modular ocean current generation (OCGen™) technology and incorporating it into ocean and tidal current generation projects.

Each TGU consists of two cross-flow turbines that drive a permanent magnet generator on a single shaft. As testing continues, ORPC Maine engineers will make adjustments, gather data, and suggest modifications that will be used to ensure the successful production of future units, the news release notes. TGUs can be shop-fabricated and shipped to project sites, where they can be combined with other modular components and assembled into much larger generation platforms called OCGen modules. These modules, according to ORPC, can be deployed in both tidal and deep-water ocean currents. The output from a single OCGen module located in a tidal area, such as ORPC’s Western Passage (Maine) site, could be enough to power more than 200 homes, ORPC says.

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Managing Cattle Operations To Protect Lakes and Rivers

While the effect of agricultural waste on waterbodies is of great concern in the water quality field, limited data have been available to quantify nutrient losses to adjacent bodies of water from pastures managed for grazing and hay production.

In Florida, forage-based livestock systems have been cited as a major cause of deteriorating water quality. Concerns about long-term effects of beef cattle browsing more than 4.5 ha (11 million ac) of Florida grazing lands led U.S. Agricultural Research Service (ARS) scientists to examine soil fertility changes in bahia-grass-based beef cattle pastures from 1988 to 2002.

Analysis of data from that research shows that cattle can be managed in an environmentally safe way, despite the large quantities of waste the animals generate, according to ARS.

For this long-term monitoring study, the pastures were managed for spring grazing and late summer haying. Soil scientist Gilbert C. Sigua and colleagues in the ARS Beef Cattle Research Unit in Brooksville, Fla., monitored changes in soil nutrients. The data they generated enabled them to predict soil chemical and physical changes likely under continuous forage-livestock cultivation and to devise measures to manage them.

Testing was done in three large pasture units with a combined area of about 1538 ha (3800 ac), of which about 1295 ha (3200 ac) were in permanent pasture. The herd used in the study — about 1000 cows, bulls, and calves — is maintained for nutritional, reproductive, and genetic research at Brooksville, according to ARS.

Overall, there was no buildup of soil phosphorus or other crop nutrients, despite the annual application of fertilizers and daily in-field loading of animal waste, ARS reports. Periodic soil analysis showed declining nutrient levels, especially of phosphorus.

Read more about this research in the February 2008 issue of Agricultural Research magazine at