July-September 2004 California Agriculture magazine

Focus on water quality: Clean water for all
Well-managed cattle grazing can reduce
sediment in streams

Also: Low-cost transparency tubes accurately measure turbidity;
efficient “manure water” irrigation protects groundwater; spray drift of herbicide (clopyralid) minimal; cotton-planting forecasts are accurate; premium for organic kiwifruit declininge

Virtually all of California’s surface water passes through the state’s 57 million acres of rangeland, raising concerns about the impact of cattle on water quality. But well-managed cattle grazing need not increase sedimentation in California rivers and streams, scientists report in peer-reviewed studies published in the July-September 2004 issue of the University of California’s California Agriculture journal.

The current issue of California Agriculture, including PDF versions of all peer-reviewed research articles, can be viewed in full online at: http://CaliforniaAgriculture.ucop.edu/0403JAS/toc.html

A peer-reviewed, 5-year study found that moderate and concentrated cattle grazing around intermittent streams in oak woodlands of the Sierra Nevada foothills did not increase streambank erosion. At the same time, a related 3-year study found that cattle trails are an important conduit for the transport of sediment into stream channels.” To reduce the formation of new trails, the authors recommend strategic placement of fencing as well as the addition of watering sites on rangeland. “These rangeland improvements should receive high priority in the allocation of agency conservation and pollution-control funding,” lead author Melvin George, UC Davis extension rangeland management specialist, wrote in California Agriculture.
Another 10-year study in the July-September 2004 California Agriculture examines the ecosystem impacts of light and moderate cattle grazing on spring-fed wetlands among oak woodlands at the UC Sierra Foothill Research and Extension Center in Yuba County. The authors measured lower insect-species diversity in the grazed wetlands, but also found that plant cover and diversity were maintained for the first 7 years of light and moderate grazing. Likewise, the removal of grazing decreased emissions of methane, a greenhouse gas, but increased levels of polluting nitrates in spring waters, highlighting the complex management tradeoffs inherent to cattle grazing in wetland areas.
“In addition to introduced cattle, spring wetland systems are grazed by wildlife of all kinds,” said lead author Barbara Allen-Diaz, UC Berkeley ecosystems science professor. “Grazing is an integral part of these systems and evolved with them. We found some negative impacts from grazing but also that it serves to maintain critical aspects of ecosystem integrity.”
Possible impacts of cattle grazing on water quality include reduced vegetative cover, changes in plant species composition, and increases in water temperature, sediments, nutrients and pathogens; livestock hooves can also compact wetland areas and break down stream banks. Maintaining the quality of water that passes through rangelands is mandated in certain regions as part of federal total maximum daily load (TMDL) regulations for streams and waterways.

News articles in the July-September 2004 issue of California Agriculture highlight the UC Cooperative Extension’s Rangeland Watershed Program, which has been working with ranchers since the early 1990s to identify rangeland water-quality problems and develop research-based solutions. Since 1997, hundreds of ranchers have taken a Ranch Water-Quality Planning Shortcourse offered by UC Cooperative Extension. As a result, nearly 400 voluntary water-quality plans have been developed, covering 1.3 million acres of rangeland. Contact: Melvin George, (530) 752-1720 or mrgeorge@ucdavis.edu; Barbara Allen-Diaz, (510) 642-7171 or ballen@nature.berkeley.edu.
In addition to the rangeland studies, the focus section on water quality in the July-September 2004 issue of California Agriculture includes peer-reviewed articles on protecting California’s critical water resources:
Transparency tube provides accurate turbidity measurements: Similar to the Secchi disc used to measure the clarity of lakes (most famously in Lake Tahoe), the transparency tube is inexpensive and easy to use, and provides accurate measurements of turbidity and total suspended solids in streams and waterways. The authors collected nearly 500 samples from Central Valley rivers, the Stockton Ship Channel, and Bay-Delta Waterways; they found that the transparency tube provided accurate, reliable measurements when compared with more expensive and time-consuming sampling methods. Contact: Randy Dahlgren, (530) 752-2814 or radahlgren@ucdavis.edu
Aerial clopyralid spraying poses little risk to aquatic areas: Clopyralid, an effective treatment for the noxious weed yellow starthistle, showed little drift potential into vernal pools and creeks when sprayed aerially. Also, scientists report for the first time that larval toads demonstrate a high tolerance to clopyralid. Contact: Joseph DiTomaso: (530) 754-8715 or ditomaso@vegmail.ucdavis.edu
Efficient “manure water” irrigation protects groundwater: Three alternative methods for irrigating cropland with manure water flushed from dairy cow stalls — furrow torpedoes, surge irrigation and shortening furrow lengths — all significantly reduced the amount of water required. More efficient irrigation with manure water can help prevent tailwater runoff and the infiltration of polluting nitrates into groundwater. Contact: Larry Schwankl, (530) 752-4634 or ljschwankl@ucdavis.edu
Plus,

• In the first long-term evaluation of its kind, UC Cooperative Extension’s “degree-day” forecast for cotton growers in the southern Central Valley was reliable more than 90% of the time when compared with actual, observed weather conditions from 1998 to 2002. Contact: Doug Munier, (530) 865-1107 or djmunier@ucdavis.edu
  
• A survey of organic kiwifruit handlers found that the traditional premium for organic product is decreasing, and it is not unusual for organic fruit to be sold through conventional marketing channels. Contact: Hoy Carman, (530) 752-1525 or hfcarman@primal.ucdavis.edu