Solar tents can easily, inexpensively and successfully kill weed seeds and rhizomes, eliminating the need for hauling weeds out of remote areas where the unwanted plants have taken hold, a UC researcher has demonstrated.

Research by Jim Stapleton, a UC Cooperative Extension advisor based at the Kearney Agricultural Research and Extension Center, was published as Feasibility of solar tents for inactivating weedy plant propagative material in the March 2012 issue of the Journal of Pest Science.

Stapleton, who specializes in plant pathology and integrated pest management, was inspired to conduct the study when a fire crew came upon a patch of Iberian starthistle growing along a stream in the Sierra foothills near Mariposa. Iberian starthistle is a robust, spiny weed native to the Middle East that, left unchecked, can dominate entire landscapes.

“Crews were going through and cutting dried plants and stacking them, but the seeds survived,” Stapleton said. “If you start moving plant material around with viable seeds, seeds are liable to spread, making the problem worse instead of better.”

Iberian starthistle is only one of many exotic, invasive plants that are capable of transforming California’s open areas into useless and unsightly tracts of land. On rangeland, for example, such weeds diminish desirable annual rangeland feed for cattle and wildlife. Weeds can shade out native wildflowers, make recreational areas inaccessible and, in dense infestations, become a fire laddering fuel.

In the past, such weeds may have been stacked and burned, but fire danger and air quality regulations have forced land managers to find alternatives.

Stapleton adapted a chemical-free, solar tent process he developed for nurseries, gardeners and small-scale farmers to kill weed seeds, insect pests and pathogens in the soil. The concept involves covering moist soil in containers with transparent plastic and allowing the greenhouse effect to raise the temperature in the soil to a level that kills harmful organisms. The solar tent has been found to have the same effect on invasive weeds and is particularly useful to control patches of weeds in inaccessible areas that get plenty of sun. It will not work where the climate is cold, cloudy or persistently foggy.

“You wouldn’t want to try this on a 40-acre area,” Stapleton said. “Eradication of weeds with solar tents is best suited for small-scale weed infestations in warm climates.”

For the research project, Stapleton constructed three replicate solar tents with concrete rubble, mulberry shoots and clear plastic tarps. He placed johnsongrass rhizomes inside black trash bags along with about one cup of water. The sample bags were left inside the solar tents for 72 hours.

“Regardless of where you are, regardless of financial resources, you should be able to construct a solar tent,” Stapleton said. “Most of the materials needed – rocks and sticks – are easy to find on site.”

Air temperature inside the sample bags rose to 158 degrees Fahrenheit. Over the three days of the experiment, the rhizomes were exposed to temperatures 140 degrees and higher for 10 hours. None of the rhizome segments treated for three days in the solar tents sprouted. In contrast, rhizomes maintained in clear vegetable storage boxes and kept indoors for comparison all sprouted.

UC Cooperative Extension farm advisor Carl Bell, a San Diego area weed expert, tested the process in Lakeside, east of the San Diego metropolitan area, where a group of volunteers were working on restoration of the San Diego River.

“There are a lot of sites in California where volunteer groups are going into canyons and other remote spots to clean up weeds,” Bell said. “They’re going to places with no roads or trails, scrambling over rocks to clean up these areas. They could construct one of these tents and return in a week to find everything in the bags overheated to a point where seeds won’t germinate and rhizomes are dead. They only have to carry out the plastic bags and tarps.”

For the demonstration, volunteers pulled weeds and built solar tents on a parking lot. They invited the public to a workshop at the site a week later.

“When we pulled out the bags of treated material after a week of cooking, it was a gooey mass of vegetative material incapable of regenerating the weeds,” Bell said.

Diagram of suggested solar tent construction:

(a) closed, black plastic trash bag, e.g., 40 gal volume, containing targeted plant material and one pint to one quart of water for free moisture presence; (b) interior framework of woody plant shoots, sitting on (c) rocks, to elevate trash bag above soil surface and allow heat to surround target; (d) sheet of black plastic film on soil surface to assist with heat accumulation and preclude escape of propagative material onto the soil; (e) clear plastic sheet, supported by (f) hoops of woody plant shoots to form a tent over the treatment bag; (g) exterior rocks, soil and/or logs sealing edges of tent canopy to minimize heat loss and preclude escape of propagative material.

(Graphic by Cynthia Stapleton, adapted from Journal of Pest Science 85:17-21. Graphic may be reprinted with credit. High resolution version.)

Even on the west side of the San Joaquin Valley, where average rainfall is a mere 7 inches per year, farmers can reap the benefits of winter cover crops without the expense of irrigation, University of California research has found. Growing a winter cover crop helps retain soil nitrogen – keeping it from leaching into groundwater – improves water infiltration, reduces runoff, increases soil organic matter and boosts long-term soil fertility.

Moreover, a vigorously growing cover crop can smother winter weeds, reducing or eliminating the need for herbicides or tillage between crops.

“Despite the many and varied benefits of cover cropping that are increasingly seen by farmers in other parts of the country, the vast majority of Central Valley farmers currently do not use them,” said Jeff Mitchell, UC Cooperative Extension specialist in the Department of Plant Sciences at UC Davis. Mitchell, a cropping systems expert, is based at the Kearney Agricultural Research and Extension Center in Parlier, Calif.

The costs and benefits of winter cover crops are being examined in an ongoing trial at the UC West Side Research and Extension Center in Five Points, Calif. Initiated in 2000, the trial is led by Mitchell, William Horwath, a professor in the Department of Land, Air and Water Resources at UC Davis, and Dan Munk, UC Cooperative Extension advisor in Fresno County, a cotton and soils expert.

Mitchell said the West Side trial addresses valley farmers’ primary concern about cover crops – water.

“When water is short, as it has been in many recent years, farmers wonder how inserting an extra crop that doesn’t bring an immediate return on investment makes sense,” Mitchell said. “But our work over the last 12 years has demonstrated that cover cropping ‘on the cheap’ – relying only on rainfall for irrigation – supplies many benefits and doesn’t cost much.”

Rainfall during the November to March winter growth period in Five Points averages 7 inches, slightly less than the 30-year average annual rainfall of 7.6 inches for the site. Winter rainfall has varied considerably during the trial, from a low of 2.9 inches in 2003 to a high of 11 inches in 2006.

From 2000 to 2010, a cover crop mix of triticale, ryegrain and pea was grown at a seed cost of $55 per acre (2012 dollars). In 2011 and 2012, the researchers used a mixture of fava bean and “tillage radish” for the cover crop, at a cost of $50 per acre.

Tillage radish is a large-rooted winter annual being marketed for its ability to improve soil condition. It’s thick, tuberous roots break up the soil surface. When it is killed in the spring and the roots decompose and shrivel, it leaves behind channels that help with aeration and water infiltration.

Over the course of the UC trial, an average of 3,400 pounds of dry biomass per acre was produced by the cover crops each year with rainfall alone. Productivity generally related to the amount of rain, with as little as 65 pounds of dry biomass per acre in 2007, when rainfall was 5.2 inches, and 6,400 pounds in 2005, when 10.1 inches of rain fell.

The timing of rainfall was also important. Rain is needed early to establish the crop and late in the season to sustain its growth when the temperature warms.

Over time, growing cover crops results in a significantly higher amount of carbon in the top foot of soil. Following eight years of cover cropping, soil carbon values in the standard tillage cover crop system, in which the cover crop was treated as a green manure and incorporated into the soil at a depth of 10 inches, was 12.2 tons of carbon per acre. Where cover crops were combined with conservation tillage, the researchers measured 12.8 tons per acre. In areas managed with conservation tillage and no cover crop, 11.7 tons per acre of carbon was in the top foot of soil. Under standard tillage and no cover crops, currently the common practice in the San Joaquin Valley, soil carbon came in at 9.9 tons per acre.

In addition to improving soil quality, farmers are investigating whether storing extra carbon in the soil will make them eligible for selling carbon credits under California Assembly Bill 32, the Global Warming Solutions Act.

“Sequestering carbon in farmland could be a means of mitigating global warming from greenhouse gas emissions,” Mitchell said. “We are working with farmers to develop a record of performance so they can document their potential for storing more carbon using conservation tillage and cover crops.”

The UC Conservation Agriculture Systems Initiative challenges Californians to look 100 years, or even 500 years, into the future and imagine how today’s common agricultural practices will have impacted the environment and society.

The United Nations estimates world population in 2300 will be about 9 billion. There is likely to be significant development in the ensuing 300 years that reduces the amount of land for farming.

“We have to be able to do more with less,” said Jeff Mitchell, UC Cooperative Extension cropping systems specialist, echoing a common theme repeated by speakers at the launch of the UC Conservation Agriculture Systems Initiative (CASI) Jan. 27. “The global demand for food will be immense.”

An overflow crowd of 125 farmers, equipment providers, public agency representatives and long-time conservation agriculture supporters participated in the launch. The meeting provided information about the evolution of the Institute, its recent research and development work on conservation agriculture systems, and its new capacity-building initiatives to increase the adoption of competitive and sustainable production systems in California’s San Joaquin Valley. 

Mitchell, other researchers and many innovative farmers have documented in more than 14 years of field research that changes in traditional farming practices – employing such technologies as precision irrigation, integrated pest management and conservation tillage – cut costs $75 to $150 per acre, reduce dust and diesel fuel emissions 60 to 80 percent, and prevent evaporation of about 4 inches of water per season from the soil surface.

This sort of objective data, plus favorable economic analyses and access to high-technology conservation equipment, are important factors in motivating farmers to change their practices, but they are not the only factors, Mitchell said. The Institute is committed to not only demonstrating and communicating the documented benefits of conservation agriculture but also identifying the drivers behind behavior change. The goal is converting 50 percent of California crop acreage to conservation practices by 2028.

“The cornerstone of sustainability is behavior change,” said Ron Harben of the California Association of Resource Conservation Districts, one of the Initiative’s founders. “Simply providing information has little or no effect on what people do.”

In parts of the U.S. and the world, conservation agriculture is common practice. World leaders in conservation agriculture include Brazil, Argentina and Paraguay, Western Australia and Canada.  Within the next ten years, Mitchell reported, more than 85 percent of the cropland in the three South American countries is expected to be converted to conservation agriculture. Adoption rates are also quite high in parts of South Dakota, Nebraska, the Pacific Northwest, and areas throughout Alabama and Georgia.   Yet implementation in California is still low.

In 2010, conservation tillage systems accounted for about 14 percent of the acreage in silage and grain corn, small grains for hay, silage and grain, tomatoes, cotton, dry beans, and melons in the nine-county Central Valley region. This was an increase from about 10 percent in 2008. Minimum tillage practices were used on about 33 percent of crop acreage in 2010, up from about 21 percent in 2008.

Mitchell said the implementation trends around the world, in the U.S. and in California “lend a certain inevitability” to its wide adoption in the San Joaquin Valley.

“This is not just about making a profit and optimizing yields,” Mitchell said. “By minimizing soil disturbance, preserving surface residue and including a greater diversity of crops in the rotation we are improving the soil resources and deepening the soil in an improved condition.”

The keynote speaker at the CASI launch was Hanford dairy farmer Dino Giacomazzi, a long-time innovator in conservation agriculture. Giacomazzi discovered conservation agriculture not long after taking over day-to-day operations of the Giacomazzi dairy from his father.

“It’s less work for more money,” Giacomazzi said. “Why aren’t people doing it? What’s the holdup?”

Perhaps in answer to his own question, Giacomazzi shared the reaction of his father to the new system being used on their farm. In their last conversation, the elder Giacomazzi lamented that, “Everything I’ve ever done, you’ve undone,” his son related at the meeting.

Dino Giacomazzi said many farmers’ tendency to be “enthralled” with tradition, their fierce independence, aversion to risk and fear of derision from neighbors contribute to their resistance to change. But accepting change is what is needed to adapt to a rapidly changing world.

Giacomazzi said the new Institute will play an important role in supporting farmers as they convert to conservation practices.

“This can’t be just a launch,” Giacomazzi said. “We must make this happen. Stay in touch.”

A video of the complete CASI January 27 launch meeting will soon be available at the Institute’s website http://ucanr.org/CASI.  

A farm advisor who has been instrumental in developing profitable niches for farmers was named "Outstanding Agricultural Educator" with a 2012 Pedro Ilic Award, for his dedication to small-scale farming.

Paul Vossen, UC Cooperative Extension advisor in Sonoma and Marin counties, accepted the award on March 5 at the California Small Farm Conference in Valencia.

"Paul has contributed tremendously to the success of the growing California olive oil industry," said Shermain Hardesty, who presented the award and is director of UC's small farm program. "Paul helps farmers connect with consumers who are willing to pay the price premiums necessary for their high-quality products. And he was one of the first to recognize 'local' as a marketing attribute."

Vossen is one of the founders of the UC Davis Olive Center. He was also instrumental in the first organic production manuals published by the university, which were for apples and olives. He conducts field research on specialty crops, including tree fruit, berries and vegetables, to share with farmers in his region and throughout California.

Vossen was nominated by Stephanie Larson and Linda Garcia, current and past directors of UC Cooperative Extension in Sonoma County.

"Paul Vossen has passion, energy and enthusiasm for his profession and his clientele," they wrote. "He easily moves from teaching farm workers to discussing olive oil production with an olive grower visiting from Spain."

Vossen knew and worked with the award's namesake, Pedro Ilic.

"One of the really neat things about Pedro was that he was so passionate about the small farmer, and I really think that's why this award lives on," he said. "He was such a hard worker and so dedicated to the small farmer."

Ilic's untimely death in 1994 prompted the UC Small Farm Program to annually honor those who carry on his legacy of personal commitment to small-scale and family farming. Ilic was a UC Cooperative Extension farm advisor in Fresno County and one of the original advisors of the Small Farm Program when it was established in 1979.