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California Agriculture, Vol. 50, No.2

Does firewood harvesting outpace tree growth?
Cover:  UC researchers monitor regeneration and stand structure in Tehama County to determine if tree growth has outpaced firewood harvest. Photo by Richard Standiford
March-April 1996
Volume 50, Number 2

Peer-reviewed research and review articles

Impact of firewood harvesting on hardwood rangelands varies with region
by Richard B. Standiford, Douglas McCreary, Sheila Barry, Larry Forero, Ron Knight
| Full text HTML  | PDF  
Policies to conserve hardwood range-lands will be more effective if developed locally.
Aerial monitoring of hardwood rangelands over a 4-year period revealed that almost 70,000 cords of firewood ware harvested annually on approximately 6,000 acres. This represents less than 0.1% of the total hardwood rangeland in the state. Over 50% of the firewood volume harvested during these 4 years was in Shasta and Tehama counties, although these two counties represent less than 10% of the hardwood rangeland acreage in the state. In Tehama County, tree growth outpaced harvest, but in Shasta County, harvest exceeded growth by 30%. Both counties' governments adopted resolutions calling for a retention of 30% crown cover following firewood harvest. This retention level attempts to balance the needs for profitable livestock management with wildlife habitat needs.
Harvesting forest biomass reduces wildfire fuel
by Gary Nakamura
| Full text HTML  | PDF  
Thinning small understory trees, which act as fuel ladders into the crowns of larger trees, may prevent uncontrollable wildfires.
Years of drought, tree mortality due to insects and the successful suppression of forest fires over the past century have created dense stands of trees and shrubs. This buildup is potentially dangerous as a reservoir of fuel for uncontrollable wildfires in California forests. The advent of biomass power plants has made removal of excess plant material from the forest economically feasible, reducing wildfire hazard and preparing fire-adapted forests for reintroduction of prescribed fire.
Grower beliefs determine hiring practices
by Sabrina J. Isé, Jeffrey M. Perloff, Steve R. Sutter, Suzanne Vaupel
| Full text HTML  | PDF  
Growers list reliability of labor source and reduced recordkeeping among reasons for using farm labor contractors.
The use of farm labor contractors (FLCs) has increased over the last decade. Of 51 Fresno County growers surveyed, at least half had used an FLC by 1991; one-third had done so by 1985. The objective of this study was to find out why some growers use FLCs, while others prefer to hire workers directly. Although grower profiles do not differ markedly, the two groups hold different perceptions about the advantages of each labor group. Direct-hire growers rate direct-hire workers higher on quality of work and productivity, whereas indirect-hire growers list reliability of labor source as a critical factor influencing their decision.
Ozone air pollution increases spray oil phytotoxicity
by William A. Retzlaff, William W. Barnett, Larry E. Williams, Theodore M. DeJong
| Full text HTML  | PDF  
Petroleum spray oil injury was more prevalent on plum trees exposed to higher ozone concentrations.
In 1992, a moderate to severe outbreak of spider mites was found in ‘Casselman’ plum trees exposed to three atmospheric ozone air pollution treatments. Five days after spraying with a summer application of a medium grade oil, phytotoxic effects were observed on the foliage of trees exposed to ambient or higher atmospheric ozone air pollution. This research indicates that ozone air-pollution stress may predispose plants to increased phytotoxicity from summer oils.
Verticillium wilt threatens coastal cauliflower crop
by Steven T. Koike, Krishna V. Subbarao, R. Michael Davis, Thomas R. Gordon
| Full text HTML  | PDF  
All of the cauliflower cultivars tested, both commercially available and experimental selections, were susceptible to the disease Verticillium wilt.
For the first time, cauliflower has been found to he a host of the destructive soil-home pathogen Verticillium dahliae. Incidence of this disease is spreading throughout cauliflower-growing regions in coastal California, resulting in crop yield and quality losses. All of the tested cauliflower cultivars, both commercially available and experimental selections, were susceptible to the disease. Initial tests indicate that non-tarped fumigants are not effective against this disease.
Overinflated tractor tires waste fuel, reduce productivity
by Kleber P. Lancas, Shrini K. Upadhyaya, Muluneh Sime, Sayedahmad Shafii
| Full text HTML  | PDF  
Using a low/correct inflation pressure for radial ply tractor tires can save significant time and money and reduce soil compaction.
Under typical California farming conditions, field experiments have shown that using a low/correct inflation pressure for radial ply tires can result in significant sayings in time and money. It can also lessen soil compaction and help control power-hop in mechanical front-wheel drive and four-wheel drive tractors. In tilled, moist Capay clay soil, the tractor using low/correct tire pressure required 20% less diesel fuel and productivity increased 5.7% during the same stubble-disking operation.
Nitrogen isotope ratios identify nitrate contamination sources
by Dennis E. Rolston, Graham E. Fogg, David L. Decker, Dianne T. Louie, Mark E. Grismer
| Full text HTML  | PDF  
Nitrates from different sources have different nitrogen isotope ratios.
Nitrate contamination of groundwater is becoming a widespread problem in California. To evaluate the utility of stable nitrogen isotopes for identifying sources of nitrate contamination, nitrogen isotope ratios (?15N) were measured on nitrate extracted from core samples taken below natural, fertilizer, on-site sewage disposal (septic) and animal sources in the Sacramento and Salinas valleys. The mean ?15N value from natural sources was not significantly different from that of fertilizer sources. The mean ?15N value from animal sources was significantly different from that of septic sources and natural and/or fertilizer sources. Nitrogen isotope ratios tend to be site specific and should be measured below suspected sources in the subsurface and in groundwater.
How does water price affect irrigation technology adoption?
by Gareth Green, David Sunding, David Zilberman, Doug Parker, Cliff Trotter, Steve Collup
| Full text HTML  | PDF  
Crop type, topography and soil type appear to be major considerations in making irrigation technology choices.
The use of water price or best management practices have been advocated by some commentators to induce adoption of low-volume irrigation technologies and to encourage water use efficiency. However, the method of water application is only one of many inputs and constraints in agricultural production. California's highly diverse topography, soil types and variety of crops influence irrigation technology choices, therefore a policy mandating adoption of modern technologies is likely to have undesirable impacts. Crop type appears to be a major consideration in technology choice, as some technologies may be incompatible with some types of crops.

Editorial, News, Letters and Science Briefs

UC can build on land-grant idea
by Richard C. Atkinson
Full text HTML  | PDF  
UC after-school programs reach inner-city kids
by Editors
Full text HTML  | PDF  
Farm programs overhauled
by Editors
Full text HTML  | PDF  
Putah Creek update
by Editors
Full text HTML  | PDF  
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California Agriculture, Vol. 50, No.2

Does firewood harvesting outpace tree growth?
Cover:  UC researchers monitor regeneration and stand structure in Tehama County to determine if tree growth has outpaced firewood harvest. Photo by Richard Standiford
March-April 1996
Volume 50, Number 2

Peer-reviewed research and review articles

Impact of firewood harvesting on hardwood rangelands varies with region
by Richard B. Standiford, Douglas McCreary, Sheila Barry, Larry Forero, Ron Knight
| Full text HTML  | PDF  
Policies to conserve hardwood range-lands will be more effective if developed locally.
Aerial monitoring of hardwood rangelands over a 4-year period revealed that almost 70,000 cords of firewood ware harvested annually on approximately 6,000 acres. This represents less than 0.1% of the total hardwood rangeland in the state. Over 50% of the firewood volume harvested during these 4 years was in Shasta and Tehama counties, although these two counties represent less than 10% of the hardwood rangeland acreage in the state. In Tehama County, tree growth outpaced harvest, but in Shasta County, harvest exceeded growth by 30%. Both counties' governments adopted resolutions calling for a retention of 30% crown cover following firewood harvest. This retention level attempts to balance the needs for profitable livestock management with wildlife habitat needs.
Harvesting forest biomass reduces wildfire fuel
by Gary Nakamura
| Full text HTML  | PDF  
Thinning small understory trees, which act as fuel ladders into the crowns of larger trees, may prevent uncontrollable wildfires.
Years of drought, tree mortality due to insects and the successful suppression of forest fires over the past century have created dense stands of trees and shrubs. This buildup is potentially dangerous as a reservoir of fuel for uncontrollable wildfires in California forests. The advent of biomass power plants has made removal of excess plant material from the forest economically feasible, reducing wildfire hazard and preparing fire-adapted forests for reintroduction of prescribed fire.
Grower beliefs determine hiring practices
by Sabrina J. Isé, Jeffrey M. Perloff, Steve R. Sutter, Suzanne Vaupel
| Full text HTML  | PDF  
Growers list reliability of labor source and reduced recordkeeping among reasons for using farm labor contractors.
The use of farm labor contractors (FLCs) has increased over the last decade. Of 51 Fresno County growers surveyed, at least half had used an FLC by 1991; one-third had done so by 1985. The objective of this study was to find out why some growers use FLCs, while others prefer to hire workers directly. Although grower profiles do not differ markedly, the two groups hold different perceptions about the advantages of each labor group. Direct-hire growers rate direct-hire workers higher on quality of work and productivity, whereas indirect-hire growers list reliability of labor source as a critical factor influencing their decision.
Ozone air pollution increases spray oil phytotoxicity
by William A. Retzlaff, William W. Barnett, Larry E. Williams, Theodore M. DeJong
| Full text HTML  | PDF  
Petroleum spray oil injury was more prevalent on plum trees exposed to higher ozone concentrations.
In 1992, a moderate to severe outbreak of spider mites was found in ‘Casselman’ plum trees exposed to three atmospheric ozone air pollution treatments. Five days after spraying with a summer application of a medium grade oil, phytotoxic effects were observed on the foliage of trees exposed to ambient or higher atmospheric ozone air pollution. This research indicates that ozone air-pollution stress may predispose plants to increased phytotoxicity from summer oils.
Verticillium wilt threatens coastal cauliflower crop
by Steven T. Koike, Krishna V. Subbarao, R. Michael Davis, Thomas R. Gordon
| Full text HTML  | PDF  
All of the cauliflower cultivars tested, both commercially available and experimental selections, were susceptible to the disease Verticillium wilt.
For the first time, cauliflower has been found to he a host of the destructive soil-home pathogen Verticillium dahliae. Incidence of this disease is spreading throughout cauliflower-growing regions in coastal California, resulting in crop yield and quality losses. All of the tested cauliflower cultivars, both commercially available and experimental selections, were susceptible to the disease. Initial tests indicate that non-tarped fumigants are not effective against this disease.
Overinflated tractor tires waste fuel, reduce productivity
by Kleber P. Lancas, Shrini K. Upadhyaya, Muluneh Sime, Sayedahmad Shafii
| Full text HTML  | PDF  
Using a low/correct inflation pressure for radial ply tractor tires can save significant time and money and reduce soil compaction.
Under typical California farming conditions, field experiments have shown that using a low/correct inflation pressure for radial ply tires can result in significant sayings in time and money. It can also lessen soil compaction and help control power-hop in mechanical front-wheel drive and four-wheel drive tractors. In tilled, moist Capay clay soil, the tractor using low/correct tire pressure required 20% less diesel fuel and productivity increased 5.7% during the same stubble-disking operation.
Nitrogen isotope ratios identify nitrate contamination sources
by Dennis E. Rolston, Graham E. Fogg, David L. Decker, Dianne T. Louie, Mark E. Grismer
| Full text HTML  | PDF  
Nitrates from different sources have different nitrogen isotope ratios.
Nitrate contamination of groundwater is becoming a widespread problem in California. To evaluate the utility of stable nitrogen isotopes for identifying sources of nitrate contamination, nitrogen isotope ratios (?15N) were measured on nitrate extracted from core samples taken below natural, fertilizer, on-site sewage disposal (septic) and animal sources in the Sacramento and Salinas valleys. The mean ?15N value from natural sources was not significantly different from that of fertilizer sources. The mean ?15N value from animal sources was significantly different from that of septic sources and natural and/or fertilizer sources. Nitrogen isotope ratios tend to be site specific and should be measured below suspected sources in the subsurface and in groundwater.
How does water price affect irrigation technology adoption?
by Gareth Green, David Sunding, David Zilberman, Doug Parker, Cliff Trotter, Steve Collup
| Full text HTML  | PDF  
Crop type, topography and soil type appear to be major considerations in making irrigation technology choices.
The use of water price or best management practices have been advocated by some commentators to induce adoption of low-volume irrigation technologies and to encourage water use efficiency. However, the method of water application is only one of many inputs and constraints in agricultural production. California's highly diverse topography, soil types and variety of crops influence irrigation technology choices, therefore a policy mandating adoption of modern technologies is likely to have undesirable impacts. Crop type appears to be a major consideration in technology choice, as some technologies may be incompatible with some types of crops.

Editorial, News, Letters and Science Briefs

UC can build on land-grant idea
by Richard C. Atkinson
Full text HTML  | PDF  
UC after-school programs reach inner-city kids
by Editors
Full text HTML  | PDF  
Farm programs overhauled
by Editors
Full text HTML  | PDF  
Putah Creek update
by Editors
Full text HTML  | PDF  

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