California Agriculture, January-February 1996
Volume 50, Number 1
Urban forests add $3.8 billion to economy
peer-reviewed research articles
Urban forestry adds $3.8 billion in sales to California economy
by Scott R. Templeton , George Goldman
Urban forests provide tree products and aesthetic, recreational, health and environmental benefits. Californians spent at least $1.080 billion to obtain these benefits and the state's urban forestry sector had sales of at least $1.248 billion in a 12-month period in the early 1990s. As a result of ripple effects, urban forestry accounted for at least $3.789 billion in total sales, $2.092 billion in income to individuals, and 64,000 jobs in this period in the state. Knowledge of this economic activity is necessary for voters and government officials who make decisions that affect management of these and other natural resources in California.
Farmers describe irrigation costs, benefits: Labor costs may offset water savings of sprinkler systems
by Dennis Wichelns , Laurie Houston , David Cone , Qiming Zhu , James Wilen
In recent years San Joaquin Valley farmers have improved irrigation methods to reduce subsurface drain water and make more efficient use of limited water supplies. Water-saving methods include sprinklers and gated pipe. However, these methods involve higher labor and energy costs, which may exceed the value of water saved when switching from surface irrigation methods, such as furrow irrigation with siphon tubes. Although more expensive, when sprinklers are used correctly they provide better leaching of salts while generating less subsurface drain water than surface methods. Public policies that reduce the capital cost of investing in sprinkler systems, and research to develop better surface irrigation methods, will assist farmers in continuing their efforts to improve irrigation water management while maintaining economic viability.
Silverleaf whiteflies show no increase in insecticide resistance
by Steve Castle , Tom Henneberry , Nick Toscano , Nilima Prabhaker , Steve Birdsall , Dick Weddle
The silverleaf whitefly (Bemisia argentifolii Bellows & Perring) continues to be a difficult pest to control in California's desert valleys. To gain a better understanding of the possible role that insecticide resistance plays in its annual outbreaks, a resistance monitoring program was established to document susceptibilities of whiteflies to various insecticides through time. Continuous monitoring during 1993 and 1994 detected no trend toward higher resistance levels. Higher toxicities of insecticide mixtures compared to single insecticides were regularly observed in bioassay results. Various factors including diverse insecticide use and altered cropping patterns may have helped to avoid serious insecticide resistance problems in the Imperial Valley so far.
Conversion to organic strawberry management changes ecological processes
by Stephen R. Gliessman , Matthew R. Werner , Sean L. Swezey , Ed Caswell , Jim Cochran , Francisco Rosado-May
A 3-year study on the Central Coast compared conventional and organic Chandler strawberry production systems on former Brussels sprouts land. Soil conditions, arthropod dynamics, soil microorganism populations and plant response factors were monitored and compared in both systems. Yields were significantly lower in the organic production system all 3 years, but the margin progressively narrowed. Price premiums for organic fruit permitted favorable per-acre returns for this system. Further research on ecological processes, improved practices and farm trials is needed to make organic systems more successful.
Rotator nozzles more uniform than spray nozzles on center-pivot sprinklers
by Blaine R. Hanson , Steve B. Orloff
In a comparison of Rotator and spray sprinklers on center-pivot sprinkler machines, uniformity of applied water was higher for the Rotator sprinklers. Under wind conditions, uniformity increased for the spray sprinklers and decreased for the Rotator sprinklers. Modifications to the sprinkler spacing are recommended when using the Rotator sprinklers.
Variable-frequency drives for electric irrigation pumping plants save energy
by Blaine R. Hanson , Claus Weigand , Steve Orloff
The constant rpm (revolutions per minute) of electric motors prevents adjusting pump performance to match variable operating conditions, and therefore the pump output is usually reduced or throttled. Variable-frequency drives of electric motors have the potential to adjust pump performance to match operating conditions by reducing motor and pump rpm. Field tests at five sites showed that pump performance at the reduced rpm could reasonably match that under the throttled conditions, but at a much lower horsepower demand. However, for economic reasons, pumping plants using a variable-frequency drive should be operated at least 1,000 hours per year.
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