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Open Access Publications from the University of California

Volume 67, Issue 4, 2013

Cultivating urban agriculture

Issue cover
Cover Caption: Complete contents, including news and editorial featuresUrban agriculture is growing statewide, as California cities increasingly allow food plants in front yards and under power lines, and bee hives and chicken coops in backyards. To help city dwellers produce food proficiently and safely, UC Cooperative Extension is developing research-based best practices for urban agriculture (page 199). In addition, the California Animal Health and Food Safety laboratory system offers free post-mortems for backyard poultry through the Backyard Flock program (page 203). This diagnostic service enables researchers to collect data on disease trends and can help amateur poultry producers keep their flocks healthy. Photo by Peter Bennett,

Research and Review Articles

Popular Backyard Flock program reduces biosecurity risks of amateur production

The California Animal Health and Food Safety laboratories provide free necropsy (postmortem examination) services to owners of backyard poultry through the Backyard Flock program funded by the California Department of Food and Agriculture. We collected and analyzed data on the number of poultry submissions to the program between 2007 and 2012, the lab totals by location and the diseases diagnosed. During those 6 years, submissions increased 383%, with chickens representing 91% of them, and the greatest increases occurred in Santa Clara, Los Angeles and Sonoma counties. The necropsy data showed that the digestive (32.5%) and hemolymphatic (16.9%) systems were the most commonly affected. Marek’s disease accounted for 13.3% of diagnoses (492 cases). With the rapid rise in the number of poultry being raised by amateur producers, biosecurity education is essential.

Testing protocol ensures the authenticity of organic fertilizers

There is a pressing need for methodology to confirm the authenticity of fertilizers labeled “suitable for organic production.” In this study, we developed a testing protocol that can be used by laboratories and regulatory agencies to detect adulteration of organic fertilizers and soil amendments with a synthetic nitrogen source. By conducting an extensive literature review and analysis of 180 commercially available raw materials, organic fertilizers, soil amendments and synthetic fertilizers, we compiled a comprehensive database of quantifiable properties of those materials. We analyzed their ammonium content, C:N ratio and stable nitrogen isotope ratio, and for each metric we set thresholds that flag products with a high probability of adulteration. The protocol can be used to authenticate organic fertilizer products and bring transparency to the industry.

Totally impermeable film (TIF) reduces emissions in perennial crop fumigation

Many perennial nursery fields and replanted orchards and vineyards in California are treated with preplant soil fumigants to control soilborne pests. In annual crops, such as strawberry, covering fumigated fields with totally impermeable film (TIF) has shown promise in controlling emissions and improving fumigant distribution in soil. The objective of this research was to optimize the use of TIF for perennial crops via three field trials. TIF reduced peak emission flux and cumulative emissions by > 90% relative to polyethylene tarp during a 2-week covering period. After the TIF was cut, emissions were greatly reduced compared to when tarps were cut after 6 days. TIF maintained higher fumigant concentrations under tarp and in the soil than polyethylene film. The results indicate that TIF can increase fumigation efficiency for perennial crop growers.


Tractor-mounted, GPS-based spot fumigation system manages Prunus replant disease

Our research goal was to use recent advances in global positioning system (GPS) and computer technology to apply just the right amount of fumigant where it is most needed (i.e., in a small target treatment zone in and around each tree replanting site) to control Prunus replant disease (PRD). We developed and confirmed the function of (1) GPS-based software that can be used on cleared orchard land to flexibly plan and map all of an orchard's future tree sites and associated spot fumigation treatment zones and 2) a tractor-based GPS-controlled spot fumigation system to quickly and safely treat the targeted tree site treatment zones. In trials in two almond orchards and one peach orchard, our evaluations of the composite mapping and application system, which examined spatial accuracy of the spot treatments, delivery rate accuracy of the spot treatments, and tree growth responses to the spot treatments, all indicated that GPS spot fumigation has excellent potential to greatly reduce fumigant usage while adequately managing the PRD complex.


Soil type, crop and irrigation technique affect nitrogen leaching to groundwater

Many groundwater resource in California are degraded by high concentrations of nitrate, most of which was transported to the groundwater in water percolating below the root zone of agricultural fields. Factors that affect the rate of water percolation — including soil type, crop and irrigation — along with nitrogen application influence the probability of this type of groundwater degradation. UC scientists have developed several useful tools, including the Nitrogen Hazard Index (NHI) and the ENVIRO-GRO (E-G) model, for use in developing best management practices (BMPs) to achieve high crop yields while minimizing groundwater degradation. We report the results of E-G simulations that quantify the effects of irrigation, soil type and organic and inorganic nitrogen (N) application amounts to corn yield and the amount of leached N. Simulation results indicate that a nitrate management strategy that also includes water management will be more effective in reducing N loading to groundwater. The research findings are discussed in the context of the track and report concept in comparison to the BMP approach.