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Open Access Publications from the University of California

Volume 71, Issue 2, 2017

Issue cover
Cover Caption: Complete contents, including news and opinion featuresA honeybee, Apis mellifera, collects pollen from an almond flower at Sloughside Farms in Yolo County. The golden bulb on the bee’s hind leg is pollen packed into a specialized structure called a pollen basket, or corbicula. Photo by Will Suckow.

Research and Review Articles

Field trials show the fertilizer value of nitrogen in irrigation water

Increased regulatory activity designed to protect groundwater from degradation by nitrate-nitrogen (NO3-N) is focusing attention on the efficiency of agricultural use of nitrogen (N). One area drawing scrutiny is the way in which growers consider the NO3-N concentration of irrigation water when determining N fertilizer rates. Four drip-irrigated field studies were conducted in the Salinas Valley evaluating the impact of irrigation water NO3-N concentration and irrigation efficiency on the N uptake efficiency of lettuce and broccoli crops. Irrigation with water NO3-N concentrations from 2 to 45 milligrams per liter were compared with periodic fertigation of N fertilizer. The effect of irrigation efficiency was determined by comparing an efficient (110% to 120% of crop evapotranspiration, ETc) and an inefficient (160% to 200% of ETc) irrigation treatment. Across these trials, NO3-N from irrigation water was at least as efficiently used as fertilizer N; the uptake efficiency of irrigation water NO3-N averaged approximately 80%, and it was not affected by NO3-N concentration or irrigation efficiency.

Yield in almond is related more to the abundance of flowers than the relative number of flowers that set fruit

Almond tree yield is a function of the number of flowers on a tree and the percentage of flowers that set fruit. Almonds are borne on spurs (short proleptic shoots that can have both leaves and flowers). Almond tree spur dynamics research has documented that previous year spur leaf area is a predictive parameter for year-to-year spur survival, spur flowering and to a lesser extent spur fruiting, while previous year fruit bearing has a negative impact on subsequent year flowering. However, a question remained about whether yields are more dependent on flower numbers or relative fruit set of the flowers that are present. The aim of the present work was to compare the importance of flower abundance with that of relative fruit set in determining the productivity of a population of tagged spurs in almond trees over a 6-year period. Overall tree yield among years was more sensitive to total number of flowers on a tree rather than relative fruit set. These results emphasize the importance of maintaining large populations of healthy flowering spurs for sustained high production in almond orchards.

Lessons learned: How summer camps reduce risk factors of childhood obesity

The purpose of this article is to present findings related to parent- and youth-reported outcomes from a nutrition- and fitness-themed summer camp targeting low-income families and to identify lessons learned in the implementation, evaluation and sustainability of a summer program. The Healthy Lifestyle Fitness Camp, offered through UC Cooperative Extension (UCCE), was a summer camp program for low-income youth at high risk for obesity. From 2009 to 2012, UCCE nutrition staff in Fresno County collaborated with the camp staff to provide a 6-week nutrition education program to the campers and their parents. Anthropometry and dietary data were collected from youth. Data about food preferences and availability were collected from youth and parents. As reported by parents in pre- to immediately post-camp surveys, Healthy Lifestyle Fitness campers consumed fruits and vegetables promoted at camp more often, relative to a comparison group of youth in a nearby non-nutrition themed camp. Summer programs may be an effective tool in the reduction of childhood obesity risk factors if implemented appropriately into the community and through the utilization of supportive partnerships such as UCCE and local parks and recreation departments.

Using InVEST to assess ecosystem services on conserved properties in Sonoma County, CA

Purchases of private land for conservation are common in California and represent an alternative to regulatory land-use policies for constraining land use. The retention or enhancement of ecosystem services may be a benefit of land conservation, but that has been difficult to document. The InVEST toolset provides a practical, low-cost approach to quantifying ecosystem services. Using the toolset, we investigated the provision of ecosystem services in Sonoma County, California, and addressed three related questions. First, do lands protected by the Sonoma County Agricultural Preservation and Open Space District (a publicly funded land conservation program) have higher values for four ecosystem services — carbon storage, sediment retention, nutrient retention and water yield — than other properties? Second, how do the correlations among these services differ across protected versus non-protected properties? Third, what are the strengths and weaknesses of using the InVEST toolset to quantify ecosystem services at the county scale? We found that District lands have higher service values for carbon storage, sediment retention and water yield than adjacent properties and properties that have been developed to more intensive uses in the last 10 years. Correlations among the ecosystem services differed greatly across land-use categories, and these differences were driven by a combination of soil, slope and land use. While InVEST provided a low-cost, clearly documented way to evaluate ecosystem services at the county scale, there is no ready way to validate the results.

Soil nitrate testing supports nitrogen management in irrigated annual crops

Soil nitrate (NO3 ) tests are an integral part of nutrient management in annual crops. They help growers make field-specific nitrogen (N) fertilization decisions, use N more efficiently and, if necessary, comply with California's Irrigated Lands Regulatory Program, which requires an N management plan and an estimate of soil NO3 from most growers. As NO3 is easily leached into deeper soil layers and groundwater by rain and excess irrigation water, precipitation and irrigation schedules need to be taken into account when sampling soil and interpreting test results. We reviewed current knowledge on best practices for taking and using soil NO3 tests in California irrigated annual crops, including how sampling for soil NO3 differs from sampling for other nutrients, how tests performed at different times of the year are interpreted and some of the special challenges associated with NO3 testing in organic systems.

News and Opinion

California's working landscapes offer opportunities for economic growth

Building sustainable livelihoods around our farms, ranches, forests and rivers.

How to study cannabis

Van Butsic is pioneering the study of how California's richest crop affects rural landscapes.

Coexisting with chaparral

Long-term studies at Hopland Research and Extension Center find no simple answers for reducing fire risk while conserving biodiversity.

After fire, the roles of rabbits and wildflowers

The dark ash left by a chaparral fire is rich in ammonium nitrogen; can the ecosystem absorb it before winter rains wash it away?

Apps for Ag winner launches community-building app in Davis

GivingGarden will connect neighbors through a produce-sharing service. It's superlocal, like NextDoor, but devoted solely to food and gardening.

Research highlights

Recently published articles from campus-based faculty and UC Cooperative Extension researchers at the Agricultural Experiment Station sites: UC Berkeley College of Natural Resources, UC Riverside College of Natural and Agricultural Sciences and UC Davis School of Veterinary Medicine and College of Agricultural and Environmental Sciences.