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Applied Research Projects at Nickels Soil Lab

Plots in the preplanning stage (no commitments from Nickels, no funding sources)

  • Pistachio rootstock trial (2025?)
    • Rootstocks, planted under the same pistachio varieties, will be compared for orchard health and production.
  • Olive oil demonstration planting (2025?)
    • Demonstrate the limited input practices that manage vigor and deliver high quality oil.
  • Low irrigation almond rootstock trial on self-fertile almond (2025?)
    • Evaluate almond production (of the same almond variety planted) on various almond rootstock irrigated with either 1) full irrigation or 2) less than full irrigation (for example, 2 acre-feet per acre, approximately 50% of expected water use of fully mature orchard).
  • Walnut orchard whole orchard recycling + nitrogen fertilizer trial. (?)
    • A productive 7-acre walnut block at Nickels would be removed, chipped, the chips spread and incorporated into the site, and a new walnut orchard planted. A nitrogen (N) fertilizer trial would then initiated in the first year of planting to determine the appropriate rate to maintain good tree growth without excessive N fertilization. Measurements of carbon flux from the soil would also be taken with an experienced collaborator.

Specific current pomology research projects. Except where noted, trials are replicated for statistical analysis and are ongoing. The first year of the study appears in parenthesis. Except where noted, the planners/organizers are F. Niederholzer, B. Lampinen and S. Cutter.

  1. Orchard recycling/fumigation trial (2019): Ag burning regulation in the Sacramento Valley may soon eliminate the option for growers to push and burn old orchards. Chipping the old orchard, spreading the chips and mixing into the soil is one way to clear a site and possibly improve the soil for the next planting. This 20-acre orchard compares tree growth and yield for almond trees (‘Nonpareil’ and ‘Carmel’ varieties on ‘Nickels’ peach/almond hybrid) with preplant chip incorporation (0, 25, or 50 tons/acre of chips from the previous orchard) with or without Telone/chloropicrin fumigation before planting. Irrigation is by full coverage micro-sprinkler. Project leader: G. Browne, USDA.
  2. Walnut rootstock trial (2019): This trial compares ‘Chandler’ walnut performance (growth and yield) using different rootstocks (industry standards plus new selections) in a replant site (walnuts following walnuts) with or without Telone/chloropicrin fumigation (preplant). Irrigation is by micro-sprinkler irrigation. Project leader: Dr. Andres Westfahl, UC Riverside.
  3. Almond spacing trial (2017): Compares nut yield, tree size, and tree health of ‘Nonpareil’ (50%), ‘Aldrich’ (25%), or ‘Kester’ (25%) almonds on a vigorous (‘Titan’; peach/almond hybrid) or less vigorous (‘Rootpac-R’; almond/plum hybrid) rootstocks at 12’, 14’, 16’, or 18’ tree spacing. All rows are 21’ apart and irrigation is by double-lined drip.
  4. Phosphorus fertilization trial (2017): Built into the spacing trial (3), this experiment compares yield of all varieties with or without phosphorus (P) fertilizer applied to replace crop P use (roughly 25 lb P2O5 per 1000 lbs kernel crop).
  5. Self-fertile vs Nonpareil/pollinizer trial (2013): Planted in 2013, this trial compares yield and gross income per acre between a solid (100%) planting of ‘Independence’ almond and a Nonpareil/Sonora/Aldrich (50%/25%/25%) planting. All trees are on Viking rootstock (20’ x 15’ spacing) with double-line drip irrigation.
  6. Compost in the berm (2013): Can compost improve almond production? Yard waste compost (5 tons/acre) was incorporated into the berms in the trial described above (5), ahead of planting in 2013. Yield and tree size (light interception) are measured each year to evaluate possible performance benefits from the compost vs no compost.
  7. Nonpareil pollinizer options (2006): What pollinizers produce the best overall returns with Nonpareil in any given year? Planted in 2006, this planting compares Nonpareil production and overall Nonpareil/pollinizer performance (yield and income) for three combinations of Nonpareil (50%) and two pollinizers (25%, each). Pollinizer combinations are 1) Monterey/Fritz, 2) Aldrich/Winters, and 3) Winters/Monterey. Spacing is 16’ x 22’ on Lovell peach seedling and irrigation is by double-line drip. Planned and planted by J.P. Edstrom and S. Cutter.
  8. Organic almond demonstration (2006): What are the biggest challenges to organic almond production in the southwestern Sacramento Vally? To look at this question, a comparison of organic and conventional almond production practices were established in a 6-acre orchard in the same production system (spacing, irrigation, etc). Nitrogen fertility and weed control are significant current challenges. Planned and planted by J.P. Edstrom, W. Krueger, and S. Cutter.
  9. Irrigation trials (2008): What benefits are there from variable rate, on-demand almond irrigation triggered by plant stress measurements? For a decade, UC Davis researchers have been testing irrigation monitoring devices to irrigate different sections of a 5-acre block (‘Nonpareil’, ‘Butte’, ‘Aldrich’) on double line drip. Project leaders: S. Upadhyaya and I. Kinseka, UC Davis
  10. Mechanical harvesting for table olives (2000): With labor costs rising, can mechanical harvesting replace labor and/or keep harvest costs low? A 2 acre olive (Manzanillo/Sevillano) orchard is used to test the mechanical harvest options for table olives. Orchards spacing is 12’ x 18’ (202 trees/acre) with single-line drip irrigation. Project leaders: L. Ferguson and W. Krueger, UC Davis.
  11. Almond pruning trial (1997): Planted on Lovell peach seedling rootstock (22’ x 16’), this 7-acre planting compares yield from almond trees (Nonpareil, Monterey, Carmel, and Aldrich) pruned annually vs those only pruned once (to select scaffolds in the first dormant season). There is no difference in yield, annual or cumulative, for each pruning practice for Nonpareil or Monterey through the life of the orchard. Planned and planted by J.P. Edstrom and S. Cutter.
  12. Almond rootstock trial (1997): A 13-acre trial compares Nonpareil nut yield on seven different rootstocks highly vigorous (Nickels, Hansen, and Brights, three peach/almond seedling) and standard size (Lovell or Nemaguard peach seedling and Viking or Atlas intra-specifc hybrid). Irrigation is by full coverage microsprinklers. Planned and planted by J.P. Edstrom and S. Cutter.



  • Micro-irrigation trial comparing yield single line drip, double-line drip, buried drip and microsprinkler irrigation. See the article reporting on this project in California Agriculture.
  • Drought trial in almonds testing if trees would survive/recover from very high levels of drought (0 to 10” irrigation water all season).

Walnut trials:

  • Hedgerow walnuts on Class 2-3 soil. Planted in 1986, this was an early walnut planting on poorer quality soils when much of the acreage was on deep soils along or near rivers and streams. Read the 2000 report to the California Walnut Board on this project by clicking HERE.
  • Pruning trial in ‘Howard’ walnuts comparing pruned and unpruned trees for 8 years starting the year after planting. See the article reporting on this project in California Agriculture.
  • ‘Chandler’ walnut pruning trial (2008) compared tree size and yield from Chandler/Paradox seedling tress under 3 pruning treatments (heavy, light or no pruning) through 2015 (8th leaf). Unpruned trees produced more crop early in the life of the orchard, but cumulative yields were not different by the fifth harvest. Click HERE to read the final report to the California Walnut Board.
  • Thousand canker disease damages walnuts in non-farm settings, but potential damage to commercial plantings was untested. Research began in 2014. Read the 2016 report by clicking HERE. High density almond production

High density almond production:

  • Research in the 1980’s examined the long-term economic value of removing every-other tree in tight (7’) tree-spacing down the row compared to keeping the trees.

Nutrition/fertility trials:

  • Soil applied potassium and foliar nutrition trials in the late ‘90s by Dr Rollie Meyer compared multiple treatments for yield benefit.
  • Postharvest nitrogen (N) fertilization study (2015-17) testing the impact of fall N application on yield the following year.
  • Soil carbon levels were determined in two orchards at Nickels (conventional and young organic) as well as several other orchards in the region. To see the article in California Agriculture, click HERE.