Efficient irrigation: Micro-irrigation work starting in the 1970's and running through the 1990's showing the value of drip or micro-sprinklers in almond production on imperfect soils (rolling terrain with gravelly topsoil and heavy subsoil).
Fertilizer trials for efficacy and efficiency focused on boron, phosphorus, potassium, and/or nitrogen (1980—today). Documented significant yield increases from fall boron sprays when trees are B deficient. Showed little difference in yield and leaf K if similar amounts of K were delivered as SOP, MOP, KTS, or MKP. Documented lack of yield benefit from fall applied nitrogen (N) fertilizer in orchards with adequate N levels in July leaf samples, providing evidence that fall N fertilization is an inefficient practice in well-managed orchards.
Almond rootstocks and planting density: Rootstock trial (1997-2023) and down-the-row trees spacing trials (1970s to present). More vigorous peach x almond hybrid rootstocks produced larger trees and higher yield at wide spacing. This trial supported the shift away from 'Lovell' peach seedling to newer roostocks (Viking and peach x almond hybrids such as Hanson, Brights, and Nickels). Closer plantings (7 to 12' down the row) can be more productive than wider (18' down the row) spacing. Removing every-other tree as the trees grow is less productive on a cumulative basis than leaving the closely planted trees.
Self-fertile vs self-infertile planting systems: Independence vs Nonpareil + pollinators (2013-present). Independence is a consistent bearer in this trial, but NP+pollinizers does better in good nut set weather.
Walnut production on marginal soils was tested beginning in the 1980’s. With micro-irrigation and fertigation, walnut production is commercially feasible on lower quality soils compared to deep, naturally fertile soils near rivers and streams on the valley floor.
Annual pruning of almonds and walnuts was documented to not improve crop yield compared to no pruning after the first year. This outcome saves growers money.