Field assessment of potential pistachio salt toxicity using the EM38

Abstract

The traditional concept of crop salt tolerance as a single soil saturation extract salinity threshold with a “% relative yield decline” function is over-simplified. This approach minimizes the real world variability in actual tree growth and yield due to the added effects of specific ion toxicity and soil texture and anoxia from soil saturation. The current salinity tolerance function for California pistachios was developed from a small plot study in an 8th-13th leaf orchard in northwestern Kern County from 1997-2002. Results from this trial and seedling growth studies in saline sand tanks at the USDA Salinity Lab indicated a threshold value of 9.4 dS m-1 ECe with an 8.4% decline above that value. A greatly expanded salinity survey across 520 km2 examining 10 commercial fields (540 ha total, 9th-15th leaf, centered 35.463 Lat., -119.500 Long.) in western Kern County with 140 individual tree data points was conducted from 2014-16. Average root zone (1.5 m depth) salinity was 1.6 to 20.5 dS m-1. A statistically significant yield reduction of 162-394 kg ha-1 (1-3%) was found in 3 year cumulative inshell yield for every unit ECe>6.5 dS m-1. However, the R2 was only 0.11. Yield by the Ln transformed EM38-ECa was R2=0.20. However, the best predictor of yield decline was the ln transforms of inshell yield and the simple sum of the uncalibrated vertical + horizontal raw EM readings adjacent to the tree, R2=0.35. The raw electromagnetic resonance readings from the EM38 will incorporate multiple factors such as possible anoxia due to high water content and poor soil structure with some influence of the soil mineralogy and pH along with total salt (EC).