Saline irrigation in young pistachio Kerman trees on UCB-1 and PG-1 rootstocks grown in field lysimeters

Authors: VANG, KAOMINE - California State University; Banuelos, Gary; MARINO, GIULIA - Kearney Agricultural Center; FERGUSON, LOUISE - University Of California - Cooperative Extension Service; SOMMERHALTER, MONIKA - California State University; REYES, HERACLIO - Collaborator

Submitted to: California Pistachio Commission Production Research Report
Publication Type: Other
Publication Acceptance Date: 1/5/2023
Publication Date: N/A
Citation: N/A

Interpretive Summary: California is facing its fifth year of severe drought; a serious reality for growers in the San Joaquin Valley (SJV). Consequently, farmers are more dependent on pumping and utilizing poor quality groundwater that often contains excessive salts, boron (B) and selenium (Se). One major crop under serious consideration for irrigating with poor quality waters is pistachio. Practical knowledge is still needed on the age when pistachio trees can receive irrigation with poor quality waters. In our multi-year field lysimeter study, we have applied saline irrigation for over 4 years on young trees from both UCB-1 and PG-1 rootstocks. In these tree and soils, we studied ion accumulation and soil chemistry changes at different depths. Overall, visual effects on tree growth or the showing of toxicity symptoms, were not observed in leaves of either rootstock, except B toxicity symptoms (e.g., necrosis of leaf margins) were observed in PG-1 trees. Among the ions, only chloride levels increased with higher saline treatments in young and old leaves and were highest in old leaves of PG-1 rootstock. Soil analyses showed that the soil salinity and B increased with salinity treatments, but no salinity changes were observed at deepest depth. In conclusion, we have shown that young pistachio trees on either UCB-1 and PG-1 rootstock, can be safely irrigated with a range of salinity levels for at least four years grown in field lysimeters.

Technical Abstract: California is facing its fifth year of severe drought; a serious reality for growers in the San Joaquin Valley (SJV). Consequently, farmers are more dependent on pumping and utilizing poor quality groundwater that contains excessive salts, boron (B) and selenium (Se). For this reason, alternative salt and B-tolerant crops must be identified, if irrigated agriculture continues to use poor quality waters. One major crop under serious consideration for irrigation with poor quality saline waters is pistachio (Pistachio vera L.). Practical knowledge is needed on the age when pistachio trees can receive irrigation with poor quality waters. In our multi-year field lysimeter study, we have completed the fourth year of saline drip irrigation with the respective salinity treatments: <1 dS/m and 6 mg B/l, 4 dS/m and 6 mg B/L, 8 dS/m and 6 mg B/L, and 12 dS/m and 6 mg B/L on UCB-1 and PG-1 rootstocks budded to Kerman. In a complete randomized block design, 18-month-old trees were transplanted into in 1.5 in deep x 0.7 m field installed tiles filled with oxalis salty clay loam soil. Trees were drip irrigated with the respective saline treatments. Overall, trees on UCB-1 rootstock showed significantly better and more consistent growth than PG-1 rootstock for saline treatments. B toxicity symptoms (e.g., necrosis of leaf margins) were only observed in PG-1 trees with treatment 1 dS/m and 6 mg B/L. Leaf photosynthesis and physiological parameters, including leaf area and leaf chlorophyll data (with LICOR measurements) and stem water potential showed no differences among treatments (irrigation salinity levels and rootstocks), however, similar seasonal differences were observed for both rootstocks. Generally, Na levels were less than 100 mg/kg DM in old and young leaves of both rootstocks, irrespective of saline treatment. Cl levels increased with higher saline treatments in young and old leaves and were highest (12,000 mg/kg DM) in older leaves of PG-1 rootstock compared to 5000 mg/kg DM in UCB-1. In contrast to Cl accumulation, B concentrations were decreased with increased saline irrigation (<400 mg/kg DM) in both young and old leaves from both rootstocks and B concentrations were higher (> 840 mg/kg DM) at lower saline treatments, irrespective of rootstock. Soil analyses show the soil EC (dS/m) increased with salinity treatments and ranged from 1 to 13 dS/m at 0-60 cm, while soluble soil B ranged from 7-10 mg B/L at the same depth. These results show that irrigation with saline waters (up to 12 dS/m and 6 mg B/L) can safely be used on pistachio trees from both UCB-1 and PG-1 rootstocks for at least 4 years. Future investigations should evaluate potential toxic effects of saline irrigation once nut clusters consistently appear and influence the competition, movement, and uptake of ions and water within the trees.