Field Evaluation of Sixteen Rootstocks for Almonds Grown in Heavy Soil and Irrigated with Water High in Sodium, Chloride and Boron

Almond (P. dulcis) acreage has approximately doubled in California during the past twenty years and now totals about 1.1 million acres. As traditional orchard land is becoming scarce, many new almond orchards are being planted in marginal soils and are irrigated with water considered to be too high in sodium, chloride and/or boron for maximum production using traditionally-used peach rootstocks such as Nemaguard and Lovell. A field trial was planted in 2011 on the west side of the San Joaquin Valley to evaluate sixteen commercially-available rootstocks budded to the almond scion ‘Nonpareil’. The soil is a Zacharias clay loam (pH 7.6, 0.5 ppm boron, 12.1 meq/l Na, 14.1 meq/l Cl, EC = 2.96 dS/m) and the trees are irrigated with ground water marginally high in salt (adjusted SAR = 8.80, 8.90 meq/L chloride, 0.84 mg/l boron). Rootstocks tested included Lovell & Nemaguard (P. persica), Empyrean 1 (a.k.a. Barrier 1) & Avimag (P. persica x P. davidiana), Rootpac R (P. cerasifera x P. dulcis), Krymsk 86 (P. cerasifera x P. persica) and several hybrids of peach and almond (Hansen 536, Brights 5, BB106, GF 677, Flordaguard x Alnem, PAC9908-01, Hansen x Monegro (HM2), Viking and Atlas. Leaves sampled from non-bearing spurs of fourth-season trees indicated that Lovell rootstock had the highest concentration of chloride (0.73%) (P<0.05), followed by Krymsk 86 and Nemaguard (0.65% and 0.43%, respectively). The critical maximum level for chloride in July-sampled almond leaves is 0.3%. HM2, Flordaguard x Alnem, GF 677, BB106, Brights 5, Hansen, Rootpac R and Viking had the lowest leaf chloride (0.18 – 0.25%). Lovell rootstock also had the highest concentration of boron in the hulls at harvest (180 ppm) while BB106, FxA, Brights 5, PAC9908-01 and Viking had the lowest hull levels of boron (102 – 109 ppm). The largest trees as measured by trunk circumference were PAC 9908-01, Empyrean 1 and Flordaguard x Alnem. The smallest trees were Krymsk 86, Cadaman, Lovell and GF 677.