Phosphorus fertilization can improve young almond tree growth in multiple replant settings

Authors: GORDON, PHOEBE - University Of California - Cooperative Extension Service; Ott, Natalia; BRAR, RAMAN - University Of California - Cooperative Extension Service; HOLTZ, BRENT - University Of California - Cooperative Extension Service; Browne, Greg

Submitted to: HortTechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/27/2023
Publication Date: 2/16/2024
Citation: Gordon, P.E., Ott, N.J., Brar, R.K., Holtz, B.A., Browne, G.T. 2024. Phosphorus fertilization can improve young almond tree growth in multiple replant settings. HortTechnology. 34(2):161-171. https://doi.org/10.21273/HORTTECH05143-22.
DOI: https://doi.org/10.21273/HORTTECH05143-22

Interpretive Summary: Young almond orchards replanted where old orchards of Prunus have been removed are subject to numerous, potentially interacting physical, chemical, and biotic stressors. Among biotic challenges, for example, is Prunus replant disease (PRD), a Prunus-specific early growth- and yield-suppressing complex mediated in part by soil microbial communities. In four orchard trials representing different almond replant practices and scenarios in California’s San Joaquin Valley, we examined impacts of phosphorus fertilization on growth of replanted almond. In all trials, phosphorus was applied in the form of triple superphosphate to tree root zones just after replanting, and the impact was assessed according to trunk cross sectional area (TCSA) growth for at least 2 years. Trial 1 occurred where old almond orchard was cleared using whole orchard recycling (WOR; i.e., which is a process in which the old trees are pushed out of the ground, chipped by a tree grinder, and finally incorporated into the soil). The land was replanted without preplant soil fumigation. Here we tested not only phosphorus fertilization with triple superphosphate but also fertilization with additional phosphorus-containing, nitrogen, micronutrient, and “complete” formulations. Trial 2 also occurred where an old almond orchard was recycled, but the soil was preplant fumigated before replanting. Here we tested only phosphorus fertilization. Trials 3 and 4 were conducted where an old peach orchard had been removed. Here phosphorus and nitrogen treatments were tested amongst additional factors, including preplant soil fumigation (trials 3, 4) and WOR chips (trial 4). In all four trials, phosphorus fertilization (142 to 170 g P2O5 tree-1) significantly increased TCSA growth within the first 2 years after planting. The growth benefit was nuanced, however, by almond cultivar, date of replanting, rootstock, and other site-specific factors. Our data indicated that, in diverse almond replant settings.

Technical Abstract: Young almond orchards replanted where old orchards of Prunus have been removed are subject to numerous, potentially interacting physical, chemical, and biotic stressors. Among biotic challenges, for example, is Prunus replant disease (PRD), a Prunus-specific early growth- and yield-suppressing complex mediated in part by soil microbial communities. In four orchard trials representing different almond replant practices and scenarios in California’s San Joaquin Valley, we examined impacts of phosphorus fertilization on growth of replanted almond. In all trials, phosphorus was applied to tree root zones just after replanting, and the impact was assessed according to trunk cross sectional area (TCSA) growth for at least 2 years. Trial 1 occurred where old almond orchard was cleared using whole orchard recycling (WOR) (i.e., it was chipped, then turned into the soil). The land was replanted without preplant soil fumigation. Here we tested separate fertilizer treatments based on various phosphorus, nitrogen, micronutrient, and “complete” formulations. Trial 2 also occurred where an old almond orchard was recycled, but the soil was preplant fumigated before replanting. Here we tested only phosphorus fertilization. Trials 3 and 4 were conducted where an old peach orchard had been removed. Here phosphorus and nitrogen treatments were tested amongst additional factors, including preplant soil fumigation (trials 3, 4) and WOR chips (trial 4). In all four trials, phosphorus fertilization (142 to 170 g P2O5 tree-1) significantly increased TCSA growth within the first 2 years after planting. The growth benefit was nuanced, however, by almond cultivar, date of replanting, rootstock, and other site-specific factors. Our data indicated that, in diverse almond replant settings, phosphorus fertilization commonly stimulates almond tree growth, though not to the extent resulting from effective preplant soil fumigation.