2017 ASHS Annual Conference

The almond industry is increasingly using trees that were produced in pots. Trees grown in pots are generally smaller have much more fibrous root systems than bare root tress. In this experiment, which started in February 2015, we planted both bare root and potted almond trees as part of a larger experiment where we also tested the impact of irrigation level (100%, 85% and 70% of normal) and pruning on both above- and belowground tree growth. The design included 4 blocks with 2 replicated treatments of each irrigation x pot x pruning combination using Nonpareil on Krymsk-86 rootstock for a total of 360 trees (n=8). Pruned versus unpruned trees were placed side by side within each irrigation. Each set of two Nonpareil trees was separated by a pollinizer tree (either Wood Colony or Monterey). The edge trees were irrigated at 100% and used for a separate experiment to test the impact of heading on growth of bare root Nonpareil trees. Pre-planting metrics showed that potted trees had 10x smaller stem cross section area and 15x less above- and belowground mass than bare root trees. However, they had twice the root length of bare root trees. Length produced per unit root mass was 16.5 m g^-1 for potted trees and 0.45 m g^-1 for bare root trees. Potted trees had a greater relative growth rate (RGR) than bare root trees and at the end of the second season were almost the same size. Differential irrigation began in 2016, where 30 inches were applied in the 100% treatment. As expected, trees receiving less irrigation had reduced RGR, however, the impact of pruning on both RGR and stem water potential was much greater than the impact of irrigation rate. On average, pruning reduced RGR by 30%, while irrigating at 70% only reduced RGR by 7-13%. Pruned trees experienced higher stem water potential (less water stress) than unpruned trees through July, at which point the pruned trees in the 100% started experiencing more water stress than unpruned trees. Data from the heading experiment on the edge trees show that deep (below 80 cm) root growth was delayed and reduced by canopy removal. Thus, once the canopy has recovered from pruning, lack of deep root growth may cause greater water stress in pruned trees later in the season.