Impact of whole orchard recycling on management of almond replant problems

Four replant trials were conducted in California’s San Joaquin Valley (SJV) to examine interactions of whole orchard recycling (WOR) and preplant soil fumigation. Soil fumigation has been used to manage Prunus replant disease and phytopathogenic nematodes, which are the most important replant problems of almond in the valley. WOR, the process of chipping or grinding an old orchard’s biomass and incorporating it into soil, is widely used in the SJV as an alternative to burning and offers environmental and agronomic benefits, but its impact on almond replant problems has not been explored in terms of crop yields. In all four trials, preplant fumigation benefited crop yields, providing evidence for site replant problem(s). WOR generally did not affect the benefit of fumigation, but on cultivar ‘Monterey’, yields in one trial were affected by significant WOR × fumigation interaction; WOR increased ‘Monterey’ yield in non-fumigated soil but not in fumigated soil. ‘Nonpareil’ yields were increased by a significant main effect of WOR, both in fumigated and non-fumigated soil. Collectively, the results indicated that WOR does not increase risk of almond replant problems, but, instead, depending on cultivar, WOR may increase almond yields, either by lessening impacts of replant problem(s) or by improving crop performance regardless of replant problem presence.