Soil health indicators for Central Washington Orchards

The objective of this study was to initiate the steps to develop a soil assessment tool for irrigated orchard soils in Central Washington, United States including defining objectives, gathering baseline data and selecting target indicators.
A total of 97 apple (Malus domestica) orchard fields were sampled in Washington, United States between 2015 and 2020. Of these plots there were 30 matched pairs (60 plots) on the same or similar soil type with matching cultivar/rootstock, tree age and training system type. One field in each pair was high performing and the other underperforming based on grower description. A subset of 32 plots (16 matched pairs) were sampled for fruit yield and fruit quality.
Soil samples were collected as 50 to 100-soil core composite samples (2.5 cm core) to a depth of 20 cm in the tree root zone (15-60 cm from trunk) where 10 to 20 random samples were taken in each of five locations of the 2 to 16 hectare field. Four 100 cm3 intact soil cores were used for bulk density analysis. Five 120 cm3 intact cores were taken for micro-arthropod analysis. All soil sampling was conducted during June and July after soils had warmed (>13 °C) and 1 to 3 months before apple harvest.
Water supply for each orchard site was determined using a grower survey of irrigation practices and on-site irrigation measurements and demand was estimated from evapotranspiration estimates based on meteorological data from the nearest weather station [1]. On site irrigation measurements included measurements of water volume per emitter per hour at ten locations within a block which was then multiplied by emitters per acre. Fields with insufficient irrigation were not included in matched plot analysis.
Fruit yield and quality were determined by collecting grower reported packing house yield data for the previous two to four years where available. For orchards where packing house data was not collected, a subset of five representative trees were selected for each orchard. At harvest, fruit per tree were counted and 20 fruit per tree collected to determine mean fruit weight and to estimate total yield. Yield was normalized to a 0-100 scale (percent yield goal) where the reported yield was divided by the yield goal identified by the grower in order to account for the yield potential of individual varieties and growing systems.