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Soil Health Indicators for Central Washington Orchards Published In PLOS one, October, 2021

To help growers in Central Washington orchards, Washington State University scientists demonstrated that Washington orchard soil health indicators should include measurements of water availability and root health in addition to standard fertility indicators to meet stakeholder management goals.

The researchers assessed soil health in ninety-seven Washington apple orchards for the study, published this month in the journal PLOS ONE. The objective of the study, done over a four-year period, was to start developing a soil assessment tool for irrigated orchard soils in Central Washington.

“This study is a first step towards identifying soil health indices growers can use to improve yield and fruit quality,” said Tianna DuPont, WSU Extension Specialist and lead author in the study.

DuPont worked with co-authors Lee Kalcsits, from WSU’s Department of Horticulture and Clark Kogan, from the Department of Mathematics and Statistics on the study.

Soil health assessment can be a critical soil testing tool. Soil health testing looks at the biological and physical as well as chemical properties of soil. Healthy soil performs critical ecosystem functions from sustaining plant growth to minimizing erosion, regulating water flow and filtering toxic materials. However few soil health testing tools have been evaluated for perennial crops in irrigated systems. This is the first study to look at soil health assessment tools for irrigated orchards in the Western US which looks at the relationship between soil health and fruit yield and quality.

Indicators measured in Central Washington orchards had a wide range but with generally lower organic matter, lower available water capacity, higher percent sand and lower wet aggregate stability than Midwest, Mid-Atlantic and Northeastern soils measured in other studies. Five percent of sites had available water capacity indicating severe water limitation and 11% had moderate limitation. Indicators of root health function showed disease pressure in many of the orchard fields sampled according to apple root health ratings and Pratylenchus penetrans nematode counts.

Available water capacity and percent sand were significantly related to yield.  Root health ratings as well as Pratylenchus nematode counts had consistent, but not significant trends with yield. High levels of mineralizable N in some orchards and subsurface compaction in 25% of orchards suggest that a measure of organic nitrogen and compaction should be included in the minimum data set used to measure soil health in Washington orchards.


Washington State University