Improving soil health in apple and pear orchards

Davis, Max and Stevens, Carly and Ostle, Nick (2025) Improving soil health in apple and pear orchards. PhD thesis, Lancaster University.

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Abstract

Commercial apple and pear orchards represent a small but important source of food production. Contemporary research has targeted ways to improve orchard ecosystem services such as pollination and natural enemies through sown wildflower strips. The potential benefits of increased plant diversity in orchard alleyways to improve soil health have not been considered. This project aimed to answer this question through four research objectives. Initially, apple and pear orchard management and its influence on soil processes was reviewed to provide context and highlight areas for further research. Then, a field study benchmarked soil health in apple orchards with and without wildflower strips. No consistent trends were found in biological, chemical, or physical soil health indicators. Following this I performed a lab study using intact soil cores from wildflower and conventionally managed orchard alleyways to measure the response (CO2) of orchard soils to drought and rewetting. No difference in responses was detected between management. Results from these studies, alongside the management review, indicated orchard management practices, such as agrochemical application and soil compaction from trafficking, may stifle any benefits plant diversity may have on soil health. A fourth chapter explored the effects of representative orchard covers in mesocosms on soil processes and aboveground productivity. A litter decomposition experiment using mesocosm litter was also performed. Significant effects on nitrogen cycling and aboveground productivity were detected in pots containing two or more functional groups, with dominant biomass Trifolium pratense likely driving these effects. Plant available nitrogen (NH₄+ + NO₃_) in soil was also shown to be significantly reduced under the presence of forbs. Litter containing two or more functional groups was also found to increase the rate of litter mass loss by 100% over six months. Overall, this thesis examines orchard soil health, and how soil health may change under management, drought stress, or how function may be influenced by plant functional groups.