Traditional and cover crop-derived mulches enhance soil ecosystem services in apple orchards

Organic mulches are a traditional method of groundcover management in temperate commercial orchards, now largely replaced by herbicides and synthetic fertilisers. As a potential contribution to improving orchard sus-tainability, we hypothesised that the addition of organic mulches would: (H1) improve soil fertility and lead to greater tree growth and yields; (H2) support a larger and more biologically active community of soil organisms, assessed as increased soil respiration and greater earthworm numbers and biomass; and (H3) increase leaf litter decomposition and burial, potentially reducing the risk of apple scab disease (Venturia inaequalis). Cuttings from two legume-based cover crop mixtures grown in the alleyway spaces between tree rows and two traditional mulch materials, straw and compost, were trialled alongside a bare soil business-as-usual control for two years, using a randomized complete block design in a conventionally managed commercial 'Gala' apple orchard in the UK.Compared to the control, the compost mulch significantly increased both soil carbon and nitrogen by over 50 %. The straw mulch effectively suppressed weeds by about 90 % and increased soil moisture by about 5 %. Cover crop cuttings increased moisture levels and increased earthworm numbers and mass by 1.7 and 1.8 times greater respectively in the double-rate 'legume-grass' cuttings treatment. Increasing the quantity of cover crop cuttings produced more positive effects; the cumulative addition of cuttings can benefit several soil-derived ecosystem services. This study took place in a commercial apple orchard, the findings may therefore be applicable to other orchard and row-grown perennial crops.

Automated summary

Organic mulches can improve soil fertility and promote tree growth and yields; they can support a more biologically active soil community; and they can increase leaf litter decomposition and burial, reducing the risk of apple scab disease.