Submitted to: Biology and Fertility of Soils
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/10/2008
Publication Date: 6/11/2008
Citation: Hoagland, L., Smith, J.L., Carpenter-Boggs, L., Reganold, J. 2008. Orchard floor management effects on nitrogen fertility and soil biological activity in a newly established organic apple orchard. Biology and Fertility of Soils. 45(1):11–18. DOI: 10.1007/s00374-008-0304-4. Interpretive Summary: The production of organically grown fruits in Washington State is increasing yearly. However, the conversion to organic certified orchards is severely limited by the availability of organic fertilizers. Specifically, producers have a difficult time providing enough nitrogen, a critical plant nutrient, to the fruit trees. This study focused on the organic fertility and weed control in newly established apple orchards. We found that maintaining a living cover on the soil under the apple tree increased fertility of the tree and reduced weeds as did the additions of amendments. None of the treatments applied in this study produced an ideal level of fertility and weed control. However, the knowledge gained can be used by orchard managers to finely tune their management for maximum benefit from living mulches and amendments.
Technical Abstract: Nutrient supply in organic systems is dependent on mineralization of organic matter; however, the intensive cultivation commonly used to control weeds can disrupt biological processes and cause undue loss of organic matter. Here we address the often-competing goals of organic fertility and weed control by evaluating alternative orchard floor management strategies for their impact on N cycling, soil quality, and tree performance in a newly established apple orchard. The standard practice of weed control using extensive tillage resulted in good tree growth with acceptable levels of leaf N and most other nutrients; conversely, soil quality did not improve. Maintenance of a living cover understory increased soil N content and availability and improved soil quality, but reduced tree growth. Application of wood chip mulch in the tree understory resulted in adequate tree growth, but it also facilitated N loss and correspondingly resulted in low tree leaf N. Clove oil herbicide provided poor weed control and resulted in lower leaf N and tree growth likely due to weed competition and did not improve soil quality. Although Brassicaceae seed meal applications enhanced N availability and soil nematode abundance, leaf N and many other nutrients were below acceptable levels. None of the treatments applied produced an ideal combination of weed control, maximum tree growth, adequate leaf nutrient content, and improved soil quality. Rather, soil quality improvements tended to be achieved at the expense of tree performance.