Submitted to: Agricultural Research Service Publication
Publication Type: Abstract only
Publication Acceptance Date: 1/20/2007
Publication Date: N/A
Citation: Interpretive Summary:
Technical Abstract: Organic orchard systems are a significant and growing component of Washington State agriculture, yet sustainable methods of nitrogen (N) fertility and weed management remain a challenge. Nutrient supply is dependent on decomposition and mineralization of organic matter, yet intensive cultivation commonly used to control weeds can disrupt biological processes and cause loss of organic matter. To address the often-competing goals of organic fertility and weed control, a number of alternative orchard floor management strategies were evaluated for their impact on N cycling, soil quality, and tree health. The standard practice of weed control using tillage resulted in trees with good growth and acceptable levels of leaf N, conversely, soil quality was in decline and may negatively impact long-term nutrient dynamics. Maintenance of a living cover understory resulted in greater N retention and availability, and rapid soil quality improvement, reduced tree growth. Covering the understory with wood chip mulch enhanced soil moisture and resulted in adequate tree growth, but also facilitated N loss and correspondingly resulted in low tree leaf N. Application of a clove oil herbicide resulted in lower leaf N and tree growth in comparison to cultivated treatments. In contrast, Brassicaceae seedmeal(BSM)enhanced N availability and soil faunal biomass, yet leaf N did not reach acceptable levels and many of the other essential nutrients were lowest in this treatment. Tree leaf chlorosis was observed following an early season BSM application and may have been the result of reduced soil iron availability. None of the treatments produced an ideal combination of weed control, maximum tree growth, adequate leaf nutrients, and improved soil quality.