Submitted to: Soil Biology and Biochemistry
Publication Type: Peer reviewed journal
Publication Acceptance Date: 11/23/2007
Publication Date: 6/16/2008
Citation: Hoagland, L., Carpenter-Boggs, L., Reganold, J., Mazzola, M. 2008. Role of native soil biology in brassicaceae seed meal induced weed suppression. Soil Biology and Biochemistry. 40:1689-1697. Interpretive Summary: Fueled by consumer demand and innovative research, organic tree fruit production is thriving, but sustainable methods of nitrogen (N) fertility and weed management remain a significant challenge. Organic production systems generally rely on complex organic materials such as composted animal manures to supply N, but only a fraction of the nutrients are in immediately available forms with the remainder released slowly as a result of microbial driven processes. Weed control typically relies on repeated cultivation during the growing season, a practice which degrades soil structure and can lead to loss of organic matter from the production system. Alternative orchard floor management strategies were implemented and evaluated for impact on N cycling, soil quality, weed control and tree health in a newly established orchard. Intensive cultivation reduced various soil quality parameters, which may negatively impact long-term tree health and fruit quality. Non-disturbed living mulch understory resulted in significant improvements in soil quality but increased competition with orchard trees leading to decreased tree growth. Application of wood chip mulch in the tree row resulted in low leaf N and reduced soil quality. Brassicaceae seed meal amendments simultaneously provided sufficient N, provided a level of weed control and adequate tree growth. However, this treatment induced leaf chlorosis which may have resulted from a deficiency in certain minerals, including iron. While these methods exhibited promise in this field trial, they will require additional study to determine optimal rates and conditions for application in organic orchard management systems.
Technical Abstract: Sustainable methods of nitrogen (N) fertility and weed management are a challenge in organic orchard management systems. Nutrient supply is dependent on decomposition and mineralization of organic matter, yet intensive cultivation commonly used to control weeds can disrupt biological processes contributing to this process. To address the competing goals of organic fertility and weed control, alternative orchard floor management strategies were implemented and evaluated for impact on N cycling, soil quality, and tree health in a newly established orchard. Weed control using extensive tillage resulted in trees with good growth and acceptable levels of leaf N and most other essential nutrients, but indicators of soil quality were in decline which could lead to negative impacts on long-term nutrient dynamics. Maintenance of a living cover within the orchard tree row enhanced N retention and availability but severely competed with young trees, resulting in reduced tree growth. Application of a wood chip mulch in the tree row improved soil moisture and resulted in adequate tree growth, but it 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 and did not positively impact soil quality parameters. Brassicaceae seedmeal (BSM) applications enhanced N availability and soil faunal biomass, yet leaf N did not reach acceptable levels and many other essential nutrients were lowest in this treatment. None of the treatments applied produced an ideal combination of weed control, maximum tree growth, adequate leaf nutrients, and improved soil quality. Rather, treatments providing soil quality improvements tended to compete with early tree performance.