Polymer-coated Fertilizers
نویسندگان
چکیده
Application of polymer-coated controlled-release fertilizers (CRF) during outplanting has resulted in variable growth responses in the Pacific Northwest (PNW). Results have been linked to several factors, including soil moisture availability. Multiple experiments were designed to examine the influence of CRF on Douglas-fir seedling root architectural development and establishment. Placement of CRF as a uniform layer beneath transplanted seedlings restricted root penetration at progressively higher CRF rates and this was attributed to damaging rhizosphere osmotic concentrations. Dry summers on many sites in the PNW may compound this effect because moisture to leach excess fertilizer salts from the root zone is absent. Application of 2.1 oz (60 g) CRF to the planting hole on a droughty site in the Oregon Coast Range impaired seedling root development and increased plant moisture stress. For all treatments, new root growth was positively correlated with xylem water potential, emphasizing the need for vigorous root growth during establishment. Drought stress may limit photosynthetic capacity and force seedlings to expend stored carbohydrates, which may impair whole-plant growth. On drought-prone sites in the PNW, negative fertilizer responses may be avoided with conservative polymer-coated CRF application rates, utilizing CRF with moisturedependent nutrient release characteristics, or avoiding field fertilization entirely.
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