Growth and nutritional response of hardwood seedlings to controlled-release fertilization at outplanting

Hardwood bareroot seedlings typically undergo transplant shock immediately following afforestation planting associated with moisture or nutrient stress. Broadcast field fertilization at outplanting with readily available nutrients has shown limited capacity to reduce nutrient stresses. Furthermore, the rapid nutrient release characteristic of broadcast fertilization leads to high levels of nutrient leaching and may stimulate growth of competing vegetation more than target trees. Application of controlled-release fertilizer (CRF) in the outplanting hole could be a useful alternative to help improve fertilizer use efficiency and alleviate competition problems associated with broadcast fertilization, thereby promoting early regeneration success of outplanted seedlings. We tested growth and nutritional response of black walnut (Juglans nigra L.), white ash (Fraxinus americana L.), and yellow-poplar (Liriodendron tulipifera L.) to 6 rates (0, 15, 30, 45, 60, and 75 g plant−1) of polymer-coated CRF applied to the root zone at outplanting in southern Indiana, USA. Fertilizer release was evenly distributed between years 1 and 2. Seedling survival was above 85% for all treatments. Compared to non-fertilized seedlings, the 60 g seedling−1 rate accelerated mean height and root-collar diameter (RCD) growth by 52 and 33% in year 1 and 17 and 21% in year 2. Nitrogen (N) and potassium (K) uptake were increased 40 and 30% at the 60 g rate compared with controls. Height and RCD growth were greater by 543 and 200% in white ash and 300 and 233% in yellow-poplar, relative to black walnut. Uptake of N and K was increased by 79 and 22% in yellow-poplar and 93 and 56% in white ash, compared to black walnut. Results suggest CRF has potential to improve early establishment success of hardwood afforestation plantings.