Arboriculture & Urban Forestry 42(2): March 2016 formulation. Previous research has shown that all three amendments in different forms influ- ence host plant physiology and soil conditions to promote tree vitality, growth, and improve trans- plant survival rates. Application of carbohydrates, such as sucrose, as a root drench or in combina- tion with a water-holding gel, improved trans- plant survival through enhanced root growth of silver birch (Betula pendula Roth.) and European beech (Fagus sylvatica L.) (Percival et al. 2004; Percival and Barnes 2007). Alterations in micro- bial populations initiated by the application of sucrose within the rhizosphere could favor root growth. In addition, carbohydrates may have functioned as direct nutrients for tree growth and influenced sugar-sensing processes that initiated changes in gene expression associated with root development (Koch 1996; Rolland et al. 2002). Nutrient reserves accumulated the previous year are of primary importance for early spring growth. The quantity of stored nutrient reserves can be increased by a supply of nitrogen fertil- izer during the growing season, due to the fact that nitrogen promotes higher leaf chlorophyll, and by default increases photosynthetic pro- ductivity later into the growing season (Tromp 1983; Cheng and Robinson 2004). Chlorophyll content in leaves is proportional to nitrogen, since leaf nitrogen is stored in the chloroplasts. Therefore, increases in nitrogen supply through fertilization are known to increase leaf chlo- rophyll content (Chandler and Dale 1994; Bondada and Syvertsen 2003), which would account for the improved leaf chlorophyll con- tent and fluorescence values recorded in this experiment following application of an organic N:P:K fertilizer singly and in combination. This research also differs from other studies in that it is the first to evaluate combinations of slow- release carbohydrates, organic nitrogen fertilizers, and biochar as soil amendments on transplant survival. Results consistently demonstrate positive effects on tree vitality (chlorophyll fluorescence, leaf chlorophyll content, and photosynthetic rates) and growth (fruit yield per tree and canopy cover- age) when these products are combined and incor- porated as a soil amendment at the time of planting (Table 2). Applications of BOOST Organic plus biochar had the highest significance in promoting 107 tree vitality and growth in most cases throughout two growing seasons. Organic fertilizer additions have also been shown to increase the organic mat- ter content and nutrient concentrations in the soil, especially nitrogen pools, although this can result in excessive nitrogen accumulation and there- fore leaching (Edmeades 2003). Biochar improves nutrient retention capacity, allowing the additions of fertilizer to be adsorbed by the porous biochar and reducing leaching of surplus nutrients (Black- well et al. 2009; Lehmann and Joseph 2009). Con- sequently, combining an organic nitrogen-based fertilizer (BOOST Organic) with biochar may per- mit greater fertilizer retention in the rhizosphere, in turn increasing nutrient accessibility in the root zone (Lehmann and Joseph 2009). In support of this, Dempster et al. (2012) recorded reductions in levels of cumulative NO3 (ammonium) leaching by approximately 20% when using eucalyptus-derived biochar in sandy soil. In addition, beneficial soil microbes, such as phos- phate-solubilizing bacteria, mycorrhization-helper bacteria, and higher rates of mycorrhizal coloni- zation are encouraged by the addition of biochar into the soil (Warnock et al. 2007). PI values as a measure of photosynthetic efficiency were signifi- cantly improved with BOOST Organic plus biochar soil amendment in the first year aſter transplanting. Transplant stress oſten deteriorates leaf cell com- ponents—including chloroplasts—damaging both photosystems I and II that manifest visibly in yel- lowing leaves (Percival 2007). Higher PI values compared to non-soil-amended controls indicate a superior operational level of photosynthetic effi- ciency, and are, by default, indicative of lower stress levels within the plant (Percival 2007). Conse- quently, a combination of these benefits may have accounted for the positive effects on tree vitality and growth recorded in this study, induced by the organic fertilizer/biochar combination. However, care needs to be taken following the addition of biochar as a soil amendment, as nutrient draw- down can occur at excessively high biochar addi- tions. Nutrient drawdown relates to the availability of nutrients and their use over time within soil. A biochar soil amendment may induce soil nitro- gen immobilization, possibly through an increase in soil microbial activity (Clough et al. 2013). 25% over 21 days, and decreased cumulative NH4 ©2016 International Society of Arboriculture - (nitrate) leached of +
March 2016
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