108 Schaffert and Percival: Influence of Biochar, Slow-Release Molasses, and an Organic N:P:K Fertilizer Table 2. The influence of soil amendments on growth, tree vitality, and mortality of Pyrus communis ‘Williams’ Bon Chrétien’ in Year 2. Treatment Control (no amendment) Molasses pellets Biochar BOOST Organic granular BOOST Organic granular + BOOST Organic granular + Molasses pellets + biochar biochar molasses pellets BOOST Organic granular + molasses pellets + biochar Tree vitality SPAD 41.5 41.3ns 45.5ns 52.3* 55.8* 50.9* 48.8* 51.1* Growth PI 4.0 4.6ns 6.2* 7.5* 7.7* 7.0* 6.1* 6.9* Pn 3.90 4.22ns 4.50* 4.62* 4.48* 4.46* 4.60* 4.39* Fruit yield/ tree (kg) 4.5 6.0* 6.2* 7.8* 7.8* 7.2* 5.9* 6.6* Crown volume 0.71 0.82ns 0.95* 0.84* 0.90* 0.82* 0.87* 0.83* Mortality (%) 0 0 0 0 0 0 0 0 Notes: All values mean of surviving trees from an initial number of 10. Asterisk (*) = significant differences between means (P = 0.05). P < 0.05 are considered signifi- cant based on Tukey’s Honestly Significant Difference test. SPAD = estimated leaf chlorophyll content, PI = chlorophyll fluorescence, Pn = light-induced CO2 fixation. Combinations of organic fertilizer and molasses also induced positive effects on tree vitality and growth, although not to the same extent as organic fertilizer plus biochar. Work by Percival and Barnes (2007), studying European beech, recorded higher mortality rates in control trees (40%) compared to a water-retaining gel, synthetic nitrogen fertilizer, and carbohydrate (sucrose) combination following transplanting, where losses were reduced to 10%. Promotion of lateral root growth can increase water availability by directly extending the rhizosphere, allowing increased water uptake, which reduces internal water deficit; a major contributing fac- tor to transplant death (Gilbertson and Bradshaw 1990; Grossnickle 2005). Exposing root systems to high levels of carbohydrates has been shown to favor root development at the expense of net pho- tosynthesis due to the repression of photosynthetic genes (Koch 1996). Sugar application to the rhizo- sphere has been acknowledged to repress shoot and leaf development in favor of root elongation due to the initiation of these storage processes. There- fore, application of slow-release sugar molasses may have influenced crucial metabolic processes, leading to the repression of genes involved with leaf growth and photosynthesis. Results for crown volume possibly reflect this priority toward root growth, as canopy coverage was not significantly increased when molasses was applied individually or in combination with BOOST Organic or biochar. In several studies, sugar has likewise been identi- fied to repress nutrient mobilization, including nitrogen (Rolland et al. 2002; Hong et al. 2012), ©2016 International Society of Arboriculture which is a possible explanation for the lack of effect on leaf chlorophyll content (SPAD values) over the two growing seasons. However, by Year 2, the sugar molasses may have been depleted within the soil and root system and exhausted of any root enhanc- ing substances, hence the greater canopy coverage and higher chlorophyll content recorded in Year 2, where the benefits of the longer soil-persisting organic fertilizer and biochar become apparent. Combining amendments enhanced tree vitality and growth 6%–18% compared to addition of each amendment alone. This may influence the economic viability of combining products (i.e., is such a per- cent increase worth the extra expense of combining products). Given that biochar degradation in the soil is low—i.e., a one-off application can last 500 to 20,000 years, as demonstrated by longevity studies of this substance in the Brazilian Amazon region of Terra Preta de Indio—the many benefits of bio- char additions to the soil will have long-term posi- tive implications on future tree growth and vitality (Blackwell et al. 2009). The value of soil amended by biochar ensures a one-off biochar soil amend- ment would prove an economically viable option (e.g., providing improved soil structure and pore space, enhanced nutrient supply to plants, higher soil nutrient retention, enhanced efficiency of fertil- izer use, reduced nutrient leaching in turn resulting in superior plant performance, and elevated tissue nutrient concentrations from 500 to 20,000 years). In conclusion, results from this investigation indicate additions of the assessed soil amendments have several benefits. All amendments decreased
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