HPF – Nutrient Management

Extract from High Production Forestry in Nova Scotia Phase 1 Final Report (July 2021), pp 8-10:

4. Nutrient Management
By definition, HPF sites are expected to produce merchantable volumes at rates of 6 m3/ha/yr or more at time of final harvest. This type of production is nutrient-demanding and will likely match or exceed the natural long-term nutrient supply rates on many sites. Therefore, soil monitoring and development of nutrient management plans are necessary components of high production forestry.

Over the last several years, NSDLF has been directly involved with several soil and site productivity related projects including: (i) development of a forest soil classification system (Neily et al. 2013), (ii) development and calibration of a forest nutrient budget model (Keys et al. 2016), (iii) development of a forest soil and tree tissue sampling program, (iv) research on ground disturbance and soil damage assessment, (v) research on forest liming, and (vi) research on soil amendment use in spruce plantations (Keys et al. 2018). All this work, combined with ongoing research, will be used to develop science-based and effective soil monitoring and nutrient management regimes for HPF sites.

Nutrient Budgets: Nutrient management starts with knowing what nutrients are available, what the demands are, and what the natural supply rates are. The Department’s nutrient budget model (NBM-NS) can be used to model species and site-specific nutrient demands and supplies under various HPF management scenarios. In addition, soil sampling program data (augmented by site-specific sampling) can be used to estimate current nutrient stores by soil/site type. Results can then be used to develop silviculture and amendment prescriptions aimed at restoring, balancing, and/or maintaining soil nutrient conditions over time (to be confirmed by soil monitoring and periodic testing). As part of this assessment, it has already been determined that HPF management cannot and will not include removal of nutrient-rich foliage and slash through either full-tree or whole-tree harvesting practices. This will also enhance biodiversity on HPF sites by periodically providing potential habitat for insects, amphibians, reptiles, small mammals, and birds.

Soil Amendments: Soil amendments come in many forms and provide a range of potential benefits. For example, as a result of decades of acid deposition, many forest soils in Nova Scotia are very low in base cations (calcium, magnesium, potassium) and would benefit from a “lime” application in the form of traditional dolomitic lime, wood ash, and/or alkaline stabilized biosolids (Pugliese et al. 2014; Lawrence et al. 2016; Keys et al. 2018). An early liming treatment will likely be part of many HPF management regimes. When available, use of wood ash generated from the Province’s new Small-Scale Wood Energy Initiative would be a natural extension of this program. Another potential liming option is use of crushed basalt that, in addition to being a slow-release nutrient source, has the potential to promote carbon sequestration through bicarbonate (HCO3-) production – a natural extension of the weathering process (Beerling et al. 2018).

Options with respect to nitrogen and phosphorous amendments include inorganic fertilizers and organic residues (e.g., manures or treated sewage). Organic amendments could also be used to offset potential losses in soil organic matter and related carbon stores. Occasional use of N-fixing nurse crops (e.g., Alnus spp.) may be another option to increase mineral soil nitrogen and carbon stores (Mayer et al. 2020). In future, there may also be options related to biochar use (Page-Dumroese et al. 2016).

Although use of soil amendments may be part of HPF management, its important to note that such use will be infrequent and/or of low rates compared to agriculture. When needed, most applications will occur in association with (i) site preparation, (ii) after planting but before crown closure, or (iii) after commercial thinning. In addition, many of these amendments will be “slow-release” so as not to cause ecosystem shock or excessive leaching.

Monitoring: Periodic monitoring of soil conditions is a necessary and important component of sustainable high production forestry. In addition to soil chemistry (including carbon stores), this includes monitoring of physical properties such as bulk density and aeration porosity that can be negatively impacted by increased machine traffic. Ongoing soil monitoring will allow confirmation of effective treatments, abandonment of ineffective treatments, and testing of alternative management approaches.