Short rotation willow (Salix spp.) biomass production systems are expected to provide seven harvest cycles at 3-year intervals [1(establishment and coppicing year) + 21 years]. However, there is limited information on the nutrient dynamics in these fast-growing systems in Ontario, Canada. It is not clear whether nutrient removal through harvest will be offset by nutrient inputs from atmospheric deposition, geo-chemical weathering, litterfall and fineroot turnover. There is also a lack of information on the need for and types of fertilizer application regimes in mature biomass stands. Once this missing information is understood, system management may be refined to maximize productivity on marginal lands in Ontario, Canada.

In this context, a project on 8-year-old willow stands is being conducted at the University of Guelph, Guelph, Ontario, Canada, looking into nutrient budgets for three unfertilized varieties of willow (Salix dascylados, S. purpurea, and S.miyabeana) and one hybrid species of poplar to determine nutrient dynamics as affected by species differences. In an ancillary study, two varieties of willow were fertilized in the spring of 2014 and 2015 to determine nutrient and yield dynamics as affected by fertilizer applications. The nutrient budgets for nitrogen (N), phosphorous (P), potassium (K), magnesium (Mg), and calcium (Ca) are being calculated in order to quantify the amount of nutrients that remain within the system after each harvest, which is once every three years. This will help determine whether short rotation woody coppice systems are able to sustain growth and production throughout its lifespan of 22 years without any external supply of nutrients.

Nutrient dynamics have been studied by quantifying inputs via atmospheric deposition, recycling via leaf litterfall and decomposition, and outputs via harvesting. So far, no significant differences in relation to nutrient cycling have been observed between species, or between fertilizer applications when comparing biomass yields from the third harvest cycle in 2015. This could indicate that fertilizer use may not be as valuable in these production systems as they are in first-generation biofuel crops, such as corn-based ethanol. The quantification of nutrient budgets for the tested woody biomass crops will enhance the understanding of nutrient cycling throughout these systems. Furthermore, it will allow for future production planning without external nutrient inputs from fertilizers. This will help reduce the carbon footprint associated with these production systems.