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Soil nutrient supply rates as an indicator of site suitability and seedling growth requirements

Hangs, R.D., Greer, K.J., and Van Rees, K.C.J. 2005. In Thin Green Line Conference on State-of-the-Art in Reforestation Proc., pp145-152. Thunder Bay, ON


Before there is widespread adoption of agroforestry practices in Saskatchewan, a clear economic advantage for producers to grow hybrid poplar must become apparent. In order to achieve this goal, there needs to be adequate survival and growth of planted seedlings, especially within the first few years. Under conditions of adequate soil moisture, reductions in the early growth of tree seedlings mainly are attributable to soil nutrient limitations. Monitoring soil nutrient availability, therefore, is important for ensuring optimal tree nutrition and promoting successful seedling establishment and growth. The objective of this study then was to evaluate the utility of measuring soil nutrient availability, using in situ burials of ion-exchange membrane (IEM; Plant Root Simulator (PRS™)-probes), at several hybrid poplar plantations in northern Saskatchewan and relating these data to plantation productivity during the early establishment phase. The results of this study support the assertion that in situ burials of IEM provide biologically meaningful data and, therefore, are a useful tool for measuring nutrient availability in tree plantations during the early establishment phase. Specifically, the PRS™-probes were sensitive enough to measure differences in soil nutrient supply rates among sites differing in past management practices, soil types, and climatic conditions. In addition, they were capable of quantifying differences in N supply rate following NH4NO3 fertilizer addition and the subsequent temporal changes in NH4 -N and NO3--N supply rates throughout the growing. Most importantly, however, the PRS™-probe data were strongly correlated (R2 0.54 to 0.98, P <0.01) with seedling growth. Further research is needed to determine the threshold soil nutrient supply rates for different hybrid poplar clones during the early establishment phase. Determining the relationship between soil nutrient supply rates and seedling growth requirements should help to support effective management strategies, in terms of proper site selection and the elucidation of possible fertilizer requirements.

Key Words

agroforestry, hybrid poplar, ion-exchange membrane, nitrogen supply rate, PRS™-probes