The effect of common Dutch white clover (Trifolium repens L.), as a green manure, on biomass production, allometric growth and foliar nitrogen of two willow clones

There is potential for soil erosion and non-point source pollution during the establishment of short-rotation woody crops (SRWC) in northern climates as a limited amount of cover remains on soils from the time of site preparation until SRWC occupies the site early in the second growing season. To counteract these impacts, green manure crops may be established and turned under early in the growing season. The effects of a green manure crop, white clover (Trifolium repens L.), on growth rates, biomass allocation, and foliar nitrogen concentrations of two willow clones (Salix sachalinensis and S. discolor) were compared in a field experiment to nitrogen fertilizer and control treatments over a period of 4 months. Willows were grown in rooting envelopes and harvested four times during the growing season to assess differences in allometric growth. White clover was found to increase the foliar nitrogen concentration of willow without compromising aboveground biomass. Fertilizer induced a 24% increase in total biomass of willow relative to the control. The rate of biomass allocation aboveground was greater relative to belowground under all treatments, and allometric coefficients were greater than 1.0. The differences in nitrogen uptake patterns and nitrogen use efficiencies of willow corresponded to the differences in biomass and foliar nitrogen concentrations between clones.