Søren Ugilt Larsen

Comparing annual and perennial crops for bioenergy production - influence on nitrate leaching and energy balance.

Production of energy crops is promoted as a means to mitigate global warming by decreasing dependency on fossil energy. However, agricultural production of bioenergy can have various environmental effects depending on the crop and production system. In a field trial initiated in 2008, nitrate concentration in soil water was measured below winter wheat, grass‐clover and willow during three growing seasons. Crop water balances were modelled to estimate the amount of nitrate leached per hectare. In addition, dry matter yields and nitrogen (N) yields were measured, and N balances and energy balances were calculated. In willow, nitrate concentrations were up to approximately 20 mg l−1 nitrate‐N during the establishment year, but declined subsequently to <5 mg l−1 nitrate‐N, resulting in an annual N leaching loss of 18, 3 and 0.3 kg ha−1 yr−1 N in the first 3 years after planting. A similar trend was observed in grass‐clover where concentrations stabilized at 2–4 mg l−1 nitrate‐N from the beginning of the second growing season, corresponding to leaching of approximately 5 kg ha−1 yr−1 N. In winter wheat, an annual N leaching loss of 36–68 kg ha−1 yr−1 was observed. For comparison, nitrate leaching was also measured in an old willow crop established in 1996 from which N leaching ranged from 6 to 27 kg ha−1 yr−1. Dry matter yields ranged between 5.9 and 14.8 Mg yr−1 with lowest yield in the newly established willow and the highest yield harvested in grass‐clover. Grass‐clover gave the highest net energy yield of 244 GJ ha−1 yr−1, whereas old willow, winter wheat and first rotation willow gave net energy yields of 235, 180 and 105 GJ ha−1 yr−1. The study showed that perennial crops can provide high energy yields and significantly reduce N losses compared to annual crops.

Biomass Yield and N Uptake in Tall Fescue and Reed Canary Grass Depending on N and PK Fertilization on Two Marginal Sites in Denmark

Perennial grass species may ensure a productive use of marginal land with limited potential for production of annual crops. We investigated the biomass yield and N uptake of tall fescue (TF) and reed canary grass (RCG) grown on two sites with coarse, sandy mineral soil, i.e., marginal wetter land areas with limited suitability for cereal production. Plots with TF and RCG were sown in April 2011, and fertilization trials were established in spring 2012 with three factors: (a) grass species, (b) PK fertilization (either no P and K or 24 and 250 kg ha−1 y−1 of P and K, respectively), and (c) N fertilization (0, 150, 300, or 450 kg ha−1 y−1 N). Three cuts were taken annually from 2012 to 2014.