Fertilization of Willow Coppice Over Three Consecutive 2-Year Rotations-Effects on Biomass Production, Soil Nutrients and Water

Short rotation coppice (SRC) willow is a promising bioenergy feedstock. Fertilization is an integrated part of the production system, but knowledge about the effects in consecutive rotations is scarce. The objective of this study was to identify an appropriate fertilization regime for achieving high yields, reducing risks of nutrient leaching and maintaining the soil nutrient stocks in SRC willow on a former arable land. Ten different fertilization treatments were applied, with different application frequencies, fertilizer types and doses over three consecutive 2-year rotations. The biomass production was determined at harvest, soil solution samples were collected monthly, water fluxes were modelled using CoupModel and nutrient budgets were calculated. The unfertilized control had a mean biomass production of 8.3, 8.3 and 9.5 odt ha(-1) year(-1), respectively, in the three rotations. This indicated that nutrients were adequately available to maintain production for at least 6 years without fertilization. When adding 60 kg N ha(-1) year(-1), biomass production tended to be higher than the control, by 33% (p = 0.055), and the treatment where 360 kg N ha(-1) rotation(-1) was added, by 31% (p = 0.08). Treatments with one-time addition of 240 and 360 kg N ha(-1) rotation(-1) had significantly higher nitrogen leaching than all other treatments. Organic fertilizers did not increase biomass production nor N leaching significantly compared to the control, but nutrient budgets indicated a nutrient build-up in the soil. We concluded that application of 60 kg N ha(-1) year(-1) is recommendable, for achieving high biomass yields, low nitrogen leaching and maintenance of the soil nutrient stock.