Review of different types of fertilizers for willow plantations

Willow (Salix) family is one of the fastest-growing woody energy crops. It has been widely used for biomass energy production in short-rotation plantations, carbon storage in longer rotation, and as a phytoremediation plant in Northern Europe. Willows could be cultivated on a wide range of soils, including marginal land, and they are readily propagated by planting un-rooted cuttings. Soil fertilization is necessary for obtaining a higher biomass yield. Different side products of energy production and municipal waste could be used for soil improvement. The aim of this research is to review fertilization practices in short-rotation willow plantations and their impact on the biomass yield. The data from the literature were collected, and different doses of various fertilizers were compared. The response to fertilization is positive if fertilizer contains complex NPK macro elements. The most appropriate dose per hectare varies depending on the soil properties, soil types, willow varieties, weather conditions, water availability, and other factors. Wood ash and peat could be used for soil improvement to solve the main characteristic marginal soils problems in Latvia – low organic content and pH value. Wood ash has high concentrations of calcium (Ca) and magnesium (Mg) and already is widely used as a liming agent in organic farming. Less demanded peat fractions, dewatered wastewater sludge, and biogas fermentation leftover digestate contain a high amount of organic matter and nitrogen, therefore, could be used as a replacement for previously used fertilizers such as cattle slurry. In addition, wastewater sludge, digestate, and wood ash are also sources of microelements. A mix of all listed products has a high potential to be used as a complex soil amendment.