Nutrient losses and nutrient retention efficiencies in temperate agroforestry systems versus conventional agricultural systems

Modern agricultural production is considered unsustainable and often is accompanied by detrimental environmental effects such as nutrient leaching losses. This results in a strong need for more environmentally friendly management systems. Alley-cropping agroforestry systems, with tree components implemented for bioenergy use, are innovative agricultural systems since they take advantage of beneficial ecological functions of both their tree and crop components. In such systems, trees can act as a safety-net against nutrient leaching as they can take up nutrients that are beyond the reach of grass/crop or at times when grass/crop demand is low. However, no comparison of nutrient losses and nutrient retention efficiencyhave yet been conducted between conventional and agroforestry systems. Our study therefore aimed to 1) quantify nutrient losses in grassland/cro pland agroforestry and conventional grassland/cropland, 2) evaluate how efficiently nutrients are being retained in both management systems (nutrient retention efficiency = (1-leaching losses/soil-available nutrient), and 3) assess whether differences in nutrient retention efficiencies between grassland/cropland agroforestry and conventional grassland/cropland are related to differences in microbial nutrient-cycling processes in the soil or differences in plant uptake of nutrients. We hypothesized that conventional systems will have higher nutrient losses and lower nutrient retention efficiencies than agroforestry systems.We investigated six paired sites of conventional grassland/cropland and grassland/cropland agroforestry with alley cropping of fast growing tree species and grass/crop, located in central Germany. Results from the growing season of 2016/2017 will be presented. Measurements in agroforestry were taken within tree strips and at various distances to the tree strips within the grass/crop strips. Soil water samples were collected monthly with lysimeters and the samples analyzed for nutrient concentrations (nitrogen, phosphorus, base cations). To calculate yearly nutrient losses, drainage flux was estimated with the model Expert-N. This study will provide the presently needed information on whether alley-cropping agroforestry systems can reduce the negative environmental impacts through leaching losses while optimizing production and therefore might be a sustainable alternative to conventional agriculture