fruit trees. Another study in Finland indicated that the use of urine and the use of urine and wood ash "could produce 27% and 10% more red beet root biomass". Urine has been proven in many studies to be a valuable, relatively easy to handle fertilizer, containing nitrogen, phosphorus, potassium and important micro-nutrients. Phosphorus recovery Another aspect that ecosan systems are trying to address is the possible upcoming shortage of phosphorus. Phosphorus has an important role for plant growth, and therefore in fertilizer production, but is a limited mineral resource. The situation is similar for potassium. Known mineral phosphate rock reserves are becoming scarce and increasingly costly to extract – this is also called the "peak phosphorus" crisis. One review of global phosphate supply suggested that if collected, phosphate in urine could supply 22% of the total demand. Benefits Benefits of ecosan systems include: Minimizing the introduction of pathogens from human excreta into the water cycle (groundwater and surface water) - for example groundwater pollution by pit latrines. Conservation of resources through lower water consumption, substitution of mineral fertilizer and minimization of water pollution. Less reliance on mined phosphorus and other non-renewable resources for fertilizer production. Reduced consumption of energy in fertilizer production: Urea is a major component of urine, yet we produce vast quantities of urea by using fossil fuels. By properly managing urine, treatment costs as well as fertilizer costs can be reduced. Challenges The ecosan approach has been criticized for being overly focused on reuse in agriculture, whilst neglecting some of the other criteria for sustainable sanitation. In fact, ecosan systems can be "unsustainable", for example, if there is too little user acceptance or if the costs of the system are too high for a given target group of users, making the system financially unsustainable in the longer term. Some proponents of ecosan have been criticized as being too dogmatic, with an over-emphasis on environmental resource protection rather than a focus on public health protection and provision of sanitation at a very low cost (for example UDDTs, which some people call "ecosan toilets", may be more expensive to build than pit latrines, even if in the longer term they are cheaper to maintain). The safety of ecosan systems in terms of pathogen destruction during the various treatment processes is a continuous topic of debate between proponents and opponents of ecosan systems. However, the publication of the WHO