The phosphorus fertilizer effect of biochar from municipal sewage sludge

Phosphate is an essential, growth-limiting plant nutrient that is regularly applied as fertilizer. Fertilizers from mined rock phosphate are getting more expensive as global phosphate reserves are limited and progressively exhausted. Phosphorus from sewage sludge offers huge potential for replacing manufactured phosphate fertilizer. The P fertilizer potential of biochars from the pyrolysis of sewage sludge has not yet been investigated in field experiments on Central European soils. Therefore, sewage sludge biochar and triple superphosphate (TSP) were tested against an unfertilized control in a randomized block-design field experiment with maize at a sandy Gleysol in Brandenburg/Northeastern Germany. Sewage sludge biochar enriched the soil in plant-available P less than TSP. The total P concentration in soil was largest in the sewage sludge biochar treatment. For maize crop yield and P uptake the order of treatments was control < TSP < sewage sludge biochar in each of the three experimental years. Yields were larger by factor 1.1 to 1.3 in the sewage sludge biochar treatment compared to control. Since our data on yield effects and P uptake are in good agreement with similar data from comparable experiments elsewhere, our investigations demonstrate a pronounced P fertilizer effect of sewage sludge biochar in sandy soils.