Plant uptake of nitrogen adsorbed to biochars made from dairy manure

Abstract

The conversion of dairy waste with high moisture contents to dry fertilizers may reduce environmental degradation while lowering crop production costs. We converted the solid portion of screw-pressed dairy manure into a sorbent for volatile ammonia (NH₃) in the liquid fraction using pyrolysis and pre-treatment with carbon dioxide (CO₂). The extractable N in manure biochar exposed to NH₃ following CO₂ pre-treatment reached 3.36 g N kg^-1, 1260-fold greater extractable N than in untreated manure biochar. Ammonia exposure was 142-times more effective in increasing extractable N than immersing manure biochar in the liquid fraction containing dissolved ammonium. Radish and tomato grown in horticultural media with manure biochar treated with CO₂ + NH₃ promoted up to 35% greater plant growth (dry weight) and 36-83% greater N uptake compared to manure biochar alone. Uptake of N was similar between plants grown with wood biochar exposed to CO₂ + NH₃, compared to N-equivalent treatments. The available N in dairy waste in New York (NY) state, if pyrolyzed and treated with NH₃ + CO₂, is equivalent to 11,732-42,232 Mg N year^-1, valued at 6-21.5 million USD year^-1. Separated dairy manure treated with CO₂ + NH₃ can offset 23-82% of N fertilizer needs of NY State, while stabilizing both the solid and liquid fraction of manure for reduced environmental pollution.