Sewage sludge biochar increases nitrogen fertilizer recovery: Evidence from a 15N tracer field study

Sewage sludge-derived biochar (SSBC) could improve nitrogen (N) use efficiency (NUE) and reduce the use of mineral N fertilizers in agriculture. However, information on the residual effect (after stopping amendment) of SSBC on NUE is scarce, but necessary, to evaluate how often biochar should be applied to agricultural crops. In this study, the residual effect of SSBC produced at different temperatures on NUE of corn, by using the N-15 isotope tracer, was investigated. The following treatments were assessed in a tropical field study carried out for four years: (a) MF-mineral fertilizer application with nitrogen, phosphorus and potassium (NPK); (b) MF + SSBC produced at 300 degrees C (B3 + MF); and (c) MF + SSBC produced at 500 degrees C (B5 + MF). The contents of soil total N (TN), N in corn derived from the soil (NDS) and from mineral fertilizer (NDMF) were determined. In addition, the N-fertilizer recovery efficiency (NFRE) in the corn grains and straw was evaluated. Application of SSBC increased N uptake by corn from both the fertilizer (NDMF) and the soil (NDS). All treatments presented similar grain yields. On average, the plants took up N predominantly from soil (88.5 kg ha(-1) in straw; 68.7 kg ha(-1) in grains) compared with mineral fertilizer (51.9 kg ha(-1) in straw; 62.3 kg ha(-1) in grains). Results of the current study indicate that SSBC is able to improve the N use efficiency, even two years after amendment, and consequently, it may reduce the use of mineral fertilizers in agriculture.

Automated summary

This study found that the use of sewage sludge-derived biochar can improve nitrogen use efficiency in corn, even two years after application is stopped. This may lead to a reduction in the use of mineral fertilizers in agriculture.