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Overuse of nitrogenous fertilizers especially urea has been considered a significant source of reactive N causing acute environmental impacts through leaching, volatilization, and N2O gas emission from fertilized crop fields. However, some recent studies have proposed that such environmental losses of N can be ignored by adapting an alternative way of combining nitrogenous fertilizer with pyrolyzed biomass (biochar). Therefore, the effect of co-application of rice-residue biochar (RB) or poultry manure biochar (PB) along with urea on N dynamics was investigated by conducting a 60-day incubation experiment. The results showed that urea led to greater N mineralization (0.2 µg N g−1 soil day−1) due to the easy availability of ammonical-N (NH4+-N) produced from hydrolysis that acted as a substrate for nitrification. Sole application of biochars (RB or PB) or their co-application with urea resulted in 38–45% and 19–28% lower N mineralization than the sole urea amended soil, respectively. The lower N mineralization in sole biochar or biochar plus urea amended soil was most likely caused due to (1) increased C:N ratio of the biochar amended soil, (2) adsorption of NH4+-N by biochar, (3) microbial immobilization of the nitrogen in the amended soil, and (4) lower urease activity in the treatments amended with biochar. Thus, it may be concluded that the co-application of biochar with urea can reduce N losses through moderation of N mineralization and make it available to plants for longer periods.

Overuse of nitrogenous fertilizers especially urea has been considered a significant source of reactive N causing acute environmental impacts through leaching, volatilization, and N

The impact of biochar on C storage and nutrient cycling when co-applied with other non-pyrolyzed organic amendments is still uncertain. Therefore, an incubation experiment for 120 days was conducted to attain an improved understanding of the capability of biochar for C accretions and nutrient release when co-applied with non-pyrolyzed organic materials like crop-residue (rice-residue) and manure (animal-manure). The results of the study showed that the individual application of biochar (RB), rice residue (RR), animal-manure (AM), or their co-application (RB+RR and RB+AM) enhanced C mineralization by 10%, 85%, 59%, 63%, and, 37%, respectively than the unamended control. Even though the input of C in RB+RR and RB+AM was 82% and 75% more compared with the sole biochar amended soil, comparatively, percentage C loss per g of C added in RB+RR and RB+AM were only 12% and 5% greater than biochar amended soil. Therefore, the results of the study indicate stabilization of C released from labile sources (RR or AM) on the biochar surface that reiterates its greater C accretion potential. Furthermore, soil available nutrients showed no significant difference between the control and sole biochar amended soil, thus validating the limitations of applying biochar individually. On the other hand, a considerable correlation between microbial biomass with plant-available nutrients in the soil co-amended with biochar and non-pyrolyzed organic materials ensured greater availability of nutrients for crop uptake. Thus, co-application of biochar with non-pyrolyzed organic materials could be more beneficial for C accretion and release of nutrients compared with their individual application to soil.