Influence of variable biochar concentration on yield-scaled nitrous oxide emissions, Wheat yield and nitrogen use...

An important source of the destructive greenhouse gas, nitrous oxide (N₂O) comes from the use of ammonium based nitrogen (N) fertilizers that release N₂O in the incomplete conversion (nitrification) of NH₄⁺ to NO₃-¹. Biochar has been shown to decrease nitrification rates and N₂O emission. However, there is little information from semi-arid environments such as in Pakistan where conditions favor N₂O emissions. Therefore, the object was to conduct field experiment to determine the impact of biochar rates in the presence or absence of urea amended soils on yield-scaled N₂O emissions, and wheat yield and N use efficiency (NUE). The experiment on wheat (Triticum aestivum L.), had a randomized complete block design with four replications and the treatments: control, sole urea (150 kg N ha^-1), 5 Mg biochar ha^-1 (B5), 10 Mg biochar ha^-1 (B10), urea + B5 or urea + B10. In urea amended soils with B5 or B10 treatments, biochar reduced total N₂O emissions by 27 and 35%, respectively, over the sole urea treatment. Urea + B5 or + B10 treatments had 34 and 46% lower levels, respectively, of yield scaled N₂O over the sole urea treatment. The B5 and B10 treatments had 24-38%, 9-13%, 12-27% and 35-43%, respectively greater wheat above-ground biomass, grain yield, total N uptake, and NUE, over sole urea. The biochar treatments increased the retention of NH₄⁺ which likely was an important mechanism for reducing N₂O by limiting nitrification. These results indicate that amending soils with biochar has potential to mitigate N₂O emissions in a semi-arid and at the same time increase wheat productivity.