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

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.