A FIELD experiment was conducted for two successive summer seasons of 2016 and 2017 to explore the effect of amending Moshtohor soil (TypicTorriorthent of 71.9% clay)
with biochar at four different rates namely 0, 13, 26 and 39 Mg ha-1 on the outcome yield of maize grains grown thereon. The effect ofthis amendment was considered in relation with reduced irrigations, i.e. 60 and 80% vs. 100% water requirements (WR). The efficiency of the applied treatments were estimated using the pyramid model after considering (1) water use efficiency (WUE), (2) soil CO2 emissions and (3) soil bulk density. Results revealed that
increasing the rate of applied biochar resulted in significant improvements in both maize grain
yield and soil physical characteristics. However, this amendment also increased the emission of soil CO2. Decreasing the amount of irrigation water resulted in significant increases in water use efficiency while recorded no significant effect on the grain yield. Moreover, the reduced irrigation water requirements improved significantly soil physical properties (soil bulk density, soil aggregation, pF characteristic curves and soil hydraulic conductivity), while, at the same time, minimized the emissions of soil CO2. Generally, the effect of biochar seemed to be more pronounced in the second growing season than in the first one. Although, the treatment of 26 Mg biochar ha-1 + 80% WR recorded the highest efficient indicator, yet the outcome yield was significantly lower than that occurred due to the application of 39 Mg biochar ha-1+60 % WR. Moreover, the calculated efficiency indicators seemed to be comparable between these two treatments. Thus, it is recommended to use only 60% of WR on soils amended with 39 Mg biochar ha-1. This treatment increased the grain yield by 1.96 fold higher than the control while saved 40% of the water requirements.