Biochar and manure amendments impact soil nutrients and microbial enzymatic activities in a semi-arid irrigated maize cropping system

•Biochar increased soil total C, and slightly varied microbial biomass and moisture.•Manure increased soil total soil N, available P, microbial biomass and moisture.•Activity of extracellular enzymes shifted with biochar, but not with manure amendment.•Limited irrigation maintained maize yield, while amendments showed no effect. To mitigate negative impacts on crop yield from water-saving limited irrigation, we tested the effect of two organic amendments on soil moisture and nutrients. In an experimental maize field in northern Colorado, we tilled in conventional steer manure (30Mgha−1) and fast-pyrolysis pine-wood biochar (30Mgha−1). We quantified impacts on gravimetric soil moisture, total carbon and nitrogen, mineral nitrogen, available phosphorus, microbial biomass, and seven extracellular enzymatic activities (EEAs). Compared to the control, manure amendments increased gravimetric soil moisture by approximately 15%, total nitrogen by 10%, available phosphorus by 45%, and microbial biomass carbon by 15% (p