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

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 (30 Mg ha−1) and fast-pyrolysis pine-wood biochar (30 Mg ha−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 < 0.05). Relative to the control, biochar increased total soil carbon by 80% and altered EEAs (p < 0.05). Biochar significantly increased α-1,4- glucosidase, β-d-cellobiohydrolase, and β-1,4-N-acetylglucosaminidase and significantly decreased β-1,4-glucosidase and phosphatase activities (p < 0.05). Despite the effects on soil moisture, nutrient availability, and microbial dynamics, neither amendment significantly impacted maize yield under limited irrigation. Ongoing measurements will allow us to fully assess longer-term impacts on yield.