Abstract: Against the backdrop of climate change, extreme drought has become the primary water constraint for agriculture in drylands. A field experiment was conducted in a severe drought year, using the waxy sorghum cultivar “Yiwuhong 4”. There were four treatments: straw strip mulching (SSM), SSM with conventional microbial fertilizer (MSM), SSM with biochar-based microbial fertilizer (BSM), and flat planting without mulching (NM) as the control. Results showed that the SSM, MSM, and BSM treatments significantly increased the average soil water storage in 1-m soil profile by 21.8 mm (a 9.0% increase) while decreased total water consumption by 30.8 mm (an 8.5% reduction) during the sorghum growth period from jointing to maturity. Moreover, these mulching treatments (SSM, MSM, BSM) optimized water consumption structure and reduced soil water depletion by 28.9-31.9 mm, with the majority of this reduction occurring in the shallow surface (0-20 cm) and deep soil layers (below 60 cm). The application of microbial fertilizer further enhanced soil moisture conservation effect of SSM. Compared to SSM alone, the MSM and BSM treatments significantly increased soil water storage by 3.1%-4.9% during the jointing to booting stage. This enhanced water status promoted vegetative growth (plant height, leaf area, stem diameter, and biomass), driving substantial increases in grains per spike (41.5%-55.6%) and grain weight per spike (18.2%-32.5%). Ultimately, these treatments achieved yield increases by 21.8%-27.7% and improved water use efficiency by 30.9%-39.4%, with BSM performing best. Thus, BSM is the recommended practice for water-saving, high-yield sorghum production under extreme drought in the hilly purple soil areas of southwest China.

Key words: extreme drought, straw strip mulching, microbial fertilizer application, water consumption characteristics, waxy sorghum yield