Deficit irrigation drives maize root distribution and soil microbial communities with implications for soil carbon dynamics

Increased food demand and water scarcity require the efficient use of agricultural water. Deficit irrigation (DI) can reduce water use with relatively small impacts to crop yield. However, the effects of DI-associated water stress on root and soil properties remain poorly understood. We examined the impact of water stress via DI on maize (Zea mays L.) root growth, soil microbial community composition, soil aggregation, and soil organic C (SOC) concentrations at two depths (0-20 and 40-60 cm) after 4 yr of treatment implementation. Water stress during the late vegetative stage increased root growth at both soil depths in all stress treatments (significantly at 40-60 cm) but led to lower microbial biomass, assessed using phospholipid fatty acid (PLFA) analysis. Moreover, water stress led to a lower abundance of arbuscular mycorrhizal fungi markers in the drier treatments. After 4 yr of treatment, we did not find significant differences in SOC. However, a trend towards higher SOC and greater root biomass in the driest treatment indicated the potential to build soil C in deeper soil layers with larger root C inputs. Soil aggregation was generally greater in deeper soils (average increase of 24%). Overall, the observations in this study indicate that DI alters root growth and soil microbial community structure with the potential to impact SOC storage and overall agroecosystem function beyond the 4-yr timeframe considered in this study.