No abstract

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.

Precise water and fertilizer application can increase crop water productivity and reduce agricultural contributions to greenhouse gas (GHG) emissions. Regulated deficit irrigation (DI) and drip fertigation control the amount, location, and timing of water and nutrient application. Yet, few studies have measured GHG emissions under these practices, especially for maize (Zea mays L.). The objective was to quantify N 2 O and CO 2 emission from DI and full irrigation (FI) within a drip-fertigated maize system in northeastern Colorado. During two growing seasons of measurement, treatments consisted of mild, moderate, and extreme DI and FI. Deficit irrigation was managed based on growth stage so that full evapotranspiration (ET) was met during the yield-sensitive reproductive stage, but less than full crop ET was applied during the late vegetative and maturation growth stages. In the first year, mild DI (90% ET) reduced N 2 O emissions by 50% compared with FI. In the second year, compared with FI, moderate DI (69-80% ET) reduced N 2 O emissions by 15%, and extreme DI (54-68% ET) reduced N 2 O emissions by 40%. Only extreme DI in the second year significantly reduced CO 2 emissions (by 30%) compared with FI. Mild DI reduced yield-scaled emissions in the first year, but moderate and extreme DI had similar yield-scaled emissions as FI in the second year. The surface drip fertigation resulted in total GHG emissions that were one-tenth of literature-based measurements from sprinkler-irrigated maize systems. This study illustrates the potential of DI and drip fertigation to reduce N 2 O and CO 2 emissions in irrigated cropping systems.