Responses of field-grown maize to different soil types, water regimes, and contrasting vapor pressure deficit

Drought is a serious constraint on crop growth and production of important staple crops such as maize. Improved understanding of the responses of crops to drought can be incorporated into cropping system models to support crop breeding, varietal selection, and management decisions for minimizing negative impacts. We investigate the impacts of different soil types (stony and silty) and water regimes (irrigated and rainfed) on hydraulic linkages between soil and plant, as well as root : shoot growth characteristics. Our analysis is based on a comprehensive dataset measured along the soil–plant–atmosphere pathway at field scale in two growing seasons (2017 and 2018) with contrasting climatic conditions (low and high vapor pressure deficit). Roots were observed mostly in the topsoil (10–20 cm) of the stony soil, while more roots were found in the subsoil (60–80 cm) of the silty soil. The difference in root length was pronounced at silking and harvest between the soil types. Total root length was 2.5–6 times higher in the silty soil than in the stony soil with the same water treatment. At silking time, the ratios of root length to shoot biomass in the rainfed plot of the silty soil (F2P2) were 3 times higher than those in the irrigated silty soil (F2P3), while the ratio was similar for two water treatments in the stony soil. With the same water treatment, the ratios of root length to shoot biomass of silty soil were higher than for stony soil. The seasonally observed minimum leaf water potential (ψleaf) varied from around −1.5 MPa in the rainfed plot in 2017 to around −2.5 MPa in the same plot of the stony soil in 2018. In the rainfed plot, the minimum ψleaf in the stony soil was lower than in the silty soil from −2 to −1.5 MPa in 2017, respectively, while these were from −2.5 to −2 MPa in 2018, respectively. Leaf water potential, water potential gradients from soil to plant roots, plant hydraulic conductance (Ksoil_plant), stomatal conductance, transpiration, and photosynthesis were considerably modulated by the soil water content and the conductivity of the rhizosphere. When the stony soil and silt soil are compared, the higher “stress” due to the lower water availability in the stony soil resulted in fewer roots with a higher root tissue conductance in the soil with more stress. When comparing the rainfed with the irrigated plot in the silty soil, the higher stress in the rainfed soil resulted in more roots with a lower root tissue conductance in the treatme