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The soil moisture dynamics of the root zone and its hydrological interactions with the vadose zone below in deep groundwater table condition has not been thoroughly elucidated to date, thereby hampering our adaption of irrigation in farmlands with a deep groundwater table. In this study, vadose zone modelling detailing the soil moisture dynamics of the root zone in farmland with a deep groundwater table in the North China Plain, was presented to investigate the regular pattern of the soil hydrological processes during crops growing periods and to examine its implications for adjustment of irrigation applications of wheat and maize. Deep percolation reached over 30% of the total water input while root zone hardly obtain any moisture supplement from the vadose zone below, during the crops growing period, from April to September in 2012 and 2013, both being typical wet years. Corresponding to the seasonal distribution of precipitation, the soil evaporation and deep percolation were concentrated in the growing period of maize, rather than in the growing period of wheat. Additionally, soil water storage in the root zone before irrigation applications in the growing periods of wheat can be 100–120 mm less than it in growing periods of maize. On the basis of these soil hydrology characteristics in the root zone, the current irrigation scheduling for wheat could be adjusted to be more adequate but less frequent, while intensity and frequency of irrigation applications for maize should both be decreased to reduce deep percolation and soil evaporation. An example simulation in the crop growing period of 2012, showed that deep percolation and soil evaporation can be decreased by 36% and 18% respectively, with little impacts on crops transpiration, under the adjusted irrigation practice. This research suggests the direction and potential of adjustment of irrigation scheduling in farmlands with a deep groundwater table from the perspective of soil hydrological processes. [ABSTRACT FROM AUTHOR]

Management and irrigation of plants increasingly relies on accurate mathematical models for the movement of water within unsaturated soils. Current models often use values for water content and soil parameters that are averaged over the soil profile. However, many applications require models to more accurately represent the soil-plant-atmosphere continuum, in particular, water movement and saturation within specific parts of the soil profile. In this paper a mathematical model for water uptake by a plant root system from unsaturated soil is presented. The model provides an estimate of the water content level within the soil at different depths, and the uptake of water by the root system. The model was validated using field data, which include hourly water content values at five different soil depths under a grass/herb cover over 1 year, to obtain a fully calibrated system for plant water uptake with respect to climate conditions. When compared quantitatively to a simple water balance model, the proposed model achieves a better fit to the experimental data due to its ability to vary water content with depth. To accurately model the water content in the soil profile, the soil water retention curve and saturated hydraulic conductivity needed to vary with depth. [ABSTRACT FROM AUTHOR]

Highlights: [•] Interaction between belowground and aboveground water ecohydrologic dynamics. [•] Water uptake simulation both at the microscopic and macroscopic levels. [•] Macroscopic models have moisture uptake pattern constant, linear and exponential. [•] Non-linear macroscopic models have improved moisture prediction efficiency. [•] To verify the modeled moisture uptake patterns, precisely obtained field data is vital. [Copyright &y& Elsevier]

An empirical relationship is developed for the nonlinear root water uptake parameter in the O-R moisture uptake model from easily measurable plant physiological parameters, such as maximum daily transpiration, maximum root depth, and time to attain the maximum transpiration. A nondimensional parameter, termed specific transpiration, that involves the plant physiological parameters is used in this empirical relationship. Data for determining this relationship are obtained by minimizing the deviations between the field observed moisture depletions of 28 crops reported in the literature, and the Richards equation-based numerically simulated soil moisture depletions combined with the moisture uptake model accounting for root water uptake. In addition to cross-validation, field experiments on three Indian crops (maize, Indian mustard, and wheat) are conducted to further validate the proposed empirical relationship. Comparisons of model predictions with field observations of soil moisture profiles and moisture depletions in different layers of the root zone show good agreement during different stages of crop growth. The results highlight the utility of the developed equation for modeling root water uptake over a wide range of crops. [ABSTRACT FROM AUTHOR]