Model Of Soil Water Dynamics Research Articles

Coupling of a nitrate production model with HYDRUS to predict nitrate leaching

Losses of nitrogen fertilizer from agricultural watersheds are among the main causes of water quality degradation in Quebec. Under maize crop, leached nitrate can reach up to 185 kg N ha−1. The synchronization of the nitrogen fertilization with crop uptake would be a way to optimize the use of nitrogen fertilizer and reduce nitrate leaching. Coupling an empirical nitrogen cycle model with a physical soil water dynamics model could simplify the optimization of nitrogen fertilizer use. The objective of this study was to couple the soil surface empirical nitrate production model adapted to the regional agro-climatic conditions of study area with HYDRUS to determine the most suitable combination in order to predict nitrate leaching into subsurface drains.In this study, we used estimation equations of nitrogen pools and transformations in nitrate. The equations, using historical field data, were combined into 60 N-release patterns taking into account a dissolution function of nitrate, 4 transformation and dissolution functions for the ammonium, 5 organic nitrogen pools and 3 N organic nitrogen from the soil and manure release functions. These N release patterns were applied in a mineral fertilizer treatment and four organic fertilizer treatments for a total of 300 unique nitrate release patterns.The results demonstrate the potential of a method to evaluate the contributions of nitrogen based on atmospheric data, crop rotation or soil particle sizes as 5% of the 300 combination gave a Nash–Sutcliffe efficiency coefficient (NSE) above 0.70. The prediction method must be different according to the source of the fertilization, organic or mineral as only 1% of the combination gave NSE above 0.70 in more than one treatment. In addition, the study showed that the soil organic nitrogen contribution to nitrate leaching tends to decrease as the organic fertilizer applications rate increases as 75% of the combination giving NSE above 0.70 in high fertilization treatment used the lower organic N pool and only 17% used the lower organic N pool for the agronomic fertilization rate and mineral fertilizer. The simulations also showed that the nitrate-leached masses are closely related to the fertilizer supply nitrogen content.

An integrated ecohydrological modeling approach to exploring the dynamic interaction between groundwater and phreatophytes

Phreatophytes play an important role in maintaining the ecological services in arid and semi-arid areas. Characterizing the interaction between groundwater and phreatophytes is critical for the land and water management in such areas but has rarely been attempted via integrated ecohydrological modeling. In this study, a plant growth model was developed and coupled with a soil water dynamics model (Hydrus-1D) to explore the groundwater dependence of Populus euphratica, a rare, ancient and endangered phreatophytic species. The integrated ecohydroloigcal model was validated with observational data collected from the Heihe River Basin (northwest China). The groundwater dependence was also investigated at larger scales using remote sensing data and regional hydrological modeling. The major study findings include the following: (1) the ecohydrological behaviors and groundwater dependence of P. euphratica can be well explained by the existing theories; (2) groundwater is the dominant water source for P. euphratica during its growing season, and groundwater subsidy can be an intuitive measure of the water-shortage risk for P. euphratica, which is conditioned on root depth, the water-holding capacity of the soil, and groundwater depth; and (3) at large spatial and temporal scales, the impact of groundwater depth on P. euphratica growth is also discernable. A groundwater depth of 1–3.5m appears to be the optimal depth range for P. euphratica growth in the study area. Overall, this study demonstrates how multi-source and multi-scale data can be effectively fused through an integrated modeling approach to generate a coherent understanding of the ecohydrological processes of phreatophytes.

Effects of Variably Layered Coarse Textured Soils on Plant Available Water and Forest Productivity

Reforestation is a primary end use for reconstructed soils following oil sands mining in northern Alberta, Canada Limited soil water conditions in this climate will restrict plant growth. The objective of this study was to evaluate the effect of soil texture (gradation and layering) on plant available water and consequently on forest productivity for reclaimed coarse textured soils. A previously validated system dynamics (SD) model of soil water dynamics was coupled with ecophysiological and biogeochemical processes model, Biome-BGC-SD, to simulate forest dynamics for different soil profiles. These profiles included contrasting 50cm textural layers of finer sand and coarser sand in which the sand layers had either a well graded or uniform soil texture. These were compared to homogeneous profiles of the same sands. Two tree species of jack pine (Pinus banksiana Lamb) and trembling aspen (Populus tremuloides Michx.) were simulated using a 60-year climatic data base from northern Alberta. Av ilable water holding capacity (AWHC) was used to identify soil water regime, while leaf area index (LAI) and net primary production (NPP) were used as indices of forest productivity. Using the published and previously validated physiological parameters, the Biome-BGC-SD was used to study the responses of forest leaf area index and potential productivity to AWHC on different soil profiles. Simulated results indicated that layering of uniform fine sand overlying coarse sand could significantly increase AWHC in the 1-m profile for coarse textured soils. This enhanced AWHC could result in an increase in forest LAI and NPP. The extent of the increase varied with coarse sand g adation and vegetative types The simulated results showed that the presence of 50cm of uniform fine sand overlyin 50cm of graded coarse sand would provide an effective reclamation prescription to increase AWHC and forest productivity.

Soil-vegetation-climate interactions in arid landscapes: Effects of the North American monsoon on grass recruitment

We used a daily time step, multi-layer simulation model of soil water dynamics to integrate effects of soils, vegetation, and climate on the recruitment of Bouteloua eriopoda (black grama), the historically dominant grass in the Chihuahuan Desert. We simulated landscapes at the Jornada ARS-LTER site with heterogeneous soil properties to compare: (1) a grass-dominated landscape in 1858 with the current shrub-dominated landscape (i.e., a change in vegetation structure), and (2) the current shrub-dominated landscape with future landscapes over a range of climate scenarios associated with the North American monsoon (i.e., a change in climate). A historic shift from high productivity grasslands to low productivity shrublands decreased simulated recruitment for most of the site; the amount of reduction depended on location-specific soil properties and changes in production. In some cases, soil properties interacted with vegetation structure: soils high in clay content maintained high recruitment even with a decrease in production. Wetter summers would increase recruitment in all vegetation types. Drier summers below 25% of current rainfall would decrease recruitment to negligible values (<0.03) throughout the landscape. We used our results to identify the conditions where recruitment of B. eriopoda is possible with and without significant modifications to soil and vegetation.

Compartmental model for nitrogen dynamics in citrus orchards

A simple model that represents the soil nitrogen dynamics in a citrus orchard is studied. This model consists of several compartments of organic and inorganic nitrogen representing the main processes that occur among the compartment of the soil column. Some of these processes are coupled to the carbon dynamics in the soil, thus, the evolution of organic carbon in the soil has been also described in the model. The dependence of these processes with soil moisture requires the coupling of a nitrogen model with a model of soil water dynamics. A compartmental model for the water has been used to simulate the dynamics of water in the root profile. The proposed model has been used to predict the soil mineral nitrogen content and the nitrate leaching in a citrus orchard placed in the area of Valencia and the obtained results have been compared with the results obtained with the nitrogen component of the widely used Leaching Estimation and Chemistry Model (LEACHM).

Analytical Derivation of Steady-State Soil Water Probability Density Function Coupled with Simple Stochastic Point Rainfall Model

In this study, a new stochastic model for the propagation analysis of fluctuations in rainfall to soil water dynamics is proposed. Based on a lumped conceptualization of soil water dynamics with rainfall forcings, which are incorporated by a simple stochastic point rainfall model, a model is derived by using cumulant expansion theory from a stochastic differential equation. The advantage of the model is to provide the probabilistic solution in the form of a probability density function (PDF), from which one can find the ensemble average behavior of the system. Steady-state PDF of soil water is analytically obtained and analyzed for different climate, soil, and vegetation conditions. The city of Daegue in Korea, which represents the driest parts of the Korean, Peninsula, is applied for a case study and the result shows that the analytically derived steady-state soil water PDF can make a good agreement to the numerically obtained steady-state PDF from a lumped conceptualization model of soil water dynamics....

Modeling invasive weeds in grasslands: the role of allelopathy in Acroptilon repens invasion

We used an individual plant-based simulation model (ECOTONE) to evaluate the importance of allelopathy and soil texture to the invasion of semiarid grasslands by the non-native perennial C 3 forb Acroptilon repens. We also assessed the sensitivity of model results to the negative effects of allelochemicals on recruitment and growth of perennial grasses. ECOTONE simulates the recruitment, growth, and mortality of individual plants on a small plot (0.12 m 2) through time at an annual time step. A daily time step, multi-layer model of soil water dynamics (SOILWAT) was incorporated into ECOTONE to represent competition for soil water on a finer temporal scale. The model was parameterized for a shortgrass community in eastern Colorado, USA, using data available from the literature. Experimental simulations examined the effects of four soil textures and a range of levels of plant sensitivity to allelochemicals on the aboveground biomass of A. repens and of native perennial grasses. Simulation results showed that A. repens dominated the aboveground biomass on a plot only if native species were affected by allelopathic interactions. At moderate levels of plant sensitivity, A. repens became dominant faster and reached a higher proportion of the total biomass on fine- than on coarse-textured soils. Community composition and rate of A. repens dominance were more affected by the sensitivity of plant growth to allelochemicals than the sensitivity of species recruitment. Allelopathic interactions were an important component of the invasion dynamics of this perennial invasive weed, and further field investigations are warranted.

Soil water dynamics model for trickle irrigated tomatoes

A soil water dynamics model for establishing the wetting pattern of point source trickle emitters under a tomato crop has been developed and verified. Infiltration from the point source trickle emitters in the presence of water extraction has been investigated by assuming a hemispherical shape of the wetted soil volume and analytic expressions have been derived for determining the position of wetting front. Water extraction by the plants has been estimated by using a macroscopic model of uptake utilizing root length. Daily values of water uptake have been used to update the volumetric moisture content in the root zone layers. The values of soil moisture content predicted by the model compared well with the field-observed values. The predicted values were used to predict the radius of the hemispherical wetted soil volume which forms a basis for deciding emitter spacing for various crops and operating conditions.

Development and Testing of Root Effectiveness Function for Soil Water Uptake

AbstractFor soil water uptake studies under cropped conditions, root effectiveness for soil water absorption is of great significance. For development of root effectiveness function, information on the age of roots present at any soil depth at any time during the crop growth period is needed. For estimation of root age and root effectiveness function, a methodology has been developed. Wheat crop was used as a test crop. It has been observed that root effectiveness for water uptake remains constant during the early period of root growth and thereafter it decreases exponentially with root age. The application of the proposed root effectiveness function was tested successfully using macroscopic model of soil water dynamics which yielded 7.83 per cent variation between observed and simulated soil water content on overall basis in the crop root zone for the entire crop growth season.

Measured and simulated water relations in a Douglas-Fir forest during the development of drought in the Apennines, Central Italy

A model of soil water dynamics (SWATRE) and of the soil-plant-atmosphere continuum (SPAC), including the plant water-retention component, were applied independently to describe the seasonal and diurnal water balance of a forest in Italy. The stand under consideration was a 26-year-old Douglas-fir ( Pseudotsuga menziesii (Mirb.) Franco) plantation with a density of 2044 trees ha −1 and average height of 14.2 m, located in the Apennines in Central Italy, 900 m a.s.l, in a mediterranean climate. Soil water potential was measured with tensiometers and psychrometers 2 or 3 times per week during the summer of 1985. The xylem water potential and leaf stomatal conductance were measured on 4 days in the period June–September 1985, at about 2–3 h intervals from sunrise to sunset. Global and net solar radiation, air temperature and air relative humidity above the canopy were measured. Soil water potentials simulated by the SWATRE model agreed well with the field measurements. The diurnal pattern of bulk stomatal resistance and xylem water potential simulated by the SPAC model also agreed with measurements. The results show that Douglas-fir is surprisingly well adapted to the drought conditions that occurred in Tuscany during the dry year 1985, and even with dry soil, shallow rooting depth and high evaporative demand, trees did not show evident water stress.

SIMULATION OF SOIL WATER DYNAMICS IN LAYERED SOILS

A numerical model of soil water dynamics was devised to simulate infiltration, drainage, evaporation, and water storage in texturally layered profiles. The layers consisted of sandlike, loamlike, and claylike soil of known hydraulic properties. Data presented on the flow patterns of the variously st