ABSTRACT Simulations for root growth, crop growth, and N uptake in agro-hydrological models are of significant concern to researchers. SWMS_2D is one of the most widely used physical hydrologically related models. This model solves equations that govern soil-water movement by the finite element method, and has a public access source code. Incorporating key agricultural components into the SWMS_2D model is of practical importance, especially for modeling some critical cereal crops such as winter wheat. We added root growth, crop growth, and N uptake modules into SWMS_2D. The root growth model had two sub-models, one for root penetration and the other for root length distribution. The crop growth model used was adapted from EU-ROTATE_N, linked to the N uptake model. Soil-water limitation, nitrogen limitation, and temperature effects were all considered in dry-weight modeling. Field experiments for winter wheat in Bouwing, the Netherlands, in 1983-1984 were selected for validation. Good agreements were achieved between simulations and measurements, including soil water content at different depths, normalized root length distribution, dry weight and nitrogen uptake. This indicated that the proposed new modules used in the SWMS_2D model are robust and reliable. In the future, more rigorous validation should be carried out, ideally under 2D situations, and attention should be paid to improve some modules, including the module simulating soil N mineralization.

There is a need for developing an accurate and simple method, which can be widely used in agro-hydrological models. The Integrated Richards Equation method is a good and simple method to simulate cyclic movement of water in the soil-atmosphere system. However, this method still has some unsolved problems and it is needed for further development if used in agro-hydrological simulation. In this study, the Integrated Richards Equation method was further developed for the agro-hydrological simulation by introducing the commonly used soil hydraulic functions, top and lower boundary conditions. Infiltration numerical experiments and a lab evaporation experiment were used for the validation of the model's capabilities of modelling infiltration and evaporation, respectively. A field evaporation experiment, which was conducted from 27 April to 21 November in 1971, at Big Ground field, Wellesbourne, UK, was used for in-site validation. Soil samples from four replicate plots were taken at 5 cm increments to a depth of 45 cm at regular intervals throughout the experiment. In total, 10 measurements of soil water content down the profile for ten different times were taken during the experiment. Numerical infiltration experiments showed that the proposed method could give good predictions for two contrasting soils, loamy sand and clay loam, under unsteady intense rainfall conditions. The results were in line with those from the complex numerical scheme of FEM. Good results were also obtained in testing the method for evaporation from coarse sand, but the method under-predicted the amount of evaporation from fine sand. The results of testing against data from the field experiment show that the predicted soil water content was in good agreement with the measured values down the soil profile, but not for the soil close to the surface. This indicates that the proposed method performed well in agro-hydrological simulations on agricultural bare soils under different complex conditions at the upper boundary. Thus the method could be applied in agro-hydrological simulations.

Es necesario desarrollar un método preciso y sencillo que pueda usarse ampliamente en modelos agro-hidrológicos. El método integrado de la ecuación de Richards es un método sencillo para simular el movimiento cíclico del agua en el suelo y la atmósfera. Sin embargo, este método tiene todavía algunos problemas por resolver, necesarios para su desarrollo adicional si se utiliza en simulación agro-hidrológica. En este estudio, el método integrado de la ecuación de Richards fue desarrollado para simulación agro-hidrológica con la introducción de las funciones hidráulicas del suelo usadas comúnmente, condiciones de frontera superiores e inferiores. Los experimentos numéricos de infiltración y el de evaporación en laboratorio fueron utilizados para la validación de las capacidades del modelo en el modelado de infiltración y evaporación, respectivamente. Un experimento de evaporación de campo realizado del 27 de abril al 21 de noviembre de 1971, en Big Ground, Wellesbourne, Reino Unido, se usó en la validación de sitio. Muestras de suelo de cuatro réplicas de parcelas fueron tomadas a 45 cm profundidad en intervalos regulares de aumento de 5 cm durante el experimento. Diez mediciones del contenido de humedad del suelo hacia abajo del perfil en diez momentos diferentes se tomaron durante el experimento. Experimentos de infiltración numérica mostraron que el método propuesto podría generar predicciones buenas de dos suelos contrastantes, franco arenoso y franco arcilloso, con condiciones inestables de lluvias intensas. Los resultados concuerdan con los de la combinación numérica compleja del modelo FEM. Resultados buenos también se obtuvieron en las pruebas del método de evaporación de arena gruesa, pero el método de arena fina predijo menor cantidad evaporada. Los resultados de las pruebas en comparación con los datos del experimento de campo muestran que el contenido predicho de agua del suelo estuvo de acuerdo con los valores medidos en el perfil del suelo, pero no con los cercanos a la superficie del suelo. Esto indica que el método propuesto realizó bien las simulaciones agro-hidrológicos en suelos agrícolas desnudos en condiciones complejas diferentes en la frontera superior. Así, el método podría aplicarse en simulaciones agro-hidrológicas.

RESUMO A avaliação quantitativa da qualidade física do solo é de grande importância para a poluição ambiental e qualidade do solo. Neste trabalho, com base na teoria S, dados de 16 locais da bacia do rio Haihe, China, foram usados para investigar os efeitos do teor de argila e da densidade do solo em três importantes índices da teoria S em escala regional. As relações entre a condutividade hidráulica não saturada Ki no ponto de inflexão e o valor de S (S/hi) foram também estudados, usando dois tipos diferentes de equações. Os resultados evidenciaram que a equação polinomial foi melhor que a linear para descrever as relações entre -log Ki e -log S; e -log Ki e -log (S/hi)2, e o teor de argila foi mais importante em influenciar o índice de qualidade do solo (S). A variação do índice S com base no teor de argila foi adequado para ajuste usando uma linha linear dupla, com o decréscimo no índice S muito mais rápido para teor de argila menor que 20 %. A densidade do solo, entretanto, foi o índice de menor importância comparativamente ao teor de argila. O índice S médio foi 0,077, indicando que a qualidade física do solo da bacia do rio Haihe estava boa.

ABSTRACT Quantitative assessment of soil physical quality is of great importance for eco-environmental pollution and soil quality studies. In this paper, based on the S-theory, data from 16 collection sites in the Haihe River Basin in northern China were used, and the effects of soil particle size distribution and bulk density on three important indices of theS-theory were investigated on a regional scale. The relationships between unsaturated hydraulic conductivityKi at the inflection point and S values (S/hi) were also studied using two different types of fitting equations. The results showed that the polynomial equation was better than the linear equation for describing the relationships between -log Ki and -logS, and -log Kiand -log (S/hi)2; and clay content was the most important factor affecting the soil physical quality index (S). The variation in the S index according to soil clay content was able to be fitted using a double-linear-line approach, with decrease in the S index being much faster for clay content less than 20 %. In contrast, the bulk density index was found to be less important than clay content. The average S index was 0.077, indicating that soil physical quality in the Haihe River Basin was good.