Model for Estimating Soil Water, Plant, and Atmospheric Interrelations: II. Field Test of Model

Abstract

A mathematical model was developed to predict water content profiles, evapotranspiration, water flow from or to the water table, root extraction, and root water potential at the surface under transient conditions.The model was field tested in 1970 and 1971. With alfalfa (Medicago sativa L.) as the crop, predicted and computed water content‐depth profiles show best agreement 48 hours after any water addition. The poorest agreement for all crops tested was right after irrigation.The computed cumulative upward water flow from the water table was 4.80 cm as compared to 0.0 cm measured for the whole 1971 season of 116 days.

Long‐Term Soil Water Dynamics in the Shortgrass Steppe

“…We used a model developed for the shortgrass steppe and validated against a data set collected during 1972 at the CPER (Parton 1978). The structure of the model is similar to that of other soil water models (Kohler andRichards 1962, Nimah andHanks 1973) and operates with a daily time step. The model simulates the movement of water through the plant canopy and 11 soil layers (0-2.5, 2.5-4, 4-15, 15-30, 30-45, 45-60, 60-75, 75-90, 90-105, 105-120, 120-135 em).…”

Assessment of solute fluxes beneath an orchard irrigated with treated sewage water: A numerical study

“…Neglecting chloride uptake by the plant roots, assuming that the effects of salinity stress and water stress on the plants are additive, the macroscopic sink term in equation is given [ Nimah and Hanks , ; Feddes et al ., ; Bresler , ] as where ψ r ( t ) is the pressure head at the root‐soil interface; ψ t ( x , t )= ψ ( x , t )+ π ( x , t ) and π ( x , t ) are the total water pressure head and the osmotic pressure head of the soil solution, respectively; R e ( x , t )= R z ( x 1 ) R k ( x 2 , x 3 ) is the root effectiveness function; R z ( x 1 ) is a normalized root depth‐distribution function; and R k ( x 2 , x 3 ) is a time‐invariant, bivariate normal distribution function [ Coelho and Or , ], accounting for the lateral distribution of the roots associated with a given tree; for more details, see Russo et al . [].…”

Numerical analysis of flow and transport from a multiple‐source system in a partially saturated heterogeneous soil under cropped conditions

“…It is assumed here that locally, the rate of water uptake by the plant roots is proportional to the unsaturated conductivity and to the difference between the total pressure head at the root‐soil interface, Ψ r , and the reduced water pressure head of the soil, ψ + π, where π is the osmotic pressure head of the soil solution. According to this approach [i.e., Nimah and Hanks , 1973a, 1973b; Feddes et al , 1974, Bresler , 1987], the sink term S w in is where R e (x, t) is the root effectiveness function, which, in turn, is proportional to the specific area of the soil‐root interface and inversely proportional to the impendence of the soil‐root interface, and is given here by where R z (x 1 ) is a normalized root depth distribution, and R k (x 2 , x 3 ) is a time‐invariant, bivariate normal distribution [ Coelho and Or , 1996], which accounts for the lateral distribution of the root effectiveness function associated with the kth tree, given by: where x′ k2 = x k2 − x 2 , x′ k3 = x k3 − x 3 , x k2 and x k3 are the coordinate locations of the kth tree at the soil surface, μ 2 and μ 3 , σ 2 2 and σ 3 2 and b k2 = x k2 ± √(3σ 2 2 ) and b k3 = x k3 ± √(3σ 3 2 ) are the mean values, variances, and the so‐called ranges, respectively, of R k (x 2 , x 3 ) in the directions along the x 2 axis and the x 3 axis, respectively. Note that b k2 and b k3 determine the lateral extent of the influence of the roots of the kth tree.…”