Influence of a gel‐forming conditioner on water retention, infiltration capacity, and water distribution in uniform and stratified sandy soils

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Abstract
The effect of an organic super‐gel conditioner (Jalma) on water retention, saturated hydraulic conductivity (K s), wetting front advance, infiltration rate, and water distribution profiles in uniform and stratified soil columns was investigated. The stratified soil column consisted of two layers: a Jalma‐treated upper layer (10 cm depth) overlaid an untreated lower layer extending to 70 cm depth. Five concentrations of Jalma (J) were used: 0, 0.25, 0.50, 0.75, and 1% (on a dry weight basis). The amount of water retained by the soil at each matric potential over the range of ‐1 to‐15,000 cm significantly increased with increase of J. The water retention curves were fitted by using Van Genuchten's model (r > .983). A sharp decrease in K s was obtained with increase of J, and the relationship was exponential (r = .999). Addition of Jalma to sandy soil created a saturation zone (5 cm depth) and a transition zone (from 5 to 10 cm depth) under ponded infiltration either in uniform or stratified profiles. The wetting front advance (Z) and cumulative infiltration (i) substantially decreased with increase of J. A simplified approach based upon Darcy's law along with the pertinent physical properties of resulting transmission zone was applied to the uniform as well as stratified profiles to compute Z and i. A good agreement was found between the computed and observed Z and i (r > .998). Addition of Jalma caused a decrease in the matric potential of wetting front (Sw). The values of S w in stratified profiles were higher than the corresponding values in uniform profiles. The initial water deficit of transmission zone (D i) increased in the uniform profile but decreased in the stratified profile with increase of J. When Jalma‐treated soil overlay untreated soil, the water content in the untreated soil (lower layer) was consistently lower than the water content at the corresponding depth in a uniform profile of the untreated soil. In general, it is suggested to add Jalma conditioner to the upper sandy layer (10 cm depth) at concentrations ranging from 0.6 to 0.8% for the best water conservation and plant benefit. However, the desired depth of wetting is considered an important factor in selection of an appropriate J.