Decreases in hydraulic conductivity with decreasing electrolyte concentration and increasing sodium adsorption ratio (SAR) of the percolating solution were assessed for seven soils of varying clay mineralogy. The decreases were particularly pronounced for soils high in 2:1 layer‐silicates, with the most labile hydraulic conductivities being exhibited by those soils containing the most montmorillonite. A soil containing considerable amorphous material was much more stable then the average, and a soil high in kaolinite and sesquioxides was virtually insensitive to variations in solution composition. No property of the solution alone was sufficient to characterize the response of the soils to a given solution, though expression of results in terms of the exchangeable sodium percentage (ESP) of the soil and the total salt concentration of the ambient solution produced more nearly similar curves for soils of similar clay mineralogy. The soils commonly demonstrated rather pronounced hydraulic conductivity decreases in the ESP range of 20 to 35 at salt concentrations of 3 to 50 meq/liter. The decreases were largely irreversible upon the reapplication of high salt or high Ca solutions to the soil, except for those soils containing greater than 10% montmorillonite on a whole‐soil basis.

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A procedure is described for predicting the hydraulic conductivity of soils in the presence of mixed‐salt solutions, after first measuring the absolute hydraulic conductivity of the soil with a single high‐salt, high‐sodium solution, and then measuring the relative hydraulic conductivity of the same sample with a low‐salt solution. Calculated interlayer swelling values for soil montmorillonite serve as a frame of reference for the predictions. Swelling values are obtained using a simplified domain model for characterizing the exchangeable‐cation distribution on Na‐Ca montmorillonites. Reliability of the procedure is established with a group of soils having variable clay content but constant clay‐fraction mineralogy. The effect of soil texture on relative hydraulic conductivity to mixed‐salt solutions appears to be adequately accounted for through the interlayer swelling values used for the predictions.

There are few growth studies evaluating within‐season effects of N on vegetative growth and N accumulation of tomato (Lycopersicon esculentum Mill.). Growth analysis of field‐grown tomato for a number of Florida locations and management systems is presented here. Severe N stress resulted in fewer and smaller, but thicker, leaves. With increasing N, average leaf area index (LAI) increased from ≈0.75 to ≈3, but radiation use efficiency (RUE) typically increased less then 30%. Lower RUE under N‐limited conditions reflected a decrease in N concentration of the most recently matured leaves from 40 mg g−1 to as little as 15 mg g−1. Over the life of well‐fertilized crops, leaf N concentrations dropped from 55 to 65 mg g−1 during initial growth to 20 to 35 mg g−1 at final harvest. Corresponding N concentrations for fruit and for stems were 30 to 35 mg g−1 and 15 to 25 mg g−1. Severe N stress affected leaf and stem N concentrations most drastically, whereas N in fruits was less variable. With lower N supply (N < 180 kg ha−1) under careful management, nitrogen use efficiency (NUE) for field‐grown tomato was ≈0.4 Mg fresh fruit (kg N)−1 and average crop N accumulation increased from 37 to 210 kg N ha−1 as N fertilization increased from 0 to 333 kg N ha−1. As a fraction of the fertilizer N applied N fertilizer recovery ranged from 0.36 to 0.74 and 0.61 to 0.96 for drip‐irrigated and subirrigated crops, respectively.

For a group of soils having variable clay content but nearly uniform clay‐fraction mineralogy, relative hydraulic conductivity in the presence of mixed‐salt solutions decreased markedly with increasing clay content, particularly at the lowest salt concentrations employed. The stability of a group of Hawaiian soils under high‐sodium, low‐salt conditions was greatly reduced by partial removal of the free iron‐oxides. Replacing the Ca in percolating NaCl‐CaCl2 solutions with Mg measurably decreased soil hydraulic conductivity, although the effect was often negligible when comparisons were made at equivalent exchangeable‐sodium‐percentages.