Showing papers in "Soil Science in 1970"

Hysteresis of pore water in granular porous bodies

Abstract: EXPERIMENTAL DATA ARE REPORTED CONCERNING THE HYSTERESIS BEHAVIOR OF POROUS BODIES OF A SUBSTANTIAL MASS MADE UP OF SAND GRAINS AND RESULTS ARE COMPARED WITH PREDICTIONS OF THE INDEPENDENT DOMAIN CONCEPT. TUBE COLUMNS OF MATERIAL ARE USED AND THE GEOMETRY STABILIZED BY OVERBURDEN PRESSURE. THE DYNAMIC METHOD UTILIZES THE FACT THAT A SUFFICIENTLY LONG COLUMN OF A POROUS MATERIAL DRAINING TO A STATIONARY WATER TABLE ATTAINS IN ITS UPPER PART A STATE OF UNIFORM MOISTURE CONTENT AND A SUCTION WHEN SUBJECTED TO INFILTRATION AT ITS UPPER END AT A CONSTANT RATE. THIS CONSTANT FLOW RATE EQUALS THE HYDRAULIC CONDUCTIVITY OF THE POROUS BODY AT THE GIVEN MOISTURE CONTENT AND SUCTION. SOME EXPERIMENTAL RESULTS CONCERNING THE HYSTERESIS OF THE HYDRAULIC CONDUCTIVITY ARE REPORTED.

Comparison of the adsorption of molybdate, sulfate and phosphate by soils.

Abstract: In acid soils, three plant-nutrient anions - phosphate, sulfate, and molybdate - may be adsorbed by mineral surfaces. The availability of phosphate and of sulfate to plants is much affected by this adsorption. It seems likely that molybdenum availability would be similarly affected by molybdenum adsorption. Thus measurements of the ability of soils to adsorb molybdate phosphate and sulfates was measured in relation to plant availability. A further objective was to test the applicability of these theories to soil.

Calculation of electrical conductivity from solution composition data as an aid to in situ estimation of soil salinity.

Abstract: TO TEST THE EXTRAPOLATION OF SATURATION-EXTRACT ANALYSES TO FIELD-WATER CONTENTS, AND TO PROVIDE A MEANS TO TEST THE PERFORMANCE OF SALINITY SENSORS, SEVERAL METHODS FOR CALCULATING THE ELECTRICAL CONDUCTIVITY (EC) OF MIXED-SALT SOLUTIONS HAVE BEEN DEVELOPED AND TESTED ON SATURATION- EXTRACT DATA FROM 193 SOILS. MOST METHODS WERE BASED ON THE ADDITIVITY OF VALUES FOR INDIVIDUAL-ION EC IN BOTH SINGLE- SALT AND MIXED-SALT SOLUTIONS. UP TO 4--6 MMHO/CM AND UP TO 15--40 MMHO/CM, THE CALCULATED AND MEASURED EC COMMONLY AGREED TO WITHIN PLUS OR MINUS 0.2 AND 1.0 MMHO/CM, RESPECTIVELY, DEPENDING ON THE METHOD USED. A SINGLE THIRD- ORDER POLYNOMIAL FOR EACH ION PROVED SATISFACTORY FOR PREDICTING THE EC OF MOST SINGLE-SALT SOLUTIONS CONTAINING THE ION AND A COUNTERION. THE MAIN EXCEPTIONS WERE SOLUTIONS CONTAINING CA2+ AND SO(SUB 4)2-, MG2+, AND SO(SUB 4)2-, OR BOTH. THE THREE SPECIES WERE SUBSEQUENTLY ALLOCATED TO (CA, MG)SO(SUB 4) AND ASSIGNED A SINGLE EC-CONCENTRATION RELATIONSHIP FOR ALL MIXED-SALT SOLUTIONS. DESPITE THE AGREEMENT BETWEEN CALCULATED AND MEASURED EC FOR SINGLE-SALT SOLUTIONS, CALCULATED VALUES FOR MIXED-SALT SOLUTIONS WERE CONSISTENTLY HIGH ABOVE AN EC OF 3 MMHO/CM. SATISFACTORY AGREEMENT WAS OBTAINED BY APPLYING A CORRECTION FACTOR TO THE VALUES OF EC CALCULATED FROM THE POLYNOMIAL METHOD. GOOD AGREEMENT OF CALCULATED AND MEASURED EC WAS ALSO OBTAINED WHEN EXPONENTIAL OR LINEAR-SEGMENT METHODS WERE USED FOR THE CALCULATIONS. THE TWO LATTER METHODS GAVE LOW VALUES FOR THE EC OF SINGLE-SALT SOLUTIONS, AND HENCE COMPENSATED SOMEWHAT FOR THE TREND TOWARD HIGH EC IN MIXED-SALT SOLUTIONS. THE LINEAR SEGMENT METHOD FOR CALCULATING EC IS SUFFICIENTLY SIMPLE FOR ROUTINE CALCULATIONS WITH A HAND CALCULATOR, BUT BOTH THE EXPONENTIAL AND CORRECTED POLYNOMIAL METHODS ARE BEST HANDLED WITH A DIGITAL COMPUTER. ALL THREE METHODS CONSISTENTLY GAVE MORE ACCURATE RESULTS THAN DID A REGRESSION OF EC ON TOTAL CONCENTRATION. /AUTHOR/

The effect of the entrapped air on the hysteresis curves of a porous body and on its hydraulic conductivity.

Abstract: EXAMPLES ARE PRESENTED OF THE ULTIMATE BOUNDARY DRYING CURVE OF A POROUS BODY. THE DIFFERENCE BETWEEN THE SATURATION MOISTURE CONTENT AND THE ULTIMATE MOISTURE CONTENT AT ZERO SUCTION REPRESENTS THE TOTAL VOLUME OF AIR ENTRAPPED DURING THE PASSAGE OF THE FIRST BOUNDARY WETTING CURVE. THE REPRODUCIBILITY OF THE HYSTERESIS LOOP WHICH CORRESPONDS TO A CERTAIN CYCLE OF SUCTION CHANGES, SUGGESTS THAT AIR IS ALWAYS ENTRAPPED IN THE SAME PORES, AS LEAST AS FAR AS THE WETTING IS REPEATED IN THE SAME REASONABLY SMOOTH AND UNIFORM MANNER. THE DIFFERENCE IN SLOPE BETWEEN THE SATURATION AND THE ULTIMATE DRYING CURVES IS A MEASURE OF THE VOLUME OF AIR ENTRAPPED IN PORES DRAINING IN A UNIT SUCTION INTERVAL. IT IS THEN POSSIBLE TO OBTAIN A FAMILY OF PRIMARY WETTING CURVES, THE STARTING POINT OF EACH OF WHICH IS DEFINED BY THE SAME SUCTION THAT LIES ON ONE OF VARIOUS DRYING CURVES, AS WELL AS TO MEASURE THE HYDRAULIC CONDUCTIVITY ALONG NUMEROUS DRYING CURVES. THE STATIC TECHNIQUE IS USED TO STUDY THE EFFECT OF THE ENTRAPPED AIR ON THE HYSTERESIS CURVES. EXPERIMENTAL RESULTS CONCERNING THE EFFECT OF THE ENTRAPPED AIR ON THE HYSTERESIS CURVES AS WELL AS ON THE HYDRAULIC CONDUCTIVITY ARE REPORTED. THE HYDRAULIC CONDUCTIVITIES ALONG THE SATURATION AND THE ULTIMATE BOUNDARY DRYING CURVES ARE PLOTTED AS A FUNCTION OF SUCTION.