The soil texture triangle used by the U.S. Department of Agriculture is converted into a new texture diagram which contains all information in the original triangle, but additionally, gives mean particle size and particle size standard deviation of soil samples. Thus, mechanical analysis information on percents of clay, silt, and sand together with particle‐size limits for clay, silt, and sand are found in a single unified system. The new diagram provides greater resolution in detecting classified soil samples within a texture region, it can be extended to cover coarse fragments, and other soil texture classifications can be incorporated into it.

SUMMARY Douglas fir [Pseudotsuga menziesii (Mirb.) Franco] seedlings responded differently regarding rate of photosynthesis when inoculated with three different ectomycorrhizal fungi. Rhizopogon vinicolor FSL788-5 caused a significant increase in net photosynthesis rate compared to non-mycorrhizal controls, while Hebeloma crustuliniforme HeCr2 and Laccaria laccata S238-A had no effect. Colonization by Rhizopogon and Hebeloma caused increased osmotic potential in the leaf symplast compared to controls, while Laccaria did not. Colonization levels for Rhizopogon, Hebeloma and Laccaria were 36, 93 and 73 % of root tips, respectively. Rhizopogon and Hebeloma produced abundant extramatrical hyphae and/or rhizomorphs, while Laccaria was smooth-mantled. Hebeloma-co\on\zed seedlings were significantly smaller than non-mycorrhizal controls; Rhizopogon seedlings were smaller, but significantly so only at P < 010. Laccaria did not affect seedling size. Only smaller Hebeloma seedlings exhibited elevated concentrations of N, P, K, and Ca over non-mycorrhizal controls. These data demonstrate a non-nutritional basis for increased rate of photosynthesis caused by some ectomycorrhizal fungi that can be explained by the increased photosynthate sink generated by extensive fungal growth associated with the mycorrhizas.

H The movement of some chemicals in soils has been treated theoretically by considering for saturated conditions, the chemical diffusion coefficient, the percolation velocity of the water, the sorbtive properties of the soil, the average particle size of the soil, and the fractional number of sorbing sites. A model has been developed for the movement of chemical in saturated soil, based on Fick's law, conservation of energy, and a sorption isotherm. 'Theoretical curves for two different boundary conditions are given for realistic values of the water velocity in the pores and the measured diffusion coefficient.he fate of herbicides in the soil is currently a prob!em of T great interest. The main parameters involved in the process of herbicide movement in soils are: the soil moisture content, the percolation velocity of the water or chemical solution through the soil voids, the sorbtive properties of the soil, the particle size distribution, the ratio of the chemically active area of the soil particles to the total surface area of soil particles, and biological degradation.Much work has been done on the movement, uptake, and degradation of chemicals which have been applied to the soil (Ashton, 1961; Burneside, Feuster et ul., 1963; Freed, Vernette, et ul., 1962;Harris and Warren, 1962;Hartley, 1964; Lambert, Porter, et ul., 1965;Talbert and Fletchall, 1965). Most of this work has been of a qualitative nature, and though very useful by itself, it does not give the understanding of the processes involved which can be derived from the development and testing of a quantitative physical model. Some quantitative models have been postulated (Burneside, Feuster, et ul., 1963;Hayward and Trapnell, 1964), and most are based on the linear diffusion-type partial differential equation. This type of equation fails to take into account leaching or convection. Several detailed analyses of the movement of chemicals in porous media can be found in the literature. These include the early work on the adsorption of chemicals in chromatography and ion-exchange resins (Kipling, 1965 ;Lapidus and Amundson, 1952; Van Schaik, Kemper, et ul., 1966; Vietter and Sladek. 1965), diffusion in proteins and polymers (Chaoand Hodscher, 1966;Houghton, 1963; Ward and Ho11:; and mixing in chemical reactors (Bischoff, 1966; BischofT and Levenspiel, 1962a, 1962b). These studies have led to several mathematical models. One early model (Kasten, Lapidus el ( I / . . 1952; Lapidus and Amundson, 1952) which has proved very useful in chromatography theory is based on the diffusional plus convective-type partial differential equation :where C is the concentration of chemical in the voids, L' i x the velocity of the carrier flowing through the voids, D is the diffusion coefficient, y is the fractional void volume, and N is moles of solute adsorbed per unit volume of packed bed. Using the same equation, other models have been developed by Houghton (1963) and Chao and Hodscher (1966). However. these models are based on nonlinear adsorption, which mal he unnec...

Apparent thermal conductivities of loamy sand, loam, and silty clay loam soils were measured with a cylindrical heat probe at several water contents and temperatures. Values of λ were also calculated with the de Vries model. Results show that the model may be used satisfactorily to calculate λ. However, improvements may be needed to account for the enhancement of vapor transfer at high temperatures (45° C) in medium to fine textured soils. The heat probe method of measuring the thermal conductivity requires a correction factor to allow for errors due to the entrapment of air at the surface of the heat probe, when used at water contents ranging from 0 to about 30% of saturation.The contribution of vapor distillation to thermal conductivity was analyzed by comparing λ at 25 and 45° C. The ratios λ45/λ25 were nearly equal to unity when < 5% of total pore space was filled with water. The ratios increased, due to vapor distillation, as water filled the pores and reached maximum values of 2.17, 2.71, and 2.96 when 22, 27, and 35% of total pore space was filled with water, corresponding to soil water potentials of −0.8, −9.0, and −8.0 bars for loamy sand, loam, and silty clay loam, respectively. As the water content increased further, the ratios decreased and approached unity when > 50% of total space was filled with water.The apparent thermal conductivity was independent of water content at very low water contents. The water molecules are in layers only a few molecules thick. The water content below which the apparent thermal conductivity is not affected by water content is a function of the soil temperature and the clay content. In our experiments these water contents were 0.03 and 0.05 cm3/cm3 at 45° C and 0.13 and 0.18 cm3/cm3 at 25° C for the loam and silty clay loam respectively.