Experiment Station Record, Volume 92, January-June, 1945 Page: 174
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174 EXPERIMENT STATION RECORD [Vol. 92
Soil moisture in relation to plant growth, P. J. KRAMER (Bot. Rev., 10 (1944),
No. 9, pp. 525-559).-A comprehensive review of the problem, listing 108 references.
Soil management in relation to water penetration, M. R. HUBERTY. (Calif.
Expt. Sta.). (Calif. Citrog., 29 (1944), No. 7, pp. 178-179, illus. 2).-Consideration
is given to the tillage operations, fertilizers, and soil amendments, and their
effect on soil compaction, since soil compaction is directly related to soil structure
and determines the rate of water entry into the soil. In order to avoid compaction
during cultivation, the operator should select a time when soil moisture conditions
are such as to support the equipment being used. When applying ammonium sulfate
or sodium fertilizers, it is a good practice to apply a number of- light applications
rather than a large single application. However, should poor penetration result
from the applications of these fertilizers, improvement can generally be accomplished
by the addition of organic matter or calcium, or both.
Soil movement as affected by slope, discharge, depth, and velocity of water,
J. F. LUTrz and B. D. HARGROVE. (Coop. U. S. D. A.). (North Carolina Sta.
Tech. Bul. 78 (1944), pp. 32, illus. 13).-By means of a constructed water channel,
illustrated in detail, laboratory studies were conducted using various-sized separates
and various slopes and amounts of water to determine the relation between (1) slope,
depth, and velocity, (2) slope and carrying capacity, and (3) depth and carrying
capacity simulating a field plat undergoing sheet erosion. It was found that the
discharge for any slope was equal to the product of depth and velocity. The velocity
required to move a soil particle was not constant for all slopes, but varied with
discharge, depth, and slope. In general, as the slope increased, depth decreased,
thereby causing an increase in the velocity required to move the particles. The
velocity required to cause initial movement of soil particles increases according to
a fifth-degree equation as slope increases. This is contrary to general belief, but
is explained on the basis of decreasing depth with increasing slope. Depth of flow
is an important factor influencing initial movement and relative loss of soil particles.
Since discharge of water is a linear function of velocity and slope, and since velocity
is a function of discharge and slope, it follows that depth and velocity can be calculated
for any given values of slope and discharge. Loss of the various particles is a
function of slope and discharge, and the relative values of each factor vary with the
size of particles. The greatest loss of soil occurs when the point of maximum
velocity is at depths (from the surface upward) between the radius and diameter
of the particles. The absolute values obtained in the laboratory probably would not
apply directly to field conditions; however, they should apply relatively. Some
mechanical analyses of eroded material from various-textured soils indicate that
Moisture retention by some irrigated soils as related to soil-moisture tension,
L. A. RICHARDS and L. R. WEAVER. (U. S. D. A.). (Jour. Agr. Res. [U. S.],
69 (1944), No. 6, pp. 215-235, illus. 8).-A study of soil-moisture retention was
made on 71 southern California soils by using porous ceramic and cellulose membranes.
It was found that for 64 of the soils the 15-atmosphere (atm.) percentage
lies in the wilting range. The soil-moisture tension at first permanent wilting for
sunflowers was found for the majority of the soils to lie in the 7- to 9-atm. range.
The soil-moisture tension at ultimate wilting was below 30 atm. for all but 3 of the
soils, and 17 out of 24 soils tested underwent permanent wilting in the range from
20 to 30 atm. The moisture equivalent is the average value over approximately the
0.1- to 1.0-atm. tension range for a moisture-retention curve that takes into account
centrifuge packing effects. Tensiometerj suction-plate, pressure-plate, pressure-membrane,
or centrifugation apparatus may be used for determining equivalent negative
pressure or soil-moisture tension; but, without disregarding osmotic effects, none
of these can be used for determining free energy, or pF, if the latter is to be taken
as a free-energy scale as originally proposed.
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U.S. Department of Agriculture. Agricultural Research Administration. Office of Experiment Stations. Experiment Station Record, Volume 92, January-June, 1945, book, 1947; Washington D.C.. (digital.library.unt.edu/ark:/67531/metadc5064/m1/187/: accessed October 23, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.