ISSN:0038-075X    

出版商:OVID    

年代:1974

数据来源: OVID

摘要:

A simulation program for a digital computer has been developed to calculate the soil moisture profile, the infiltration rate, and the cumulative infiltration under conditions of one-dimensional, vertical unsteady infiltration into soil. The simulation program does not require an advanced mathematical knowledge, nor does it require much computer programming skill. The results of the simulation technique are compared with existing solutions for one-dimensional infiltration for Yolo light clay, and good agreement is found. The simulation program does not require a uniform soil or an initially uniformly distributed moisture content in the soil. The simulation program is provided for the reader's benefit. It can be easily changed to include evaporation from soil. Due to its simplicity the simulation program that we have developed may be more appealing than existing techniques to calculate moisture profiles, infiltration rates, and cumulative infiltration.

ISSN:0038-075X    

出版商:OVID    

年代:1974

数据来源: OVID

摘要:

A three-parameter stress-strain equation of the form τ = ϵ/a+bϵnis proposed and is being compared with the experimental stress-strain response of sand. The fitting is found to be excellent up to the failure. With the help of relevant boundary conditions, the constantsa, b, andnare expressed as a function of shear strength (Tmax), initial tangent modulus (Ei), and failure strain (ϵf). Experimental correlation is made between initial void ratio (e0) and normal stress (σ) with the parametersa, b, andn.

ISSN:0038-075X    

出版商:OVID    

年代:1974

数据来源: OVID

摘要:

Evaluation of salinization of ground water in an area of diverse irrigation agriculture requires a field-scale approach. Data reduction methods are suggested and illustrated that relate four crop classes (no crop, grapes, row and truck crops, and orchards) to magnitudes and variabilities in soil salinity to a depth of 6.1 m, and evaluate relative importance of the crop classes as contributors to soil salinity. Data on soil salinity were used to obtain a projected ground-water salinity probability curve. The ground-water salinity probability curve based on domestic water well sampling over a 3-year period compared favorably with the projected curve.

ISSN:0038-075X    

出版商:OVID    

年代:1974

数据来源: OVID

摘要:

Ponderosa pine (Pinus ponderosa) seedlings were grown for one year in 10-in. pots containing 6400 grams of soil. Two soils were studied, one of which was phosphate deficient and the other was deficient and phosphate-fixing according to standard pot tests with lettuce and barley, and P diagnosis by the Truog chemical test. The pine seedlings showed a slight P response on the deficient soil and a moderate response on the P-fixing soil. The needles and stems were analyzed for total P and for P soluble in 2 percent acetic acid. For total P the critical concentration in the needles was .09 percent and in the stems .08 percent. For the P soluble in acetic acid the critical P values were just under .03 percent in both needles and stems. These values were considered useful for diagnostic purposes in determining P status of ponderosa pine seedlings. It was suggested that the ratio of acid-soluble P in needles to that in stems approached a value of one in P-deficient seedlings and that this ratio could be more useful than single values of either total P or acid-soluble P.

ISSN:0038-075X    

出版商:OVID    

年代:1974

数据来源: OVID

摘要:

Particles of single superphosphate were incubated at a range of levels with a soil for periods ranging up to 217 days and at temperatures which ranged from 10°C to 35°C. In a separate study, particles of superphosphate were incubated at a range of water contents. The effectiveness of the phosphate for plant growth was then compared with that of a control treatment in the glasshouse. The index used to measure relative effectiveness was the ratio of the exponents in an exponential equation used to describe the plant response.Effectiveness of phosphate did not decrease in a treatment which was incubated air-dry after an initial wetting to near field capacity. Effectiveness decreased in a treatment incubated at just below permanent wilting point but the decrease was not as large as in the treatments incubated at a higher water content.The decrease in effectiveness was greatly affected by the temperature of incubation. It was possible to describe the effects of time and temperature by the empirical rate equation:dα/dt=k(1 — α)nwhere α is the proportion of the phosphate converted into an ineffective form. The rate constantkwas found to be proportional to exp (−E/RT) whereEis analogous to the energy of activation andTis the temperature in °K. It was found that the value ofEwas 19,600 calories per mole. This indicates that there was a more than threefold increase in the rate of change for each 10°C increase in temperature. The value ofnwas about 3.

ISSN:0038-075X    

出版商:OVID    

年代:1974

数据来源: OVID

摘要:

Sodium as the acetate was added to irrigation waters to study the effects of higher Na levels in water and soils upon cotton fruiting and shedding, growth, and yields. One Acala variety (1517D) and one American Pima variety (Pima S-2) were included in the 2-year study, conducted in outdoor lysimeters. Boll and fiber properties were also examined.Virtually all effects of added sodium (increased from 58 percent in the water to 71 and 80 percent) were undesirable, and most of these adverse effects were highly significant.They included: (1) reductions in growth and yields, (2) increases in square and boll shed, (3) reductions in numbers of fruiting forms initiated, (4) decreases in weights of seed cotton, seed, and lint per boll, and (5) decreases in fiber length, strength, and micronaire. A reddish leaf mottling of older leaves was a visible characteristic of high Na.Under field conditions the adverse effects of Na reported herein may be offset by the balancing effects of other ions. However, in light of this study, sodium must be considered to have specific toxic effects on cotton in addition to its osmotic influence. The effect on fiber properties is of particular significance.

ISSN:0038-075X    

出版商:OVID    

年代:1974

数据来源: OVID

摘要:

Three desert perennial plant species [Lycium andersoniiGray,Atriplex confertifolia(Torr. & Frem.) Wats., andAtriplex hymenelytra(Torr.) Wats.] were grown in soil in a glasshouse with different sources of Na (NO−3, Cl−, H2PO−4) to evaluate their effects upon cationanion balance in the plants. Each anion greatly increased leaf content of itself with only minor, if any, interactions with other anions. The milliequivalent sum of anions measured (N, P, Cl), therefore, increased in each plant part with the soil applications. Simultaneously there were usually modest increases in the milliequivalent sum of cations. The cation-anion ratio was decreased markedly when NaNO3was added. The ratio was usually over one which means that considerable bicarbonate absorption and organic acid synthesis must occur in all three species. Maximum content of Cl and N in leaves was withL. andersonii, 13.51, and 6.37 percent, respectively, when each was added. There were some compensations among other cations as Na was increased so that a somewhat constant sum of cations was maintained although there were significant differences.L. andersoniiappeared to be an accumulator of Li andA. hymenelytraof Cd.

ISSN:0038-075X    

出版商:OVID    

年代:1974

数据来源: OVID

摘要:

The purpose of this paper is to describe and give specifications for a soil sampler which can be used to take a sample from a specific depth zone without contamination occurring from adjacent zones. Data are presented which compare the sampling characteristics of conventional samplers with the new sampler and show the superiority of the new sampler. Samples were taken from a zone less than 1 in. below a fertilized zone without appreciable contamination from the fertilized zone. The sampler is recommended for use in field studies where the exact location of fertilizer elements in the soil profile is desired.

ISSN:0038-075X    

出版商:OVID    

年代:1974

数据来源: OVID

摘要:

Broken Albrights fragipan material was treated with aqueous solutions of from 0.1 to 1.0 percent concentrations of vinyl acetate maleic acid copolymer (VAMA) for 1 min or 12 hr, air-dried, and subjected to a series of wetting and drying cycles (to simulate field conditions) in the laboratory. Approximately one-half of the treated samples were also subjected to overburden weight equal to 2 ft of soil material. Data from the weighted and unweighted studies indicate that fragipan material can be successfully stabilized under simulated field conditions. The amount and duration of stability depends on 1) the concentration of the aggregating agent, and 2) the duration of the contact of the aggregating agent with the fragipan material. In general, increased concentration of VAMA treatment results in a regular decrease in the amount of slumping. The greater the time of contact, other factors constant, the greater the stabilization. This undoubtedly is the result of deeper penetration of the VAMA into the fragipan material with resultant greater stabilization. Overburden weight is also a significant factor. Static weight tends to pack the material into a tighter mass, thus sealing off more water-conducting pores and channelways. At the termination of the study (15 cycles), some of the treated materials were still adequately stabilized, but a projection of the data indicates that even these treatments would fail if subjected to additional cycles. Thus, if extended stability is to be obtained in the field, natural aggregating processes will have to assume the stabilizing function or additional treatments will be necessary. These data indicate further testing in the field is necessary to determine the feasibility of this method for stabilizing broken fragipan material.

ISSN:0038-075X    

出版商:OVID    

年代:1974

数据来源: OVID