摘要:

Improving the aggregate stability of a 2-cm deep surface layer, effected by treatment with a polyurea soil conditioner, significantly increased the water infiltration during simulated rainfall and substantially reduced the evaporation.For the same potential evaporation rate of 5 mm day-1, differences in total mean water loss occurred due to different climatic conditions. For a wind speed of 5 km h-1and relative humidity of 40%, water losses under untreated and treated surfaces were 50 and 38%, respectively, of the total amount of infiltrated water. With a wind speed of 15 km h-1and relative humidity of 80%, water losses were 30 and 11%, respectively.

ISSN:0038-075X    

出版商:OVID    

年代:1984

数据来源: OVID

摘要:

We present variance analysis for identifying the different components (instrument, calibration, and location) of the errors involved in estimating the spatial mean water content values from neutron probe readings. We measured soil moisture by two neutron probes at 17 locations regularly spaced on the field. For each probe, unique calibration curve was used for the whole field with both biased and unbiased treatments of the linear correlations. All the measurements at a specified depth were normally distributed regardless of their location, and no spatial structure has been shown for the sampling scheme.In situations of site homogeneity or a large number of sampling points, the calibration component is the greatest contribution to the total variance. It is reduced by considering the unbiased statistical treatment of the neutron probe calibration curve. For higher levels of field heterogeneity, the location component becomes the major contribution to the variance of mean values. It can be decreased by increasing the number of sampling points.Finally, the suitable number of sampling points necessary to provide mean water content values with a prescribed precision is given for the experimental site by applying the central limit theorem.

ISSN:0038-075X    

出版商:OVID    

年代:1984

数据来源: OVID

摘要:

From this investigation we have concluded that, besides exchangeable sodium, soluble CO3+ HCO3also contributes to the gypsum requirement of sodic soil if its concentration exceeds 5 meq/100 g. A multiple regression equation (Y = 3.094 + 0.681 X1+ 0.901 X2) has also been worked out to calculate the additional contribution from soluble CO3+ HCO3to the gypsum requirement.

ISSN:0038-075X    

出版商:OVID    

年代:1984

数据来源: OVID

摘要:

We studied the effect of salinity and SAR on the modified Gapon selectivity coefficient (kg‘) using Yolo loam soil and two (sodic) coal mine overburden materials designatedsurfaceanddeep. The SAR treatments varied in value from 5 to 80 (mmol/L)1/2in an electrolyte solution (NaCI + CaCI2) concentration range of 10 to 500 meq/L.When all treatment effects were combined, the kg' values were 0.0097, 0.0087, and 0.0079 (mmol/L)-1/2for Yolo loam, surface, and deep overburden, respectively. In contrast to the other two systems, the deep overburden exhibited a steadily declining value of kg' (0.014 to 0.0055 (mmol/L)-1/2with increasing electrolyte concentration. In all cases the kg' values were found to be less than the commonly used value of 0.015 (mmol/L)-1/2.

ISSN:0038-075X    

出版商:OVID    

年代:1984

数据来源: OVID

摘要:

The Morrow Plots, which were established in 1876 at Urbana, Illinois, are the oldest experimental plots in America, and they contain the longest continuous corn (Zea maysL.) plot in the world. This paper reports changes in the content of nitrogen and organic carbon in the dark-colored soil on the Morrow Plots during 70 years, 1904 to 1973, under different cropping systems and soil treatments.In comparison with continuous corn culture, crop rotations retarded the decline in soil nitrogen and organic carbon. However, crop rotations without soil treatment did not maintain the soils in a high state of productivity. Crop rotation plus appropriate fertilization produced the highest crop yields and also maintained soil nitrogen and organic carbon at the highest levels.

ISSN:0038-075X    

出版商:OVID    

年代:1984

数据来源: OVID

摘要:

Particle size distribution was determined on loess sections from southcentral and northern Idaho; West Yellowstone, Montana; eastern Nebraska; Vicksburg, Mississippi; and Macon Ridge, Louisiana, using the Coulter Counter TA II. The Coulter Counter allows for 15 subdivisions in the silt-size range and provides sensitivity in interpreting loess particle size distribution. Loess materials can be identified by a characteristic particle size distribution in the medium and coarse silt fractions, which distinguish them from nonloess materials. The method would be helpful in soil classification, soil parent material studies, and research on loess.

ISSN:0038-075X    

出版商:OVID    

年代:1984

数据来源: OVID

摘要:

We examined the relationships between soil bulk density values and organic and mineral contents for two large data sets collected in a wide range of sediment and marsh types in Louisiana. Bulk densities ranged from 0.05 to 0.60 g/ml, and organic carbon contents varied between < 4 and 43%. Bulk density was directly related to mineral content, but was independent of organic content. Mean organic carbon density was remarkably constant at 26 mg/ml soil. A mathematical expression, bulk density = 100 K/organic carbon, describes the curvilinear relation between organic carbon content and bulk density. For flooded wetlands, K is equal to the mean organic carbon density of the soil.

ISSN:0038-075X    

出版商:OVID    

年代:1984

数据来源: OVID

摘要:

We present experimental results of ponded infiltration in a vertical column for two cases: when air is free to escape from the medium, and when air is confined and can escape only through the soil surface. We show that, in the second case, air pressure reaches a constant value, independent of depth and time. The primary effect of this air pressure is to decrease the water potential at the surface and thus to reduce the infiltration rate to about one-third of its value when air is free to escape.The confined air pressure value can be predicted if permeabilities of soil to air and water are known with precision near saturation.A simple analytical model is presented, which predicts the cumulative infiltration with a good precision, if air pressure or water content at the soil surface is predicted or in practice measured directly.

ISSN:0038-075X    

出版商:OVID    

年代:1984

数据来源: OVID

摘要:

We recently reported greenhouse and field experiments showing the ability of the NH4HCO3-DTPA soil test of Soltanpour and Schwab to separate Fe- and Zn-deficient soils from nondeficient soils (Havlin and Soltanpour 1981,1982). After eight weeks of crop growth in the greenhouse studies, the test soils were resampled, and NH4HCO3-DTPA-extractable Fe and Zn concentrations are reported here. Objectives of the present work were (1) to establish the ability of the NH4HCO3-DTPA soil test to measure the changes in Fe and Zn levels in soils fertilized with Fe-EDDHA (ferrick ethylenediamine di-(o-hydroxyphenyl acetate)) and ZnSO4fertilizers and (2) to relate the variability in levels of extractable fertilizer Fe and Zn to properties of the 40 Colorado soils.Extraction of fertilizer Fe and Zn by NH4HCO3-DTPA from soils receiving Fe-EDDHA or ZnSO4averaged 43 ± 6% and 57 ± 8%, respectively, indicating that the NH4HCO3-DTPA soil test provides a measure of the residual value of Fe and Zn fertilizers. Multiple linear regression analysis successfully accounted for much of the variability in extractability of fertilizer Fe and Zn; multiple coefficients of determination were 76 and 70%. Clay content and presence of lime were the most important soil properties in explaining variability in fertilizer Fe extractability, and clay content and soil pH were most effective for fertilizer Zn extractability.

ISSN:0038-075X    

出版商:OVID    

年代:1984

数据来源: OVID

摘要:

Using13C, solid-state NMR, we examined sludges and composts obtained from varied locations. A minimum of sample preparation is required with this technique. The samples are simply dried and ground before they are packed into the rotor. The spectra of the sewage sludges examined are composed of four broad envelopes of chemical shifts representative of carbonyl carbon, aromatic carbon, aliphatic carbon adjacent to -OH or -N, and aliphatic carbon.The intensities of the carbonyl carbon, aliphatic carbon adjacent to -OH and -N and aliphatic carbon resonances were less in the compost spectra, when compared with the intensity of the aromatic carbon resonances, than in the sewage sludge spectra. Spectra of four reference compounds (stearic acid, cellulose, lignin, and protein (keratin)) are included to assist in the interpretation of the sample spectra. Interrupted decoupling experiments were conducted to simplify these complex spectra and estimate the amount of nonprotonated (branched and carbonyl) carbon they contain. This preliminary solid-state, NMR study of sludges demonstrates that this technique is an effective tool for studying these complex systems.

ISSN:0038-075X    

出版商:OVID    

年代:1984

数据来源: OVID