摘要:

Electrical potentials were observed for the upward entry of water into columns of air-dry mixtures of sand and kaolinite. The electrical potential difference was measured between two bright platinum electrodes, one being in the water chamber at the inlet (lower) end of a column, and the other being one of five separate electrodes placed in the sand-kaolinite at various positions along the column. Time records of electrical potential at the various electrodes, obtained with a high-resistance electrometer and a strip-chart recorder, exhibited characteristic negative peaks that could be very closely associated with the arrival of the visual wet front at the various electrodes. Thus, although the observed electrical potentials cannot be used to infer streaming potentials for the unsaturated flow process of water entry into air-dry soil, it does appear that such potentials can be used to trace quantitatively the progress of a wet front through the soil, under circumstances wherein visual observations are not possible or feasible.

ISSN:0038-075X    

出版商:OVID    

年代:1975

数据来源: OVID

摘要:

The polyphosphate to soil ratio that yielded stable suspensions required for particle-size analysis of calcareous saline soils depended mainly on the amounts of soluble and exchangeable cations, especially Ca and Mg. Without removing soluble salts and organic matter, 5 g of polyphosphate per 50 g soil per liter of suspension provided stable suspensions for most saline calcareous soils in Imperial Valley. When the exchangeable plus soluble Ca and Mg exceeded about 20 me in 50 g soil, then 5 g polyphosphate were not adequate to provide stable suspensions, and excess salts had to be removed. It was possible in some of these latter soils to obtain stable suspension without removing salts by either increasing the dispersant to soil ratio or the pH or both.The reactions of polyphosphate with solid CaCO3involve mainly surface interactions and hydrolysis of carbonate without any appreciable change in soluble constituents. The polyphosphates do not appreciably change the particle-size distribution of CaCO3in soils.The reactions of Ca and Mg ions with polyphosphate involve their coordination with the polyphosphate anion to form soluble complexes with reduction in pH. Depending on pH and solute concentration, Ca++ ions in excess of 5 to 7 me/g polyphosphate initiate breakdown of the soluble complexes and precipitation of Ca-phosphates. No precipitation of Mg complexes occurs under similar conditions.

ISSN:0038-075X    

出版商:OVID    

年代:1975

数据来源: OVID

摘要:

A thermodynamic theory is presented for the response of a tensiometer in an anisotropically loaded soil. It is argued that the tensiometer pressure is independent of the orientation of the head of the instrument, implying that a scalar moisture potential is applicable to such soils. This moisture potential is characterized in terms of other measurable properties of the soil-water system. It is suggested how to infer, for loads which produce deformations small in comparison with those due to typical changes in moisture content, the moisture potential of an anisotropically loaded system from that of the same system under isotropic loading.

ISSN:0038-075X    

出版商:OVID    

年代:1975

数据来源: OVID

摘要:

Direct SEM observations indicate that reduction in hydraulic conductivity of soils leached with mixed NaCl-CaCl2solutions of low electrolyte concentrations are related to fine particle dispersion and the formation of a more continuous network of these particles at higher SAR values. This causes blockage of the larger pores in the soil and reduces the rate of water flow by increasing the proportion of small size pores. The changes in a sandy and in a clayey soil were quite similar. Dispersion of the fine particles seems to start at low SAR values (< 8), but the formation of the network becomes apparent only at SAR > 16.

ISSN:0038-075X    

出版商:OVID    

年代:1975

数据来源: OVID

摘要:

Temperature distributions were monitored in the laboratory in air-dry and moist soil under and around buried and surface stones submitted to a diurnal heat wave. Only with surface stones were temperatures different under the stone compared to surrounding soil. During the heating period, temperatures beneath the stone were cooler than in adjacent air-dry soil. During the cooling period, they were warmer. When soil is sufficiently dry that water moves mainly in the vapor phase, it is hypothesized that condensation could occur on the undersides of surface stones during the early part of the day. Such moisture accumulation may be of significance to desert fauna and flora.

ISSN:0038-075X    

出版商:OVID    

年代:1975

数据来源: OVID

摘要:

The influence of 7.2°, 22°, and 37°C temperature levels on the extent and rates of rice straw decomposition and loss of soil organic matter was investigated in two soils at 60 percent WHC using tracer techniques. About a third of straw-C was lost at 7.2°C within a 4-month incubation period. At all temperature levels, the percentage of straw-C loss after 6 days followed the path of power functions. Differential equations were deduced to describe the instantaneous rate parameter,vi, which decreased with time in asymptotic fashion. Temperature dependence ofviis consistent over the range 7° to 22°C but less so over the range 22° to 37°C. Soil-C loss increased with increasing temperature regardless of straw incorporation. Addition of straw always promoted native soil carbon loss at all temperature levels.Mineralization of straw nitrogen at 7.2° and 22°C was about the same but at 37°C mineralized nitrogen appeared to be lost, possibly as gaseous nitrogen. Soil inorganic nitrogen content increased with increasing temperature, as did the native soil carbon loss.

ISSN:0038-075X    

出版商:OVID    

年代:1975

数据来源: OVID

摘要:

This greenhouse experiment was conducted to evaluate the soil temperature and soil aeration effects during the wheat grain filling stage on the yield of grain and concentrations and total amounts of nutrients in the grain.Plants grown at 25°C soil temperature yielded lower amounts of grain per pot than those plants grown in 15°C and 5°C soil temperatures. Although the concentrations of most of the determined nutrients in the grain from plants grown at 25°C soil temperatures were higher than those found in the grain from plants grown at 5°C and 15°C soil temperatures, the total amounts of nutrients per pot found in the grain of plants grown at the 25°C soil temperature were lower than in the grain per pot of plants grown at 5° and 15°C soil temperatures.Reduced aeration to wheat plant roots for 30 days during the grain filling stage by flooding or supplying N2to the roots of the plants reduced the amount of grain produced per pot and also the total amounts of nutrients in the grain as compared to the yield and amounts of nutrients found in the grain from plants grown at the adequate supply level of soil aeration. The concentrations of nutrients in the grain were not markedly influenced by reduced soil-aeration during the grain filling stage.The concentrations of N, P, K, and Na, in grain from plants grown under reduced soil aeration conditions and 25°C soil temperature, were higher than those concentrations in grain from plants grown at the lower soil temperatures. In the presence of an adequate soil aeration, the differences in soil temperature did not influence nutrient concentrations in the grain.

ISSN:0038-075X    

出版商:OVID    

年代:1975

数据来源: OVID

摘要:

Chester and Hagerstown silt loam soils were preincubated for 1 to 5 weeks with 5000 ppm C (1:1 sucrose and cellulose) and 50, 100, or 200 ppm N containing 5.25 percent excess15N as nitrate. Losses of labeled N, presumably by denitrification, were higher for the Hagerstown (65 to 70 percent) than for the Chester soil (10 to 20 percent). The N recovered was almost completely converted to organic forms. Extending the incubation from 1 up to 5 weeks had little effect on the incorporation of15N into organic forms or on recovery values. In subsequent incubations for periods up to 26 weeks, mineralized N from soil and15N-labeled sources was calculated in terms of availability ratios. These ratios did not vary greatly with time of preincubation or of mineralization period. Mineralization rate and potentially mineralizable15N increased with the total amount of incorporated15N in soils. The fraction of incorporated15N that was potentially mineralizable in both soils ranged from 34.6 to 53.2 percent, while the proportion of potentially mineralizable indigenous soil N ranged from 15 to 17.9 percent.

ISSN:0038-075X    

出版商:OVID    

年代:1975

数据来源: OVID

ISSN:0038-075X    

出版商:OVID    

年代:1975

数据来源: OVID

ISSN:0038-075X    

出版商:OVID    

年代:1975

数据来源: OVID