摘要:

This study describes the phosphorus status of sodic soils formed under the influence of sodium carbonate, aquic natrustalf, and its possible leaching during their reclamation. Uncultivated, barren sodic soils contained high amounts of Olsen's extractable phosphorus, which decreased with depth, and the amounts were highly correlated with the electrical conductivity of the soil. The incubation studies conducted at saturated moisture content with differential amounts of gypsum at 0, 25, 50, 100, and 200 percent of laboratory-determined gypsum requirement (GR) showed that Olsen's P decreased with increases in the rate of gypsum applied.The leaching studies conducted in the field showed that phosphorus in sodic soils moved down, along with other soluble salts, though the peak P concentration lagged behind the other salts. Leaching studies conducted in plexiglass columns in the laboratory brought out that substantial leaching of P, up to 60 ppm P, could occur when sodic soils are leached as such or after surface application of gypsum. It seems that under natural conditions, Na2CO3, which is the predominant salt in sodic soils, reacts with native calcium phosphate to form highly soluble sodium phosphates, which are leached during reclamation.Gypsum, mixed with soil at a rate of 100 percent GR and above, decreases the leaching of phosphorus. It seems due to (1) immobilization of soluble P by CaSO4through the formation of less soluble Ca-P compounds; (2) common ion effect to decrease solubility of Ca-P compound; and (3) lowering of soil pH, which in turn decreases the soluble P in the pH range of 8.3 to 10.

ISSN:0038-075X    

出版商:OVID    

年代:1981

数据来源: OVID

摘要:

We investigated the effect of nitrogen forms on the kinetics of N loss in a small-scale soil-plant system, simulating overland flow conditions with controlled alternate aerobic-anaerobic cycles. The substantial gaseous N losses of applied15NH4+-N (18.47 to 30.65 percent) indicate the presence of favorable oxidation-reduction conditions for the simultaneous occurrence of nitrification-denitrification reactions. Gaseous loss through NH3volatilization was unlikely in this study, due to slightly acidic to neutral soil conditions. The15NO3--N accumulation in both the15NH4+- and15NO3--N treatments was negligible, indicating that15NO3--N was not stable under the experimental conditions. The rate of gaseous N loss computed by a zero-order kinetics model was 3.93 μg15N per gram per day for the15NO3--N treatments and 2.09 μg15N per gram per day for the15NH4+-N treatments. The conversion of NO3--N to NH4+-N as a consequence of respiratory reduction was not evident in the study.

ISSN:0038-075X    

出版商:OVID    

年代:1981

数据来源: OVID

摘要:

We conducted detailed mineralogical and chemical investigations into the clay, silt, and sand fractions separated from the topsoils of Andosols formed from felsic parent ash under a humid temperate climate. We concluded that the primary factors influencing the mobility sequence CaO, Na2O > SiO>2> MgO > A12O3, Fe2O3, K2O in these soils are as follows: (1) Al2O3and Fe2O3, very low solubility in soil solution; (2) K2O, preferential retention by volcanic glass and formation of a randomly interstratified chloritized 2:1 mineral-illite (formation of mica structure); (3) MgO, formation of 2:1 minerals (incorporation of magnesium into octahedral sheets); (4) SiO2, formation of 2: 1 minerals and possibly quartz; and (5) CaO and Na2O, facility in release from the parent ash, high solubility in soil solution, and absence of clay minerals containing significant amounts of both elements.Volcanic glass (silicic) appears to be the most important parent mineral, and its weathering and abundant formation of 2:1 minerals are strongly related to the mobility sequence of chemical elements we obtained, which is unique compared with other geochemical studies.

ISSN:0038-075X    

出版商:OVID    

年代:1981

数据来源: OVID

摘要:

We measured phosphate retention by 18 Ando soil samples at different pH values (4 to 8.5) and phosphorus concentrations (10-3to 2 M). A general regression equation held for each soil: log Y = α pH + β log [C] + c, where Y = phosphorus retention and [C] = phosphorus concentration. By multiple regression analysis, the Y values were correlated with the status of aluminum and iron analyzed by selective dissolution using pyrophosphate, dithionite-citrate, and oxalate-oxalic acid as reagents. Aluminum bound with humus, Alpyr, reacted with phosphate depending little on pH and markedly on phosphorus concentration, whereas aluminum and iron in allophane, (Al + Fe)oxa, depending markedly on pH and moderately on phosphorus concentration. Aluminum and iron in allophanelike constituents (Al + Fe)dit-pyrshowed features similar to aluminum bound with humus. The molar reactivity of aluminum and iron toward phosphate (P/Al or Fe) at 0.5 M increased in the order: (Al + Fe)dit-pyr(0.3) < (Al + Fe)oxa(0.4) < Alpyr(0.5) < Fepyr(0.8) at pH 5.0, and (Al + Fe)oxa(<0.1) < (Al + Fe)dit-pyr(0.3) < Fepyr(0.5) < Alpyr(0.6) at pH 8.0.

ISSN:0038-075X    

出版商:OVID    

年代:1981

数据来源: OVID

摘要:

A physiological plant disorder in California rice, associated with soluble sulfides, hydrosulfides, and insoluble metallic sulfide production in the soil, causes severe injury to plants. Under flooded cultural conditions, roots become blackened, leaves develop a gray-green color, wither, and die, and panicles usually produce sterile florets.We studied the effects of straw, sulfate amendments, and temperature on acid-volatile and water-soluble sulfides in two acid soils (San Joaquin sandy loam and Willows clay). Straw amendments significantly increased the acid-volatile and water-soluble sulfides in both soils. The amounts of acid volatile sulfide produced were further enhanced by the addition of sulfate and by higher temperature. Although low temperature significantly reduced the production of acid-volatile sulfide, it enhanced the accumulation of water-soluble sulfides. High concentrations of water-soluble sulfides found in Willows clay in the presence of straw and sulfate may be responsible for the observed poor growth of rice under field and glasshouse conditions. Sulfide can be adsorbed by kaolinite, and the amounts of sulfide adsorbed increased with increasing concentrations of sulfide in solution. Sulfide retention was controlled by the availability of surface adsorption sites, because the sulfide adsorption increased with increasing gram volume ratio. Low temperature adversely affected the adsorption of sulfide by kaolinite.

ISSN:0038-075X    

出版商:OVID    

年代:1981

数据来源: OVID

摘要:

Measurements of the natural terrestrial gamma radiation flux near the soil surface are used to infer areal soil moisture. Airborne gamma radiation data are collected over a network of 240 flight lines (each approximately 6 square kilometers) in the upper Midwest and used to calculate real-time, areal soil moisture values. Ground-based soil moisture data collected along calibration flight lines indicate that airborne soil moisture values can be calculated with an RMS error of 3.2 percent soil moisture, which is 40 percent less than the mean standard deviation of the ground-based soil samples. The airborne soil moisture values calculated using data from three primary background surveys tend to be 1.5 percent less than the ground-sampled soil moisture values.

ISSN:0038-075X    

出版商:OVID    

年代:1981

数据来源: OVID

摘要:

Moisture content measured in the soil correlated strongly with the curvature of the soil surface. At the concave parts of the landscape, the moisture content was as high as 14 percent, and grain yields were as high as 1734 kilograms per hectare. At the convex parts, the moisture content was as low as 5 percent, and the grain yields were as low as 408 kilograms per hectare.The correlation coefficient between the measured moisture and the calculated surface curvature was 0.9 and was significant at the 0.1 percent level. The observation tends to support our theory about the horizontal flow component of infiltrating water.The new theory and the supporting observations point toward an important source of nonuniformities in moisture distribution in nonleveled fields, which nonuniformities are far greater than those caused by common irrigation systems.

ISSN:0038-075X    

出版商:OVID    

年代:1981

数据来源: OVID

ISSN:0038-075X    

出版商:OVID    

年代:1981

数据来源: OVID

ISSN:0038-075X    

出版商:OVID    

年代:1981

数据来源: OVID

ISSN:0038-075X    

出版商:OVID    

年代:1981

数据来源: OVID