摘要:

Simulation of the water balance of a small 0.05-ha field of dryland rice (grown on non-submerged soil) requires knowledge of the soil's hydraulic conductivity functions. We compared three methods to generate such functions: direct measurement in the laboratory on samples from soil horizons occurring within the field (Method 1); use of average hydraulic conductivity functions measured in a 50-ha dryland rice region surrounding the field (Method 2); and deriving the hydraulic conductivity function through model calibration (Method 3).Differences in hydraulic conductivity functions obtained by the three Methods were large. The impact of these differences on simulation results using a soil-water balance model was evaluated. Simulated and observed water contents in 0 to 0.4-m depth were compared for two representative 0.05-ha fields within the 50-ha dryland rice area during three monsoon seasons and one dry (non-monsoon) season. Good agreement between observed and simulated soil water contents was obtained with input derived from either of the three Methods. Best results were obtained with Method 1, but differences in model performance were small because simulation results were relatively insensitive to hydraulic conductivity input data. Implications for sampling strategies are discussed.

ISSN:0038-075X    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

A theoretical review is presented on different approaches used for mathematical equations describing water and soil movement associated with transient pore water flow and soil deformation. Through a careful analysis of the governing equations, concepts used in different fields of engineering are found to be exactly equivalent. The comparison of soil water flow equation applicable to non-rigid porous media with the equation for consolidation reveals that under saturated conditions, both the compression index Ccand the coefficient of compressibility avare equivalent to the slope of soil moisture retention characteristic (MRC) and differential moisture capacity (dΘ/dΨ). Further, the coefficient of consolidation Cvis found to have the same physical meaning as the soil moisture diffusivity (D). Although both approaches originate from the same physical basis, practical applications have been limited to specific fields of soil engineering. It appears, however, that the approach used in soil physics retains wider applicability because it provides solutions of soil deformation (i) even under no external load, (ii) for unsaturated flow, and (iii) in a two-dimensional mode.

ISSN:0038-075X    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

Nonosmotic tensiometers are widely used for measuring soil water potential, but they cannot usually be used for pressure potentials below −98 kPa. This study investigated the possibility of measuring pressure potential below −98 kPa with a tensiometer. The measuring system was a microtensiometer connected to a pressure transducer; it was purged carefully and calibrated in the range 0 to −90 kPa. Two laboratory experiments were performed. In the first one, the porous cups of several tensiometers were subjected to evaporating conditions, and measurements were made every minute. In the second one, tensiometers were installed at four depths of an evaporating soil column (silt loam); water content profiles in the soil were also measured with a gamma radiation attenuation method, and soil hydraulic properties were determined at different depths of the sample. In both experiments, pressure potentials computed from an extrapolation of the calibration lines of the tensiometers could be temporarily smaller than −98 kPa (during 10 h in the second experiment, and down to - 140 kPa in the first experiment). In agreement with old published results and from a simple analysis of the vaporization in a liquid, it was concluded that these results were physically realistic. These results also stress the purge quality to improve the response time of tensiometers during transient water flow experiments.

ISSN:0038-075X    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

Field studies that extend over large areas are commonly blocked in an attempt to minimize experimental error. In an experiment that was designed to determine the effects of exposure to acidic rain and ozone on seedling loblolly pines through three years of growth, principal component and cluster analyses were conducted on the pretreatment soil chemistry of each plot in an attempt to make the plots in each block as homogeneous as possible. After one growing season, a series of edaphic measurements were taken in each plot to quantify soil drainage and aeration. Analyses of covariance were then conducted using the edaphic measures as covariates to determine their effectiveness in controlling experimental error. Even though the chosen blocking pattern was effective in reducing experimental error, the edaphic variable, MOTTLING (depth to mottling clay), was an effective covariate. MOTTLING reduced the experimental error by an additional 25 to 46%. Block sums of squares were also reduced by as much as 94% but still retained significance, suggesting that though there was a strong relationship between the blocking pattern and the MOTTLING pattern, blocking still accounted substantially for variability due to other unknown factors.

ISSN:0038-075X    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

Calcite supersaturation in soil solutions has been attributed to errors in measuring Ca2+and CO32-activities, metastable forms of CaCO3or soluble silicates, and organic matter mineralization. Laboratory batch suspensions of soils under controlled CO2and temperature were studied to clarify the mechanism producing calcite supersaturation. Treatments included the addition and removal of organic matter prior to reaction and the use of toluene to suppress microbial activity. The soil solutions were sampled over time and analyzed for Ca2+and CO32- activity. Carbonate activity was determined by two methods: 1) a double titration procedure that separates non-carbonate alkalinity from carbonate alkalinity and 2) acidification and outgassing of dissolved inorganic carbon species as CO2. Calcium activity was determined by two methods: 1) specific ion electrode and 2) total Ca analysis plus ion speciation modeling. Calcium-organic matter complexation was taken into account in the speciation calculations. It was found that calcite supersaturation in soil suspensions was not an artifact of inaccurate Ca2+or CO32-activity values. Rather, calcite supersaturation occurred because rapid organic matter mineralization increased the Ca and HCO3concentrations. These elevated Ca and HCO3concentrations persisted because of the slow precipitation kinetics of calcite. Attempts to block organic matter mineralization with toluene only slowed down the reaction in the soils. Removal of organic matter with H2O2resulted in Caoxalate formation, and oxidation of the oxalate to HCO3-produced elevated CO32-activities.

ISSN:0038-075X    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

Diniconazole was sorbed by four soils in amounts 7 to 20 times that for metolachlor, by Ca-organic matter (Ca-OM) in amounts twice that for metolachlor, and by Camontmorillonite (Ca-Mont.) in amounts similar to metolachlor. Sorption of diniconazole greatly increased and desorption decreased from Ca-OM and Ca-Mont as solution pH decreased. Sorption by the soils, as indicated by Freundlich K values, were highly correlated with the organic carbon content of the soils for diniconazole and with organic carbon and clay contents of soils for metolachlor. Sorption of diniconazole was through physical sorption forces at neutral pH levels and was by way of cation exchange forces at low pH levels.

ISSN:0038-075X    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

Water quality in the Everglades Agricultural Area (EAA) is influenced by the management of surface water and soils. Phosphorus release from organic soils in the EAA under long-term drained or intermittantly flooded soil conditions is not clearly understood. The purpose of this investigation was to study the effect of long-term (325 days) drained and flooded conditions on soluble P release measured on selected Florida Histosols. Five surface organic soils from the EAA were packed in columns and leached with 0.01 M CaCl2followed by distilled water every 25 days for 1 year. Drained columns were incubated with a minus-NP solution after applying 100-cm water suction, while flooded columns were incubated using the same nutrient solution under a 3-cm depth flood. Repetitive flooding increased the amounts of total P and soluble reactive P (SRP) in leachates. Total P mineralized from flooded cultivated Histosols was up to two times higher than under drained cultivated conditions. Total P mineralized from an uncultivated Paho-kee flooded was 6.4 times higher than from the same uncultivated Histosol drained. Similar results were also observed in amounts of SRP mineralized under flooded and drained conditions. The Torry series was the only organic soil that showed no significant treatment differences in SRP or total P mineralized. A large percentage (55 to 90%) of the total P was mineralized in the form of SRP. The P mineralization rate ranged from 5.60 to 72.0 kg P ha-1yr-1for drained soils and from 36.0 to 87.9 kg P ha-1yr-1for flooded soils. Generally, P release rates decline with time. These results also indicate that higher P release occurs under periodic flooding and draining.

ISSN:0038-075X    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

Ethylene is a plant growth-regulating substance that is produced by plants and soil microorganisms. Ethylene production and accumulation in soils is stimulated by the addition to the soil of compounds such as methionine, which serves as a direct precursor in ethylene biosynthesis, and by flooding, which encourages anaerobiosis. The objective of this laboratory study was to determine if the addition of either non-composted or composted broiler litter stimulated ethylene production in three ana-erobically incubated agricultural soils from eastern Arkansas. A completely randomized design was used, with non-composted and composted broiler litter as the two sources applied at three rates each. Check treatments received no litter. Both non-composted and composted poultry litter significantly increased production of ethylene in soils under flooded conditions, compared with the unamended control. At the highest rate of addition of non-composted litter (9.4 g kg-1), ethylene production in the Hilleman, Foley, and Bosket soils was 821, 678, and 327 nmol kg-1soil, respectively. At the same rate of addition of composted litter, ethylene production in these same soils was 491, 440, and 254 nmol kg-1soil. There were significant differences among soils in the quantities of ethylene produced, with the soil having the coarsest texture and lowest organic carbon content, the Bosket, producing the least ethylene. More ethylene was produced per gram of added carbon with non-composted litter than with composted litter. Differences in the abilities of the two wastes to promote ethylene production in soils may be due to differences in the bioavailability of carbon in the two materials. The compost had a lower total organic C content and a higher humic acid content than the non-composted material. The yield response of lowland rice to applications of poultry litter may be due in part to enhanced ethylene accumulation in the waste-amended soils.

ISSN:0038-075X    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

The evolution of chemical and physical properties in a series of minesoils aged between 0 and 5 years, developed from spoil materials of the Meirama opencast lignite mine in Galicia (NW Spain), was studied. The soils are recovered without use of top-soil and are subject to identical management. In the surface horizon (0–7 cm), total C and N, CEC, and pyrophosphate-ex-tracted Al2O3and Fe2O3increased with soil age. Oxalic-oxalate-extracted Al2O3and Fe2O3, on the other hand, increased with soil age in all the horizons studied. Rapid recovery in terms of physical properties was also observed: bulk density dropped, while total porosity, percentage of macro-pores, and hydraulic conductivity increased, and aggregates showed greater stability on immersion in water.The results indicate that mineral weathering and organometallic complexation are the dominant processes at these early stages of eda-phogenesis and that properties associated with gas exchange showed more rapid development than those associated with water movement.In spite of the above rapid modifications, the characteristics of the oldest soils in the series were still very different from those of native Galician soils.

ISSN:0038-075X    

出版商:OVID    

年代:1993

数据来源: OVID

ISSN:0038-075X    

出版商:OVID    

年代:1993

数据来源: OVID