摘要:

A field method for measuring saturated hydraulic conductivity, Ks, was developed to characterize water flow in highly-weathered soils of Sitiung, Indonesia. Soils in this area are known to absorb large volumes of rainwater rapidly. However, Ksdata obtained on soil cores do not corroborate field-observed rapid infiltration rates. In the field method, a constant rate irrigation was applied to a field plot, delineated to a depth of 120 cm, and bordered on the surface to contain a depth of ponded water. The rate of irrigation was sufficient to maintain the ponding depth at a constant level as well as cause water to overflow from the ponded surface. The difference between the steady-state irrigation and overflow rates was considered to be the instantaneous flux and was assumed applicable to all depths. Simultaneous tensiometric measurements of pressure head as a function of depth provided the hydraulic gradients needed for calculation of Ksusing Darcy's law. Hydraulic gradients deviated considerably from unity, and soil saturation did not exceed 92% of porosity. Laboratory-measured Ksvalues for the stable-structured topsoil agreed well with the field data. However, those for the subsoil were 2 to 3 orders of magnitude lower than the field-measured values. The susceptibility of the subsoil to compaction during core extraction and slaking when in contact with free water appeared to be responsible for the highly reduced rates of flow in the laboratory samples. The subsoil pore structure was preserved only as long as it was overlain by the stable structured topsoil. Results suggest that measurements of water flow on small soil cores may, in some cases, be of questionable value. The field method provided accuratein situdata on plot-size areas. The field plot method used in this study causes minimal disturbance of the soil while the effects of sample confinement and overburden are represented fully in the measurements.

ISSN:0038-075X    

出版商:OVID    

年代:1998

数据来源: OVID

摘要:

Supplemental irrigation is expanding in the Northern Great Plains. Limited access to water of suitable quality for sustained irrigation and uncertainty about the impact of the use of marginal water on the soil resource will limit adoption of this practice. The objectives of this study were to determine the effect of irrigation water quality and amount on the infiltration rate, Q, at 50, 100, and 150 mm tensions, (h), and to relate the change in Q to changes in soil salinity and sodicity caused by irrigation. Tension infiltrometers were used to determine Q for soils at two sites in central North Dakota. Each site had 18 nonweighing lysimeters supporting alfalfa (Medicago sativaL.) that had been irrigated at three levels of irrigation (1ET, 2ET, and 3ET) for at least 10 years with either good quality surface water [electrical conductivity (EC) 0.1 S m−1, sodium adsorption ratio (SAR) 4] or poor quality simulated groundwater (EC 0.34 S m−1, SAR 16). At the site having sandy soils, Q, averaged over irrigation levels, was greater [Q(50) = 5.34 μm s−1, Q(100) = 3.74 μm s−1, Q(150) = 2.96 μm s−1] in soils irrigated with good quality water than in soils irrigated with poor quality water [Q(50) = 3.06 μm s−1, Q(100) = 2.31 μm s−1, Q(150) = 2.01 μm s−1]. Level of irrigation had no effect. At the site having loam textured soils Q was lower under the two higher irrigation levels than under the 1ET level, likely the result of greater replacement of divalent cations with Na+at the higher leaching rates. At this site Q, averaged over irrigation levels, were greater [Q(50) = 3.08 μm s−1, Q(100) = 2.55 μm s−1, Q(150) = 2.02 μm s−1] in soils irrigated with good quality water than in soils irrigated with poor quality water [K(50) = 2.05 μm s−1, K(100) = 1.63 μm s−1, K(150) = 1.28 μm s−1]. Reductions in Q were directly related to increases in soil SAR (e.g., at the 1ET level of irrigation, SAR = 3 in soil irrigated with good quality water and SAR = 6 in soil irrigated with poor quality water) resulting from irrigation. These results suggest that these sulfatic soils are sensitive to Na+-induced deterioration. Soil physical deterioration was apparent at SARs much lower than the SAR 13 used to describe soils as sodic. Soil water compatibility in these soils is critical for sustainable irrigation.

ISSN:0038-075X    

出版商:OVID    

年代:1998

数据来源: OVID

摘要:

The effect of land use, total metal content and soil parameters on the distribution of Cd, Zn, and Cu between the solid phase and soil solution is examined in a large field survey.In situsoil solution samples were obtained by centrifugation of field moist soil samples from six depth layers (0 to 80 cm) in 30 Dutch forest and arable soils. The soils vary in texture, pH, organic matter content, and land use and represent major soil types in the Netherlands. Total metal contents in arable soils exceeded those of forest soils because of manure and fertilizer application and decreased with depth in both land use types. Cd and Zn solution concentrations were higher in forest soils and increased strongly below pH 5.5 despite the low total metal content. Cu solution concentrations were higher in agricultural soils and increased with dissolved organic carbon. Multiple linear regression showed that CEC and pH explained 49% (for Cu), 79% (for Cd), and 83% (for Zn) of the measured variation in distribution coefficients (Kd). In acid forest soils (pH < 4.5; Zntotal< 10 mg kg−1; Cdtotal< 0.3 mg kg−1), 80% of all measured Zn and Cd solution concentrations exceeded current ground water quality standards as a result of the high metal solubility at low pH. Taking into account the low acid buffering capacities in these soils, continuous acidification may cause further increase in the soil solution concentration of the metals considered in this paper.

ISSN:0038-075X    

出版商:OVID    

年代:1998

数据来源: OVID

摘要:

In a previous study utilizing fallow field lysimeters of an undisturbed, loamy sand soil treated with14C-metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl) acetamide], 2 to 5% of the applied14C was mobile to soil depths of 56 to 96 cm. The objective of this 120-day study was to determine the temporal distribution of14C-metolachlor and/or metabolite(s) in soil water from similar field lysimeters and their possible contribution to groundwater contamination. Undisturbed soil column field lysimeters (20.3-cm i.d. × 101-cm long; 16 gauge steel) were driven into a conventionally tilled Dothan loamy sand (fine-loamy, siliceous, thermic Plinthic Kandiudult) and treated with14C-metolachlor and tritiated water (3H2O) and subjected to natural rainfall or irrigation. Percent recovery of metolachlor and/or metabolite(s) in the soil, as based on14C measurement, was 62% at 30 days, 63% at 60 days, 51% at 90 days, and 49% at 120 days. Recovery of3H2O was 36, 24, 6 and 0.25% of the applied for the same time periods. By 30 and 60 days after application (DAA),3H2O had distributed symmetrically in the soil profile, whereas, a large percentage of the14C was retained in the upper 24 cm. No14C and <1% of the applied3H2O was recovered in leachate the first 30 days. Cumulative recovery of14C in leachate was <1% of that applied at 60 days, 3% at 90 days, and 7% at 120 days. Cumulative recovery of3H2O in leachate for the same time periods was 22, 39, and 39% of that applied. The symmetrical breakthrough curve for3H2O indicated no preferential flow or immobile water, whereas the breakthrough curve for14C was asymmetrical as a result of the sorption-desorption processes. Peak concentrations of14C and3H2O in the leachate occurred at 94 and 63 DAA, respectively. The sorptive tendencies of both radiolabeled species distinguished the magnitude of movement, with3H2O much more mobile than14C-metolachlor and/or metabolite(s). Assuming that all14C in leachate was parent, average metolachlor concentrations in leachate were less than the National Health Advisory level, which may indicate that metolachlor should be considered a low risk chemical because of its potential to contaminate groundwater in soils with low organic matter and high clay content in the subsoil.

ISSN:0038-075X    

出版商:OVID    

年代:1998

数据来源: OVID

摘要:

This study was designed to compare rates of herbicide dissipation and leaching in side-by-side microplots that have been under no-till and plow-till practices for various time periods. Microplots were established within eight field plots (0.1 to 0.25 ha) that had been in no-till for 1 or 4 years, resulting in 1-year and 4-year no-till and 1-year and 4-year plow-till treatments. Before application of atrazine, alachlor, and cyanazine, surface crop residues were removed from the no-till treatments to ensure comparable and uniform applications to soil surfaces. Soil samples were collected at 8, 14, 21, and 32 days after application at depth increments of 0 to 1.5, 1.5 to 3, 3 to 5, 5 to 10, and 10 to 20 cm (weed root zone). The leaching rate was slower in the no-till than in the plow-till treatment. Atrazine and cyanazine levels in the top 1.5 cm of soil, relative to the remaining soil profile, were nearly 50% higher in the 4-year no-till than in the 4-year plow-till microplots. The leaching trend of the 4-year plow-till was similar to that of the 1 year for both no-till and plow-till soils. Regardless of the tillage age differences, the concentrations of atrazine and cyanazine were higher in the no-till than in the plow-till microplots for the 8-day sampling, contrary to observation in previous studies where crop residues were present on the no-till system at the time of herbicide application. Dissipation rates for all three herbicides were approximately linear and in the order of cyanazine > atrazine > alachlor. Also, results indicate distribution of residues within the soil profile were different for atrazine and cyanazine than for alachlor. This observation is most likely caused by the differences in herbicide formulations.

ISSN:0038-075X    

出版商:OVID    

年代:1998

数据来源: OVID

摘要:

Studies were conducted to determine atrazine sorption (partitioning), bioavailability (soil solution concentrations), and dissipation in the top 0 to 1.5, 1.5 to 3, and 3 to 5 cm of soil as a function of tillage. Paired microplots (plow-till vs no-till) were established in replicated long-term tillage field plots, such that treatments included 4-year plow-till, 4-year no-till, 1-year plow-till, and 1-year no-till. Organic carbon content in the top 0 to 1.5 cm was about 75% greater in 4-year no-till soil than in 4-year plow-till soil; at lower depths, organic carbon contents were consistently lower in 4-year no-till soil. Soil solution concentrations of atrazine in the top 0 to 1.5 cm of soil were approximately twofold lower in 4-year no-till soil than in 4-year plow-till soil (5.4 μg mL−1vs 10.1 μg mL−1) 8 days after application. This was caused by increased sorption and higher gravimetric moisture contents. Soil solution concentrations of atrazine in the 1.5 to 3- and 3 to 5-cm soil depths were also lower in 4-year no-till soil compared with plow-till soil, apparently as a result of increased leaching in plow-till. Soil solution concentrations for 1-year plow-till and 1-year no-till soils were intermediate. Relative percentages of atrazine recovered in the top 5 cm of soil were comparable with tillage treatments (> 80%) through Day 21, indicating that the bulk of atrazine remained within the zone of weed germination. Rates of dissipation and leaching (0-5 cm) were comparable for plow-till versus no-till soil. These data indicate that atrazine bioavailability is diminished significantly in no-till soils, which may contribute to losses of atrazine efficacy.

ISSN:0038-075X    

出版商:OVID    

年代:1998

数据来源: OVID

摘要:

Characterization of degradation of an Alfisol caused by clearing and long-term cultivation and the effect of the degradation on leaf (Cajanus cajan) decomposition and nutrient (N and P) release were studied in the humid zone of southwest Nigeria. Degradation of the Alfisol as a result of land clearing and 17-year continuous cropping led to loss of soil biota and deterioration of soil physical and chemical properties. Compared with nondegraded soil, the degraded soil was 38% lower in soil organic carbon, 55% lower in exchangeable bases, 56% lower in microbial biomass, and had 44% lower microarthropod density, 34% less silt, and 88% less water infiltration; it also had 13% higher bulk density and 14% more sand. Soil pH was lower in the degraded than in the nondegraded soil. The macrofauna community in the degraded soil was termite-dominant (Ancistratermes cavithorax), whereas it was earthworm-dominant (Hyperiodrilus africanus) in the nondegraded soil. Leaf decomposition and nutrient release were lower in the degraded soil than in the nondegraded soil during the 150-day experiment. Higher decreases in leaf decomposition and nutrient release in the degraded soil were observed when macrofauna were excluded. Macrofauna-mediated leaf decomposition and nutrient release in the degraded soil were higher than in the nondegraded soil. Irrespective of soil degradation, macrofauna-mediated decomposition and nutrient release resulted in net nutrient mineralization.

ISSN:0038-075X    

出版商:OVID    

年代:1998

数据来源: OVID

摘要:

Surface runoff of nutrients after land application of animal manures is influenced by climate, physical and chemical properties of the soil, and land use. The objective of this study was to characterize the surface soil properties from a riparian forest to an adjacent ridge top at a site in the Ozark Highlands. Sampling transects (60 m long) were established in five soil map units, 7.6-cm-diameter × 10-cm-deep cores extracted at 3-m intervals, and samples analyzed to determine relevant soil physical and chemical properties. Ponded infiltration measurements were also completed on four of the transects. Soil test phosphorus and phosphorus saturation ranged from 10 to 31.4 mg kg−1and 9.1 to 18.4%, respectively, and reflect the recent history of limited poultry litter or fertilizer application. Soil samples from each transect had similar average silt content (range = 67.2-73.9%), but the soil in the riparian forest (Razort silt loam) had more clay and significantly less sand and coarse fragments. The Razort soil also had a higher cation exchange capacity (CEC) (20.7 cmol kg−1) and infiltration rate (5.29 cm h−1). Trends in clay content, infiltration rate, and CEC suggest that the riparian forest and adjacent alluvial pasture may act as nutrient sinks in this landscape. Results of this study will be combined with grazing management and hydrologic analyses to develop best management practices for poultry litter applications and to provide baseline data for the assessment of long-term effects of litter application on soil properties.

ISSN:0038-075X    

出版商:OVID    

年代:1998

数据来源: OVID

ISSN:0038-075X    

出版商:OVID    

年代:1998

数据来源: OVID