Search

Solute leaching on the field-scale is a poorly understood, complex process affected by local soil variation and landscape position. We hypothesized that Br ion leaching is a function of landscape position in a well-structured, clayey soil on a Piedmont toposequence that had been in pasture for the previous 30 yr. Dry KBr, mixed with sand at a ratio of 12 g sand to 1 g KBr, was surface-applied at a rate of 314 kg Br [ha.sup.-1] on 24 May 1994 along two transects and allowed to move into the soil under natural rainfall conditions. Soil cores 0.90- and 2.00-m-long were taken 13 June and 20 Dec. 1994, respectively (corresponding to 20 and 210 d after Br application and 15 and 63 cm rain, respectively). The cores were subdivided into increments 10 or 15 cm, oven dried, and analyzed for Br. Centers of Br mass at both sampling times were significantly deeper in the footslope position (31 and 82 cm for June and December, respectively) compared with the shoulder and linear slope positions combined (25 and 70 cm for June and December, respectively), which was possibly due to lower clay contents (44 vs. 50% clay) and lower water retention (37 vs. 43 cm in the top meter in December) for the footslope vs. the linear and shoulder slopes combined, respectively. Predicted leaching depths were calculated from measured soil water content profiles and were positively correlated with observed depths to the center of Br mass for the Dec. 20 sampling ([r.sup.2] = 0.35, P [is less than] 0.007). Anion leaching may be partially controlled by landscape position, and soils susceptible to initial rapid leaching may not necessarily be susceptible to sustained rapid leaching throughout the year.

The influence of forest operations on forest soil and water continues to be an issue of concern in forest management. Research has focused on evaluating forest operation effects on numerous soil and water qualify indicators. However, poorly drained forested watersheds with organic soil surface horizons have not been extensively investigated. A study was initiated in the Tidewater region of North Carolina to gain a better understanding of the impact of harvesting operations on poorly drained organic soils. Soils on the study site, having >80% organic matter (OM) content to a depth of 60 cm below the soil surface, were classified as shallow organic soils. Soil physical properties were examined by collecting soil cores from control and treatment watersheds in a nested design. Compaction caused by the harvest operation increased bulk density (Db) from 0.22 to 0.27 g cm-3, decreased saturated hydraulic conductivity (ksat) from 397 to 82 cm h-1, and decreased the drained volume for a given water table depth. However, Db following the harvest remained low at 0.27 g cm-3. The drained volume at equilibrium following the lowering of the water table from the soil surface to a depth of 200 cm was reduced by 10% from that of control watershed as a result of harvesting. [ABSTRACT FROM AUTHOR]

Presents a study which evaluated the effects of animal powered tillage on nutrient dynamics and soil properties at Claveria, Philippines. Methodology; Results; Discussion.

Sedimentation basins are built at construction sites to reduce the load of suspended solids in runoff water discharged into surface waters. However, these basins are not effective in reducing turbidity caused by fine suspended particles such as clay and silt. The objective of his field study was to evaluate the efficiency of moulding plaster (CaSO4-0.5 H2O) as a chemical flocculant for reducing the turbidity of water discharged from sedimentation basins equipped with a floating skimmer device. Following each of 14 rainfall events, sedimentation basins at two urban construction sites were either treated with moulding plaster or left untreated, and the turbidity and chemical properties of the impounded water and discharge water were monitored as the basins drained during a 50- to 70-h time period. Each sedimentation basin was equipped with a floating skimmer device that discharged water at a controlled rate from 5-cm below the surface of the imPounded water. The turbidity of discharge water from untreated basins ranged from 100 to 1650 NTU (nephelometric turbidity units), while a surface-applied moulding plaster treatment of 450 to 520 m decreased the turbidity to g L- 1 <50 NTU. The time required for the discharge water from treated basins to reach either 100 NTU (2--20 h) or 50 NTU (5--52 h) was inversely proportional to theconcentration of dissolved moulding plaster. Chemical flocculation using plaster reduced the turbidity of discharge water to<50 NTU whileproducing dissolved SO4 concentrations of <250 mg L-1. [ABSTRACT FROM AUTHOR]

A high-suspended solids load in surface waters is one of the biggestwater quality problems in the Piedmont region of the southeastern USA. Sedimentation basins at construction sites are designed to redace suspended solids in discharged water, but they are not effective in reducing turbidity. A survey of sedimentation basin water at two urbanconstruction sites showed that turbidity levels during a 9- to 12-moperiod were always greater than the 50-NTU (nephelometric turbidity units) standard adopted in North Carolina for surface waters. Furthermore, water chemistry varied over time, with pH ranging from 5.8 to 8.9 and electrical conductivity (EC) ranging from 3.0 to 23.0 mS m-'. Laboratory experiments demonstrated that temporal variations in the water chemistry were likely caused by contact with concrete and crushed stone. Laboratory flocculation experiments were completed to evaluate the efficiency of calcium sulfate compounds (hemihydrate, agricultural gypsum, and phosphogypsum) as chemical tlocculants for reducing the turbidity of sedimentation basin water from two field sites and for different pH conditions. Moulding plaster (hemihydrate) was a moreefficient flocculant than agricultural gypsum and has fewer environmental restrictions on its use than phosphogypsum. Moulding plaster application rates of 350 to 700 mg L -1 were needed to reduce the turbidity of unstirred sedimentation basin water to 50 NTU within 3 h after addition of the flocculant. To achieve a given turbiditylevel, less flocculant was required for longer flocculation and settling times, or when sedimentation basin water had a lower pH. [ABSTRACT FROM AUTHOR]

Farming systems that minimize the rate of soil degradation and optimize food crop yields are needed to sustain soil productivity on sloping, acid, infertile soils in the humid tropics. Research was conducted on two Oxisols with slopes ranging from 22 to 30% to evaluate the performance of several contour hedgerow systems, with and without the addition of 60 kg N ha-1 per crop, on rice (Oryza sativa) and maize (Zea mays L.) production. Contour hedgerows were double rows of the tree legume Gliricidia sepium (G); Gliricidia and the native grass Paspalum conjugatum (GPas); Gliricidia and an exotic fodder grass Penisetum purpureum (GPen); double rows of Penisetum (Pen); and a conventional open field (C) farming system without hedgerows. Gliricidia prunings and all crop residues were applied to the soil surface in the alleys, but Penisetum was harvested. Food crop yields in all hedgerow treatments tended to be less than the Control for the first two years, presumably due to the displacement of land planted to the food crop. In the third and the fourth years, the rice and maize yields of Treatments G and GPas exceeded the Control, most consistently when N was not applied. Penisetum reduced food crop yields regardless of N application presumably due to nutrient removal in the fodder. The results indicate that Gliricidia in a contour hedgerow increases food crop yield on strongly acid Oxisols by recycling nutrients and partially supplementing the N demand by the food crops. [ABSTRACT FROM AUTHOR]