摘要:

The loss of phosphorus (P) on overland flow and subsurface drainage from soils receiving long-term applications of fertilizer and manure has been linked to the accelerated eutrophication of fresh waters. This loss is initiated by the release of P from soil to solution, which for overland flow can be estimated by water extraction and for subsurface drainage waters by 0.01MCaCl2extraction. Although this release is rapid, the information available on the kinetics of P loss is insufficient to support improved soil P management. In this study, an isotopic exchange kinetics (IEK) approach was used to assess the effect of two solutions (water and 0.01MCaCl2) and different soil-to-solution ratios on soil isotopically exchangeable P (Et). Results are described by a compartmental analysis that quantified the amount of P isotopically exchangeable within 1 min (E1min), 30 min (E30min), 24 hr (E24hr), and between 24 hr and 3 months (E24hr-3mo). The quantity of P in each compartment was then compared with the concentration of P in overland flow and subsurface drainage waters. Isotopically exchangeable soil P within 1 min (1:5 soil to solution ratio) was correlated most closely with the concentration of P in overland flow (r2= 0.84 with water) and subsurface drainage waters (r2= 0.93 with 0.01MCaCl2). For overland flow, a significant correlation was maintained at a soil-to-solution ratio of 1:100 for more exchangeable P pools than at other ratios (1:5 or 1:10). Similarly, the relationship between isotopically exchangeable P in 0.01MCaCl2(but not Et in water) and subsurface drainage waters P was maintained for exchange times up to 24 hr, reflecting the greater contact period of subsurface drainage water with soil compared with overland flow. The results suggest that the concentration of P in overland flow and subsurface drainage waters is dependent on the rapid or short-term (1 min and <24 hr) kinetics of soil exchangeable P and that the IEK approach can explain, and with further work may predict, the amount of P that can potentially move from agricultural soils to overland flow and subsurface drainage waters.

ISSN:0038-075X    

出版商:OVID    

年代:2001

数据来源: OVID

摘要:

Application of phosphoric acid (H3PO4) to lead (Pb)-contaminated soil may be a remedial strategy forin situimmobilization of soil Pb. Treatment homogeneity with three application methods was assessed by determining microscale pH variability through both conventional and spatial variance analyses. Soil containing an average 2570 mg Pb kg−1near a smelter in Jasper County, Missouri, was treated with H3PO4(10 g P kg−1) utilizing three methods: rototilling, pressure injection, and surface application. An undisturbed soil core (10 cm deep, 10 cm wide, 2.5 cm thick) was taken from each plot 30 days after treatment. Soil pH was measured at 1-cm horizontal and vertical intervals with a pH-sensitive glass microelectrode. Horizontal and vertical variations of soil pH were estimated by variance analyses, and the spatial variability was assessed by semivariogram function. Addition of H3PO4to the soil decreased pH significantly and increased total variability in the measured zone. The pH variability in the vertical direction differed significantly, but that in the horizontal did not. Higher total variability caused by the treatment methods resulted from increased spatially dependent variability, which may be attributed to strong trends of pH with soil depth. Rototilling resulted in the lowest variation and smallest spatial variances, suggesting the most effective mixing of soil with added H3PO4among the methods tested. This study demonstrated that microscale pH measurements and analyses of total and spatial variances may aid in assessing the efficacy of H3PO4treatment in Pb-contaminated soil.

ISSN:0038-075X    

出版商:OVID    

年代:2001

数据来源: OVID

摘要:

Apparent electrical conductivity (ECa) of soils can be measured easily by nondestructive methods and, therefore, could be useful in the mapping of soil properties, which influence ECa. The influences of soil structure, bulk density, clay and water content, EC of the soil solution, and cation exchange capacity (CEC) on ECawere examined in laboratory experiments for 19 soils at 16 to 18 water contents. Soil structure increased variability in ECabut had no other influence. Bulk density also had no influence when the other variables were used on a volume basis rather than on a weight basis. This agrees with the concept that an electric current has to pass a given volume between two electrodes but not a constant mass. Cation exchange capacity, which depends primarily on charged sites of the clay and organic matter fractions, correlated less with ECathan clay content alone, indicating that the charged sites of organic matter are less important. Despite the humid climate, the EC of the soil solution varied considerably in the soils, which could be explained by differences in fertilizing history which, in turn, influenced ECa. Water content had a comparably small influence, which increased near the wilting point and below. In a multiple regression, volumetric clay content, EC of the soil solution, and logarithmic water content influenced ECaat a ratio of 1 : 0.8 : 0.4. This regression explained 84% of the variation and performed equally well on a validation data set of 145 soil-moisture combinations. This is superior to an existing model. Thus, ECaoffers the opportunity to improve high-resolution mapping of these three properties by selecting conditions under which the variation can be assigned mainly to a single factor. Together with the ease of ECameasurement, this is especially useful for precision agriculture.

ISSN:0038-075X    

出版商:OVID    

年代:2001

数据来源: OVID

摘要:

Above-canopy precipitation (ACP) reaches the soil under corn (Zea maysL.) as throughfall (TF) and stemflow (SF). We hypothesized that this results in heterogeneous nutrient inputs to soil and that the corn canopy modifies the chemical composition of ACP because of dry deposition and crop leaching. Therefore, we examined the quantity and quality of ACP, TF, and SF in corn fields on Oxisols of the Brazilian savanna during two vegetation periods and estimated the dry deposition rates with a Na tracer technique. Throughfall accounted for 70 to 75% of the ACP. Evaporation losses of intercepted water were close to zero. In TF and SF, volume-weighted mean (VWM) concentrations in μg L−1of Ca (TF: 581/SF: 565), Cl−(826/1330), Cu (2.4/1.9), K (2110/5710), Mg (199/403), Mn (1.3/1.2), N (1550/770), Na (493/586), S (376/184), and Zn (9.3/24) were generally higher than in ACP (Ca: 117, Cl−: 265, Cu: 1.0, K: 152, Mg: 44, Mn: 0.48, N: 199, Na: 246, S: 62, and Zn: 5.6 μg L−1). The average contributions of SF to the total nutrient input were similar to its contribution to the total water input (27%) for Ca (27%), Mn (28%), and Na (30%), higher for Cl−(37%), Mg (43%), Zn (50%), and K (51%), and lower for Cu (23%), N (16%), and S (15%). This indicated leaching of Cl−, Mg, Zn, and K from the stems and uptake of Cu, N, and S by the plants. Dry deposition contributed 50 to 55% to the average total deposition during the rainy season (October-April) of 3520 g Ca (Ca), 8050 g Cl−, 35 g Cu, 4690 g K, 1370 g Mg, 15 g Mn, 7460 g N, 7590 g Na, 2090 g S, and 199 g Zn ha−1. Leaching from the corn canopy was most pronounced for K (41 kg ha−1) > Ca (5.1) > S (2.6) > Mg (2.4). On average, 76% of the 12 kg N ha−1that reached the soil was organic, indicating that N was also leached. In contrast, there was almost no leaching of Mn (3.5 g ha−1) and, on average, even net uptake of 1.3 g Cu and 0.1 g Zn ha−1. The total deposition, on average, accounted for 3.9% (K) to 46% (Zn) of the nutrient demand of the corn plants. However, it represented <6.5% of the nutrient input with fertilizers. Our results demonstrate that the spatial distribution of the nutrient input to soils under corn is element-specific and that deposition contributes to the micronutrient nutrition of corn grown on nutrient-poor Oxisols.

ISSN:0038-075X    

出版商:OVID    

年代:2001

数据来源: OVID

摘要:

Brazilian pepper (Schinus terebinthifoliusRaddi), an exotic invasive plant, is native to South America. In south Florida, this plant has invaded abandoned agricultural lands, poorly managed pastures, roadsides, and canal banks extensively. The "Hole-in-the Donut (HID)", approximately 4000 ha within the Everglades National Park, is a major site of invasion of this exotic plant. This area was previously short hydroperiod prairie and pineland, but it is now a monospecific stand of Brazilian pepper. It has been hypothesized that this transformation is related to rock-plowing soil (crushing the limestone bedrock to increase soil depth) and to intensive vegetable production 25 to 70 years ago. The objectives of this study were to compare the chemical and physical differences of soils from four land uses (undisturbed land, rock-plowed farm land, non-rock-plowed farm land, and restored land) and the mineral nutrient contents of Brazilian pepper and sawgrass (Cladium jamaicenseCrantz). Farming in the HID area changed the soil chemical properties significantly through rock-plowing and the application of agrichemicals necessary for commercial vegetable production. Rock-plowing increased the percenage of rock fragments and the soil pH. Total concentrations of nutrients (N, P, Zn, and Cu) in soils were elevated in both rock-plowed and non-rock-plowed farm lands. Plant-available nutrients in soil of rock-plowed farm land increased about 3 times for P, 6 times for Zn, and 10 times for Cu. As a result of the increased soil fertility, concentrations of P and Zn in Brazilian pepper leaves were 5 and 3 times higher, respectively, than those in sawgrass. High correlation coefficients between leaf P and total and plant-available P in soils indicate that P enrichment in farmed soils facilitated the invasion of Brazilian pepper in this area.

ISSN:0038-075X    

出版商:OVID    

年代:2001

数据来源: OVID

摘要:

Soils formed in dark-colored glacial till (chroma 3, value < 4) are common in southern New England. The low chroma, low-value colors reflect the carboniferous nature of the sedimentary and metasedimentary rocks that compose the till. Much of this till is very dense, resulting in soils with seasonal high water tables. The inherent dark colors of the soils make it difficult to use hydromorphic features to estimate depths of seasonal saturation. We examined thin sections to determine if micromorphology could be used to elucidate the apparent lack of hydromorphic features in seasonally saturated Bw horizons formed in dark till. Observation wells were monitored for 18 months to establish water table seasonal fluctuations in soils on shoulder positions. Hydromorphic features were examined in the field and in thin sections to correlate with the seasonal water table levels. Soils showed seasonal saturation and were classified as Humic Epiaquepts and Typic Humaquepts. Water levels frequently rose into the upper Bw horizons. One of the soils examined met hydric soil criteria based on hydrology. Hydric soil indicators such as a depleted matrix (F3) were absent. The dark parent materials were most likely preventing the observation of morphologic indicators of reducing conditions. Redoximorphic features were not identified by field observations in the seasonally saturated upper Bw horizons. Thin sections of the upper Bw horizons revealed redoximorphic features that were too faint, fine, or had boundaries too diffuse to be observed in the field. Identifying hydromorphic features in lower horizons and, with the aid of magnification, tracing these features carefully into overlying horizons may help identify the depth to aquic conditions in low chroma-low value seasonally saturated soils.

ISSN:0038-075X    

出版商:OVID    

年代:2001

数据来源: OVID

摘要:

The need for spatial information on soil properties at the field level is increasing, particularly for its applications in precision agriculture and environmental management. One important soil property is clay content; however, costs involved with obtaining soil data at the field scale are prohibitive. Geostatistical techniques have been used with some success to improve the accuracy of spatial prediction of soil properties, especially those based on easy-to-obtain ancillary information. There is also, however, the need to determine optimal spacing for generating the ancillary data for spatial prediction. In this paper, we used ancillary variables along with spatial prediction models to determine an optimal method for estimating clay content at the field scale. We also determined the optimal spacing for generating the ancillary data for spatial prediction. The ancillary variables used were apparent soil electrical conductivity (ECa) obtained with EM38 and EM31 and digitized bands (red, green, and blue) of aerial photographs of the bare soil. The spatial prediction models tested are generalized additive models using various combinations of ancillary data (e.g., ECaand red, green, and blue data) and the geostatistical methods of ordinary-, regression- and co-kriging. The results suggest that the linear regression of average clay content with ECa(EM38) data used in combination with kriging of regression residuals was most accurate (RMSE = 3.03). The generation of ECadata on 24-m transect spacing was optimal for prediction. Doubling and tripling the transect spacing (i.e., 48 and 72 m) cause relative reductions in precision of 17% and 12%, respectively.

ISSN:0038-075X    

出版商:OVID    

年代:2001

数据来源: OVID

ISSN:0038-075X    

出版商:OVID    

年代:2001

数据来源: OVID