摘要:

Soil water infiltration is an important surface hydrological process. Most mathematical models describing soil water infiltration and soil water distribution are complicated. The objective of this paper was to present an algebraic model for one-dimensional transient soil water infiltration. The algebraic model contains three parameters, and the influence of the parameters on the algebraic models was analyzed. A one-dimensional infiltration experiment was performed. Model parameters were determined from the experimental data, and the transient soil water content distributions and the infiltration times were calculated with the algebraic model. The calculated soil water content and infiltration time values were compared with observed data. The results indicate that the model reflects the features of the transient soil water infiltration process.

ISSN:0038-075X    

出版商:OVID    

年代:2003

数据来源: OVID

摘要:

Soil respiration (CO2evolution and O2uptake), alkaline phosphatase activity, resin-extractable phosphate, and dissolved organic C dynamics were compared during a 36-day incubation of soil collected from within crop rows of conservation tillage (CT) (CT = no-till and ridge-till) and moldboard plow/disc tillage (PT) plots in a high-temperature, semiarid climate after 9 years.Significantly (P<0.05) greater total soil organic C, N, and extractable P were found in CT soils. Organic C was 14.2,13.4, and 10.3 g kg−1in the no-till, ridge-till, and PT treatments, respectively. Organic N was 1.41 1.26, and 0.95 g kg−1, whereas resin-extractable P was 11.4, 9.3, and 6.4 mg kg−1for the same treatments.CO2production in CT treatments was 916% and 758% greater, respectively, for the no-till and ridge-till treatments than for the PT treatment. Highest O2uptake occurred in the CT (NT and RT) treatments, which were 435% and 359% higher, respectively, than uptake in PT. Respiratory quotients (RQs) were similar among the CT treatments, but they were significantly (P<0.05) higher than those in PT. This suggests that there may be a difference in substrate composition caused by tillage, and consequent differences in microbial respiratory activity indicate that biological controls of phosphorus mineralization are becoming better established, although absolute changes in soil organic C and N concentrations were modest. Dissolved organic C ranged from a high of >50 μg C g−1soil in CT to <20 μg C g−1soil in PT.Significant correlations between soluble P and biological activity indices (respiration, RQ, and phosphatase activity) indicate that even modest improvements in soil organic matter can have measurable impacts on P mineralization.These results suggest there may be differences in soil substrate quality that result from conservation tillage and which lead to differences in microbial activities, as well as to improvements in P cycling and soil quality, from even modest gains in soil C in high-temperature subtropical soils.

ISSN:0038-075X    

出版商:OVID    

年代:2003

数据来源: OVID

摘要:

The study of the distribution of various forms of Zn under fluctuating oxidation-reduction (redox) conditions is necessary to improve predictions of Zn solubility and bioavailability when Zn is added to soils with large quantites of organic C that oxidize over time. We conducted plant-soil interaction studies to determine the effect of redox potential in flooded and unflooded soils on the solubility and uptake of Zn by rice (Oryza sativaL., Calrose-76), wheat (Triticum aestivumL.), and barley (Hordeum vulgareL.) in a growth chamber. Sequential extractions were used to fractionate Zn in biosolids-amended and unamended A horizon samples (25-cm depth) of three soil series of a typical toposequence from the Coastal Plain of Maryland: a Galestown loamy sand (Psammentic Hapludults), a Bertie silt loam (Typic Hapludults), and an Othello silt loam (Typic Endoaquults). Addition of organic C (as biosolids) increased the leaf dry matter yield, but not leaf tissue Zn concentration, compared with Zn-amended soil with no organic C addition. Flooding decreased leaf dry matter yield and Zn concentrations in the leaf tissue of all plants, especially in the organic waste-amended soils. Among the crops, rice had higher levels (P< 0.05) of Zn (7.4–34 μmol/g) than did wheat (0.3–4.3 μmol/g) and barley (1.2–6.1 μmol/g). Exchangeable Zn (25 to 48% of added Zn) extracted by Ca(NO3)2was correlated with the concentration of leaf Zn of the three crops (r= 0.62, P < 0.05), whereas the fraction of nonexchangeable Zn (48 to 78% of added Zn) extracted by 100 mMNH2OH · HCL in 1MHNO3was negatively correlated with leaf Zn (r= −0.49,P< 0.05). Reduced soil conditions depressed exchangeable Zn and enhanced nonexchangeable Zn in all of the ponded soils, apparently the result of the enhancement of surface-induced hydrolysis of Zn caused by increases in pH after flooding. The addition of organic C increased the fraction of Zn in nonexchangeable forms in the flooded soils, whereas the Zn levels in nonexchangeable forms in the unflooded soils were not affected by the addition of organic C. Thus, Zn availability to the crops was more dependent on pH changes induced by flooding than on the addition of organic C.

ISSN:0038-075X    

出版商:OVID    

年代:2003

数据来源: OVID

摘要:

The low capacity of acid sandy soils to bind P is one reason for the leaching and runoff of P from these soils. Various soil amendments have been used to reduce P leaching. This study was conducted to show the effect of CaCO3, dolomite, gypsum, and CaCl2on P retention by the Ap horizon of a Spodosol. Phosphorus sorption was studied in a batch experiment at an initial P concentration range of 0 to 10 mg L−1. The amendment rate used was 0.05 mmol of either Ca or Ca + Mg (and also 0.1 mmol in the case of CaCO3and gypsum) per g of soil. The influence on P retention of time after soil amendment (1 h to 1 week) was assessed. P adsorption was described by Langmuir and Freundlich equations. All amendments, except for CaCl2, increased soil pH and P retention by soil. CaCO3was more effective then dolomite, the carbonates (CaCO3and dolomite) were more effective in their interaction with the soil, and gypsum increased P retention by itself, its effect was weakened upon interaction with soil. Sorption of P in soil amended with gypsum was faster than sorption in soil amended with CaCO3. The effect of the amendments under study was mainly to provide Ca ions, which must be accompanied by an increase in pH to increase P retention.

ISSN:0038-075X    

出版商:OVID    

年代:2003

数据来源: OVID

摘要:

Fluvial terrace chronosequences provide excellent opportunities for evaluating pedogenesis. We evaluated soil development on Quaternary terraces of the Tallapoosa River of central Alabama. Our objective was to ascertain pedogenic markers for these relatively low terraces. Past studies and other evidence suggest landscape ages ranging from contemporary floodplains to mid- to late Pleistocene terraces. The six pedons evaluated ranged from Typic Udifluvents and Fluventic Dystrudepts on the floodplain to fine-loamy and coarse-loamy Typic Paleudults on relatively higher terraces. Soil physical properties (particle size, bulk density, 15 bar H2O content), soil chemical properties (total and extractable elements, cation exchange capacity, Fe and Al extractions, heavy mineral content), morphological properties, and micromorphological properties were evaluated. Many soil physical and chemical properties (averaged for B horizons) are related to the soil chronosequence, including properties established in earlier studies as being indicative of soil development. The effective cation exchange capacity and cation exchange capacity 100 g−1clay (P≤ 0.05 and 0.01, respectively), oxalate-extractable Fe (P≤ 0.05), oxalate-extractable Fe/dithionite extractable Fe (P≤ 0.10), and total K/total Ti (P≤ 0.05) all decreased at higher levels. In addition, Mehlich extractable Cu (P≤ 0.10), Fe (P≤ 0.05), and Zn (P≤ 0.05), along with total Mg (P≤ 0.01), Mn (P≤ 0.10), and Ca (P≤ 0.10) decreased with higher terrace levels. Principal component analysis and cluster analysis indicated that soils on terrace levels < 5500 years B.P. are similar, and soils on levels > 5500 years B.P. are similar. The first principal factor, which accounted for 65% of the variance and is composed of both chemical and physical properties, separated terrace levels satisfactorily. The results are generally consistent with decreasing inherent fertility with increasing soil development.

ISSN:0038-075X    

出版商:OVID    

年代:2003

数据来源: OVID

摘要:

Knowledge of the capacity of soils to retain SO42−is fundamental for assessing SO42−leaching and availability. Research was carried out to characterize 18 subsurface horizons from 15 Oxisols, and to investigate their ability to retain SO42−. Yellow Latosols (Y soils) and red Latosols (R soils) from the state of São Paulo (Brazil) were studied along with Oxisols from Galicia (Spain) (G soils). Organic C, pH, ECEC, clay percentage, and amounts of Fe and Al extractable with ammonium oxalate, dithionite-citrate, and citrate-ascorbate were measured. The hematite/ (hematite + goethite) ratio of the soil samples was estimated by second-derivative diffuse reflectance spectroscopy. Sulfate sorption was studied by adding 0.4 or 1.6 mM solutions of K2SO4, initially acidified to pH 3.0, to the soils (ratio of soil:solution, 1:10). The pH-H2O values of the soils studied were generally low, with mean values of 4.6, 5.0, and 5.3, for the Y, R, and G soils, respectively. Levels of dithionite-citrate extractable Fe (Fed) in the Y soils (26 g kg−1) were significantly lower (P< 0.05) than those in the R and G soils (50 and 67 g kg−1, respectively). The hematite rich soils (R soils) sorbed significantly (P< 0.01) greater amounts of SO42−than the other two groups of soils (9.0 compared with 6.8 and 6.9 mmol SO42−kg−1, respectively), in which goethite predominated, although the mean amount of SO42−sorbed per unit of Fedfollowed the order G soils < R soils < Y soils. The lower amounts of SO42−per unit of Fedof the G soils compared with the other soils, in spite of containing the greatest amounts of goethite, may be related to their lower clay content, lower degree of Fe substitution by Al, and higher pH values than the other soils studied. Therefore, differences in soil components and properties, related to the dissimilar environments of formation, lithology, and age, may explain these patterns. The results indicate that SO42−retention in Oxisols cannot be predicted on the basis of the dominant type of Fe oxide/oxy-hydroxide (either goethite or hematite) or on the quantity of these minerals in the soils.

ISSN:0038-075X    

出版商:OVID    

年代:2003

数据来源: OVID

摘要:

Precision agriculture technologies are pointing to the necessity of using sensors to collect soil information to assist in fertilizer dose evaluation. This study evaluates the effect of increasing doses of lime, thermophosphate, and organic matter on spectral reflectance of a tropical soil. We analyzed the most common tropical soil in Brazil, a medium texture Typic Haplortox occurring in the state of São Paulo, Brazil. Physical chemical and mineralogical analyses were carried out both before and after treatments. A spectroradiometer with a 450–2500-nm spectral range was used in the laboratory to capture spectral data. The application of increasing doses of lime increased the reflectance intensity as a result of the presence of calcium. The application of thermophosphate altered reflectance intensity primarily because of the presence of phosphorous. Organic matter reduced the reflectance when compared with the control. Chemical variations promoted by fertilizer application altered the intensity of reflected energy mainly between 826 and 2500 nm. However, there were no significant changes in soil absorption features except when applied to the organic product. The high values of determination coefficients for calcium and organic matter indicate that they can be estimated through soil-reflected energy, and, consequently, will be useful in precision farming systems.

ISSN:0038-075X    

出版商:OVID    

年代:2003

数据来源: OVID

ISSN:0038-075X    

出版商:OVID    

年代:2003

数据来源: OVID