摘要:

Traditional methods for the analysis of soil processes are based on measuring and modeling the distribution of chemical compounds and determining their transformation rates. These approaches have formed the basis of our understanding of soil biogeochemical processes, and they have demonstrated the fundamental role of microbes in regulating these processes, but they do not provide a complete view of the complexity of the microbial contribution to soil function. Recent research has revealed the tremendous diversity of microorganisms responsible for catalyzing a variety of soil processes. Such functional redundancy within soil microbial communities may have significant impacts on process rates and ecosystem stability. Therefore, the analysis of functional diversity and its dynamics in the environment is essential for understanding the biogeochemistry of soil systems. Until recently, methodological limitations hindered investigation of the relationship between microbial diversity and soil processes. Over the last decade, innovative molecular approaches to the study of natural microbial communities and the functional genes responsible for biogeochemical processes have given us new insight into this relationship. One new approach, DNA microarray analysis, promises to be especially useful for the analysis of these functional genes.

ISSN:0038-075X    

出版商:OVID    

年代:2003

数据来源: OVID

摘要:

Manure application rate recommendations have been based almost exclusively on nitrogen (N) management considerations, which can result in over-application of phosphorus (P) and its accumulation in soil. Low-phytate (LP) corn (Zea maysL.) was introduced into swine (Sus scrofa domesticus) feed to reduce the amount of P in manure. Unlike ruminants, swine cannot utilize phytate, the major form of P in normal hybrid corn. The objectives of this study were to determine extractable P following swine manure application from different manure sources and compare the relative P availability of LP-manure to standard (S) manure. A laboratory incubation study was conducted using a Waukegan silt loam, a Verndale sandy loam soil, and five levels of total P (Pt) from three P sources (KH2PO4, S-manure, LP-manure). Extractable P from manures of swine fed low-phytate corn and standard corn diets were compared with a soluble P (KH2PO4) source. Slope ratio procedure was used to determine a phosphorus availability index (PAI). The effect of the P application rate on extractable Bray-1 P was linear (r2>0.97). Small but significant P mineralization was observed for the Verndale sandy loam soil. Mineralization of organic P was detected only at the highest LP-manure application rate for the Waukegan silt loam soil. Relative to KH2PO4, the LP-manure and S-manure had PAI of 0.55 and 0.61, respectively. Swine manure P availability was about 60% that of the KH2PO4source for both manure sources. The total P concentration for the LP-manure was 42% lower than that for the S-manure. The important factor in the difference between manure sources is the 42% lower total P content for the LPmanure, not a difference in availability. Further evaluation of available P from LP-manure is needed under field conditions.

ISSN:0038-075X    

出版商:OVID    

年代:2003

数据来源: OVID

摘要:

Colloidal movement in the soil profile is of great concern because of its suspected role in facilitating transport of contaminants to groundwater. Laboratory studies were conducted to determine the effects of excessive phosphorus (P) application on the transport of colloidal iron oxides in the surface layer of a Wabasso sand (sandy, siliceous, hyperthermic alfic haplaquods). Soils were packed in columns, and the surface layer was treated with five phosphorus application rates. A total of five pore volumes of deionized water were applied to soil columns under conditions of alternating saturated and unsaturated flow, and leachates were collected and analyzed for iron (Fe) and P concentrations. Excessive P application altered characteristics of the soil and the stability of iron oxides in the soil solution and, thus, accelerated transport of colloidal iron oxides in the soil. Concentrations of Fe in the leachates, ranging from 0.1 to 33.4 mg/L, depended on the rate of P application and varied with leaching sequence. The Fe in the leachates was mainly particulate Fe, which averaged 38.0–94.1% of total Fe in the leachates. The highest concentration of Fe in the leachate generally occurred in the soils receiving P levels as high as 1- to 3-fold of maximum phosphate adsorption calculated from a Langmuir equation. Elevated Fe transport in the form of iron oxide also increased the migration of P and trace elements in particulate forms.

ISSN:0038-075X    

出版商:OVID    

年代:2003

数据来源: OVID

摘要:

The concentration (Ct) of phosphate ions (Pi) in soil solution is the primary variable on which plant nutrition with phosphorus and eutrophication depend. The description of soil mobile Pi (Pm) is a necessary step in the modeling ofCtkinetics. The description of the change in the content of soil mobile Pi (ΔPm) must take into account the initial amount of mobile Pi (Pm,0). The change in the content of soil mobile Pi has been described by ΔPm=a(Cbt−x)tc,wherea, b, x,andcare fitted parameters. We tested the suitability of a derived simplified equation where the native sorbed Pi, i.e.,x,is calculated from the measured initial Pi concentration in solution (C0): ΔPm=a(Cbt−Cb0)tc.Both equations were compared for their suitability for describing the kinetics ofCt.Two sorption and one sorption-desorption experiments were performed on soil samples taken from plots having different P fertilizer histories in two long-term field trials located on Luvisols. The differences in conditions between experiments included (i) number of Pi addition rates (up to 120 mg P kg−1), (ii) soil-to-solution ratio, and (iii) period of contact between soil and solution (up to 7 days).In the adsorption domain, both equations fitted experimentalCtvalues (r2>0.99) closely. In the desorption domain, however, some slight discrepancies were observed between measuredCtvalues and those calculated by the simplified equation. They were probably the result of overestimation ofC0. Thus, the proposed simplified equation accounts for the participation in the soil solution Pi dynamics of the initial mobile Pi content of the soil that determines the initial Pi concentration in solution (C0).

ISSN:0038-075X    

出版商:OVID    

年代:2003

数据来源: OVID

摘要:

Soil infiltration controls the partitioning of rainfall into surface runoff, groundwater recharge, and soil moisture. Understanding seasonal variability and the influence of soil erosion pavement on infiltration is critical to increasing our ability to predict runoff. Our objective was to evaluate seasonal variability in infiltration and the importance of erosion pavement. A tension disc permeameter was used to measure infiltration seasonally for 3 years with soil erosion pavement in place and for up to 1 year after the pavement was removed. Seasonal and erosion pavement effects were evaluated using saturated hydraulic conductivity, flow-weighted characteristic pore size, and macropore capillary length data. There was a significant season-by-year interaction for conductivity with the erosion pavement in place. Conductivity was substantially lower in the fall season, whereas the rates were similar for the other seasons. Differences in years within seasons were also observed. The calculated soil pore structural components of size and length could not account for the seasonal changes in conductivity. The pore size and length remained comparatively constant for the seasons and years. To account for the low fall hydraulic conductivity, it was concluded that raindrop impact from the high intensity summer thunderstorms closed some pores or interconnections. Freeze-thaw cycles from late fall through spring apparently opened the pores, resulting in increases in conductivity. Soil erosion pavement removal caused an immediate significant decrease in hydraulic conductivity and pore size and an increase in pore length that lasted longer than a year. Results indicate that soil erosion pavement is important in maintaining soil surface structural integrity to maintain the higher conductivity. Disc permeameter measurements were clearly able to show seasonal and erosion pavement influences on soil conductivity and that soil erosion pavement must be incorporated into hydraulic runoff models to improve predictions.

ISSN:0038-075X    

出版商:OVID    

年代:2003

数据来源: OVID

摘要:

A greenhouse study utilizing two experiments was used to evaluate the effects of applying browse leaves, or feces derived from these feeds, at equal organic-N application rates (120 kg ha−1), alone or with fertilizer N (30 kg ha−1), on feces and leaf decomposition in soil, on maize (Zea maysL.) dry matter (DM) yield, nitrogen (N), and phosphorus (P) uptake, and on soil chemical properties. Decomposition rates of amendments varied considerably due to amendment type, browse species, and fertilizer N. Maize DM and cumulative N uptake were most affected by browse species, followed by browse species & amendement interaction, browse & N effect, amendment type, and, to a lesser extent, by fertilizer N. Although more N and P were recycled in feces than in leaves, browse leaves decomposed faster, and some had greater positive effect on maize yield than feces. Fertilizer N increased maize DM by 10%, N uptake by 31%, and P Uptake by 6% and enhanced N mineralization from most organic amendments. The relatively high cell wall content of feces may have been an effective sink for fertilizer N, which when remineralized provided more N to maize than soils amended with leaves. Whereas most of the P contained in feces mineralized and was taken up by maize, P was slightly less available in some soils amended with leaves. The results are discussed in relation to the importance of ruminants in enhancing the soil fertility of the humid forest lowlands of West Africa.

ISSN:0038-075X    

出版商:OVID    

年代:2003

数据来源: OVID

摘要:

Application of sewage sludge to agricultural lands is one way to address the high demand for a low supply of commercial fertilizers in Nigeria. This study was conducted to investigate the morphological and chemical properties of sludge-amended soils after about 37 years of sludge application. Two soils on a 5-ha sewage farm and a soil at a nearby, unamended site were selected for the study. Soil at all three sites would have been mapped and classified in the same soil series before application of sewage sludge. The unamended soil was a fine-loamy, kaolinitic, isohyperthermic Rhodic Kandiustult. Compared with the unamended soil, the sludge-amended soils had better aggregation in the surface horizon, greater total soil C and N, and higher levels of exchangeable bases. After 37 years of sewage sludge amendment, a higher base saturation percentage in the subsurface horizons of one sludge-amended soil led to its classification as an Alfisol instead of an Ultisol. Base saturation in the subsurface of the other amended soil was very close to that required for Alfisols, but it would still be classified as an Ultisol.

ISSN:0038-075X    

出版商:OVID    

年代:2003

数据来源: OVID