摘要:

We analyzed six different infiltration equations—those of Kostiakov (1932), Horton (1940), Mezencev (1948), Green and Ampt (1911), Philip (19576) and Par-lange et al. (1985)—for precision, parameter time-dependence, and applicability for predictive use. The tests were carried out by comparison with reference solutions, i.e., analytical, experimental, or numerical for two different head conditions at the soil surface.The results show that all the infiltration equations but those of Kostiakov and Horton, satisfy sufficiently well the imposed precision criterion. Only one model, however, the Parlange infiltration equation, has the advantage of using parameters that are constant in time and independent of the number of data points chosen for their evaluation procedure. The parameters entering into the other algebraic infiltration equations have to be considered as fitting parameters without physical significance and representative only of the experiment for which they are determined.

ISSN:0038-075X    

出版商:OVID    

年代:1988

数据来源: OVID

摘要:

We conducted a laboratory experiment on the interrelationships among five rates, it (0 to 1.6%), of a gel-forming conditioner (Jalma—containing 24.5% humic acids and 3.8% polysaccharides), water penetrability (Λ), weighted-mean diffusivity (λ), swelling index (S), and effective mean pore radius (λ) of a loamy sand, a sandy loam, and a loam. For each of the three soils, the results indicated a highly significant linear increase inSand a consequent exponential decrease in r, λ, and D with increase ofR.The effects of Jalma on these parameters were more marked on the loamy sand than on the other two soil samples.Addition of 0.2,0.4,0.8, and 1.6% Jalma to the loamy sand sample significantly reduced Λ by about 19, 55, 83, and 98%, respectively, and D by about 38, 76, 96, and 100%, respectiely. The highest rate almost completely sealed the soil independent of its texture and reduced D to almost zero. We concluded that 0.4% Jalma is the optimum rate for soil water conservation. We argue that Jalma addition causes swelling of the soil matrix, reduces the effective mean pore radius, and consequently reduces Λ and D. The effective mean pore radius proved to be a reliable predictor of D and Λ of the soil samples studied independent of their texture: Λ = 2.548r0.49(r2= 0.960), and D = 3.303r1.075(r2= 0.958).

ISSN:0038-075X    

出版商:OVID    

年代:1988

数据来源: OVID

摘要:

In a series of laboratory incubation studies, we evaluated the effects of temperature, moisture, and nitrogen amendment on nitrogen mineralization rates in the acidic Lakehurst and Atsion sands of the New Jersey Pinelands. The average potentially mineralizable nitrogen (No) values for the Lakehurst and Atsion sands were 87 and 94 μg/g (170 and 630 kg N/ha), respectively. Mineralization constants (k) were 0.0501 and 0.0756/wk at 25 and 35°C, respectively, for the Lakehurst sand and 0.0327 and 0.0452/wk for the Atsion sand. Maximum mineralization occurred at 35°C for both soils withQ10values ranging from 1.8 to 2.1. Optimal soil moisture tensions for nitrogen mineralization were between −0.01 and −0.03 MPa. A soil moisture tension of −0.1 MPa reduced nitrogen mineralization with the Lakehurst sand, but not with the Atsion sand. Amendment of the soil with ammonium sulfate increased mineralization with the Atsion sand, but had no effect on the Lakehurst soil. Conversely, ammonium chloride amendment increased the nitrogen mineralization rates in the Lakehurst, but not the Atsion sand. Urea amendment inhibited nitrogen mineralization with both soils. No nitrate accumulation was observed in any of the nitrogen-amended samples.

ISSN:0038-075X    

出版商:OVID    

年代:1988

数据来源: OVID

摘要:

A field experiment compared the ability of several phosphoroamide compounds to retard urea hydrolysis on a fallowed notill (NT) and conventionally tilled (CT) silt loam soil (pH 5.70). Treatments consisted of urea prills (200 kg N ha-1) with and without inhibitors (4.0 kg ha-1) and a no-fertilizer check. Fertilizers were surface-applied to 10-cm-diameter polyvinyl chloride (PVC) cylinder microplots partially embedded in the soil. Duplicate microplots were removed at intervals after fertilization and analyzed for the quantity of urea remaining. Results indicate that, of the compounds tested, phenyl phosphorodiamidate (PPD) most effectively inhibited urea hydrolysis. Addition of PPD reduced the initial (first 4 to 10 d after fertilization) rate of hydrolysis by 60 to 70% in three of four trials conducted. A laboratory study conducted on a soil at two contrasting initial pH values (5.6 and 7.4) showed that PPD was more effective in the acidic than in the alkaline soil. Two other inhibitors (UI4 and UI5) retarded hydrolysis to a greater degree than did PPD in the alkaline soil. In the same laboratory study phosphoroamide (UI6), not tested in the field, was found to be least effected by soil pH and showed promise as a urease inhibitor in both acidic and alkaline soils. Field and laboratory studies indicate that urea was hydrolyzed 2.3 to 3 times faster when added to corn-residue-covered surfaces than to bare soil. This finding suggests that the residue contained high levels of urease activity.

ISSN:0038-075X    

出版商:OVID    

年代:1988

数据来源: OVID

摘要:

Using mass-loss and CO2-evolution techniques, we evaluated the decomposition of peat in an ombrotrophic bog in northern Minnesota. We also compared decomposition potentials, using uniform material (cellulose), between the bog and a nearby minerotrophic fen. Mass loss decreased with increasing depth in the peat due to environmental and substrate limitations. Mass-loss from cellulose was greater in the fen than in the bog.

ISSN:0038-075X    

出版商:OVID    

年代:1988

数据来源: OVID

摘要:

Applications of ammonium-based N and P fertilizers have been shown to increase silica concentrations in soil solutions. Recent evidence also suggests that silica compounds are leached and deposited in lower profile zones as potential cementing and blocking agents. Mollisols in northern Idaho are suspected to be conducive to such phenomena because of surface acidification and the presence of a plow pan in the vicinity of the pH transition zone.The objectives of this study were to determine (1) the relationship between ex-tractable silica and the presence of well-developed plow pans in Mollisols of the Palouse of northern Idaho and (2) profile conditions that may cause or enhance silica deposition. Soil samples collected by horizons and depth within horizons were allowed to equilibrate with H2O or Na-acetate (buffered at pH 4.8) before extraction with immiscible displacement. Silica concentrations in H2O extracts were significantly higher in the plow pan zones relative to amounts found above and below in soils containing well-developed pans. Soil profiles with poorly developed pans were shown not to contain increased levels of silica. Data suggest that silica is being deposited or precipitated in well-developed plow pan zones probably as a result of physical and chemical changes that occur in that zone. At lower depths in the soil profile silica is apparently being sorbed at soil particle surfaces, which appears to be correlated to increasing pH with soil depth. Consequently, it is postulated that as pH increases the silica compounds become more reactive and surface sorption is increased.

ISSN:0038-075X    

出版商:OVID    

年代:1988

数据来源: OVID

摘要:

I studied the effects of erosion on pore size distributions and corn root ramification with depth, using Hg intrusion porosimetry. In particular, I examined the paired erosion phases of two fine-textured Illinois soils, one dominated by smectite and the other by hydrous mica. Total porosites of each moist, clayey soil sample were reduced as much as 8% when oven-dried, having the potential to alter pore size classes and corresponding volumes. The proposed method requires sampling fine-textured soils in the field when the profiles are moist (approximately at field capacity) and transporting them to the laboratory in moisture tins. In the laboratory, soil samples are rapidly frozen in liquid N and freeze-dried prior to being intruded with Hg using a porosimeter. The freeze-dried method was selected so measured soil pore sizes approximated those that the corn root tips would encounter when growing into soils at a similar moisture content. The water retention differences (WRD) measured by water-release methods appeared to correlate well with the freeze-dried (50 to 0.5 μm in equivalent diameter) pore class volumes that were not subjected to shrinkage upon drying or swelling associated with unconfined soil sample saturation and equilibration methods. The pore size classes and corresponding volumes varied with soil series, clay mineralogy, and depth. For both the subsoil and parent material, the fine-textured Clarence soils dominated by hydrous mica had much smaller transmission pore volumes and water storage volumes. Topsoil loss resulted in a greater reduction in rooting volume and water-storage capacity of the Clarence soils and resulted in greater corn yield reductions. Efforts to restore the soil productivity of the Clarence and Hoyleton soils will require an increase in the total soil porosity, water-storage pore volumes, transmission pore volumes, and rooting depth.

ISSN:0038-075X    

出版商:OVID    

年代:1988

数据来源: OVID

摘要:

Potassium deficiency in alfalfa is usually recognized as a spot chlorosis in older leaves. This symptom has been observed in the western United States in irrigated alfalfa growing on alkaline (i.e., calcareous) soils. A second kind of K-deficiency symptom also has been observed in the region. It appears as a chlorotic leaf margin where the white tissue is localized toward the leaf tips. As the K-deficiency severity increases, the chlorotic margin extends toward the leaf base. Chlorotic spot and margin symptoms occur on separate plants growing in proximity. The soils involved are low in available K and are neither saline nor sodic.Alfalfa is known to absorb varying amounts of Na, depending on K soil availability. The physiological role of Na in alfalfa is not well understood, but it is believed that K relations of this plant cannot be fully described if Na is ignored. The purpose of this study was to seek an explanation of the causes and effects of different visual expressions of K deficiency in alfalfa through an analysis of K-Na plant relations.An experiment was conducted on a calcareous, low-K soil where both K-deficiency symptoms were present. Sodium uptake was extremely high in chlorotic margin plants. Sodium concentrations of whole aboveground plants were: marginal chlorosis, 0.22 mol/kg; spot chlorosis and also K-fertilized plants, 0.05 mol/kg. Observed K/Na ratios were 0.60 in chlorotic margin plants, 3.81 in chlorotic spot plants, and 5.60 in K-fertilized plants. Sodium concentration of the chlorotic margin plants was higher in leaves than stems (0.368 and 0.099 mol/kg, respectively), though in the chlorotic spot plants the opposite was true (0.010 and 0.036 mol Na/kg, respectively). Potassium fertilization eliminated both symptoms, increased herbage yield, and resulted in an increase in K and a decrease in Na in plants.A model was proposed to explain the chlorotic margin symptom of K deficiency in alfalfa. The two different K-deficiency symptoms, together with associated differences in K-Na concentrations and partitioning within the plant, are believed to reflect the genetic diversity of alfalfa.

ISSN:0038-075X    

出版商:OVID    

年代:1988

数据来源: OVID

摘要:

Accurately calibrating a neutron probe for the field measurement of soil water content is not a simple task. The most straightforword calibration technique is done in the field by determining the volumetric soil water content of soil cores taken around the access tube and relating it to the instrument reading. Although the sampling procedure is time-consuming and sometimes arduous, it is probably the most accurate method currently in use. Plastic cylinders of different outside diameters have been found to be valuable intermediate standards for transferring the field calibration from one neutron probe to another when the detector type, source strength, and geometry are similar. This new technique will greatly facilitate the calibration of any number of neutron probes in many different soils.

ISSN:0038-075X    

出版商:OVID    

年代:1988

数据来源: OVID

摘要:

The in situ measurement of sorptivity with infiltrometers using the falling head method is fundamental in soil physics. We reexamine the theory underlying the method and find that small but significant corrections have to be made to previous results. The new theory is used to analyze experimental observations of infiltration into a sandy soil. The results are accurate enough to demonstrate the dependence of sorptivity and conductivity on density variations of about 5%.

ISSN:0038-075X    

出版商:OVID    

年代:1988

数据来源: OVID