bluuebunny/crossref_metadata_2025 huggingface dataset:
History and Challenges in Soil and Water Conservation and Management
Authors: Browning George M.
Published: July 2010

Soil and crop management practices have been used for centuries in some parts of the world, but in the United States it was not until the 1930's that the public became concerned over the abuse of land. In response a series of emergency and long‐range programs were initiated on the conservation and wise use of natural resources. Information generated by the publicly supported agricultural research system undergirded these programs. The net effect has been major improvements in how our natural resources are used. The job is far from done. Among the challenges and opportunities for additional research in the future are: (i) refine the universal soil loss equation and extend the data base to those areas where it is not available now, (ii) complete soil survey as soon as possible, (iii) strengthen our present effort to assure greater efficiency of water use for agricultural purposes, (iv) develop extensive quantitative information on the relationship between weather variables in a growing season and the yield of different crops, (v) assemble, summarize, and evaluate existing information and develop new information when needed relative to specific sets of conditions for use by all concerned in the development of realistic and practical land use plans, (vi) generate additional data essential in developing sound programs to improve the environment and at the same time maintain our capacity to meet future food requirements, (vi) improve existing tillage systems and develop new ones tailored to meet a wide range of soils, crops, and climatic conditions, and (viii) develop knowledge and plans whereby strip‐mining operations can be carried out without permanent damage to the environment and soil productivity.
Assessing Two Diagnostic Methods for Enumeration of Nitrate Reducing and Denitrifying Bacteria in Soil‐plant Root Associations
Authors: Volz M. G.
Published: July 2010

Most probable number (MPN) determinations were made of NO3‐ reducing‐ and denitrifying bacteria in soil samples taken at time of crop harvest from fallow sites and from root zones of fertilized field plots of tomato (Lycopersicon esculentum L.), soybean (Glycine max L. Merr.), or corn (Zea mays L.) plants cultivated in pure stand or in association with nutsedge (Cyperus esculentus L.), a competitive weed. Diagnostic methods utilized were inoculated Difco NO3‐ broth and Giltay's medium (citrate‐nitrate‐asparagine + mineral salts), incubated with and without the exclusion of atmospheric O2, respectively.

The NO3‐ broth method usually yielded both numerically larger and significantly different (5% level) MPNs for NO3‐ reducers (5 of 7 cases larger, 3 significant) and denitrifiers (6 of 7 cases larger, 3 significant) from a given soil inoculum when compared with identical enumerations performed with Giltay's medium.

When selected soil inocula were incubated anaerobically in Giltay's medium, MPNs of neither NO3‐ reducers nor denitrifiers were increased significantly as compared with the aerobic procedure. Therefore, larger MPNs of soil NO3‐ reducers and denitrifiers observed when NO3‐ broth is utilized are probably more due to improved nutritional environs than to ambient oxygen status. As a result, a more complete estimate of these soil bacterial populations, especially those from the vicinity of plant roots is thought to be obtained using the NO3‐ broth procedure.
Growth Rate‐Nutrient Concentration Relationships During Early Growth of Corn as Affected by Applied N, P, and K
Authors: Terman G. L. , Noggle J. C. , Hunt C. M.
Published: July 2010

Three greenhouse pot experiments with corn (Zea mays L.) were conducted to study effects of multiple rates of applied N, P, and K on growth and yield—nutrient concentration trends. Harvests were made each 4 or 6 days from 15 to 56 days after plant emergence. Growth and plant nutrient concentrations and uptake increased with rate of each applied nutrient at adequate levels of other nutrients. Applied N also increased both P concentrations and uptake in young corn plants. Yield response to applied K resulted only in dilution of N and P concentrations at even the earliest harvest. Concentrations of all nutrients were soon diluted to lower levels with increase in dry matter and/or age of plants, so that comparative results varied with time of harvest. Growth rates increased with adequacy of nutrient supply and more favorable growth conditions; they declined greatly soon after depletion of applied N. The limited soil volume in pot experiments, rate of growth, and time of harvest all greatly influence the effects of one nutrient on plant concentrations of other nutrients.
Diurnal Soil Water Regime in the Tilled Plow Layer of a Warm Humid Climate
Authors: Bruce R. R. , Thomas A. W. , Harper L. A. , Leonard R. A.
Published: July 2010

The soil water content in 10 depth intervals in the surface 15 cm of soil was determined hourly for 9 days in June at 83° 25′W, 33° 52′N. Over the same period at 15‐min intervals soil temperatures were measured at eight depths, windspeed and air temperatures at six elevations, atmospheric water vapor pressures at three elevations, incident solar and net radiation at one meter. From the microclimate data, flux of water vapor at the soil surface was calculated, which was then used to compute soil water flux at several depths by using soil water content data. The diurnal soil water content and soil water flux patterns are compared for a dry period before a rainfall event and afterward. Dramatic diurnal variation of the soil water content at depths < 2 cm was observed. This variation during periods of no rain is related to daily radiation inputs at the soil surface, which generated the observed temperature and soil water gradients responsible for soil water redistribution. Occurrence of rainfall and infiltration events during the measurement period show additional dynamics of the field system. Description of the diurnal soil water dynamics in the plowlayer provide a basis for examining soil processes dependent upon soil water regime.
Measurement of Soil Gaseous Diffusion Coefficients by a Transient‐State Method with a Time‐dependent Surface Condition
Authors: Rolston D. E. , Brown B. D.
Published: July 2010

Precise measurement of the gaseous diffusion coefficient in soils is necessary for calculating the flux of gas resulting from soil respiration, denitrification, or fumigation. Gaseous diffusion coefficients of soil columns and a field soil were determined by fitting a solution of the transient‐state diffusion equation for a time‐dependent surface condition to measured N2 concentration profiles. The time‐dependent surface condition was experimentally imposed by pumping argon at a constant rate into a chamber placed within the soil and on the soil surface. The argon and air mixture exited the chamber through several exit ports. The N2 concentration at the soil surface and within the soil profile was determined several times within a 5‐hour period after initiation of the argon flow. A solution of the diffusion equation for a non‐constant initial condition can also be used for determining the diffusion coefficient for cases where the initial gas concentration is not constant with depth. Diffusion coefficients for a field soil determined from the transient‐state solutions compared favorably with those determined from laboratory measurements on undisturbed soil cores and field measurements of CO2 flux.
Denitrifying Bacteria can be Enumerated in Nitrite Broth
Authors: Volz M. G.
Published: July 2010

Denitrifying‐ and NO3‐ reducing bacteria in air dry, moist, and organic matter amended Yalesville fsl (Typic Dystrochrept), lake water, and in both effluent and drainage field soil from a septic tank system were enumerated using Difco nutrient broth, which contained either or both NO3‐ and NO2‐ and was incubated anaerobically. Most probable numbers (MPN) of denitrifiers (1.3 × 103 to 1.1 × 107/g) were always less than those of NO3‐ reducers (1.5 × 106 to 8.1 × 107/g) in the same sample, and constituted from 0.02% to 70% of bacteria capable of aerobic growth on yeast extract agar. Further, for a given sample, denitrifier populations as estimated in nutrient broth + NO2‐ (NO2‐ broth) were always statistically equivalent to or larger than those determined using nutrient broth + NO3‐ (NO3‐ broth). Therefore, NO2‐ broth may be preferable to NO3‐ broth for estimating denitrifier populations in soil and water samples. Nitrite broth retains the nutritional advantages of nutrient broth but also represses competitive growth effects of NO3‐ reducing bacteria. Further, in order to determine when in vitro denitrification has occurred, one needs only to assess colorimetrically the presence of NO2‐ following culture tube incubation.
Corn and Alfalfa Production as Influenced by Irrigation and Salinity
Authors: Hanks R. J. , Sullivan T. E. , Hunsaker V. E.
Published: July 2010

Yields of corn and alfalfa were determined where both salinity and water stress were imposed. Yields of corn (Zea mays L.) at Logan, Utah in 1975 were decreased by salinity or water stress (caused by low irrigation levels) in direct relation to the decrease in evapotranspiration. The decrease in evapotranspiration was caused by a decrease in soil water depletion, indicating that salinity influenced soil water availability. Corn yields at Vernal, Utah in 1974 were decreased by salinity, but to a considerably lesser extent by low irrigation, probably because of water flow upward into the root zone from a water table. Alfalfa (Medicago sativa L.) yields at Vernal in 1974 were not decreased by salinity or by low irrigation rates, because of water supplied by a water table and used by roots below the zone of salinity.
Fall Soil Water: Effect on Summer Soil Temperature
Authors: Willis W. O. , Wierenga P. J. , Vredenburg R. T.
Published: July 2010

Soil temperature with depth (to 150‐cm) and time (April through September) was measured in field plots in North Dakota to determine the effect of three depths of wetting in late fall before freezing on the growing season soil temperature the following year. All plots were planted with spring wheat [Triticum aestivum, ssp. vulgare (Vill., Host) MacKey var. Selkirk] and received identical treatment during the growing season. The data indicate that a high soil water content in the fall may cause soil temperature in the 30‐ to 120‐cm depth to be 1 to 2°C lower than normal during the next year's growing season, particularly if that season has lower‐than‐normal precipitation. By using soil temperature values from the 15‐cm and 120‐cm depths as the upper and lower boundaries, calculated soil temperatures agreed better with measured values than when 0.2‐cm and 120‐cm depths were used as boundaries.
Enzymatic Activities Related to the Decomposition of Coniferous Leaf Litter
Authors: Spalding Brian P.
Published: July 2010

The rate of CO2 evolution at 23°C and 75% moisture content for a diverse group of coniferous leaf litter samples from Oregon was measured. Significant correlations (1% level) were observed between the rate of CO2 evolution and the activity of amylase, cellulase, and xylanase (r = 0.71, 0.58, and 0.44, respectively) in 0.05M potassium acetate, pH 5.0 extracts of the litter. The amounts of extractable hexose, phenolics, and reducing substances were also correlated with the rate of CO2 evolution (r = 0.74, 0.53, and 0.73 respectively). Peroxidase and invertase activities were not correlated with the rate of CO2 evolution. Litter extracts showed zero‐order kinetics for the hydrolysis of carboxymethylcellulose, xylan, starch, and sucrose. All carbohydrase activities were destroyed by a 15 min exposure to a boiling water bath.
Drainage Flux in Permeable Soil Underlain by a Coarse‐Textured Layer
Authors: Clothier B. E. , Scotter D. R. , Kerr J. P.
Published: July 2010

Drainage from a permeable soil underlain by a coarse‐textured layer is investigated. Simplified theory is used to develop a model relating the drainage flux at the base of the soil to the water storage in the soil. Despite significant hysteresis in the water retentivity curve of the overlying soil and in the hydraulic conductivity‐pressure potential relationship of the coarse layer, hysteresis had little effect on the storage‐flux relation. The model fairly successfully simulated field drainage as measured by a lysimeter and field profile water storage as found by neutron moisture probe measurements. The decline in the drainage flux after the profile has been wetted depends on the depth and retentivity of the soil and the hydraulic conductivity of the underlying coarse layer. To use the model only simple field measurements to find the storage‐flux relationship are needed.
Water Infiltration and Runoff under Rain Applications
Authors: Hachum Ahmed Y. , Alfaro Jose F.
Published: July 2010

Experiments to verify the validity and to evaluate the performance of rain infiltration models based on extending the Green and Ampt approach are lacking in the literature. There are severe gaps between theory, validity, and practicality of these models. In this study, a physically‐based model for describing infiltration into a homogeneous deep stable soil profile with uniform initial water content distribution is presented. The derivation of the model is based on the concept of mapping the actual wetted soil zone into an equivalent rectangular saturated zone with constant effective hydraulic conductivity and capillary pressure head at the abrupt wetting front. The model takes into account the intial water mobility in the soil profile and predicts the system response under any rainfall pattern. The proposed model is further simplified, for practical purposes, by grouping three basic input parameters into a single parameter, the Surface Saturation Index.

The validity of the model was tested and strongly supported by the results of laboratory experiments conducted on samples of three soils, two silt loams and a silty clay loam, under five different (variable and constant) water application rate patterns. It was found that the amount of runoff from a nearly symmetrical convex variable rainfall pattern was very close to that which resulted from its equivalent average constant application rate pattern, regardless of the significant differences between the times at which runoff begins and the characteristics of infiltration rates thereafter.
Rates and Patterns of Water Uptake in a Douglas‐Fir Forest
Authors: Nnyamah Joe U. , Black T. A.
Published: July 2010

The forest water balance was studied in a thinned (840 stems/ha) and an unthinned (1,840 stems/ha) Douglas‐fir forest [Pseudotsuga menziesii (Mirb.) Franco] during two consecutive summers. Soil water content was measured with the neutron meter. Soil water potential was measured with tensiometers and dew‐point hygrometers over a range of 0 to −15 bars. These data were used to compute water extraction rates and patterns for the root zone over a four‐week drying period. The results showed a gradual downward shift of the zone of maximum root water uptake as the soil dried. The fully developed root system of Douglas fir showed less hydrotropic response than the developing root systems of annuals reported in the literature. There was good correlation between water uptake rate and rooting density. During the drying period, water flux into the bottom of the root zone, estimated by the use of Darcy's law, increased from 8 to 15% of the evapotranspiration at the thinned site and from 2 to 8% at the unthinned site. Soil profile water depletion corrected for flux out of or into the bottom of the root zone agreed well with evapotranspiration computed from micrometeorological energy balance data. Water with‐drawal from trunk storage accounted for only 2% of the total evapotranspiration over the four‐week drying period.
Growth and Wood Properties of Longleaf Pine Following Silvicultural Treatments
Authors: Van Lear D. H. , Saucier J. R. , Williams J. G.
Published: July 2010

Thinning, fertilizer, and prescribed burning treatments were applied to a pole‐size longleaf pine (Pinus palustris Mill.) plantation in the Upper Coastal Plain of South Carolina. Thinning levels were 11.5, 18.4, 25.3 m2/ha of residual basal area, plus an unthinned treatment. Fertilized plots received 90 kg/ha P plus 168 kg/ha N. Half of the plots were burned prior to thinning and fertilization. Heavier levels of thinning produced a larger diameter response than fertilization, while burning had no effect during the two years following treatment. Diameter response to thinning resulted from increased formation of latewood, while the response to fertilization resulted from increased formation of earlywood during the first growing season after treatment. Because of these differences in growth response, thinning tended to produce wood of higher specific gravity while fertilization produced wood of lower specific gravity.
Nitrogen Response Relationships of Some Volcanic Ash Soils
Authors: Geist J. Michael
Published: July 2010

Methods of assessing the N fertility status of ash soils and their relationship to plant parameters were studied in the greenhouse. Soils were collected from forested areas in the Blue Mountains of northeast Oregon. Highly significant regression relationships were obtained between soil N supply and N uptake of orchardgrass tops (R2 = 0.97) or top yield (R2 = 0.80) with responding ash soils. A polynomial regression model provided for organic, mineral, and fertilizer N supply sources. Soil organic N supply had a significant influence on plant performance over both narrow and broad ranges of fertilizer addition.
Characteristics of Silica Sorption and Solubility as Parameters to Evaluate the Surface Properties of Tropical Soils: II. The Index of Silica Saturation
Authors: Herbillon A. J. , Gallez A. , Juo A. S. R.
Published: July 2010

Silica solubility of some Alfisols and Ultisols from southern Nigeria was studied. The concentration in soluble silica obtained after a 3‐day contact with a NaCl solution appears to be controlled by the most soluble silicate mineral present in the clay fraction. The index of silica saturation (ISS) is defined as the ratio of the amount of silica soluble in the NaCl extract and the index of silica reactivity of a given sample. ISS appears as a parameter which can be used to describe the surface properties resulting from the processes of silication and desilication taking place within the pedons and along the slopes in toposequences. In this study, ISS ranges from 9 × 10−4 to 685 × 10−4. The interest of ISS as a criterion for soil taxonomy is discussed.
Steady‐state Solute Convection in Two Dimensions With Nonuniform Infiltration
Authors: Batu Vedat , Gardner W. R.
Published: July 2010

The steady‐state unsaturated flow equation in two dimensions is solved for an exponential unsaturated conductivity using the Kirchhoff transformation. Streamlines, travel times, and isochrones are calculated for an infiltration rate which is a piece‐wise linear function of horizontal coordinate. Results are compared with the equivalent solutions for a saturated soil. In addition to solutions in dimensionless form, an example is presented for Plainfield sand. The results confirm that surface variations in infiltration rate may be propagated to a considerable depth, particularly in sandy soils. This may account, in part, for the variability in solute leaching frequently observed in the field.
A Neutron Activation Method for Determining Submicrogram Selenium in Forage Grasses
Authors: Cook K. A. , Graham E. R.
Published: July 2010

Neutron activation as a method for the analysis of submicrogram amounts of Se in fescue and orchard leaves was evaluated. It was observed that the Se content of National Bureau of Standards orchard leaves was 0.078 ppm compared with the NBS reported value of 0.080 ppm Se. The relative standard deviation for the orchard leaves was found to be 5.3%.

Following irradiation and nitric‐perchloric acid digestion, Se was extracted from a 4M HBr solution using benzene containing 1% phenol. The method is sufficiently sensitive to measure with accuracy 0.010 ppm Se in 0.250 g of material. The method is straightforward and accurate and requires the extraction of Se in benzene which is completely free of phosphorus.
Denitrification in Four California Soils: Effect of Soil Profile Characteristics
Authors: Gilliam J. W. , Dasberg S. , Lund L. J. , Focht D. D.
Published: July 2010

The effects of soil profile characteristics upon rate and products of denitrification were investigated using four soils in laboratory columns under steady‐state water flow conditions. A general relationship existed between soil texture and amount of denitrification. Soils with heavy textured subsoils readily reduced added NO3−. However, the soil with the lowest clay content had restricted water flow in the surface horizon and reduced the greatest amount of NO3−. The relationship between soil texture and denitrification is a result of the relationship between water flow and denitrification. It was concluded that any soil condition which impedes water flow will be positively related to denitrification and that spatial variability in denitrification is likely to be as great as observed variability in water movement.

The ratio of N2 to N2O found during denitrification was extremely variable with measured values from 100:1 to 1:4. The low concentrations of N2O measured during denitrification occurred in soils where the denitrification was occurring deep in the soil profile, but there was no indication that this low concentration was a result of further reduction of N2O as N2O diffused through the soil profile. Our data indicate that it is currently not possible to accurately predict relative amounts of N2 and N2O which will be produced during most denitrification in soils, and that estimates of that N2O produced from agricultural lands have a large uncertainty factor.
Inhibition of Urease Activity by Heterocyclic Sulfur Compounds
Authors: Gould W. D. , Cook F. D. , Bulat J. A.
Published: July 2010

The inhibition of both jack bean urease and soil urease by several heterocyclic mercaptans was investigated. The following compounds not previously tested as urease inhibitors were found to be effective inhibitors of jack bean urease: 1,3,4‐thiadiazole‐2,5‐dithiol; 5‐mercapto‐3‐phenyl‐1,3,4‐thiadiazole‐2‐thione; and 5‐amino‐1,3,4‐thiadiazole‐2‐thiol. The disulfides of the latter two compounds were found to be very potent inhibitors of jack bean urease. The results are consistent with an inhibition mechanism involving a thiol‐disulfide exchange reaction between a disulfide and one or more of the sulfhydryl groups of urease. The results also imply that inhibition of urease by the heterocyclic mercaptans was due to trace amounts of the corresponding disulfides or polysulfides in the mercaptan preparations. A number of heterocyclic mercaptans, two disulfides, and a number of known urease inhibitors were evaluated as soil urease inhibitors, and the following compounds were the most effective: 1,4‐benzoquinone ∼ hydroquinone > 2,5‐dimethyl‐1,4‐benzoquinone ∼ catechol ∼ 1,3,4‐thiadiazole‐2,5‐dithiol ∼ 2,6‐dimethyl‐1,4‐benzoquinone.
Neutron Activation Analysis of Standard Soils
Authors: Koons R. D. , Helmke P. A.
Published: July 2010

Four standard soils prepared by the Canadian Certified Reference Materials Project were analyzed for 25 elements to test for inhomogeneities within samples and to demonstrate the use of neutron activation for soil analysis. Five subsamples, weighing about 100 mg apiece, from each of two splits of each standard soil were analyzed. The precision of measurement as measured by the coefficient of variation was < 5% for 20 elements. No soil had more than four elements that differed significantly in concentrations between two splits at the 95% level of significance. Eight of the 12 differences that are significant occur for elements whose coefficient of variation is 2% or less.
Calibration Stability and Response Time for Salinity Sensors
Authors: Wood J. D.
Published: July 2010

Commercially produced salinity sensors removed from field and lysimeter experiments lasting from 3 to 5 years were tested for calibration stability relative to the original factory calibration. Significant changes in calibration occurred in up to 14% of the sensors after 4 and 5 years of use. Response to a step‐change in salinity was also examined for commercial units in a field installation. Calculated response factors were lower than those found in a previous laboratory experiment. However, response was sufficiently rapid to assure accurate readings if changes in salinity occur in time intervals exceeding 5 days.
Fixation of Iron Applied as FeEDTA: Effect of Calcium Concentration and Soil Solid Phase
Authors: Lahav N. , Zipori I.
Published: July 2010

Iron fixation from FeEDTA was measured in three soils at various water contents and Ca concentrations as a function of time for periods up to 30 hours, using a batch technique. In the three soils under study the general pattern of the fixation reaction can be described as a first‐order reaction if adsorption is assumed to be much faster than fixation reaction. The rate constant is markedly affected by Ca concentration: in Rehovot sand and Nazaret clay loam (0 and 61% CaCO3, respectively) the reaction rate constant increases sharply as added Ca increases from 0 to 5 mM, followed by a moderate and more or less linear increase up to Ca concentration of 100mM. In Zophar sandy loam (69% CaCO3), the reaction rate constant shows a maximum at Ca concentration of 50mM and then decreases.

In Rehovot sand and Nazaret clay loam the fixation process can be described by two independent first‐order reactions taking place simultaneously on the solid phase surface and in the liquid phase. Zophar sandy loam does not fit this model. It is suggested that the solid surface area affects the fixation reaction in addition to the effects of pH and Ca concentration.

The effect of Ca on Fe‐FeEDTA fixation is discussed in connection to average and local Ca concentrations. High Ca concentrations near the root surface, formed due to transpiration stream, constitute a “chemical barrier” for the movement of Fe‐FeEDTA toward the root.
A Century of Soil Development in Spoil Derived from Loess in Iowa
Authors: Hallberg George R. , Wollenhaupt Nyle C. , Miller Gerald A.
Published: July 2010

During the past century well‐drained soils have formed in leached loess spoil materials under prairie vegetation along railroad cuts in Iowa. The spoil material was deposited on an existing Tama Variant soil which reveals the effects of 100 years of burial.

In 100 years' time a 31‐cm A horizon has developed in the spoil, available phosphorus recycling has been measured, and the translocation and accumulation of illuvial clay and fine silt has occurred. The organic carbon content reached a maximum of 2.6% and exceeds 0.58% to depths of 40 to 46 cm. This 100‐year‐old A horizon, however, does not meet the color criterion for a mollic epipedon. Organic carbon content seems to build up rapidly in the first 30 to 50 years of soil development. After this time a slower more steady‐state rate of increase seems to take place.

In 100 years' time the buried soil shows a 1% decrease (from 2.6 to 1.6%) in organic carbon in the upper 20 cm. Most of this difference resulted from the degradation of fibrous organic matter after burial. Accompanying this loss of organic matter is an increase in bulk density, which has impeded soil water movement. This density contrast has enhanced the accumulation of illuvial clay and fine silts in both the lower portion of the 100‐year‐old soil and in the buried A horizon.
Ionic Composition of Forest Soil Solutions and Effects of Clearcutting
Authors: McColl J. G.
Published: July 2010

Soil solutions were sampled with porous‐cup suction devices during a rainy season (December 1974–May 1975) from adjoining uncut and clearcut Eucalyptus globulus forest areas in the Berkeley hills, California. Concentrations of K+, Ca2+, Mg2+, NO3‐, HCO3‐, and pH and specific conductance were lower in the clearcut. The high exchange capacity of the clay‐loam soil, the limited amount and duration of rainfall, and the removal of slash and litter from the clearcut were factors contributing to these results which differ from those of similar studies of the effects of clearcutting elsewhere.

The relative proportions of Na+, Cl‐, and SO42‐ were higher, and those of K+, Ca2+, NO3‐, and HCO3‐ were lower in the clearcut compared to the forest; the proportions of Mg2+ were the same. The relative ionic composition of soil solutions in the clearcut resembled that of the acid rain (pH 5.0). The higher proportion of HCO3‐ in the forest was due to throughfall inputs, root respiration, and decomposition of the forest floor. No NH4+ was detected in soil solutions from either area.

Concentrations of most ions were correlated between and within soil horizons, although K+ was an exception due to clay fixation. During anaerobic conditions, Mn and Fe and associated Cu and Zn were mobilized in the soil solution.

Increased quantity of soil water following clearcutting resulted in increases in total amounts of most ions in solutions in the lower portion of the profile in the clearcut, compared to the uncut forest.
Effectiveness of Rhizobium trifolii Populations Associated with Trifolium subterraneum L. in Southwest Oregon Soils
Authors: Hagedorn C.
Published: July 2010

Indigenous Rhizobium trifolii populations were found to nodulate Trifolium subterraneum L. (c.v. Mt. Barker) but were largely ineffective or poorly effective in nitrogen fixation with this host. The rhizobia were isolated from numerous locations in southwest Oregon which contained subclover stands of widely varying quality. Rhizobium populations were greater in soils containing subclover stands while smaller populations were detected both in soils which had previously contained a subclover stand and those soils which had never been planted to subclover. Regression analysis of soil and rhizobia data showed significant correlations between the size of the rhizobial populations, the degree of fineness of texture (% silt + % clay) and the organic matter content while effectiveness was associated with the level of base saturation and the content of exchangeable bases. The requirements for a high quality inoculum in the presence of large ineffective populations and the agronomic implications for increasing subclover production are discussed.
Irrigation Water Salt Concentration Influences on Sediment Removal by Ponds
Authors: Robbins C. W. , Brockway C. E.
Published: July 2010

Irrigation water salt concentration effects on sediment pond efficiency were investigated to demonstrate the necessity of considering the salt concentration in the irrigation waters when designing sediment retention ponds. The influence of dissolved salt was determined by adding concentrated CaCl2 solutions to three ponds and then measuring electrical conductivities and sediment concentrations at the pond outlets. Increasing the salt concentration increased the sediment removal efficiencies when the retention time in the pond exceeded 1 hour or the inflow sediment concentration exceeded 500 ppm for the three soils studied. Adding salt to laboratory soil sample suspensions increased the settling rates for the two soils studied. That data indicate that the salt concentration in irrigation water is an important factor in determining sediment pond size and retention time. Using pond design criteria obtained from sediment ponds receiving water of a given salt concentration to design ponds that will receive water with a different salt concentration should include adjustments for salt concentration differences. A simple laboratory test is suggested to predict which soils will respond to irrigation water salt concentration changes that are likely to result in sediment pond efficiency changes.
A Simple Chemical Method for Evaluating the Agronomic Potential of Granulated Phosphate Rock
Authors: Chien S. H. , Hammond L. L.
Published: July 2010

A simple, chemical method which does not involve shaking the sample and which employs an H‐resin was used to evaluate the solubility of two granulated phosphate rocks over a range of granule sizes. It was found that the solubility decreased drastically as the granule size increased from the average diameter of 0.05 mm to 1.00 mm. The conventional citrate extraction method which involves shaking the sample cannot be used in this case because the granules disintegrated upon being shaken and this results in essentially the same solubility value being recorded for all samples regardless of the granule size. A highly significant linear relationship between the drymatter yield of corn (Zea mays L.) (6 weeks in greenhouse) and the solubility of the granulated rocks suggests that the proposed H‐resin method can be used to predict the potential of granulated phosphate rock for direct application.
Water Relations of Fritted Clay
Authors: van Bavel C. H. M. , Lascano R. , Wilson D. R.
Published: July 2010

Experiments and calculations were performed to characterize the water relations of fritted clay, a material which has been found suitable for growing experimental plants. Its dry bulk density is 0.67 kg/liter, particle density 2.50 kg/liter, total porosity 0.73, and saturated hydraulic conductivity 9.5 × 10−4 m/sec. The desorption relation was measured and the unsaturated hydraulic conductivity as a function of water content was calculated. Much water drains from the saturated material by gravity. After drainage from commonly used containers, the material holds 0.31 by volume of plant‐available water, and has an air‐filled porosity of 0.28. Its water relations are excellent for plant growth purposes.
Relation Between Rheological Properties and Dry‐state b Dimension of Various Na‐smectites
Authors: Margheim J. F. , Low P. F.
Published: July 2010

The liquid limits of pastes of five different Na‐smectites were determined with the conventional liquid‐limit device. In addition, the penetration rate of a Teflon cone into each paste was determined at different water contents by means of a precision penetrometer. The water content at which a curve of penetration rate versus water content showed maximal curvature was called the “critical” water content. Both the liquid limit and “critical” water content were shown to decrease as the b dimension of the Na‐smectite increased. Since recent work has shown that the specific surface area of a Na‐smectite depends on its dry‐state b dimension, plots were made of the liquid limit and critical water content against specific surface area. They showed that both indicators of consistency increased curvilinearly with specific surface area. However, at a given state of consistency, the interparticle distance was not the same in the different smectite‐water systems but depended on the b dimension. Reasons for these findings were discussed in relation to the theory of plastic flow.
Chemical Characterization of the Gaseous and Liquid Environments of Subsurface Drain Systems
Authors: Meek Burl D. , Grass Luther B. , MacKenzie Arnold J.
Published: July 2010

Chemical composition of subsurface drain effluents was determined in the field as a function of location (various depths and soil textures), entry point of the solution into the drainpipe, and distance from outlet (with or without a water trap). Liquid samples were analyzed for Fe, Mn, NO3‐N, HCO3, organic carbon, electrical conductivity, pH, and dissolved oxygen, and gas samples were analyzed for O2 and CO2.

Manganese ranged from < 0.1 to 6.1 ppm and Fe ranged from < 0.1 to 14.2 ppm which illustrated the wide range of oxidation‐reduction conditions present in the soils drained by subsurface drain lines. Chemical composition changed little during the season.

Water entering the upper portion of the drain lines was lower in Mn, which was the result of short flow paths through soil zones with higher O2 levels, than the water moving through longer flowlines which entered the bottom of the drains. The solutions in the drain lines were undersaturated with respect to the drain line atmosphere, which indicated that O2 flows downward through the drain trench backfill. This is an important factor in the oxidation of Fe and Mn in subsurface drain lines. However, longitudinal movement of O2 into drain lines, via the outlets, is a minor factor contributing to the precipitation of Fe and Mn and does not account for the extensive amount of precipitation of Fe or Mn within the drain system.
Reactions of Phosphate Rocks, Rhenania Phosphate, and Superphosphate with an Acid Soil
Authors: Chien S. H.
Published: July 2010

The amounts of water‐soluble P in various phosphate materials after their reaction with Weston soil (pH 4.5) at a rate of 400 ppm P followed the order: Rhenania phosphate > CSP > North Carolina rock > Araxa rock. Addition of 150 ppm Si in the form of Na2SiO3 to the soil treated with CSP significantly decreased the P‐retention capacity of the soil. The water‐soluble P level was maintained at 100–150 ppm in the soil treated with CSP and silicate during the whole course of incubation (10 weeks). Addition of silicate, however, did not eliminate P retention completely.

Liming the soil with Ca(OH)2 decreased the water‐soluble P in the soil treated with CSP. In contrast, soluble silicate increased the water‐soluble P as the rate of application increased, despite the fact that soil pH increased. The amounts of water‐soluble P in the soil treated with Rhenania phosphate and CSP together at the ratio of 1:1 (as P) were found to be greater than the calculated sum of water‐soluble P in the soil treated with Rhenania phosphate and CSP separately. This suggests that the silicate in Rhenania phosphate decreased the soil P‐retention capacity and thus increased the level of water‐soluble P in the soil. It appears that Rhenania phosphate should be a potential P fertilizer source for those tropical acid soils with relatively high P‐retention capacity in some developing countries, provided its cost can be justified.
Direct In‐field Measurement of Nitrous Oxide Flux from Soils
Authors: Ryden J. C. , Lund L. J. , Focht D. D.
Published: July 2010

A method was developed whereby nitrous oxide (N2O) effusing from a soil surface could be contained and selectively trapped for subsequent analysis. Containment of N2O was achieved by inserting a steel cover box with inlet and outlet ports into the soil. The enclosed air space above the soil surface was continuously swept by drawing external air through the cover at a flow rate of 20 liters/hour. N2O in the air swept from the enclosed airspace was adsorbed on 5Å molecular sieve. Adsorbed N2O was displaced for gas chromatographic analysis by addition of water to the molecular sieve in a closed system. N2O evolved from the soil surface was distinguished from that drawn into the cover during operation by concurrent measurement of the amount of N2O adsorbed from an equivalent flow of the external atmosphere. The adsorption and recovery of N2O by molecular sieve was affected by the N2O concentration in the air flow and the amount of N2O passed through the molecular sieve. Preliminary experiments in which N2O‐air mixtures were passed through 20g molecular sieve demonstrated that for N2O concentrations up to 34 µg N/liter, a flow rate of 20 liters/hour and sampling periods of 4 hours or less, complete recovery of N2O passed into the molecular sieve was achieved upon displacement with water. N2O released into the enclosed air space from an unsealed syringe was also quantitatively recovered providing a flow rate of at least 20 liters/hour was used to sweep the cover box. Flow rates of 10 to 40 liters/hour through covers inserted into moist soil had no effect on the measured rate of N2O evolution from the soil surface. Preliminary measurements at an irrigated, fertilized (120 kg N/ha) celery‐production block on a Haploxeroll indicated an overall mean N2O flux of 9.42 g N/ha per hour over a period of 76 hours. There was a diurnal variation in the N2O flux with mean peak fluxes of up to 15.8 g N/ha per hour occuring during the early afternoon. The method provides a basis for monitoring N2O flux from field soils under on‐going agricultural practice.
Shrub‐induced Spatial Patterns of Dry Matter, Nitrogen, and Organic Carbon
Authors: Barth R. C. , Klemmedson J. O.
Published: July 2010

Spatial patterns of dry matter, nitrogen, and organic carbon were investigated for velvet mesquite [Prosopis juliflora (Swartz)] DC and for palo verde [Cercidium floridum Benth.] ecosystems in the Upper Sonoran Desert of Arizona. Standing understory vegetation and litter originating from the overstory shrub decreased in weight as distance from the shrub center increased. Litter originating from understory vegetation displayed weak spatial patterns in dry weight. Gradients in percentage N and percentage carbon of understory vegetation, understory litter, and shrub litter were generally lacking. However, percentage soil N and organic carbon decreased as horizontal distance from the shrub center and depth to 60 cm from the surface layer increased; soil pH under both shrubs changed with depth and horizontal distance. Quadratic response surfaces for these three soil properties differed significantly between velvet mesquite and palo verde. Limited sampling of honey mesquite (Prosopis juliflora var glanulosa Torr.) ecosystems in the Chichuahuan Desert in New Mexico showed spatial patterns of dry matter and soil properties that differed somewhat from those of Sonoran Desert shrubs.
The Applicability of Dual Gamma Scanning to Freezing Soils and the Problem of Stratification
Authors: Goit J. B. , Groenevelt P. H. , Kay B. D. , Loch J. G. P.
Published: July 2010

The attenuation of a dual energy gamma beam provides a powerful technique for studying the swelling phenomenon associated with soil freezing. However, the development of a stratified system due to the formation of a discrete ice lens in the same plane as the gamma beam requires special attention. Erroneous results are obtained when attenuation equations which are developed for homogeneous mixtures are applied to stratified media. The calculated dry bulk densities are then always lower than the averaged actual dry bulk densities and sometimes even negative. The calculated water contents are then always higher than the averaged actual water contents and sometimes in excess of 1 g/cm3. Stratification may also occur during the shrinking of unfrozen soil when cracks form in the same plane as the gamma beam. The equation describing the attenuation of a gamma beam in a stratified medium is formulated. A technical modification in the scanning procedure is suggested in order to solve the appropriate equations and to locate the interface.
A Comparison of Various Laboratory Methods for Predicting the Agronomic Potential of Phosphate Rocks for Direct Application
Authors: Chien S. H. , Hammond L. L.
Published: July 2010

The reactivity of seven phosphate rocks was estimated by five methods (neutral ammonium citrate first and second extractions, 2% citric acid, 2% formic acid, ammonium citrate pH 3, and absolute citrate solubility). These measurements were evaluated by crop response data obtained from a greenhouse experiment with guinea grass (Panicum maximum) and a field experiment with beans (Phaseolus Vulgaris L.), both on acid Colombian soils. Neutral ammonium citrate (second extraction), 2% formic acid, and ammonium citrate pH 3 solubilities were best correlated with these agronomic data.

Factors such as: (i) calcite depression of apatite solubility in neutral ammonium citrate, (ii) the “grade” effect (total P content) on the apparent solubility, and (iii) the textural effect of apatite‐silica intermixing, need to be considered when correlations of chemical reactivity of the various phosphate rocks and their agronomic effectiveness are compared.
Dissolution and Transport of Gypsum in Soils: I. Theory
Authors: Glas T. K. , Klute A. , McWhorter D. B.
Published: July 2010

A model was developed describing the dissolution and subsequent transport of gypsum from a soil column by combining the one‐dimensional convection‐dispersion equation with a kinetic expression for the dissolution process. The resulting partial differential equations were solved numerically by the method of lines. Results are presented showing the effect of the various parameters in the model on calculated concentration‐time curves.
Orthophosphoric Acid as a Phosphorus Fertilizer in Trickle Irrigation
Authors: O'Neill M. K. , Gardner B. R. , Roth R. L.
Published: July 2010

Traditional P fertilizers have demonstrated relative immobility in soils. When used in trickle irrigation, these fertilizer materials tend to form precipitates in the irrigation lines which cause clogging problems and eventual breakdown of the system.

The movement of P in Superstition sand was determined after spot placement of treble superphosphate (TSP) and injection of orthophosphoric acid (OP) with a trickle system. Rates of P application, based on the recommended rate of TSP for citrus in the Yuma, Arizona area were: check, 28 kg P/ha as TSP and 14, 28, 57, and 114 kg P/ha as OP. The experiment was conducted over the two irrigation periods; one for 3 days and the second for 24 days. Phosphorus was delivered to a greater soil volume when applied as OP than TSP, which should result in more plant available P in the root zone. The OP treatments lowered the pH of the irrigation water enough to eliminate clogging problems of P precipitates in the irrigation lines.
Boron Distribution in Soils and Waters of Egypt
Authors: Elseewi Ahmed A. , Elmalky A. E.
Published: July 2010

Saturation extract, hot water‐soluble, acid‐soluble, and total B fractions were determined in soil samples from profiles representing six geographically diverse areas in Egypt. Saturation extract and hot water‐soluble B averaged 0.6 µg/ml and 1.3 µg/g. Acid‐soluble and total B averaged 10.2 and 113 µg/g. The acid fraction showed a curvilinear relationship with CaCO3 content of the soil, and averaged 12.5% of the total B. Total B, on the average, was twice as high in clay samples as in sandy samples, and decreased by about 32% beyond the 60‐cm depth of the soil profile. Concentrations of saturation extract B were either similar to or a reasonable multiple of Nile‐Water B, indicating that the latter is a direct source of at least water soluble B in these soils. Concentrations of water and acid‐soluble B suggest that B status in soils of Egypt is above the sufficiency level, and that under proper soil and water management the incidence of toxicity is unlikely.
Influence of Six Years of No‐tillage and Conventional Plowing on Fertilizer Response of Maize (Zea mays L.) on an Alfisol in the Tropics
Authors: Lal R.
Published: July 2010

The effects of four rates of N (0, 40, 80, and 120 kg/ha) and three rates of P (0, 13, and 26 kg/ha) on maize (Zea mays L.) response were investigated for no‐tillage and conventionally plowed plots on an Alfisol in southwestern Nigeria. These, experiments were conducted for three consecutive seasons. Notillage treatments yielded more than conventionally plowed plots in all three seasons. The mean yields were 2.90 and 2.42 metric tons/ha, respectively. There was no effect of P on grain yield. Nitrogen application had a significant effect on grain yield in all three seasons. Relative grain yield in the plowed plots without N application was 0.85 of that in no‐tillage plots. These results, obtained 6 years after adopting these tillage systems, are contradictory to those obtained in the first year of adopting these tillage practices. Leaf concentration of N was affected only by levels of N application.