bluuebunny/crossref_metadata_2025 huggingface dataset:
Predicting Soil Temperatures to Indicate Winter Wheat Mortality
Authors: Larsen J. K. , Brun L. J. , Enz J. W. , Cox D. J.
Published: July 2010

Tillage effects on soil temperature that affect winter wheat survival (Triticum aestivum L.) were investigated from 1981 to 1985 at Fargo, ND. Tillage systems used all 4 yr were reduced (disked) and no‐till tall stubble (seeding directly into 20‐cm standing stubble). Conventional tillage (plow, disk, and harrow) in 1981–82 and 1982–83, and no‐till short stubble (seeding directly into 5‐cm stubble) in 1983–84 and 1984–85 comprised the third tillage system used for comparisons. Survival of winter wheat in the no‐till tall stubble system was near 100% in each of the 4 yr, while in 2 of the 4 yr, survival was 50% or less in the other tillage systems. Differences in survival were attributed to warmer soil temperatures in the tall stubble system. Hourly soil and air temperature measurements and snow depth were used to develop a statistical model that predicts daily minimum crown depth (3 cm) soil temperatures (R2 = 0.92). An independent set of data was used to test the model; soil temperatures within the range considered critical for winter wheat were predicted to an accuracy of 1 °C. Predicted crown depth soil temperature may be used to indicate winter wheat mortality.
Aggregation and Aggregate Stability in Forest and Range Soils
Authors: Strickland T. C. , Kerle E. A. , Sollins P. , Schimel D. S.
Published: July 2010

A simple method for measuring aggregation and aggregate stability across soils of widely varying structure and texture is presented. The method uses standard techniques of particle‐size analysis to measure yield of fine particles (<26‐µm estimated spherical diam.) after three types of dispersion treatments: shaking in water or in sodium oxalate (Ox), and sonication in sodium pyrophosphate (PPi). PPi sonication, which provided maximum dispersion, served as our benchmark; it was substantially more effective than the commonly used stirring in hexametaphosphate. Aggregation was then calculated as yield of fines after PPi sonication minus yield of fines after the water shake, the minimum dispersion treatment. Aggregate stability was measured by comparing yield of fines after the Ox shake, the mild dispersion treatment, with that after the water shake; aggregate instability was then calculated. The five soils studied varied markedly in both aggregation and aggregate stability, suggesting that mechanisms of aggregate stabilization differ markedly across soil types. Despite these differences, our method of quantifying mild dispersion by shaking with Ox, which should have negligible effect on subsequent microbiological studies, relative to complete dispersion by PPi sonication should be consistent and applicable over a reasonably wide range of soil types.
Lodgepole Pine Fertilization Screening Trials: Four‐year Growth Response Following Initial Predictions
Authors: Weetman G. F. , Fournier R. M. , Schnorbus E.
Published: July 2010

The use of fertilizer screening trials was examined to determine if the pattern of 4‐yr basal area (BA) increment response by treatment agreed with the predictions based on first season needle weight response. Screening trials can diagnose stand nutritional status and subsequent response. Nitrogen, P and K in various combinations were applied to 17 lodgepole pine (Pinus contorta var. latifolia Engelm.) stands in the interior of British Columbia, Canada. Of these, 14 had been precommercially thinned. Remeasurement of 15 stands after 4 yr showed that 50 to 150 kg N ha−1 produced significant growth responses in many stands. Nitrogen applied at rates of 50, 100, and 150 kg ha−1 increased BA growth of individual trees by an average of 27, 41, and 48% over the control, respectively. Adding P at 50 kg ha−1 significantly improved BA growth in only two stands, while the effect of K was not significant. Graphical diagnoses of shifts in unit fascicle weight and foliar concentrations and contents in the first growing season following fertilization generally corresponded with subsequent 4‐yr BA response in 11 of the 15 installations. Stands responsive to N fertilization were weakly responsive to thinning. Nonresponsive stands reacted to thinning, presumably because N was not limiting growth. The best fit of multiple regression analyses between basal area response and stand factors yielded an R2 of 0.57, with needle weight and foliar N and P levels as important variables.
Nitrogen Use Efficiency and Nitrogen‐15 Balances in Broadcast‐seeded Flooded and Transplanted Rice
Authors: De Datta S. K. , Samson M. I. , Kai‐Rong Wang , Buresh R. J.
Published: July 2010

Increased irrigated areas, availability of short‐duration modern rices (Oryza sativa L.) and cost‐efficient herbicides, and high labor cost have motivated Asian farmers to shift from transplanting to broadcast seeding in flooded rice. Information on fate of N in broad‐cast‐seeded flooded rice (BSFR), however, in Asia is limited. Thus, two field experiments were conducted on a Vertic Tropaquept to evaluate efficient N management practices in BSFR using 15N‐labeled fertilizers and to compare the performance of BSFR and transplanted rice (TPR) under similar N management practices. For urea, basal deep placement (DP) as supergranules and a three‐split application gave the lowest mean 15N losses (4 and 11%, respectively) and highest mean grain yields (6.9 and 7.1 Mg ha−1, respectively) for BSFR. Mean 15N losses from urea applied to BSFR were 20 and 18%, respectively, for the researchers' split (RS) (two‐thirds basally incorporated into mud plus one‐third at 5 to 7 d before panicle initiation) and the farmers' split (FS) (one‐half topdressed into water at 15 d and one‐half topdressed at 10 d after panicle initiation). The agronomic efficiency (kg grain per kg applied N) for 40 kg applied urea‐N was 57, 43, and 28 with DP, RS, and FS, respectively. Under the same urea management practices, the mean plant recovery of 15N was greater for BSFR (47%) than for TPR (37%). This resulted in lower 15N loss for BSFR (20%) than for TPR (32%). However, total plant N accumulation was similar for BSFR (96 kg ha−1) and TPR (95 kg ha−1), and mean grain yields over the two experiments were not different (P = 0.05) between BSFR and TPR. Transplanted rice produced 10 kg more grain per kilogram of applied N than did BSFR, in part because mean grain yield in the absence of applied N was 0.3 Mg ha−1 lower with TPR. Results suggest that considerable potential exists to increase N use efficiency and grain yield in BSFR by manipulating N fertilizer and water management practices.
Effect of Two Urease Inhibitors on Floodwater Ammonia Following Urea Application to Lowland Rice
Authors: Buresh R. J. , De Datta S. K. , Padilla J. L. , Samson M. I.
Published: July 2010

One proposed strategy for overcoming N loss by ammonia volatilization from urea applied to flooded rice (Oryza sativa L.) fields is to amend urea with a urease inhibitor. The inhibitor, in theory, would delay urea hydrolysis and thereby prevent the buildup of ammonia in the floodwater. Field studies were conducted at two locations in the Philippines to determine the effect of two urease inhibitors, phenyl phosphorodiamidate (PPD) and N‐(n‐butyl) thiophosphoric triamide (NBPT), on the vapor pressure of ammonia (pNH3) following application of urea to floodwater. Three rates of urea were applied two‐thirds dosage at 18 d after transplanting (DT) and one‐third dosage at 5 to 10 d after panicle initiation (DAPI). The amendment of urea with either PPD or NBPT retarded the disappearance of urea from floodwater and reduced the buildup of floodwater ammoniacal‐N. NBPT generally matched or exceeded PPD in ability to reduce pNH3 at each N rate and timing for both locations. Whereas PPD only delayed the buildup in pNH3, particularly at higher N rates, NBPT effectively prevented a buildup in pNH3. For the 10 d following the first N application, NBPT reduced the mean pNH3 at 1400 h by 95, 96, and 98% for 23, 47, and 93 kg N ha−1, respectively, at one location. The corresponding reductions with PPD were 82, 54, and 25%, respectively. At the other location, NBPT reduced the mean pNH3 following the first N application by 97, 77, and 79% for 23, 47, and 93 kg N ha−1, respectively. The corresponding reductions with PPD were 79, 77, and 28%, respectively. The results suggested that urease inhibitors can effectively reduce ammonia loss from urea broadcast into the floodwater of rice fields.
Effect of Fertilizer Phosphorus Particle Size on Phosphorus Fertilizer Efficiency
Authors: Sander D. H. , Eghball B.
Published: July 2010

Five field experiments were conducted over 3 yr (1983–1985) to evaluate the effect of P fertilizer particle size on winter wheat (Triticum aestivum L.) yield and P uptake. In 1983, an introductory experiment indicated that the P fertilizer particle size could greatly affect fertilizer P effectiveness. Studies in 1984 and 1985 confirmed these observations. In these studies ammonium polyphosphate (11‐24‐0, N‐P‐K), at particle weights of 0.00019, 0.0009, 0.025, 0.93, and 22 mg were applied at P rates of 8.4, 16.8, and 25.2 kg P ha−1 on four different soils. Wheat grain yields were increased significantly by applied P on all four soils. Grain yields were affected by P fertilizer particle size only, however, on the Ascalon and Holdrege soils (Aridic and Typic Argiustoll, respectively) where yield increases from applied P were greatest. Maximum grain yield occurred at approximately the intermediate particle size studied (0.025 mg), although optimum particle size was dependent on P rate. As the P rate increased, particle size became less of a factor influencing fertilizer effectiveness. Wheat grain yield at the 8.4‐kg ha−1 P rate was 0.31 Mg ha −1 less for the 22‐mg particle compared to the 0.025 mg particle. Calculations indicated that the 22‐mg fertilizer particles had an average distance of 2.8 cm from one another in the band area, compared to 0.003 cm or a continuous band for the 0.025‐mg particles. Phosphorus uptake and other yield components generally paralleled the results with grain yield. Fertilizer P efficiency in terms of fertilizer P uptake, reached a maximum of 47% with a particle size of 0.15 mg and an application rate of 8.4 kg P ha−1 on the Holdrege soil. This was a 20% increase in efficiency over a normal farm fertilizer size of 20‐mg particle 1. While optimum fertilizer size probably ranges from 0.025 to 1 mg per particle, the optimum size in these experiments in terms of both yield and fertilizer efficiency was generally less than the 20‐mg particle size reported for farm fertilizers. Results indicate that greater root proliferation in continuous P bands may be responsible for an increase in fertilizer P uptake and efficiency compared to discontinuous P bands.
A Rapid Method of Soil Carbonate Analysis Using Gas Chromatography
Authors: Amundson Ronald G. , Trask Joanne , Pendall Elise
Published: July 2010

A rapid and sensitive method of soil carbonate analysis, utilizing gas chromatography, is presented. The analysis of soil samples by gas chromatography and the Chittick methods produced comparable results (r = 0.96, slope = 1.11). However, the gas chromatograph method was much more rapid. There was also a linear relationship between the results of soils analyzed by both the gas chromatograph and Hg manometer methods (r = 0.99). The gas chromatograph underestimated CaCO3 contents at low concentrations, however, and overestimated it at high concentrations relative to the manometer method. The gas chromatograph method was the most sensitive and had the lowest possible detection limit (0.008 mg CaCO3) of the methods compared. The results of the study indicate that the gas chromatograph method is much more rapid than previously reported chromatography methods and has the potential to be used for the rapid analysis of samples low in CaCO3.
Temporal Persistence of Spatial Patterns of Soil Water Content in the Tilled Layer Under a Corn Crop
Authors: van Wesenbeeck I. J. , Kachanoski R. G. , Rolston D. E.
Published: July 2010

The temporal persistence of the spatial pattern of soil water storage (0∼0.2 m) under a corn (Zea mays L.) canopy during drying and recharge periods were examined using spatial coherency analysis and transfer function theory. The corn crop caused both drying and recharge to occur at very specific scales, equal to the crop row spacing. The calculated transfer function, or time varying spectrum showed the scale at which the change in the spatial pattern was occurring and quantified the increase or decrease in variance at that scale. The spatial pattern of the drying coefficients, a measure of the relative drying rate, also varied systematically with significantly higher drying rates in the row area developing as the growing season progressed. The increase in relative drying rate in the row area caused the spatial pattern of drying to change at a scale equal to the crop row spacing. The calculated transfer function of the drying coefficients over the growing season indicated a steady increase in variance at that same scale, while the variance at other scales did not change significantly. An equation is developed relating the transfer function of soil water content in space to the spectrum of the process causing the change in the spatial domain.
An Investigation of Iron(III)‐Fulvic Acid Complexes by Mössbauer Spectroscopy and Chemical Methods
Authors: Kodama H. , Schnitzer M. , Murad E.
Published: July 2010

Three iron(III)‐fulvic acid (FA) “complexes” were prepared in the laboratory. One of these was doped 50% with 57Fe and contained 1.54% total Fe. The other two “complexes” contained 0.80 and 4.70% Fe, respectively. At room temperature, Mössbauer spectra of the Fe(57Fe)‐FA “complex” consisted of a paramagnetic doublet. The isomer shift (δ/Fe) was 0.30 mms−1 and the quadrupole splitting (ΔEQ) was 0.75 mms−1, typical of ferric iron. At 78 K the spectrum showed a magnetic component superimposed upon the quadrupole doublet. In the spectrum recorded at 4.2 K the magnetic contribution increased. An analysis of the Mössbauer data suggests that Fe(III) in laboratory‐prepared Fe(III)‐FA “complexes” occurs partly in the form of organic complexes and partly as inorganic species. Support for this view also comes from ESR data published in the literature. A study of the resistance of Fe in the “complexes” to base hydrolysis, showed that iron was associated with the FA by at least two, possibly three, different mechanisms and that the interaction products exhibited differing chemical stabilities.
Soil Microbial Biomass and Organic Component Alterations in a No‐Tillage Chronosequence
Authors: Staley T. E. , Edwards W. M. , Owens L. B. , Scott C. L.
Published: July 2010

A no‐tillage (NT) chronosequence that had been continuously cropped to maize (Zea mays L.) for 0, 1, 2, 4, 7, 9, 15, or 20 yr on a Westmoreland silt loam (fine‐loamy, mixed, mesic Ultic Hapludalf) was examined for differences in microbial biomass, and soil organic C, N, P, and S. In the plowzone of the NT sites, biomass‐C, total C (TC), soluble organic C (SOC), total Kjeldahl N (TKN), organic P (OP), and organic S (OS) levels were generally greater in the soil surface (0 to 7.5 cm) layers than in the 7.5‐ to 15‐cm layers. In contrast, biomass‐C under conventional tillage (CT or 0‐yr NT site) in the soil surface layer was ∼50% of that in the 7.5‐ to 15‐cm layer, whereas levels of the organic components were nearly identical. Biomass‐C and organic component levels in the soil surface layers under NT were from 27 to 83% greater than those under CT. Opposite tillage method effects on these properties were usually found for deeper soil layers. Soil organic components, but not biomass‐C, were significantly (p ≤ 0.05) related to years under NT in the soil surface layer. Only biomass‐C was significantly (p ≤ 0.10) related to years under NT in deeper soil layers. When just “typical (i.e., nonmanured, moderate N‐rate)” sites were included in the regression models, only biomass‐C and SOC reservoir contents (total to 45 cm) varied significantly (p ≤ 0.10) with years under NT. Soil biomass‐C reached a maximum (786 kg·ha furrow‐slice−1) in the soil surface layer after only 1 yr under NT, approaching a level nearly equivalent to that under an improved pasture, then equilibrated in about 10 yr to a level approximately 30% greater than that under CT. These observations suggest that continual NT induces a predictable dynamic in soil biomass‐C, but not soil organic components, that is generally insensitive to a range of management differences. As a consequence, management practices designed to improve nutrient use‐efficiency, especially by controlling microbial mineralization/immobilization activity, should not only take into consideration tillage method but years under the tillage method as well.
Net Mineralization of Carbon and Nitrogen Under Aerobic and Anaerobic Conditions
Authors: Gale P. M. , Gilmour J. T.
Published: July 2010

A study was conducted to compare the net C and net N mineralized during the decomposition of alfalfa (Medicago sativa L.) under aerobic and anaerobic conditions. Dried and ground alfalfa was mixed with soil at a rate of 5 g kg−1 and incubated either aerobically at optimum water in a CO2—free atmosphere or anaerobically (flooded) in an N2 atmosphere. The decomposition process was followed by measuring the CO2 and CH4 evolved, water soluble organic C, and inorganic N. Aerobic C mineralization was best described using CO2 evolution as a first‐order kinetic process. Three distinct phases of decomposition were observed (rapid, intermediate, and slow) with rate constants (k) of 0.123, 0.059, and 0.0095 d−1, respectively. Under anaerobic conditions, CO2 evolution remained fairly constant throughout the experiment. The decomposition rate constant for anaerobic CO2 evolution was 0.006 d−1. Carbon mineralization under anaerobic conditions was best described as the sum of CO2 and CH4 evolved plus the water soluble organic C produced. This treatment resulted in three distinct phases of anaerobic decomposition. The C mineralization rate constants for the rapid and intermediate phases were 0.118 and 0.024 d−1, respectively. No rate constant was determined for the slow phase. A computer simulation model was used to estimate the C and N mineralized under both aerobic and anaerobic conditions. The linear relationship between the predicted and observed mineralization was evaluated. For C mineralization the slope was 1.1 and that of N mineralization was 1.0, with R2 values of 0.961 and 0.946, respectively.
Comparison of Total Nitrogen by Four Procedures and Sequential Determination of Exchangeable Ammonium, Organic Nitrogen, and Fixed Ammonium in Soil
Authors: Antisari Livia Vittori , Sequi Paolo
Published: July 2010

Eight soils were analyzed for total N by: (i) steam distillation of NH3 yielded after conventional H2SO4 digestion, (ii) HF‐H2SO4 digestion, (iii) HF‐HCl treatment in a microwave system, or (iv) a CHN analyzer. Comparison of results showed that the customary Kjeldahl methods underestimate total N in soils. After determination of exchangeable NH4, soil organic matter was destroyed by treatment with a reagent composed of hydrogen peroxide plus pyrophosphate plus NaCl to prevent swelling of clays, buffered at pH 5 to avoid loss of NH3. Organic N was calculated as the sum of NH4 and NO3 determined in the resulting solution produced during organic matter oxidation. Soil residues were analyzed for fixed NH4 using the three above mentioned procedures. It was deduced that underestimation of total N given by the customary Kjeldahl method depends on inefficiencies of acid digestion in releasing NH4 trapped in clay lattices. Values for total N calculated from the sum of exchangeable NH4, organic N, and fixed NH4 are fairly consistent with those determined directly.
Evaluation of a Method to Predict Nitrogen Mineralized from Soil Organic Matter Under Field Conditions
Authors: Cabrera M. L. , Kissel D. E.
Published: July 2010

Methods to estimate the amount of N mineralized from soil organic matter are needed for accurate fertilizer recommendations. We conducted laboratory and field studies to evaluate the method of Stanford and Smith for predicting N mineralized under field conditions. Soil samples were incubated to determine their N mineralization potentials and first‐order rate constants of mineralization. To predict N mineralized in the field, the rate constants of mineralization were adjusted by soil temperature, and the amount of N mineralized predicted with the N mineralization potentials and adjusted rate constants were further adjusted by soil water content. Nitrogen mineralized in the field was measured in sorghum [Sorghum bicolor (L.) Moench] plots established on Haynie (coarse‐silty, mixed, calcareous, mesic Mollic Udifluvent), Kahola (fine‐silty, mixed, mesic Cumulic Hapludoll), and Richfield (fine, montmorillonitic, mesic Aridic Argiustoll) soils in 1983 and 1984. Nitrogen mineralized was also measured in fallow plots on Haynie and Wymore (fine, montmorillonitic, mesic Aquic Argiudoll) soils in 1984. The method only accurately predicted the amount of N mineralized in 104 d in fallow plots on Haynie soil. In all other cases, the method significantly overpredicted by 67 to 343% the amounts of N mineralized in the field. Among possible causes for the overpredictions may be an improper soil water content factor and the drying and sieving of the samples before incubation.
Involvement of Bacterial Siderophores in the Remedy of Lime‐induced Chlorosis in Peanut
Authors: Jurkevitch E. , Chen Y. , Hadar Y.
Published: July 2010

A Pseudomonas putida strain isolated from peanut (Arachis hypogaea L.) roots excreted yellow‐green fluorescent siderophores (pigments) when grown under Fe‐deficient conditions. The pigments were purified in their Fe complex form. Chromatography yielded eight peaks, the first two representing >90% of the total. Physico‐chemical characteristics of the materials exhibiting these two peaks were similar to those of the pseudobactin‐pyoverdine class of siderophores. In two growth chamber experiments peanut plants grown on a highly calcareous soil were able to use the Fe from unpurified Fe‐siderophore produced by P. putida cultures. When supplied with 11 mg Fe kg−1 soil as Fe‐siderophore the chlorophyll concentration in the leaves was 75% of that of FeEDDHA (ethylenediamine di‐o‐hydroxyphenylacetic acid)‐treated plants. Control plants that were not fertilized with Fe contained only 35% chlorophyll of that of FeEDDHA‐treated plants. Nonferrated siderophores were ineffective in correcting Fe deficiency. Relative chlorophyll concentration in the leaves of the treatment supplemented with Fe‐siderophore and bacterial cells was similar to that of applications that did not contain bacterial cells. In a second experiment, 100% remedy of the deficiency was achieved when 19 mg Fe kg−1 soil as Fe‐siderophores was applied in comparison to 1.2 mg Fe kg−1 soil as FeEDDHA. The degree of remedy of chlorosis was independent on the frequency of application (two or four times a month). In these treatments total bacterial and fluorescent pseudomonad counts [colony‐forming units (cfu) g−1 dry roots] were significantly higher than in the unfertilized and FeEDDHA treatments. The level of DTPA (diethylenetriam‐inepentaacetic acid) extractable Fe at the end of the growth period in both experiments was significantly higher in Fe‐siderophore amended soils than in FeEDDHA‐treated soils. In a third experiment, the siderophore Ferrioxamine B (FOB) was used as a source of Fe. Iron applications of 22.5 and 45 mg Fe kg−1 soil as FOB were required to reach 70 and 97%, of the chlorophyll concentration of the FeEDDHA‐treated plants, respectively. It was concluded that bacterial siderophores may serve as a remedy to lime‐induced chlorosis in plants grown in calcareous soils.
Comparison of Four Methods for Interpreting the Shoemaker‐McLean‐Pratt (SMP) Lime Requirement Test
Authors: Doerge T. A. , Gardner E. H.
Published: July 2010

Using a lime requirement (LR) test not calibrated under field conditions or on soils which differ greatly from those used to calibrate the procedure may lead to erroneous results. The objectives of this research were, (i) to compare under field conditions the accuracy of four methods of interpreting the SMP LR test, and (ii) to quantify the random, constant, and proportional error associated with each method. Lime applications ranging from 0 to 14.6 Mg ha−1 were made to field plots on two acid soils in northwest Oregon. Surface soil samples taken prior to liming were analyzed according to four methods of interpreting the SMP lime requirement test, namely the original SMP single buffer (SB), McLean's double buffer (DB) and two modified SMP procedures currently used in Oregon and Washington (Modified SB and Modified SB + initial pH, respectively). Statistical models from these four methods were algebraically solved to permit calculation of predicted pH values due to lime amendment which were compared to soil pH measured one and two years after liming. The proportional errors associated with the Original SB, DB, Modified SB and Modified SB + initial pH procedures were 1.2, 1.3, 0.19, and 0.06, respectively. The magnitudes of the constant and random errors associated with these same four methods were 7.8, 8.6, 0.64, and 0.26 pH units; and 0.83; 0.77, 0.19, and 0.25 pH units, respectively. All methods not calibrated under field conditions under‐predicted soil pH values resulting from applications of lime by an average of 0.5 to 0.7 pH units. These results emphasize the importance of employing field conditions and soils from similar geographical areas when calibrating LR tests.
Long‐term Tillage and Nitrogen Fertilization Effects on Organic Nitrogen and Carbon in a Semiarid Soil
Authors: Rasmussen P. E. , Rohde C. R.
Published: July 2010

Maintaining or improving soil organic matter has high priority in agriculture because of its beneficial effect on soil physical, chemical, and biological properties. Soil organic N and C were measured 44 yr after establishment of a long‐term experiment to evaluate tillage and fertilizer effects in a winter wheat (Triticum aestivum L.)‐fallow rotation on a coarse‐silty mixed mesic Typic Haploxeroll. Main treatments consisted of three primary tillage systems, one conventional (moldboard plow) and two stubble mulch (offset disc, subsurface sweeps). Subplots consisted of six N treatments, 493, 728, 986, 1221, 1714, and 2207 kg N ha−1 applied over 44 yr. Organic N and C in the top 75 mm of soil were 26 and 32% higher, respectively, in the two stubble mulch systems than in conventional tillage, and equal below 75 mm. Stubble mulch plots contained 245 kg more N ha−1 than conventionally tilled plots, representing the conservation of 5.7 kg N ha−1 yr−1. Nitrogen fertilization increased soil N linearly in all tillage treatments, with 18% of the applied N incorporated into the soil organic fraction. Applied N also increased soil C linearly on plots with previous S application. Soil C was higher on plots with no previous S than on comparable plots with previous S, however, which suggests an S deficiency that altered S, but not N, transformations in soil. Identical N fertilization effects on soil organic N and C in both stubble mulch and conventional tillage suggests that N transformations were the same in both systems.
Spatial Variability of Wheat Yield and Soil Properties on Complex Hills
Authors: Miller Michelle P. , Singer Michael J. , Nielsen Donald R.
Published: July 2010

Surface soil and wheat yield were sampled on a 400‐ by 250‐m grid to determine the relationship between wheat yield and soil properties influenced by erosion. The study, located in the Dunnigan Hills northwest of Sacramento, CA, began in October 1983. Five transects over complex slopes were made 50 m apart. Every 20 m, along each transect, depth to parent material, surface soil thickness, depth to carbonates, landscape position, and percent slope were recorded. In addition, soil samples were collected to determine particle size, percent organic C, water retention at 33 and 1500 kPa, and pH. One meter square plots of wheat were harvested at each of the 100 sites previously sampled. Subsoil samples were taken at select sites to determine organic C and particle size. Every meter along a 50‐m transect, surface soil thickness and percent sand in the surface soil were determined to assess the nugget effect of these variables. Standard regression analyses showed no correlation between percent slope and yield or soil properties. Semivariograms and cross‐semivariograms showed a strong spatial dependency between soil properties and wheat yield. Total above ground biomass increased from the knolls to the swales, while harvest index increased in the reverse direction. Particle size distribution varied by landscape position as a result of both mechanical and water erosion. Harvest index was shown to be positively correlated with percent clay <2 µm but not correlated with percent sand. Surface soil thickness was not found to be spatially correlated with crop growth.
Soil Sulfate‐Sulfur and Growth Responses of Nitrogen‐fertilized Douglas‐fir to Sulfur
Authors: Blake John , Webster S. R. , Gessel S. P.
Published: July 2010

Two studies were conducted to determine the growth response of N‐fertilized Douglas‐fir [Pseudotsuga menziesii (Mirb.) Franco] to S supplements. The relationship between response and soil SO4‐S extracted with Morgan's solution, 1.22 M NaOAc + 0.53 M HOAc (pH 4.8), was used to establish critical levels for S. Douglas‐fir seedlings were grown in the greenhouse in the surface mineral layer (0 to 0.15 m) of 20 forest soils from western Washington and Oregon. On the average, significant increases in total dry weight (17.5%), stem diameter (10.1%), and height (6.9%) occurred when soils were fertilized with N and S in comparison to N alone. Using the Cate‐Nelson procedure, growth responses to N and S were most likely to occur when soil SO4‐S was below 14 mg S kg−1. Twenty eight installations were established in the field containing five N treatments, three rates of N as urea, and one plot of 336 kg N ha−1 with P, K, Ca, and S. Differences in percent basal area growth between N alone and N with P, K, Ca, and S were significantly related to soil SO4‐S. Over the initial 5‐yr period, response over N alone was improved by 74% when soil SO4‐S was <20 mg S kg−1. When the N with P, K, Ca, and S plots were retreated with only N and S, response over the next 3 yr was more than doubled compared with N alone. Identification of S responsive stands was improved by the inclusion of stand age weighted subsoil SO4‐S concentrations.
Potential for Buffering of Acidic Precipitation by Mineral Weathering in a Forested Entisol
Authors: Bockheim J. G. , Leide J. E. , Li C.S. , Wentz D. A.
Published: July 2010

Bulk precipitation, soil‐water, and groundwater chemistry were monitored at Round Lake, a small, forested catchment receiving acidic precipitation (pH 4.6) in northwestern Wisconsin. The groundwater basin retained H ion and released nonhydrolyzable cations (NHC = Ca, Mg, Na, K) and Si. The percentages of plagioclase feldspar, hornblende, olivine, and augite increased with depth in soils from the catchment; quartz, orthoclase feldspar, and weathered mica decreased with depth. Thermodynamic stability indices estimated from water‐quality and mineralogic data, and from the WATEQF chemical speciation model indicate that the soil‐water and groundwater are undersaturated with respect to hornblende, chlorite, olivine, augite, plagioclase, and orthoclase feldspars and that these minerals may be undergoing dissolution. Minimally disturbed soil cores were leached with dilute H2SO4 and distilled water (pH 3.0 to 5.7). When the pH of the extracting solution was ≥4.5, Ca was released in the greatest amounts, followed by Si, Mg, K, Na, and Al. This ranking is similar to that for cations in groundwater. Leaching with a pH 3.0 solution released Si in the greatest amounts from the C horizon, followed by the Bw2, Bw1, and A + B/E horizons. This trend parallels the depth distribution of weatherable minerals in the very fine sand fraction. Results from the laboratory leaching study confirm the chemical modeling studies, indicating that mineral weathering (hydrolysis) can contribute to buffering within the groundwater basin at Round Lake.
Effects of Soil Physical Structure on Solute Transport in a Weathered Tropical Soil
Authors: Sollins P. , Radulovich R.
Published: July 2010

Effects of soil structure on solute transport were studied in a clayey, well‐aggregated Oxic Dystropept under grass and secondary forest at La Selva, Costa Rica. Both fine pores (<0.1 µm) and coarse pores (>30 µm) are abundant, as indicated by a water content of 0.37 m3 m−3 at −1500 kPa matric potential, the shape of the moisture release curve, and an initial infiltration rate (at field capacity) averaging 3900 mm hr−1. Field application of Rhodamine B dye without ponding (simulating heavy rainfall) showed preferential flow along decayed‐root channels, animal burrows, cracks, and other macropores. Dye application to intact cores under conditions of ponded steady‐state flow gave a good correlation between flow rate and total stained area (p <0.01 under forest; p < 0.05 under grass). Solute (CaCl2) breakthrough occurred very rapidly, often after < 0.1 pore volumes had percolated; however, relative concentration of the effluent did not exceed 0.95 even after five pore volumes had percolated. These results indicate that most water flows between aggregates or through macropores (as preferential or channelized flow), even when the fine pores are not fully saturated, and in effect bypasses the fine pore space. When solution inflow was interrupted after ∼1.8 pore volumes, then resumed after 10 min pause, relative concentration of the effluent dropped by 10 to 40%, then rose again. This indicates that solute diffused slowly into the aggregates. Taken together the results suggest that this soil strongly resists leaching. Preferential water flow may serve to prevent nutrient loss from the matrix of all highly aggregated soils and of all noncultivated soils in which animal activity and turnover of woody roots create abundant macropores.
Experimental Validation of the Monophase Structure Model for Montmorillonite Solubility
Authors: Kittrick J. A. , Peryea F. J.
Published: July 2010

Previously published solubility data for Belle Fourche montmorillonite were plotted on pH or pH‐pK+ vs. pSi(OH)4 axes, in order to determine the proper model for representing smectite formulas in hydrolysis reactions. The resulting line slopes did not agree with predictions based upon a model where smectite and exchangeable ions are considered to be separate phases. A model where exchanger and exchangeable ions form a single macroscopic phase (monophase) generated a line slope that agreed with the data within experimental error. Agreement between the monophase model and the data suggests that the experimental requirements for phase meta‐equilibrium and K saturation were sufficiently met to show that smectite solid solutions behave as thermodynamic phases over the time span of the experiments.
Measurement of Nitrous Oxide Dissolved in Soil Solution
Authors: Davidson E. A. , Firestone M. K.
Published: July 2010

Degassing of soil solution as soil water enters springs and streams may be a significant pathway of N2O release into the atmosphere. A simple method is presented to sample soil solution to include gases dissolved in solution. Small porous cup lysimeters connected to narrow diameter nylon tubing were flushed with N2 gas; a vacuum was applied with an evacuated serum bottle; and solution and gases were captured in the bottle. Concentrations of N2O in soil solution of a grassland in central California varied from below ambient to 13 times ambient. At a wet riparian zone site, N2O in soil solution appeared to be related to NO‐3 concentration, which can be determined from the same soil solution sample.
Distribution of Selenium in Soils of Agricultural Fields, Western San Joaquin Valley, California
Authors: Fujii Roger , Deverel S.J. , Hatfield D.B.
Published: July 2010

Soils from three agricultural fields in the Panoche Creek alluvial fan area in the western San Joaquin Valley, California, were analyzed for soluble, adsorbed, and total concentrations of selenium (Se) to assess the distribution and forms of Se in relation to the leaching of Se from soils. This assessment is needed to evaluate the importance of soil Se in affecting ground water concentrations. Soil samples were collected from three fields with drainage systems of different ages (6, 15, 1.5 yr) and different Se concentrations in drain water (58, 430, 3700 µg L−1, respectively). Concentrations of soluble Se and salinity were highest in soils from the field drained for 1.5 yr and lowest in the field drained for 6 yr. Of the total concentration of soil Se from all three fields, the proportion of adsorbed and soluble Se ranged from 1 to 11% and <1 to 63%, respectively. Most of the soluble Se was present as selenate and most of the adsorbed Se was found to be selenite. Consistent with a model of evaporative concentration of Se and salinity in soils and shallow ground water in this area, most of the variance in soluble Se is explained by salinity (r2 > 0.68) in saturation extracts of soils sampled from below the water table. In contrast, most soluble salts and Se apparently have been leached from the unsaturated soils in the fields drained for 6 and 15 yr. For the leached soils, dissolution and precipitation of evaporite minerals containing Se may no longer control concentrations of soluble Se.
Survival of Rhizobium in an Oxisol Subjected to Incremental Simulated Erosion
Authors: Habte M. , El‐Swaify S.A.
Published: July 2010

The survival of four strains of Rhizobium was monitored as a function of time at constant moisture potential and temperature in soils from sites subjected to incremental simulated erosion. Populations of two of the strains were either stimulated or unaffected by simulated erosion representing up to 37.5 cm of surface soil removal. Populations of the remaining two strains were also stimulated or unaffected by simulated erosion not exceeding 15 cm of surface soil removal. Simulated erosion in excess of this level, however, significantly decreased the survival of these strains. Strain tolerance to erosional losses of soil closely paralleled tolerance to soil acidity. Declines in the populations of the erosion‐intolerant strains were accompanied by declines in soil pH, organic C, total N, extractable P, and extractable Ca, Mg, and K. The adverse effects of simulated erosion on the sensitive rhizobia was eliminated, however, by liming the eroded soil samples to pH 6.0. Liming improved the survival of the bacteria in these soil samples largely by improving the supply of Ca. Our results demonstrate that the adverse effect of erosional soil losses on the survival of Rhizobium in the Wahiawa soil could be overcome either by increasing the supply of Ca or by selecting rhizobial strains that are insensitive to erosion.
Evaluation of Nitrogen‐15 Tracer Techniques for Direct Measurement of Denitrification in Soil: III. Laboratory Studies
Authors: Mulvaney R. L.
Published: July 2010

Laboratory studies were conducted to evaluate the assumption of isotopic uniformity that underlies mass spectrometric determination of dinitrogen (N2) and nitrous oxide (N2O) evolved during denitrification in soil treated with 15N‐labeled fertilizer. In these studies, a gas chromatograph (GC) and mass spectrometer (MS) were used to analyze replicate atmospheric samples containing N2O generated through oxidation of 15N‐labeled NH2OH, evolved from 15N‐treated soil slurries incubated at constant moisture content (1 kg H2O kg−1), or evolved from 15N‐treated soil subjected to wetting and drying cycles. Both instruments gave almost identical values in analysis of N2O derived from a single pool of 15N‐labeled NH2OH or from two pools having similar, but not necessarily the same, enrichments. The MS gave lower values for N2O derived from two pools differing markedly in their enrichment of 15N. The values measured by GC and MS differed significantly (0.05 level) for about 50% of the soil atmospheric samples analyzed; however, the differences usually did not exceed 10% and probably resulted from analytical error rather than lack of isotopic uniformity in the NO−3 denitrified, because in about half of these cases, the greater value was obtained by MS.
Mineralization of Carbon and Nitrogen from Freeze‐ and Oven‐Dried Plant Material Added to Soil
Authors: Moorhead K. K. , Graetz D. A. , Reddy K. R.
Published: July 2010

Drying organic material before soil incorporation is a common procedure used in mineralization or decomposition studies. A laboratory study was conducted to determine the effect of drying methods on plant C and N and associated mineralization patterns in soil. Freeze‐ and oven‐dried water hyacinth (Eichhornia crassipes [Mart] Solms) was added to a Kendrick soil (loamy, siliceous, hyperthermic Arenic Paleudults) at a rate of 5 g kg−1 and incubated in the dark at 27 °C for 90 d. Oven drying in paper bags significantly increased the lignin content and decreased the mineral content of the plant material compared to freeze drying. The total C and N was not significantly different for the two materials. The mineralization of C from freeze‐dried plant material was more rapid during the initial stage of decomposition and remained significantly higher throughout the incubation. At 90 d, 50 and 41% of the plant C had evolved as CO2 for the freeze‐ and oven‐dried plant material, respectively. Mineralization of 15N from the plant material accounted for 33% of the applied N of the freeze‐dried material and 23% of the applied N of the oven‐dried material. Nitrogen mineralization and CO2 evolution were linearly correlated (r = 0.998) for the oven‐dried plant material, but less correlated (r = 0.770) for the freeze‐dried material.
Effects of Soil Properties on Plant‐Available Phosphorus Determined by the Isotopic Dilution Phosphorus‐32 Method
Authors: Sen Tran T. , Giroux M. , Fardeau J. C.
Published: July 2010

A procedure using 32P isotopic exchange kinetics was suggested to characterize the availability of soil P. The ratio of the radioactivity remaining in the solution over the total radioactivity (r1/R) was closely and inversely proportional to the maximum P‐fixation capacity (M) estimated by the Langmuir isotherm (r = 0.82**, significant at the 0.01 probability level) and to the P‐buffering capacity (Mb) (r = 0.71**). The 1/r1/R) ratio was also correlated with oxalate‐Al (r = 0.69**) and oxalate‐Fe (r = 0.35**). The kinetic parameter, n, described as the decrease of radioactivity remaining in the solution with time, was related to the soil pH (r = −0.52**), the prevailing form of soil P (Mehlich ratio Q, r = −0.50**), the P‐fixation capacity (r = 0.44**), and organic matter (r = 0.44**). The isotopically exchangeable P (E1 value) was closely related to the plant P uptake on soils having low P‐adsorption capacity (Group III, r = 0.90**). However, E1 value may overestimate the available P on high P‐fixing soils especially for acid Spodosols (Group I, r = 0.47**). The water soluble P (M1) or the labile P pool (M1 + M2) showed a curvilinear (logarithmic) relationship with plant P uptake and the correlation coefficient was higher than that obtained from E1 when grouping all soils together. The effect of soil properties on the relation between plant P uptake and E1, log M1, or log (M1 + M2) was confirmed by the increase of the coefficient of determination (R2) of the multiple regression including soil parameters as second variable. An exponential relationship was observed between relative yield (%) and E1, M1, (M1 + M2); the R2 value was 50.4, 65.1, and 68.1%, respectively. The three classes of soil P fertility (poor, medium, rich) were established for E1, M1, and (M1 + M2) according to the Cate and Nelson procedure.
Physical Properties of Constructed and Undisturbed Soils
Authors: Potter K. N. , Carter F. S. , Doll E. C.
Published: July 2010

There is a growing impetus to use soil properties to determine if reclamation efforts are adequate to restore productivity. Constructed mine soils were studied 4 and 11 yr after reclamation to determine physical and hydrological properties. Soils constructed using similar methods and with similar vegetation histories were compared to each other and to an equivalent undisturbed soil. Bulk density was greater in the topsoil and subsoil materials of the constructed soils than in the undisturbed A and B soil horizons. Macropore volume (pore radii > 15 µm) was greater in the topsoil and subsoil materials at the 11‐yr site relative to the 4‐yr site but was significantly lower than that in the undisturbed soil. Small pore volume (pore radii from 4.5 to 0.1 µm) in the reclaimed topsoil materials was similar to the undisturbed A horizon soil but was larger in reclaimed subsoil materials than in the undisturbed B horizon. Saturated hydraulic conductivity (Ks) of the reclaimed topsoil was about 25% that of the undisturbed A horizons and the reclaimed subsoil Ks was less than 10% that of the undisturbed B horizon. The reduction in Ks was attributed to the increase in bulk density and disruption of soil structural units and associated interpedal pore spaces during mining and soil construction. No significant differences in Ks were found between constructed minesoils 4 and 11 yr after reclamation. The results of this study show that soil properties may be useful for evaluating reclamation success after soil construction.
Nitrogen Fertilization of Young Yellow Poplar and Loblolly Pine Plantations at Differing Frequencies
Authors: Johnson Dale W. , Todd D. E.
Published: July 2010

Loblolly pine (Pinus taeda L.) and yellow poplar (Liriodendron tulipifera L.) seedlings from 1–10 seedling stock were established in the Tennessee Valley near Oak Ridge and fertilized with 300 kg ha−1 of urea‐N over a period of 3 yr according to two regimes: annually in one spring application (100 kg ha−1) and quarterly (25 kg ha−1 quarter−1). Two plantation blocks for each species, one consisting of seedlings preinoculated with mycorrhizae and one without preinoculation, contained three replicate plots per treatment. Annual fertilization produced greater growth and N recovery in both loblolly pine plantations than did quarterly fertilization, the latter not being significantly different from the controls. Growth responses in yellow‐poplar plantations were less certain and not statistically significant, probably due to moisture stress for this species on this site. There was no evidence of prolonged (> 2 yr) enhancement of soil available N following either quarterly or annual fertilization. Quarterly fertilization produced the earliest and generally the most pronounced increases in soil solution NO−3 concentrations in all cases, followed by annual fertilization and control, respectively. These results, combined with laboratory incubations, indicated that quarterly fertilization benefited the nitrifying bacteria more than the trees on this site, particularly in the case of loblolly pine.