bluuebunny/crossref_metadata_2025 huggingface dataset:
Modeling Elevated Carbon Dioxide Effects on Water Relations, Water Use, and Growth of Irrigated Sorghum
Authors: Grant R. F. , Kimball B. A. , Wall G. W. , Triggs J. M. , Brooks T. J. , Pinter P. J. , Conley M. M. , Ottman M. J. , Lamorte R. L. , Leavitt S. W. , Thompson T. L. , Matthias A. D.
Published: July 2010

Elevated concentrations of atmospheric CO2 (Ca) are believed to raise sorghum [Sorghum bicolor (L.) Moench] productivity by improving water relations. In ecosys, water relations are simulated by solving for the canopy water potential (ψC) at which water uptake from a model of soil–root–canopy water transfer equilibrates with transpiration from the canopy energy balance. Simulated water relations were tested with ψC, water uptake, and energy exchange measured under ambient (363 μmol mol−1) and elevated (566 μmol mol−1) Ca and high vs. low irrigation in a free air CO2 enrichment experiment during 1998 and 1999. Model results, corroborated by field measurements, showed that elevated Ca raised ψC and lowered latent heat fluxes under high irrigation and delayed water stress under low irrigation. Changes in ψC modeled under ambient vs. elevated Ca varied diurnally, with lower ψC causing earlier midafternoon stomatal closure under ambient Ca. Modeled changes in sorghum water status caused elevated Ca to raise seasonal water efficiency under high and low irrigation by 20 and 26% (vs. 20 and 13% measured) in 1998 and by 9 and 27% (vs. 6 and 26% measured) in 1999. Ecosys was used to generate an irrigation response function for sorghum yield, which indicated that yields would rise by ≈13% for a range of irrigation rates if air temperatures were to rise by 3°C and Ca by 50%. Current high sorghum yields could be achieved with ≈120 mm or ≈20% less irrigation water if these rises in temperature and C
a were to occur.
Intercropping Berseem Clover with Barley and Oat Cultivars for Forage
Authors: Ross Shirley M. , King Jane R. , O'Donovan John T. , Spaner Dean
Published: July 2010

Intercrops of berseem clover (Trifolium alexandrinum L.) and silage cereals offer potential for high quality forage and partitioning of yield between silage harvest and fall grazing. Forage yield and quality of cereal–berseem clover intercrops may differ among oat (Avena sativa L.) and barley (Hordeum vulgare L.) cultivars and with semidwarf or early maturing cereal cultivars. Berseem clover was intercropped with five oat and four barley cultivars at Edmonton, Alberta, in 2000 and 2001 on orthic black chernozem (Typic Cryoboroll) soil. Forage yield, composition, and quality were measured with a two‐cut harvest. Silage‐stage yield (Cut 1) averaged 9.9 Mg ha−1 of dry matter (DM) with 18% berseem clover by dry weight. Berseem clover regrowth (Cut 2) averaged 2.8 Mg ha−1 DM with crude protein (CP) of 215 g kg−1. Intercrops with oat cultivars had greater Cut 1 DM yield, and intercrops with barley had greater yields of Cut 2 DM and total CP. The earlier maturity of barley provided for longer periods of berseem clover regrowth. Intercrops with semidwarf barley had equal yields of total DM and CP and greater Cut 2 DM yield than those with conventional‐stature barley. Intercrops with early maturing oat cultivars had equal total DM yield and greater yields of Cut 2 DM and total CP than those with late‐maturing oat cultivars. Forage quality indicators suggested that intercrops with barley were superior to those with oat. To maximize fall forage and increase the legume component of silage harvest, early maturing and shorter‐stature cultivars of oat and barley are recommended for cereal–berseem clover intercrops.
WebGro: A Web‐Based Soybean Management Decision Support System
Authors: Paz Joel O. , Batchelor William D. , Pedersen Palle
Published: July 2010

WebGro is a web‐based soybean [Glycine max (L.) Merr.] decision support system built on the CROPGRO‐Soybean model. The purpose of WebGro is to help soybean producers in the midwestern United States understand how different stresses interact to limit soybean yield in their fields. Stresses include water, soybean cyst nematode (Heterodera glycines), herbicide injury, Rhizoctonia root rot disease (Rhizoctonia solani), and hail damage. The user can set up a field scenario by selecting cultivar, planting date, plant population, soil type, and the nearest weather station using a web form. Different stress levels can then be entered, and the model can be run interactively by simulating the effects of one or more stresses at a time. A summary table of model simulations is generated and presented onscreen allowing users to examine individual and combined effects of plant stresses. The results are stored on the server, thus allowing the users to view these results in another session. WebGro also offers interactive graphical output that lets users view daily changes in soybean biomass weight for a specific field or scenario. WebGro is available at http://webgro.ae.iastate.edu
Soil Heat Flux Plates: Heat Flow Distortion and Thermal Contact Resistance
Authors: Sauer Thomas J. , Ochsner Tyson E. , Horton Robert
Published: July 2010

Persistent concern regarding surface energy balance closure encourages increased scrutiny of potential sources of error. Laboratory and field experiments addressed heat flow distortion and thermal contact resistance errors during measurement of soil heat flux (G) using the flux plate technique. Steady‐state, one‐dimensional heat flow experiments determined flux plate thermal conductivities (λm) and measured the effect of air gaps and thermal heat sink coatings on plate performance. Use of measured instead of manufacturer‐specified λm and plate dimensions in a heat flow distortion correction improved the consistency but not the average disagreement between imposed sand G and corrected plate heat flux density (Gm). Consistent underestimates of G in dry sand by 20 to 25% after heat flow distortion correction was attributed to thermal contact resistance effects. A convex air gap 0.1 to 1.32 mm thick across 5.9% of the plate face area reduced Gm by up to 9.7%. A thin layer of a thermal heat sink compound with λ 0.18 W m−1 K−1 greater than the plate λm (1.0 W m−1 K−1) did not increase Gm in a clay soil but increased Gm by ∼6% in quartz sand. A 6.5% increase in Gm was also observed for plates treated with the same heat sink compound in a silt loam soil under field conditions. Thermal contact resistance errors are probably <10% in moist, medium‐textured soils and can be minimized by careful plate installation. Relatively greater errors in Gm may occur due to thermal contact resistance in dry sand and due to heat flow distortion when soil λ >> λm
An Advanced Method for Deriving Latent Energy Flux from a Scanning Raman Lidar
Authors: Cooper D. I. , Eichinger W. E. , Archuleta J. , Hipps L. , Neale C. M. U. , Prueger J. H.
Published: July 2010

One of the fundamental issues with lidar‐derived evapotranspiration estimates is its reliance on tower‐based measurements of Monin–Obukhov similarity variables, specifically the Obukhov length (L) and the friction velocity (u∗). Our study indicates that L can be derived in the atmospheric surface layer directly from lidar range‐height scans by estimating the integral length scale (ILS). Data from both three‐dimensional sonic anemometers mounted on towers and lidar data collected during two subsequent field experiments were analyzed using autocorrelation analysis to estimate the ILS. The ILS values were then transformed into L values using a power‐law similarity model and were compared to coincident tower‐based observations. The comparisons between tower‐based eddy covariance sensors and lidar data show that the lidar‐derived L values are within the expected uncertainty and variability of standard point sensor measured observations. An additional model for estimating the friction velocity from the Obukhov length was also derived, and both L and u∗ were used to calculate the latent energy flux from lidar without external measurements. The evaporative fluxes from the standard method and the new advanced method were compared with eddy covariance fluxes, and it was found that the advanced method is superior.
Temporal Changes in Soil and Biomass Nitrogen for Irrigated Wheat Grown under Free‐Air Carbon Dioxide Enrichment (FACE)
Authors: Adamsen F. J. , Wechsung G. , Wechsung F. , Wall G. W. , Kimball B. A. , Pinter P. J. , LaMorte R. L. , Garcia R. L. , Hunsaker D. J. , Leavitt S. W.
Published: July 2010

Increasing atmospheric CO2concentrations are expected to increase plant production and demand for N and other nutrients. The objectives of this investigation were to characterize and quantify the temporal trends in soil mineral N and aboveground biomass N during the growing season of wheat (Triticum aestivumL.) with adequate N, ambient and elevated CO2, and two levels of water stress. The free‐air CO2enrichment (FACE) technique was used to enrich the air from 370 to 550 μmol mol−1CO2. Spring wheat was planted in late December of 1992 and 1993 and harvested at the end of May. Each main plot (CO2level) was split into two irrigation treatments to replace 100 and 50% of the potential evapotranspiration. Soil and plant samples were taken for N analysis six times each year. Elevated CO2lowered soil mineral N concentrations in the top 0.3 m of soil as much as 40% and increased aboveground biomass N by as much as 16% compared with the ambient treatment. Before anthesis, irrigation level had little effect on either soil mineral N or aboveground biomass N, but at harvest in 1992–1993 and at dough stage in 1993–1994 deficit‐irrigated plots had higher soil mineral N (p< 0.05) and lower aboveground biomass N than plots that received adequate irrigation. There was little variation in the concentrations of N in the aboveground biomass among treatments within a sampling date. The data suggest elevated CO2may lead to rapid N uptake, which could result in increased early vegetative growth.
Responses of Short‐Season Corn Hybrids to a Humid Subtropical Environment
Authors: Bruns H. Arnold , Abbas H. K.
Published: July 2010

Corn (Zea mays L.) hybrids commonly grown in the lower Mississippi River valley often encounter heat and drought stress during reproductive growth, which impairs yield and increases preharvest mycotoxin contamination. Four short‐season hybrids developed for production at ≥ 40° N latitude and two hybrids adapted to the Midsouth USA were grown at Stoneville, MS (33°26′ N, 90°55′ W), in 2002 and 2003 using N fertility treatments of 112 kg N ha−1 preplant, 224 kg N ha−1 preplant, or 112 kg N ha−1 preplant + 112 kg N ha−1 side‐dress at growth stage V6 (six leaves). Growing degree units at 10°C base temperature required for growth stages R1 (silking) and R6 (physiological maturity) of the four short‐season hybrids were 50 and 100 units greater, respectively, than when grown in their adapted environments. Yields of two of the short‐season hybrids compared well with the adapted hybrids. Kernel weights and grain bulk density differed among hybrids but were not below levels subject to dockage. Aflatoxin and fumonisin levels were higher in 2002 than 2003. Three of the short‐season hybrids did have aflatoxin levels in 2002 at least three times greater than the other three hybrids. Plots receiving 224 kg N ha−1 preplant yielded more than the other N fertility treatments. Kernel weights were 10 mg greater for the higher N fertility treatments. Nitrogen fertility had no effect on mycotoxins. Short‐season hybrids need to be individually evaluated for production potential in the lower Mississippi River valley.
Comparison of Crop‐Based Indicators with Soil Nitrate Test for Corn Nitrogen Requirement
Authors: Ma B. L. , Subedi K. D. , Costa C.
Published: July 2010

Nitrogen amendment based on soil mineral N content before planting is unreliable in humid regions. A field experiment was conducted for 3 yr to (i) determine the appropriate rates and timing of N applications in the humid environment of eastern Ontario, Canada (45°23′ N, 75°43′ W); (ii) evaluate the ability of nondestructive plant‐based methods compared with presidedress soil nitrate concentration test in discriminating fertilization N rates near sidedress time; and (iii) document how yearly variations in environmental conditions affect the ability of different approaches to assess corn (Zea mays L.) N status. Two hybrids were grown under eight combinations of rates and timing of N application in a factorial experiment. Leaf greenness and canopy reflectance were simultaneously measured from the V5 to V8 stages and at three occasions thereafter. Plant total N and soil available N NO3− and NH4+ at V6 were analyzed. Relationships of parameters collected early in the growing season vs. grain yield, harvest index, and total plant N uptake at maturity were determined. In 2 yr (2000 and 2002), grain yields increased significantly with fertilizer rates up to 120 kg N ha−1. While soil mineral N and plant N concentrations differentiated 0 N from preplant N at 40 kg N ha−1, both leaf chlorophyll and canopy reflectance measured at V6 stage responded linearly to fertilizer N up to 120 kg N ha−1. We concluded that these leaf and canopy optical measurements could be used as crop‐based indicators for early‐season N amendment.
Plant Availability of Phosphorus in Swine Slurry and Cattle Feedlot Manure
Authors: Eghball Bahman , Wienhold Brian J. , Woodbury Bryan L. , Eigenberg Roger A.
Published: July 2010

To utilize manure P for crop production, P release and plant availability needs to be quantified. An incubation study was conducted to determine P availability from swine (Sus scrofa) and cattle (Bos taurus) feedlot manure in three soils. Treatments for each manure included temperature (11, 18, 25, and 32°C), water regime [constant 60% water‐filled pore space (WFPS) vs. four dry‐down cycles of 60 to 30% WFPS], time, and soils (Catlin silt loam, Sharpsburg silty clay loam, and Valentine fine sand). In another study, synthetic P fertilizer was used to determine the fraction of P that becomes unavailable with time to compare with manure P. Time, soil, and manure application were factors that influenced soil test P and water‐soluble P during incubation. At the low synthetic P fertilizer rate of 6 μg g−1, about 12 kg P ha−1, none of the applied P remained available in the Catlin soil while about one‐third remained plant available in the Sharpsburg soil and two‐thirds in the Valentine soil. At the high P rate, 68 mg kg−1, 38 to 83% of fertilizer P remained available in the three soils. Phosphorus availability was 60 to 100% of applied cattle manure P and 52 to 100% of swine slurry P in the three soils. Phosphorus availability in the Sharpsburg soil was 100% of P in both manure types. Phosphorus availability from manure is high, and manure can be used similar to inorganic P fertilizer in soils where P‐based application is made in areas susceptible to P loss in runoff. In P‐deficient soils, a P availability of 70% should be used.
Livestock Use as a Non‐Thermal Residue Management Practice in Kentucky Bluegrass Seed Production Systems
Authors: Holman Johnathon D. , Hunt Carl , Johnson‐Maynard Jodi , VanTassell Larry , Thill Donn
Published: July 2010

Kentucky bluegrass (Poa pratensis L.) postharvest residue has historically been burned to maintain stand productivity and profitability. Recent regulations were imposed that prohibit or restrict field burning since it negatively impacts air quality. Stand life is reduced from approximately 8 yr in a burn system to 3 yr in current nonburn systems, resulting in increased production costs and potential for soil erosion. Postharvest grazing might remove as much residue as burning, and maintain stand life longer than the current nonthermal practice of raking, baling, and mowing postharvest residue. This study determined treatment affect on seed production, cattle (Bos taurus) stocking density required to remove as much residue as burning, supplement requirements for cattle grazing Kentucky bluegrass residue, and value of Kentucky bluegrass residue utilized by cattle in bale + graze (BG) and graze‐only (G) residue management treatments. Graze treatments yielded comparable to burning. The stocking density required to remove 80% of the residue in 30 d by G ranged from 17 to 23 animal units (AU) ha−1 and BG ranged from 9 to 14 AU ha−1. Nutritive value of Kentucky bluegrass residue ranged from 35 to 52 g kg−1 crude protein (CP), 390 to 438 g kg−1 acid detergent fiber (ADF), 716 to 763 g kg−1 neutral detergent fiber (NDF), and 388 to 473 g kg−1 48h in vitro true digestibility (IVTD). Daily requirement needed to be provided by supplement was less when fall plant regrowth was increased, and in G since dry matter (DM) intake tended to be greater in G than BG. The calculated value of baled Kentucky bluegrass residue on a DM basis averaged $33.27 Mg−1. The calculated value of grazed Kentucky bluegrass residue on a DM basis ranged from $38 to $74 ha−1 in BG, and $133 to $240 ha−1 in G. Overall, BG required fewer cattle than G, but G was the most profitable grazing treatment.
Soil Oxygen Contents and Ion Uptake by Corn
Authors: Shapiro R. E. , Taylor George S. , Volk G. W.
Published: July 2010

A method was developed to maintain the oxygen content of soil air in pots at different levels by means of a controlled diffusion technique.

The yield of plant tops and roots was reduced by low soil oxygen contents. Decreasing the soil oxygen contents also reduced the percentages of K, Mg, P, and N found in the plant tops, while the percentage values for these elements in the roots increased. These results indicated that low soil oxygen may affect the translocation of ions from the roots to the tops more than absorption of these elements from the soil.

Elements other than potassium, particularly phosphorus, were of importance in explaining reduced yields with low soil oxygen contents.

When gaseous diffusion between soil and the atmosphere was eliminated after a period of normal plant growth, the percentages of K and Ca in the tops were reduced while the percentages of these elements increased in the roots. Again, the data indicated a translocation effect resulting from poor aeration.
Possible Relationships of Cation‐Exchange Capacity of Plant Roots to Cation Uptake
Authors: Huffaker R. C. , Wallace A.
Published: July 2010

The K, Ca, and Mg contents of different plant species grown under similar conditions could be related in a majority of cases by CEC1/CEC2 = K2/K1 = (Ca1 + Mg1/Ca2 + Mg2)1/2, where the subscripts 1 and 2 represent different species. It was shown that K1/K2 should be expected for single‐salt solutions while K2/K1 is expected when K is mixed with divalent cations. Data on root CEC and plant contents of K, Ca, and Mg obtained from a large number of citrus, corn, and soybeans grown in soil gave correlation coefficients as follows:
urn:x-wiley:03615995:saj2sssaj195803615995002200050007x:equation:saj2sssaj195803615995002200050007x-math-0001 Even though the correlations were significant, the relations appeared to be far from simple and in some cases did not hold. For example, plants grown in sand corresponded less in the divalent ratios because of high Mg contents in corn. In some cases CEC ratios corresponded well with K1/K2 rather than K2/K1.
Correlations of Soil pH and Percent Base Saturation as Influenced by Soil‐Forming Factors
Authors: Blosser D. L. , Jenny Hans
Published: July 2010

Eighty soils collected more or less at random over a large area gave very low correlations between soil pH and percent base saturation. In the same area, soils chosen according to soil‐forming factor ordinations gave very high correlations between the two soil properties. Climate was the dominant determining factor.
Shortleaf Pine Site‐Index Relationships in the Ozark Highlands
Authors: Graney David L. , Ferguson Edwin R.
Published: July 2010

By carefully limiting the area of application and the soils included in individual analyses, practical equations were developed for predicting shortleaf pine (Pinus echinata Mill.) growth on major soils in the Ozark Highlands. Large pits were dug to adequately classify the soils, and soil properties were determined by standard techniques. Shortleaf pine site index at age 50 was correlated with aspect, slope shape, loss‐on‐ignition of the A1 and Ap1 horizons, depth to fragipan, and latitude. Regression equations developed for limestone and dolomite soils, sandstone soils, and fragipan soils predicted site indexes within an average of 0.6 m (2 feet) on confirmatory plots.
Inherited and Detrital 2:1 Type Phyllosilicates in Soils Developed from Mazama Ash
Authors: Dudas M. J. , Harward M. E.
Published: July 2010

Previous studies of soils developed from Mazama ash have indicated the occurrence of a complex suite of 2:1 and 2:2 type phyllosilicates. Before interpreting the phyllosilicates as weathering products from the ash, it must be established that they have formed in situ. Origin of 2:1 and 2:2 type phyllosilicates in soils of the coarse Mazama pumice in central Oregon was traced to the pyroclastic lithic fragments in the deposit. Clay minerals separated from lithic fragments included chlorite, chloritic intergrades, mica, smectites, and possibly vermiculite. The inherited origin of these crystalline clays corrects previous suggestions of origin which involved weathering of ash.

For volcanic ash soils in forested areas located at distances farther than 100 km from the source at Crater Lake, 2:1 type clay minerals separated from ash horizons were shown to be relics from underlying paleosols. Crystalline clay suites in different ashy profiles exhibited greater similarity to their respective palesol clay fraction than to other profiles in the same ash deposit. Once incorporated into ashy horizons, palesol clay high in montmorillonite exhibited partial chloritization and samples high in mica exhibited some loss of interlayer K. Uprooting of trees is believed to be the major mechanism involved in mixing ash soils with palesols in forested areas where the Mazama deposit is relatively thin (< 100 cm).
Detachment of Soil Aggregates by Simulated Rainfall from Heavily Manured Soils in Eastern Nebraska
Authors: Mazurak A. P. , Chesnin Leon , Tiarks A. E.
Published: July 2010

A field experiment was established to measure the effects of annual applications of high rates of manure for the production of crops under irrigation. The effects of incorporating the manure into the soil by disk plowing to depths of 10 cm, 20 cm, and 30 cm on the stability of the soil mass was measured under simulated rainfall conditions. The effect of simulated rainfall on soil surface compaction as influenced by rate of application of manure and depth of incorporation was measured with a penetrometer.

The amount of soil material detached from undisturbed soil cores by simulated raindrops was curvilinearly related to the rainfall intensity. When the plots were disk plowed to a depth of 10 cm, soil detachment increased from 55 mg/cm3 of water for the nonmanured plots to 89 mg/cm3 for the 415 metric tons/ha per year. The amount of soil particles detached by the raindrops was reduced about 15 mg/cm3 of water as the depth of disking the manure into the soil was increased from 10 to 30 cm. Aggregate size distribution of the splashed material showed that prior application of manure to the soil increased the amount of soil aggregates in the large diameter classes. The penetrometer resistance of the crust formed by the waterdrops decreased from 36 kg/cm2 for nonmanured plots to 4.4 kg/cm2 for the plots receiving 360 metric tons of manure/ha/year.
Statistical Modeling of the Variability of Selected Colo Soil Properties
Authors: Collins M. E. , Fenton T. E.
Published: July 2010

Forty‐seven soils representing the Colo soil series (fine‐silty, mixed, mesic Cumulic Haplaquolls) as mapped on 0 to 2% slopes in the Upper Midwest were described and sampled to determine selected physical, chemical, and morphological properties to use in statistical modeling. The soils were sampled in Iowa (35 pedons), Nebraska (4), Missouri (4), Illinois (2), and Minnesota (2), and studied in the following groups: all Colo pedons, by master horizon, and by the presence or absence of postcultural sediments (PCS). The groups were statistically analyzed by using means, ranges, standard deviations, coefficients of variation, correlation coefficients, and multiple regression equations. The objectives of this study were to (i) characterize the Colo soil throughout its geographic range; (ii) stratify the data to study the relationship between selected soil physical, chemical, and morphological properties; and (iii) develop statistical regression models using several soil chemical and physical properties of one soil series. Ranges in soil properties such as particle size, hydrogen‐ion activity, and total carbon (TC) content are restricted by the limits of the official series used as guides in mapping. Therefore, these properties did not have as wide a range as other soil properties studied‐available, total (TP), organic (OP), and inorganic phosphorus (IP) or organic carbon/organic phosphorus (OC/OP) and organic phosphorus/total phosphorus (OC/TP) ratios which are not defined for the series. The Colo samples were stratified according to master horizon designations. TC, OP/TP, OP, and OC/OP means were highest in the A horizon and decreased with increasing depth in the profile. Soil properties used to define the series had a narrower range (e.g. particle size, TC amount) than other soil properties especially in the A horizon. Forty‐five percent of the pedons sampled had some evidence of PCS. The sand, silt, clay, and TC means were similar for those soils with or without PCS as were IP, OC/OP, and OP/TP. The ranges differed but were not as great as anticipated. If less than 50 cm thick, PCS should not be considered part of the mollic epipedon. Still all the soils studied had a mollic epipedon greater than or equal to 91 cm thick. Morphologically, the majority of the Colo soils described had an A‐B‐C horizon sequence. A B horizon was described to indicate “structural” alteration of original material. Alluvial‐derived soils are reported to be in an early stage of development and, therefore, should have little alteration of the original material. As indicated by some of the Colo soil properties, this assumption is not necessarily correct. As a result of this study, the genesis of some soils derived from alluvial sediments in the Upper Midwest is better understood.
Extraction of Radiostrontium Coprecipitated with Calcium Carbonate in Soil
Authors: Spalding B. P.
Published: July 2010

The fraction of soil 90Sr coprecipitated with calcium carbonate (CaCO3) was determined by extraction into 0.1M hydrochloric acid (HCl)‐0.5M potassium chloride (KCl) after an initial extraction with either 1M ammonium acetate (NH4OAc) or 1M KCl to remove soluble salts and exchangeable cations. This procedure was tested on soil samples supplemented with 85 g CaCO3/kg containing coprecipitated 85Sr. The 85Sr and calcium (Ca) in this Ca(85Sr)CO3 behaved identically in the extraction sequences. In the absence of soil, about 95% of the Ca(85Sr)CO3 dissolved into the 0.1M HCl‐0.5M KCl following the KCl extraction. In the presence of soil, a significant amount of both 85Sr and Ca remained undissolved in this extractant but were subsequently removed by extraction with 8M HNO3. Ammonium acetate, however, extracted more Ca and 85Sr from Ca(85Sr)CO3, with or without soil, than did KCl. The extraction procedure was also applied to a group of 16 90Sr‐contaminated soil and streambed sediment samples which contained from 0 to 7.9 g carbonate‐carbon/kg (0 to 66 g CaCO3/kg). The amount of Ca + Mg extracted by 0.1M HCl‐0.5M KCl, following KCl extraction, was well correlated with but slightly lower than the amounts expected for a complete dissolution of the CaCO3. Pre‐extraction with NH4OAc, rather than KCl, dissolved significantly more CaCO3 resulting in a lower estimate of the soil CaCO3. Several soil samples, taken from a radioactive waste burial trench that had received sodium carbonate (Na2CO3) treatment injections, revealed that up to 98% of the total 90Sr was observed in a CaCO3 phase. Untreated soils typically exhibited 80 to 95% of their 90Sr in a cation exchangeable form, i.e., extractable by either NH4OAc or KCl.
Transient Microsite Models of Denitrification: I. Model Development
Authors: McConnaughey P. K. , Bouldin D. R.
Published: July 2010

Past models of denitrification are reviewed. None of these models include a description of anaerobic volume and transient solute diffusion to and away from zones of N reduction. In this paper, models describing denitrification in the anaerobic zone of a saturated homogeneous soil are presented. The models consider the reduction sequence: nitrate (NO−3) → nitrite (NO−2) → nitrous oxide (N2O) → dinitrogen (N2). Anaerobic volume was described by an approximate solution to a moving boundary problem. Transient diffusion of NO−3, NO−2, N2O, and N2 was allowed throughout the saturated soil, while reduction of the nitrogenous species occurred only in the anaerobic region. Four types of reaction terms were considered, resulting in a zero‐order model, a Michaelis‐Menten model with differential rates of reduction, a Michaelis‐Menten model with NO−3 and NO−2 inhibition of N2O reduction, and a competitive inhibition model. The use of an operational Vmax which reflects electron donor availability was proposed.
A Comparison of NH4HCO3‐DTPA, NaHCO3, CaCl2, and Na2‐EDTA Soil Tests for Phosphorus
Authors: Labhsetwar V. K. , Soltanpour P. N.
Published: July 2010

The NH4HCO3‐DTPA soil test of Soltanpour and Schwab was developed for simultaneous determinations of availability indices for P, K, Zn, Fe, Cu, Mn, and other elements. In this paper NH4HCO3‐DTPA was compared with NaHCO3, CaCl2, and Na2‐EDTA soil tests for P in a greenhouse study. Five rates of P: 0, 50, 100, 150 and 200 mg kg−1, were applied to 11 Colorado soils and yield response of alfalfa (Medicago sativa L.) to P was measured. Phosphorus levels in soil extracts were measured using inductively coupled plasma spectrometry. The NH4HCO3‐DTPA extracts also were analyzed for P colorimetrically. The inductively coupled plasma spectrometric method gave higher values (1.7 mg kg−1 on the average) for P than the colorimetric method probably due to inclusion of organic P. The Nelson and Anderson analysis of variance method indicated that all tests were equally effective in separating soils that required fertilizer P from non‐responding soils with r2 values of 0.52, 0.50, 0.60, and 0.50, for NH4HCO3‐DTPA, NaHCO3, CaCl2, and Na2‐EDTA soil tests, respectively. However, the NH4HCO3‐DTPA is more economical because it is designed to extract other elements simultaneously, thereby saving considerable time. The r2 value was 0.58 for colorimetric method. The greenhouse critical levels of P were 9.4, 27.6, 0.46 (0.23 mg L−1 in solution), and 36.8 mg kg−1 for NH4HCO3‐DTPA, NaHCO3, CaCl2, and Na2‐EDTA soil tests, respectively.
Silicate and Phosphate Influence on Kaolin‐Iron Oxide Interactions
Authors: Golden D. C. , Dixon J. B.
Published: July 2010

Interactions between kaolin and iron oxide minerals are important in understanding the physical properties of highly weathered soils. This study shows that anions (silicate and phosphate) play a major role in determining the type and strength of particle associations, both during and after the formation of the iron oxide minerals in soils. The presence of silicate as an adsorbed anion on kaolinite inhibited iron oxide cyrstallization from ferric hydroxide gel and facilitated an intimate coulombic association between fine positively charged iron oxide particles and kaolin minerals whereas adsorbed phosphate did not affect the crystallization of iron oxide or the kaolinite iron oxide association. Mossbauer spectroscopy was used to demonstrate the existence of strong attractive forces between fine iron oxide particles and the kaolinite surface. The specific adsorption of silicate ions by associated kaolinite‐iron oxide systems, disrupted the attractive forces between kaolinite and iron oxides and effectively dispersed the system in most cases. This was taken as an evidence for the existence of coulombic type attractions. Attractions which could not be disrupted by silicate treatment were observed in cases where goethite was formed by the oxidation of Fe2+ ions in the presence of kaolinite and halloysite.
A Mechanistic, Numerical Model of Sedimentation, Mineralization, and Decomposition for Marsh Sediments
Authors: Morris James T. , Bowden William B.
Published: July 2010

This paper describes a computer model that relates measured nutrient profiles to organic matter diagenesis in marsh sediments. Processes included in the model are sedimentation of exogenous and endogenous organic and inorganic matter, decomposition, above‐ and belowground biomass and production, and N and P mineralization. The shape of organic nutrient profiles in marsh sediments is controlled by the relative rates of nutrient mineralization and inputs of organic and inorganic matter. Sediment inputs were specified for a freshwater, tidal marsh on the North River, Massachusetts, and the model was solved for nutrient mineralization rates by fitting the model to observed nutrient profiles. Model calculations of net annual N and P export from a 1‐m sediment column, 9.6 to 17.5 g N m−2 yr−1 and 1.19 to 2.02 g P m−2 yr−1, were sensitive to small changes in estimates of belowground production and the fraction of organic material that is refractory, constants in the model that are poorly known for marsh ecosystems. These export rates are about 55 to 78% and 71 to 85% of the annual sediment inputs of organic N and P, respectively. The fate of nutrients exported from the sediment was not specified, but it could include plant uptake, denitrification, and net loss to the adjacent tidal river. The model demonstrates that mature marshes with deep sediments recycle proportionally more of the nutrients required by primary producers than young marshes with shallow sediments. Model calculations indicated that the greatest changes in C, N, and P occur in the upper 2 cm of sediment. Labile organic C decomposed most rapidly which caused the relative concentrations of organic N and P to increase. Below this thin surface zone C loss became negligibly small, but there was a gradual decline in concentrations of organic N and P as they continued to mineralize slowly within the upper 60 cm of sediment. Apparently, only refractory C, N, and P compounds remained below the 60‐cm depth. The predicted ratio of N/P loss from sediment ranged from 8.2 N/1 P to 9.55 N/1 P (g/g) and was constant over depth; this compares to a ratio of about 11 N/1 P in litter of the dominant macrophytes. This model is sufficiently general as to be useful in studies of sediment formation and nutrient cycling in other systems.
Illuvial Band Formation in a Laboratory Column of Sand
Authors: Bond W. J.
Published: July 2010

Experiments are described in which thin clay bands were formed by illuvial processes in a laboratory column of fine sand containing <1% clay. It is hypothesized that band formation resulted from dispersion of clay in the sand and its subsequent deposition, which was triggered by layers of small pores within the sand column, and/or by exceeding the maximum possible suspension concentration. The results permit a number of comments to be made about the occurrence and formation of illuvial clay bands, as well as precautions that should be taken when carrying out water flow experiments in sandy soils.
Manganese Phosphate Equilibrium Relationships in Soils
Authors: Boyle F. W. , Lindsay W. L.
Published: July 2010

Solubility diagrams were developed using log K° values for MnHPO4·3H2O, Mn3(PO4)2·3H2O, Mn5H2(PO4)4·4H2O and MnPO4·1.5H2O. The latter mineral was found to be more stable than hydroxyapatite and thus capable of controlling soil‐solution P at pH values <7.2 and pe + pH values between 13.5 and 17. Controlled redox cells were used to maintain suspensions of several soils at fixed redox levels above pe + pH = 13.5. After 28, 56, 84, and 140 d, samples were taken, and the clear filtrates were analyzed. The activities of Mn2+ and H2PO‐4 were calculated by speciating total Mn and P in solution. Ionic activity products were calculated and compared to the activity products of pure Mn phosphates. This study helps to explain the beneficial effects of phosphate in alleviating Mn toxicities and the importance of Mn phosphates as reaction products of Mn and P fertilizers in soils.
Organic Oxidation and Manganese and Aluminum Mobilization in Forest Soils
Authors: Pohlman Andrew A. , McColl John G.
Published: July 2010

A kinetic model is presented that describes the initial and rapid redox processes between polyhydroxyphenolic acid and soil or manganese oxide suspensions. The rate constants derived by the model were similar in magnitude in both suspensions for the organic reductants studied. Polyhydroxyphenolic acids with para‐ and ortho‐OH groups were rapidly oxidized by manganese oxides with spectral evidence suggesting that the reaction leads to polymeric humic products by way of benzoquinone derivatives. In contrast, polyhydroxyphenolic acids with meta‐oriented phenolic‐OH groups were not oxidized by soil or by manganese oxide suspensions within the 120‐min reaction period, presumably because these compounds were not capable of being oxidized to benzoquinone intermediates. The oxidative process was also accompanied by formation of Mn2+ both from soil and from manganese oxide suspensions. The rate of Mn2+ formation by gallic acid from Challenge A horizon soil suspensions containing a total of 3.6 × 10−4 mol L−1 Mn content was comparable to the rate from birnessite suspensions containing a total of 2.5 × 10−4 mol L−1 Mn content. The appearance of Mn2+ in soil suspensions within the reaction period was attributed mainly to reduction rather than clelation by the organic reductants or their products of oxidation. Dissolution of soil Mn also occurred by 2,5‐dihydroxybenzoic, and 3,4‐dihydroxybenzoic acids, but not by 2,6‐dihydroxybenzoic and 3,5‐dihydroxybenzoic acids. Humic products formed from oxidation by Mn were quite effective chelators of Al. The rates of Al dissolution by humic products from Blodgett A horizon soil in suspensions were comparable to the rates in the original organic acids, and were 3 to 6 times faster in dissolving Al than mineral acid at comparable pH levels. The parallel behavior in reactivities of both soil and manganese oxide suspensions towards polyhydroxyphenolic acids suggests that manganese oxides are being reduced in both systems.
Volcanic Glass Influence on Selected Soil Properties in Western Nebraska
Authors: Uzochukwu G. A. , Lewis D. T.
Published: July 2010

Volcanic glass exerts an influence on surface area, water‐holding capacity, and cation‐exchange capacity. This study was conducted to quantify the volcanic glass in the Mitchell (coarse‐silty, mixed [calcareous], mesic Ustic Torriorthent) and Tripp (coarse‐silty, mixed, mesic Aridic Haplustoll) soils in western Nebraska and to determine the influence of glass on cation‐exchange capacity, surface area, and water retention at 1.5 MPa. These properties are important in understanding soil response to management practices. Surface area and water retention at 1.5 MPa increased with depth in the soils. The increasing water retention at 1.5 MPa with depth was associated with volcanic glass, which might indicate more amorphous material in the clay fraction. The ratio of water retention at 1.5‐MPa tension to clay (g/kg) determined by standard analysis was greater than 0.6, suggesting that clay should be estimated by calculation (water content at 1.5 MPa × 2.5) for Mitchell and Tripp soils.
Factors Affecting Zinc Uptake in Cropping Systems
Authors: Hamilton M. A. , Westermann D. T. , James D. W.
Published: July 2010

Zinc availabilities can change with different cropping management practices. The objective of this study was to identify some of the causative factors associated with previous crops contributing to Zn uptake differences in a subsequent crop. Field studies over 3 yr evaluated the Zn availability after four precropping treatments: bean (Phaseolus vulgaris L.), corn (Zea mays L.), wheat (Triticum aestivum L.), and fallow, across two Zn fertilization rates (with and without 11 kg Zn ha−1 as ZnSO4), using the ‘Viva’ bean as a test crop. Soil samples taken before and after the test crop were analyzed for extractable P, Zn, Cu, Mn, and Fe, and organic matter. Soil respiration during the test crop was periodically estimated the last cropping year. Whole plant samples estimated nutrient concentration and uptake. Soil Zn extracted by diethylenetriaminepentaacetic acid (DTPA) was increased by Zn fertilization but not affected by precropping treatments. Zinc uptake by bean was significantly higher after precropping with corn and lower after fallow regardless of Zn fertilization. Uptake differences were most pronounced during early plant growth. Phosphorus and Cu uptake varied with treatment in a similar pattern as Zn uptake, and were positively correlated with each other. Zinc uptake was also positively correlated with soil organic matter and negatively correlated with soil P. Soil respiration rate was significantly lower after the fallow treatment compared with other precropping treatments. Vesicular‐arbuscular mycorrhiza (VAM) colonization in the test crop roots was higher after corn and lower after fallow regardless of soil Zn concentrations. Colonization was positively correlated with Zn, P, and Cu uptake during early plant growth. The VAM colonization, soil respiration, and DTPA‐extractable Zn were selected by a stepwise regression procedure as the important variables affecting Zn uptake during early plant growth. These results emphasize the importance of the soil's biological activities on Zn availability and may help explain some field observations where chemical soil tests appear to fail.
Effect of Soils on the Behavior of Immobilized Enzymes
Authors: Gianfreda Liliana , Bollag Jean‐Marc
Published: July 2010

The use of immobilized enzymes, such as oxidoreductases and hydrolases, in contaminated soils offers a simple, efficient, and inexpensive method for solving pollution problems in the soil environment. Investigations on the behavior of a laccase (from the fungus Trametes versicolor), a peroxidase (from horseradish [Armoracia rusticana P. Gaertner, Meyer & Scherb.]), and an acid phosphatase (from wheat [Triticum aestivum L.] germ) were conducted in the presence of sand, various soils, and soil‐sand mixtures. The enzymes were either free or immobilized on three natural supports (a montmorillonite, a kaolinite, and a silt loam soil). On immobilization, laccase and peroxidase retained high activities, whereas immobilized acid phosphatase showed reduced activity. The affinity of laccase and peroxidase for their substrates remained practically unchanged (similar Michaelis constant [Km] values) and higher Km values (low substrate affinity) were obtained for immobilized acid phosphatase. By increasing the amount of soil in the soil‐sand mixtures or the content of organic matter in soil, an inhibitory effect on the activity of free and immobilized enzymes was observed. The reusability of immobilized laccase and peroxidase, both in the absence and presence of soil, was evaluated by repeated incubation cycles with 2,4‐dichlorophenol. After several incubation cycles, the immobilized enzymes retained different activity levels. Furthermore, in the presence of soils, the inhibitory effect decreased after each incubation cycle, indicating that the observed inhibition was, at least in part, due to soluble soil components easily extracted with the buffered substrate solution. Our results indicate that immobilized enzymes introduced into the soil environment have catalytic activity, but their performance is affected by organic or inorganic soil constituents.
Genotypic Variation in Promotion of Rice Dinitrogen Fixation as Determined by Nitrogen‐15 Dilution
Authors: Shrestha R. K. , Ladha J. K.
Published: July 2010

Rice (Oryza sativa L.) genotypes capable of stimulating associative N2 fixation (NFS) are desirable to reduce dependence on fertilizer N. A pot experiment was conducted during the 1993 dry season to assess differences in NFS among 70 genotypes of diverse origin and growth duration and to validate the use of 15N enrichment of mineralized soil N as reference for N2 fixation measurement. The soil used had a stable 15N enrichment that was obtained by incubating and frequent mixing with (15NH4)2SO4 (6.3 kg N ha−1) in submerged condition for 6 wk. The 15N enrichment of soil NH+4‐N dropped exponentially, showing an initial rapid decline to half of the original level within 2 wk, followed by a slower, nonsignificant rate of decline after 5 wk. Whole plant 15N atom % excess was inversely correlated with growth duration and ranged from 1.78 in Oking Seroni (late genotype) to 2.45 in PTB‐18 (early genotype). It was, therefore, necessary to compare NFS among genotypes of the same growth duration. Enrichment was lowest in the roots, suggesting this as the site of active N2 fixation; it was highest in the shoot and intermediate in grain. Nitrogen derived from air (Ndfa) estimated using 15N enrichments of mineralized soil N and reference rice genotype correlated highly (r = +0.998**). Percentage Ndfa ranged from 1.5 to 21.0, with an average of 10.2. Yelsulbyeo, Pankaj, and Oking Seroni had the highest Ndfa among early, medium, and long growth duration genotypes, respectively. Genotypes with high Ndfa, grain yield, and N uptake are Oking Seroni, IR29337‐36‐3, OR‐142‐99, and Pankaj.
Mapping Field‐Scale Physical Properties of Soil with Electrical Resistivity
Authors: Banton O. , Cimon M.‐A. , Seguin M.‐K.
Published: July 2010

The spatial variability of physical properties that significantly influence the fate of water and solute in soils needs a large number of measurements to be quantified. Surface electrical resistivity techniques could be used as a simple and practical method to determine this spatial variability. Electrical sounding and profiling measurements were taken on a small agricultural field (30 by 60 m) under two different soil conditions (dry and wet conditions). The soil profile is composed of three layers: a highly permeable sandy loam (alluvial terrace) overlying a gravelly sandy till that covers a friable sandy to silty shale. The soil physical properties (grain size distribution, porosity, hydraulic conductivity, bulk density, and organic matter content) of the uppermost layer were measured in the laboratory on undisturbed soil cores taken at three different depths on a 6 by 15 m grid in the field. Correlations were established between these parameters and the electrical conductivity. The best correlations were between the electrical conductivity and the sand, silt, clay, and organic matter contents. Their correlation coefficients, r, were, respectively, 0.64, 0.53, 0.64, and 0.65 for the dry conditions and 0.54, 0.45, 0.53, and 0.52 for the wet conditions. No relation was established between the electrical conductivity and the porosity, the bulk density, or the hydraulic conductivity. The correlation coefficients were, respectively, 0.04, 0.16, and 0.10 for the dry conditions and 0.14, 0.12, and 0.14 for the wet conditions. Electrical conductivity seems to be more influenced by the soil texture, i.e., by the electrical properties of the soil constituents, than by the structure, i.e., the water‐related properties. Besides, the two sets of electrical resistivities obtained in dry and wet conditions are not significantly different, as shown by the regression between them (slope = 0.92, r = 0.71) and by the isoresistivity maps. This study seems to indicate that the electrical method could be used to evaluate the spatial variability of some soil properties when their variability is sufficiently large, i.e., when the investigation scale or the level of contrast is large enough.