bluuebunny/crossref_metadata_2025 huggingface dataset:
Phosphorus Forms and Desorption Patterns in Heavily Fertilized Calcareous and Limed Acid Soils
Authors: Delgado Antonio , Torrent José
Published: July 2010

Phosphorus desorption from fertilized soils is significant for agriculture and the environment. This study was aimed at characterizing the forms in which P occurs in calcareous and limed acid soils and their influence on P desorption patterns. The P forms of two limed acid and three calcareous soils of Europe were characterized by chemical extraction, isotopic exchange, and sequential fractionation. Phosphate desorption was studied using resins and goethite as ion sinks. Total P ranged from 705 to 1400 mg kg−1Isotopic exchange revealed more surface‐adsorbed P in the limed acid than in the calcareous soils. Calcium phosphates predominated in the calcareous and Al and Fe phosphates in the limed acid soils; one limed acid soil contained significant amounts of Ca phosphates. The mixed cation and anion exchange resins (ACER) were more effective in desorbing P than the anion exchange resin (AER) and goethite. The desorption curves indicated significant differences in the degree of homogeneity of the P desorption reactions, the greatest and lowest degree of homogeneity corresponding with calcareous soils. The proportion of ACER‐extractable P that was plant‐available P was >50% for the limed acid and <20% for the calcareous soils. The proportion of ACER‐extractable P that was released to 0.002MCaCl2was >60% for the limed acid and <40% for the calcareous soils. Plant P availability was thus poorer in the calcareous soils than in the limed acid soils.
Tillage Effects on Carbon Fluxes in Continuous Wheat and Fallow–Wheat Rotations
Authors: Curtin D. , Wang H. , Selles F. , McConkey B. G. , Campbell C. A.
Published: July 2010

The traditional cropping system in semiarid regions of the Canadian prairies involves frequent summer fallowing with several tillage operations to control weeds during the fallow period. Recently, there has been a trend toward reduced tillage and more intensive cropping, but the impact of this shift in management on sequestration of atmospheric CO2 remains uncertain. In 1995 and 1996, we measured fluxes of CO2 in a tillage experiment that had been initiated in 1982 on a silt loam (Typic Haploboroll) in southwestern Saskatchewan. The experiment comprised two spring wheat (Triticum aestivum L.) rotations (continuous wheat [Cont. W] and fallow–wheat [F–W]), each with conventional tillage (CT) and no‐till (NT) treatments. In Cont. W, CO2 fluxes tended to be lower under NT than under CT (mean annual flux was ≈20 to 25% less for NT than CT). In F–W, tillage effects on mean annual CO2 flux were significant (P < 0.05) in the wheat phase only (NT ≈ 10% less than CT). Tillage had negligible effect on C inputs in crop residues. Lower CO2 fluxes under NT than under CT were attributed to slower decomposition of crop residues placed on the surface of NT soil than when they were incorporated. With good growing conditions (and thus large inputs of residues) between 1989 and 1996, there was an accumulation of partially decomposed residues on the surface of NT soil. Carbon in surface residues represented about one‐half of the C gained by NT soil. In Cont. W, surface residue C (in 1996) amounted to 3.6 t ha−1 under NT vs 1.4 t ha−1 under CT. Residue C amounts were smaller in the F–W system: 1.7 t ha−1 (NT) and 0.7 t ha−1 (CT). Based on our results, producers on medium‐textured soils in the semiarid Canadian prairies who switch from the traditional wheat production system (conventionally tilled fallow–wheat) to continuous no‐till cropping could, potentially, sequester 5 to 6 t C ha−1 in soil organic matter and surface residues in 13 to 14 yr.
Biomass and Residue Cover Relationships of Fresh and Decomposing Small Grain Residue
Authors: Steiner J. L. , Schomberg H. H. , Unger P. W. , Cresap J.
Published: July 2010

Maintaining residue cover provides diverse conservation benefits. Exponential relationships have been developed to estimate cover from biomass of randomly distributed, flat residues, but a large portion of crop biomass remains standing after harvest. Our objective was to determine how relationships between biomass and soil cover change in no‐tillage small grain fields as residues decompose and shift from standing to flat. Winter and spring wheat (Triticum aestivum L.), winter barley (Hordeum vulgare L.), and spring oat (Avena sativa L.) were grown at Bushland, TX, on Pullman clay loam (fine, mixed thermic Torrertic Paleustoll) in 12 field plots in three randomized complete blocks. For each crop, differential seeding rate, fertilization, and irrigation produced a range of biomass. During decomposition, differential irrigation increased environmental variability (13, 5, and 0 applications to sub‐sub‐plots). Ash‐free residue biomass was measured seven times in 14 mo, after taking photographs to determine soil cover of 1‐m2 sites. For crop‐date combinations, coefficients were determined from total (kt, m2 g−1) or flat (kf, m2 g−1) biomass. Regression indicated kt increased with time (P < 0.0001 for all crops, except spring wheat with P < 0.0041). Across crops, the relationship indicated that decomposition affects cover provided by total biomass. Across crops, the weak relationship indicated that cover could be estimated from flat biomass with kf ≈ 0.0175 for extended periods. These findings can improve estimation of residue cover for no‐tillage fields and indicate that residue orientation should be considered in biomass‐to‐cover relationships.
A New Perspective on Soil Thermal Properties
Authors: Ochsner Tyson E. , Horton Robert , Ren Tusheng
Published: July 2010

The soil thermal properties—heat capacity (C), thermal diffusivity (α), and thermal conductivity (λ)—are important in many agricultural, engineering, and meteorological applications. Soil thermal properties are largely dependent on the volume fraction of water (θ), volume fraction of solids (vs), and volume fraction of air (na) in the soil. In many natural settings θ,vs, andnavary greatly over time and space, but data showing the effects of these variations on thermal properties are not readily available. We used a heat‐pulse method to measure the thermal properties of 59 packed columns of four medium‐textured soils covering large ranges of θ,vs, andnaThe measured data reveal the commonly overlooked but dominant influence ofnaon soil thermal properties. Notably, the measurements show that the λ of these soils at 20°C can be accurately described as a decreasing linear function ofnaGood agreement exists between the measured data and common models for λ andC
Comparison of the thermal properties of four wettable and four water‐repellent soils
Authors: Bachmann J. , Horton R. , Ren T. , van der Ploeg R. R.
Published: July 2010

Water repellency is a widespread phenomenon, but its effect on most physical soil properties is still unknown. The present study deals with the thermal conductivity and volumetric heat capacity of wettable and water‐repellent (hydrophobic) sandy and silty soils. Thermal conductivity and volumetric heat capacity were determined by heat pulse measurements. Heat pulse measurements were made on samples of eight soils (four pairs of wettable soil and the corresponding water‐repellent counterpart). Water repellency either was caused by soil organic matter showing natural repellency or induced by chemical treatment of wettable soils with dichlorodimethylsilane (C2H6SiCl2). Thermal conductivity was also predicted with the models of de Vries and of Campbell. Almost all measured conductivities were larger than those predicted by the de Vries model. For the wettable soils, most of the conductivities in the soil water saturation range between 0.20 and 0.75 differed by more than 0.5 W m−1 K−1 The hydrophobic soils however, showed only in the range around a saturation degree of 0.20 to 0.50 values that deviated more than 0.5 W m−1 K−1 from the predictions. The Campbell model underestimated the conductivity at low saturation for wettable and hydrophobic soil, but overestimated it at high saturation for the wettable soil. Thermal conductivity for either dry or water‐saturated soil was predicted satisfactorily by both models. It was found further that soil wettability had no systematic impact on heat capacity. It is concluded that soil thermal conductivity decreased as soil hydrophobicity increased, whereas the volumetric heat capacity was not affected by soil wettability.
Soil Property Changes during Conversion from Perennial Vegetation to Annual Cropping
Authors: Wienhold Brian J. , Tanaka Donald L.
Published: July 2010

Management practices for conversion of land supporting perennial vegetation to crop production are needed. Effect of haying (hayed or not hayed), cropping (annual crop with no‐tillage, minimum tillage, or conventional tillage, and no‐tilled perennial crop), and N fertilization (0 or 67 kg ha−1) on soil properties were measured in 1995 and 1997 at a Conservation Reserve Program (CRP) site in North Dakota having an Amor loam (Fine‐loamy, mixed, superactive, frigid, Typic Haplustoll) soil in a spring wheat (Triticum aestivumL.), winter wheat, pea (Pisum sativumL.) rotation. Soil physical properties were not affected negatively by the management practices used. Haying and tillage practices influenced soil chemical properties. Organic C and total N content declined (1.2 Mg ha−1for C and 0.1 Mg ha−1for N) from 1995 to 1997. In hayed plots, organic C and total N increased as tillage intensity decreased while in non‐hayed plots no pattern was observed. Haying and tillage influenced soil biological properties. Potentially mineralizable N at 0 to 0.05 m increased as tillage intensity decreased in 1997. In the 0.05‐ to 0.15‐m depth, potentially mineralizable N increased from 1995 (118 kg ha−1) to 1997 (146 kg ha−1). By 1997, soil properties in hayed plots responded to cropping practices similarly to those in established cropping systems in this region. In non‐hayed plots, management induced patterns had not developed by 1997. Haying, conservation tillage, and annual cropping are viable approaches for converting land to annual crop production.
Field‐Scale Electrical Conductivity Mapping for Delineating Soil Condition
Authors: Johnson Cinthia K. , Doran John W. , Duke Harold R. , Wienhold Brian J. , Eskridge Kent M. , Shanahan John F.
Published: July 2010

Traditional sampling methods are inadequate for assessing the interrelated physical, chemical, and biological soil properties responsible for variations in agronomic yield and ecological potentials across a landscape. Recent advances in computers, global positioning systems, and large‐scale sensors offer new opportunities for mapping heterogeneous patterns in soil condition. We evaluated field‐scale apparent electrical conductivity (ECa) mapping for delineating soil properties correlated with productivity and ecological properties. A contiguous section of farmland (250 ha), managed as eight fields in a no‐till winter wheat (Triticum aestivum L.)–corn (Zea mays L.)–millet (Panicum miliaceum L.)–fallow rotation, was ECa mapped (≈0‐ to 30‐cm depth). A geo‐referenced soil‐sampling scheme separated each field into four ECa classes that were sampled (0‐ to 7.5‐ and 7.5‐ to 30‐cm depths) in triplicate. Soil physical parameters (bulk density, moisture content, and percentage clay), chemical parameters (total and particulate organic matter [POM], total C and N, extractable P, laboratory‐measured electrical conductivity [EC1:1], and pH), biological parameters (microbial biomass C [MBC] and N [MBN], and potentially mineralizable N), and surface residue mass were significantly different among ECa classes (P ≤ 0.06) at one or both depths (0–7.5 and 0–30 cm). Bulk density, percentage clay, EC1:1, and pH were positively correlated with ECa; all other soil parameters and surface residue mass were negatively correlated. Field‐scale ECa classification delimits distinct zones of soil condition, providing an effective basis for soil sampling. Potential uses include assessing temporal impacts of management on soil condition and managing spatial variation in soil‐condition and yield‐potential through precision agriculture and site‐specific management.
Denitrification Potentials in Restored and Natural Bottomland Hardwood Wetlands
Authors: Hunter Rachael G. , Faulkner Stephen P.
Published: July 2010

Wetland restoration projects are frequently evaluated by their hydrologic roles and vegetation characteristics, but their success in restoring biogeochemical processes, such as denitrification, is less well known. To determine how restoration of structure affects specific ecosystem processes, denitrification potential, soluble organic C (SOC) concentrations, and soil moisture were measured seasonally over a 1‐yr period in replicated natural bottomland hardwood (BLH) wetlands (NAT), restored BLH wetlands with hydrology reestablished (RWH), and restored BLH wetlands without hydrology reestablished (RWOH). Denitrification potential was significantly higher in NAT wetlands (657 ng N2O‐N g−1soil h−1) than in RWOH (167 ng N2O‐N g−1soil h−1) (P= 0.07). Soil moisture was highest in NAT wetlands and lowest in RWOH (P= 0.01), but no differences were measured in SOC concentrations in three out of the four seasons sampled. Because RWOH wetlands exhibited denitrification potentials which were significantly lower than NAT wetland sites, these results demonstrate that a BLH wetland restored without the natural hydrologic regime reestablished will not be a replacement for a natural BLH wetland in terms of biogeochemical processes such as denitrification.
Particle‐Size Distributions
Authors: Shirazi Mostafa A. , Boersma Larry , Johnson Colleen Burch
Published: July 2010

Conventional soil texture classification systems use different definitions of particle‐size distributions (PSDs). For example, sand in the International Soil Science Society (ISSS) system equals the combined separate limits of coarse silt and sand in the USDA system. Because relationships between texture and other soil properties are affected by these differences, the ability to merge survey data in environmental studies is limited. Previous research calculated two PSD statistics, namely the geometric mean particle diameter (dg) and its standard deviation (σg), which do not depend on separate limits. We expanded the development of the PSD statistics dg and σg to compare the USDA and ISSS systems, develop relationships with soil properties, include rock fragments, and simplify the USDA texture classification to facilitate the use of soil survey data in environmental research. We found that (i) for equal clay and sand fractions, the texture of a soil sample as described by the USDA system has larger dg and σg values than in ISSS; (ii) for equal clay and sand fractions, soil samples have larger values of cation‐exchange capacity (CEC) in the ISSS than in the USDA system; (iii) small differences between some of the traditional 12 USDA classes are reflected in the dg and σg values for samples containing rocks, thereby presenting a rationale for simplification; and (iv) with this rationale, the 12 USDA classes were aggregated into five classes.
Water Ponding Depths Affect Temporal Infiltration Rates in a Water‐Repellent Sand
Authors: Feng G.L. , Letey J. , Wu L.
Published: July 2010

Water‐repellent soils exhibit a positive water entry pressure head, hp The effects of imposing differing water pressure head values, by using differing water ponding depths, h0, on infiltration into water‐repellent soils was investigated. A sand, with particulate size between 0.05 and 2.0 mm, was treated with two concentrations of octadecylamine to create a sand with hp values of 8.4 and 3.5 cm. The hydraulic conductivity, K, of the water‐repellent sands increased with increasing values of h0 The K of the treated sand was equal to K of untreated sand when the ratio h0/hp was ≈3.1 for each treated sand. The infiltration rate increased with increased time for lower h0 values, but decreased with increased time for higher h0 values. The transition from increasing to decreasing infiltration rates with time occurred when h0/hp was approximately equal to 2.6. The infiltration rate behavior of an aqueous ethanol solution was consistent with theoretical relationships based on liquid surface tension. A positive hydraulic head was created at the interface of an overlying wettable and underlying water‐repellent layer that affected the infiltration rate consistent with the effects of h0 on a nonlayered water‐repellent sand. The following mechanism is proposed to explain the increase in infiltration rate with time. In water‐repellent materials, positive hydraulic heads can be created within the profile during infiltration, which can increase as the depth to the wetting front increases. The higher hydraulic head induces an increase in hydraulic conductivity, which contributes to increased infiltration rate. Alternatively, if the depth of ponded water is sufficient to cause a hydraulic conductivity equal to that of the wettable material, the infiltration rate behavior is the same as traditionally observed for wettable soils.
Deep Banding Phosphorus and Potassium Fertilizers for Corn Managed with Ridge Tillage
Authors: Borges Rogerio , Mallarino Antonio P.
Published: July 2010

Broadcast fertilization leads to stratification of soil P and K in the ridge‐till system, which may reduce fertilizer use efficiency. This study evaluated the response of corn (Zea mays L.) to broadcast or deep‐band (15‐ to 20‐cm depth) placements in 15 site–years. Fertilization rates were 0 to 56 kg P ha−1 and 0 to 132 kg K ha−1 Soil‐test P (STP) and K (STK) were higher in the top 15‐cm layer of the ridges. Phosphorus increased early plant growth (V5 stage) in five sites, early P uptake in nine sites, and grain yield in seven sites. Yield was increased by P when STP was <22 mg P kg−1 (Bray‐1) in the top 15‐cm layer of ridges or <18 mg P kg−1 in the top 15 cm of ridges and valleys. The P placements seldom differed (the deep‐band P was better in one site). Potassium increased growth in 6 sites, K uptake in 14 sites, and grain yield in nine sites. The deep‐band K increased yield over the broadcast K in four sites. The yield response to broadcast K across sites was not correlated with STK, but the response to deep‐band K was negatively and linearly correlated with STK from various sampling positions. Corn responded to deep‐band K in soils with above‐optimum STK according to current soil‐test interpretations. The results showed that both placements usually were similarly effective for P, and that deep banding often was superior for K.
Simple
Authors: Dürr C. , Aubertot J.-N. , Richard G. , Dubrulle P. , Duval Y. , Boiffin J.
Published: July 2010

A model predicting seedling emergence is described and applied to sugarbeet (Beta vulgaris L.). The input variables are the soil surface texture, soil temperature, rainfall, aggregate size distribution and position in the seedbed, sowing depths, characteristics of the seeds (initial seed mass distribution, germination time, and hypocotyl elongation distributions). A three‐dimensional seedbed layer is created where the aggregates and seeds are placed. Soil water content is assumed not to limit sugarbeet emergence (sowing conditions in northern Europe). The time needed to reach the soil surface is calculated using germination thermal time, soil temperature, the presence or absence of aggregates, and the hypocotyl elongation function. The ability of seedlings to break through the soil surface is a function of crust development and moisture. The seedling growth after emergence is calculated with reference to seed mass distribution, emergence delay, and the presence or absence of mechanical obstacles. The emergence prediction was tested in field experiments with four seedbeds, from fine earth to cloddy structure, and a sowing depth of 17 to 35 mm. The predicted number and sizes of clods encountered by seedlings and the calculated hypocotyl length were not significantly different from measured ones. Predicted germination times were longer than the observed ones (differences <5°C d); final rates were well predicted. Predicted vs. measured final emergence rates differed by less than 10%; changes with time differed from 15 to 30°C. This was due to the hypocotyl elongation functions, which must be improved. Further improvements will be to predict soil water content variations and effects on emergence via water stress and soil strengthening.
Determination of Atmospheric Volume for Direct Field Measurement of Denitrification in Soil Cores
Authors: Horgan B.P. , Mulvaney R.L. , Branham B.E.
Published: July 2010

When denitrification is measured directly using 15N, the emission of labeled N2 and N2O is calculated from the volume of atmosphere confined within a closed chamber. This volume is readily estimated by measuring chamber height with a ruler; however, underestimation will occur with unsaturated soil because of air‐filled porosity. A much greater complication arises when plants are present, due to the volume occupied by the aboveground biomass and the internal volume available for gas exchange. A method was developed to measure atmospheric volume from dilution of a standard addition of Ne introduced prior to circulation of air within a closed‐chamber system. Ion‐current measurements to determine Ne, from which the volume was obtained by regression, were performed during mass spectrometric analysis for 15N‐labeled N2 Volume measurements by this method were accurate to within 3%, as compared with gravimetric measurements of air‐filled porosity for bare soil varying in moisture content. When introduction of Ne into a darkened chamber was delayed to ensure stomatal closure, volume measurements for a turfgrass system were accurate to within 2.5%, based on the difference obtained before and after connecting a mason jar to provide a known volume. A more accurate method of measuring atmospheric volume will improve the accuracy achieved in direct measurement of denitrification.
Nutrient Dynamics in Relation to Geomorphology of Riverine Wetlands
Authors: Johnston Carol A. , Bridgham Scott D. , Schubauer-Berigan Joseph P.
Published: July 2010

Variation in water depth and soil properties associated with geomorphic structures can affect riverine wetland nutrient dynamics by altering biogeochemical processes. We examined the seasonal influence of soils and geomorphology on nutrient forms and concentrations in riverine wetlands in northeastern Minnesota (silty soils) and northwestern Wisconsin (clayey soils). Soil, water, and plant biogeochemistry were contrasted between and within the wetlands according to geomorphic features (riverbed, levee, and backwater zones). There were few inter‐wetland differences, and most were the result of differences in river water chemistry and levee elevation between the two sites. Levees were hot spots of NO3–N, with spring porewater NO3–N concentrations (340 μg L−1at Fond du Lac, 44 μg L−1at Pokegama) that were orders of magnitude higher than elsewhere in the wetlands. Summer denitrification potential was high in the levees (≈6 nmol N2O g−1h−1) and in organic backwater zones (8.3 nmol N2O g−1h−1at Fond du Lac, 4.8 nmol N2O g−1h−1at Pokegama), but denitrification was consistently NO−3‐limited throughout both wetlands. Riverbeds were zones of highest P concentration in soil, vegetation, and summer surface water. Sedimentation rates were higher in riverbeds (289 g m−2d−1at Fond du Lac, 54 g m−2d−1at Pokegama) than in backwaters (80 g m−2d−1at Fond du Lac, 17 g m−2d−1at Pokegama). The two backwater zones had comparably low summer surface water concentrations of NO3–N (≈4 μg L−1), NH4–N (≈6 μg L−1), total P (TP) (≈80 μg L−1), total suspended solids (TSS) (≈6 mg L−1), and volatile suspended solids (VSS) (≈4 mg L−1). This seasonal convergence of surface water chemistry implies that biotic processes common to the two backwater areas override their substrate differences. Backwaters were hydrologically connected to the river mainstem via openings in discontinuous natural levees, but the different water chemistry of riverbed vs. backwater zones indicated minimal water exchange between them. This hydrologic zonation of riverine wetlands by geomorphic structures was the major source of intra‐wetland variability.
Bermudagrass Management in the Southern Piedmont USA
Authors: Franzluebbers A.J. , Stuedemann J.A. , Wilkinson S.R.
Published: July 2010

Improved forage management impacts on soil organic C and S depth distribution and surface residue accumulation could be large, but detailed temporal data are not available. We evaluated the factorial combination of three levels of N fertilization [inorganic, crimson clover (Trifolium incarnatum L.) cover crop plus inorganic, and broiler litter] and four levels of harvest strategy (unharvested, low grazing pressure, high grazing pressure, and hayed monthly) on soil bulk density, soil organic C, and total S, and surface residue C and S during the first 5 yr of ‘Coastal’ bermudagrass [Cynodon dactylon (L.) Pers.] management. Soil bulk density of the 0‐ to 6‐cm depth responded very little to management, but across treatments it decreased 0.06 Mg m−3 yr−1 due to increasing soil organic matter with time. Soil organic C did not respond significantly to fertilization strategy during the 5 yr, but total S of the 0‐ to 6‐cm depth was greater under broiler litter than under other fertilization strategies at the end of 3, 4, and 5 yr. Low and high grazing pressure were similar in their effect on soil organic C accumulation, averaging 140 g m−2 yr−1 Most of the net change in soil organic C occurred in the 0‐ to 2‐cm depth. Soil under unharvested and hayed management accumulated organic C at rates less than one‐half of those observed under cattle grazing. Cattle grazing shunted C more directly from forage to the soil, which contributed to greater sequestration of soil organic C than with haying or unharvested management.
Alkaline Fly Ash Effects on Boron Sorption and Desorption in Soils
Authors: Matsi T. , Keramidas V. Z.
Published: July 2010

Application of alkaline fly ash to soils is expected to result in an increase in B sorption capacity. If fly ash is B‐rich, B phytotoxicity might occur depending not only on B loads and magnitude of soil sorption capacity for B, but also on the strength of B retention by sorption surfaces of the fly ash amended soils. This strength determines the ease through which B releases into the soil solution. Aged‐alkaline fly ash was applied to one calcareous and two acid soils at rates equal to 0, 5, 20, and 50 g kg−1 of soil, and the impact of fly ash addition on B sorption in these soils was characterized, by means of the parameters (affinity and maximum) obtained through fitting B sorption data to the nonlinear Freundlich, Langmuir isotherms, and the phenomenological equation of Keren et al. Boron was added to the untreated and the fly ash‐treated soils, left in contact for 30 d, and its desorbability was studied. It was observed that although B sorption maximum of soils tended to increase upon fly ash addition, the affinity of B to sorption sites remained practically unaltered in most of the cases. Boron sorption was an exothermic reaction and the greatest part (more than 60%) of sorbed B in the fly ash‐treated soils could be easily desorbed within 24 h, reaching 80% for the acid soils and 100% for the calcareous soil after 120 h of desorption time. It was concluded that although there was a tendency of an increase in B sorption capacity in most cases upon fly ash addition, this increase was not generally accompanied by an increase in strength of B retention by soil surfaces. A major part of added B in the fly ash‐treated soils remained labile enough to be released in the soil solution in a short time.
Immobilization of Fertilizer Nitrogen in Rice
Authors: Bird Jeffrey A. , Horwath William R. , Eagle Alison J. , van Kessel Chris
Published: July 2010

A recent transition in rice straw management, from open‐field burning to soil incorporation in combination with winter‐fallow flooding, has led to uncertainty in evaluating long‐term N fertility. A 2‐yr field study of15N‐labeled fertilizer and crop residue was initiated in the fourth year of a rice straw management trial to examine the impacts of winter flooding and straw management on N fertilizer immobilization and crop uptake. After six seasons of residue incorporation and winter flooding, no effect on total soil C or N was observed. During the fifth and sixth year of the field study, microbial biomass C and N were greater for straw incorporation than for straw burned. Microbial biomass contained a sizable portion of soil‐recovered15N fertilizer after the first (23%) and second (10%) crop season of the15N study. The half‐life of the15N in the biomass ranged from 0.55 to 0.87 yr. One year after15N‐fertilizer application, greater recovery of15N in the soil from straw incorporation versus burning (22.2 versus 18.7%) resulted in a slight increase in residual fertilizer N recovery in grain in the second growing season of the15N study. Increased soil15N recovery 1 yr after fertilizer application in the straw incorporation treatment, however, was offset by higher grain recovery of15N in the burned treatment during the first growing season. Hence, the net result of these competing soil and plant sinks for fertilizer N led to similar15N losses after 2 yr (50.3 ± 2.2%) under burned and incorporated straw. The cumulative effects of straw incorporation resulted in greater net N mineralization, an increase in microbial biomass N, and greater recovery of15N in soil one year after application. Clearly, an active, labile N pool was formed when straw was incorporated that led to a reduction in fertilizer N dependency for rice.
Pedogenic Fractionation and Bioavailability of Uranium and Thorium in Naturally Radioactive Spodosols
Authors: Morton L. S. , Evans C. V. , Harbottle G. , Estes G. O.
Published: July 2010

Plant uptake of radionuclides into the human food chain is one of many vectors used for calculating exposure rates and performing risk assessment. This study provides a pedogenic assessment of soil–plant relationships in terms of their relationships to nuclide bioavailability. The objectives of this study were (i) to identify associations of U and Th with pedogenic fractions and with soil properties, and (ii) to evaluate U and Th bioavailability in terms of soil processes. We collected composite samples of leaves, stems, AE and Bs horizons from 10 plots containing a Spodosol with naturally high levels of 238U and 232Th. Additional replicate subsamples of fine (<63 μm) soil material were also extracted with citrate–bicarbonate–dithionite (CBD), ammonium oxalate (AO), sodium pyrophosphate (PP), and Mehlich reagent (M3). Concentrations of 238U and 232Th were determined for soils and plants by neutron activation analysis or by gamma spectroscopy. Results indicated that Th was translocated preferentially to plant leaves while U showed little preferential translocation. The CBD extractant removed the most U and Th from soils. The PP extraction ranked second for U, and AO ranked second for Th removal. The M3 extraction was equally inefficient in the removal of both U and Th. Neither Th, nor Th uptake, was closely associated with organic fractions. In contrast, U distribution and plant uptake of U were more closely correlated to organically bound oxide fractions.
Soil Salinity under Traditional and Improved Irrigation Schedules in Central Spain
Authors: Caballero R. , Bustos A. , Román R.
Published: July 2010

Traditional irrigation management in some semiarid zones waste water relative to crop evapotranspiration requirements. Improved irrigation schedules (irrigation depths were adjusted to seasonal crop consumption), however, may reduce deep percolation and fail to provide adequate leaching of salts. We hypothesized that salt discharge induced by rainfall may partially offset the need for a larger leaching fraction from irrigation water. The experiment was conducted near Madrid, Spain, on a sandy loam Typic Xerofluvent, between February 1993 and May 1997. The crop sequence was corn–wheat–corn–oat (Zea mays L.–Triticum aestivum L.–Z. mays L.–Avena sativa L.), and the irrigation treatments were applied only to corn. The salt concentration of the irrigation water was monitored 23 times in 24 plots and that of the soil solution at 0.5‐m, 0.9‐m, and 1.4‐m depths was monitored 61 times. Net salt losses (salt input through irrigation minus salt removed through drainage) were 1 and 0.64 kg m−2, respectively. In plots under the improved irrigation schedule, 88% of salt discharge occurred after periods of heavier‐than‐usual rainfall against 55% in traditionally irrigated plots. During the experiment, mean electrical conductivity (EC) of the soil solution in the top 0.5 m of soil was 0.61 ± 0.26 S m−1 in plots with the improved irrigation schedule. The corresponding estimate of the EC of the saturated paste extract was 0.34 S m−1, lower than the reported threshold value for corn (0.5 S m−1). These methods can therefore be recommended for semiarid areas where occasional heavy rainfall will remove some of the accumulated salt.
Water Budget Approach to Quantify Corn Grain Yields Under Variable Rooting Depths
Authors: Timlin D. J. , Pachepsky Y. , Snyder V. A. , Bryant R. B.
Published: July 2010

This study investigated the relationships between corn (Zea mays L.) grain yield and weather over a range of soil rooting depths with and without irrigation. The purpose was to test if variability of corn grain yield over a range of soil rooting depths could be reduced if water is supplied via irrigation. An additional goal was to test a simple water balance simulation model which calculates a seasonal moisture stress index based on relative evapotranspiration deficits. Such a water budget model could be used to estimate variations in corn grain yields as a function of spatial differences in soil depth and available water holding capacity in site specific agriculture. Corn grain yields were measured over a 3‐yr period from 70 plots at the Cornell University Robert Musgrave Research Farm at Aurora, NY, USA. Soil depths ranged from 0.2 to 1 m. During one year of the study, paired irrigated and non irrigated plots were placed at locations that had varying soil rooting depths. Irrigation resulted in significant increases in grain yield with the greatest response occurring on the soils with less than 0.5 m of rooting depth. Yields under irrigation were similar at all soil depths suggesting that, as soil depth decreased on these soils, water was the major limiting factor. The water budget model gave satisfactory estimates of grain yields as a function of soil depth and available water capacity and appears to be a useful tool to estimate corn grain yield as a function of soil depth and available water. The estimated potential yields can be used as a guide for site specific soil management given variations in available water holding capacity that affect potential soil productivity.
Measured and Modeled Unsaturated Hydraulic Conductivity of a Walla Walla Silt Loam
Authors: Chen C. , Payne W. A.
Published: July 2010

There are numerous methods of estimating unsaturated soil hydraulic conductivity [K(θ)], ranging from direct measurement in the laboratory or field, to models that use only basic soil data, e.g., texture or water release curves (WRC). We evaluated K(θ) for a Walla Walla silt loam (coarse‐silty, mixed, superactive, mesic Typic Haploxeroll) using two field methods and the Mualem–van Genuchten model (MVG). Field methods were the internal drainage method (ID) and the Klaij and Vachaud method (MKV), which was modified to include hydraulic head (H), and used 20 yr of data from a dryland field experiment. Four approaches to estimate WRC were compared for the MKV, and two approaches to estimate parameters of the MVG. For water contents >0.20 m3 m−3, the MKV gave K values that were two orders of magnitude less than those obtained from internal drainage experiments conducted under wetter conditions. When MVG parameters were predicted by the Rosetta model, which uses pedotransfer functions, K values approached those of the MVK. However, when model parameters were estimated from internal drainage and saturated hydraulic conductivity (Ksat) data, K(θ) values were closer to those of the internal drainage experiments. The study reaffirms the difficulty of reconciling K(θ) determined by different methodologies, and of extrapolating to values of θ outside those measured. It also demonstrates the sensitivity of the MVG and pedotransfer functions to different sources of input values. Advantages and disadvantages of the different approaches to determining K(θ) are discussed.
Nature of Clay–Humic Complexes in an Agricultural Soil
Authors: Laird David
Published: July 2010

The most stable forms of organic matter in soils are the clay–humic complexes. An understanding of mechanisms and processes influencing the formation of clay–humic complexes may facilitate development of agricultural management systems that increase the long‐term sequestration of C in soils and improve soil quality. The specific objective of this study was to visualize associations between humic substances and clay minerals separated from a typical agricultural soil. The soil sample used in this study was from the Ap horizon of a Webster (fine‐loamy, mixed, superactive, mesic Typic Endoaquoll) soil located near Waseca, MN. The whole soil clay fraction (<2 μm particle‐size fraction) was separated by a relatively mild sedimentation technique, and coarse, medium, and fine clay fractions (0.2–2.0, 0.02–0.2, and <0.02 μm size fractions, respectively) were separated from a portion of the whole clay sample by an aggressive sonication‐centrifugation technique. All samples were Ca‐saturated, dialyzed, and freeze‐dried. The samples were analyzed by scanning electron microscopy to obtain images of clay–humic complexes and energy dispersive x‐ray analysis to obtain maps of elemental distributions. Two distinct types of clay‐associated humic substances were identified. The first type exists as diffuse filamentous films that cover basal surfaces of 2:1 phyllosilicates in the medium and fine clay fractions. The second type exists as discrete particles of high‐density metal–humic substance complexes in the coarse clay fraction.
Temporal Erosion‐Induced Soil Degradation and Yield Loss
Authors: Sparovek Gerd , Schnug Ewald
Published: July 2010

Intensification of tropical agricultural systems by increasing fertilizer input and technology is a current trend in developing regions. Under intensive management, erosion impacts on crop productivity may not be detected in the short term. However, long‐term impacts are expected because erosion rates in tropical agroecosystems are usually greater than the rate of soil formation. A temporal function of soil‐depth change was defined and namedlife timeConceptually, soil's life time is the time until a minimum soil depth needed for sustaining crop production is reached. The life‐time function was applied to the Ceveiro watershed (1990 ha) located at the Southeastern part of Brazil, and compared with sugarcane (Saccharum officinarumL.) yield loss estimations. Soil erosion prediction was made employing the Water Erosion Prediction Project. The mean soil erosion rate for the area was 15 Mg ha−1yr−1, and sugarcane showed the highest mean value of 31 Mg ha−1yr−1The half life time of the watershed, i.e., the time until 50% of the area reach the minimum soil depth, was estimated to +563 yr in relation to present time. The estimated time for sugarcane's productivity to be reduced to 50% of the present value (half yield life time) was +361 yr. The life‐time function was similar to the estimated long‐term impacts of soil erosion on crop productivity. Therefore, the life‐time function was considered as an integrative indictor for agricultural sustainability, useful for land‐use planning and for the definition of tolerable soil erosion.
Organic Matter Dynamics and Carbon Sequestration Rates for a Tillage Chronosequence in a Brazilian Oxisol
Authors: de M. Sá João Carlos , Cerri Carlos C. , Dick Warren A. , Lal Rattan , Filho Solismar P. Venske , Piccolo Marisa C. , Feigl Brigitte E.
Published: July 2010

Amounts and rates of C sequestration under no‐tillage are not known for a major ecological region of south Brazil. These were assessed in a Brazilian Oxisol under a plow and no‐tillage chronosequence located in Paraná State. The chronosequence consisted of six treatments: (i) native field (NF); (ii) 1‐yr plow conversion of native field to cropland (PNF‐1); (iii) no‐tillage for 10 yr (NT‐10); (iv) no‐tillage for 20 yr (NT‐20); (v) no‐tillage for 22 yr (NT‐22); and (vi) conventional tillage for 22 yr (CT‐22). Soil samples were collected from five depths. No‐tillage, compared with the NF treatment, caused a significant increase in soil organic C (SOC) storage. More than 60% of this increase occurred in the 0‐ to 10‐cm soil layer. There was a decrease in the amount of SOC in the CT‐22 compared with the NF soil treatment and 97% of this loss also occurred in the 0‐ to 10‐cm layer. There was a close relationship between the SOC content and the amount of crop residues input (R2= 0.74,P≤ 0.05). There were increased SOC concentrations in the finer particle‐size fractions (<20 μm) of no‐tillage surface soil compared with the NF or CT‐22 soils. However, the percentage of SOC derived from crop residues in no‐tillage treatments, as assessed by 13C natural abundance (δ), was generally greater in the coarse (>20 μm) than in the finer (<20 μm) particle‐size fractions. The C sequestration rate for no‐tillage was 80.6 g C m−2yr−1for the 0‐ to 20‐cm depth and 99.4 g C m−2yr−1for the 0‐ to 40‐cm depth. The no‐tillage C sequestration potential for South Brazil was estimated as 9.37 Tg C yr−1
A Technique to Measure Fine‐dust Emission Potentials During Wind Erosion
Authors: Chandler David G. , Saxton K. E. , Kjelgaard J. , Busacca A. J.
Published: July 2010

Suspendable‐size soil particles are released during wind erosion and transported downwind, impacting regional air quality. Of particular concern are those particles with a mean aerodynamic diameter of <10 μm (PM10) and the finer subset of those <2.5 μm (PM2.5). To estimate the air quality impact of wind erosion, the potential release from nondispersed soil of PM10and PM2.5particles must be quantified for both those readily entrained existing particles and those generated by aggregate abrasion. A new laboratory technique was devised to determine the potential emission of these size particles by both processes from nondispersed soil samples. An emission cone in which the soil sample was suspended and rotationally abraded in an air stream was coupled with a standard measuring instrument for either PM10or PM2.5. Data of nondispersed soil samples compared with those dispersed showed significantly less emission potentials for the nondispersed. The PM2.5portion of the PM10values ranged from 30 to 55% indicating significant air quality impacts by wind erosion in this region based on either standard. Results from Washington State showed spatial patterns closely related to soil morphology, and a linear relationship between dispersed and self‐abrader PM10, but not PM2.5.
Simulation of Soil Carbon Dioxide Flux During Plant Residue Decomposition
Authors: Wang H. , Curtin D. , Jame Y. W. , McConkey B. G. , Zhou H. F.
Published: July 2010

Based on information obtained from recent studies, we modified the CENTURY model to improve simulation of short‐term soil respiration, especially in soils with surface‐applied crop residues. This involved adding N availability as a factor controlling the decomposition rate. Translocation by filamentous fungi was assumed to be the mechanism supplying mineral N to residues decomposing on the soil surface. When available N is nonlimiting, the N availability factor is 1, otherwise decomposition rates of all pools of soil surface and belowground organic matter are reduced proportionately until N supply meets demand. The modified model was evaluated using CO2 flux data from a laboratory experiment which included different wheat (Triticum aestivum L.) straw types (fresh and weathered straw), straw placements (incorporated and surface‐applied) and soil water regimes (continuously moist and alternating moist‐dry conditions). In general, CENTURY successfully simulated daily CO2 fluxes in these treatments, except for an underestimation in the first day after watering and an overestimation immediately after rewetting dry soil in the moist‐dry water regime. For treatments with surface‐applied straw, CENTURY overestimated soil respiration, while the modified version gave substantially better simulations. The correlation between measured and simulated total (in 77 d) respiration was improved by model modification. CENTURY underestimated the soil mineral N remaining in the soil at the end of the experiment. The modified model gave improved mineral N simulations for the surface straw treatments.
Nitrogen Dynamics of Decomposing Corn Residue Components Under Three Tillage Systems
Authors: Burgess M. S. , Mehuys G. R. , Madramootoo C. A.
Published: July 2010

Corn (Zea mays L.) residues returned after grain‐corn harvest are a heterogeneous mix of leaves, stems, husks, and cobs with a rather high overall C/N ratio. Considerable N immobilization has been reported from laboratory studies of decomposing corn residues, with less and variable N immobilization reported from field studies. The primary objectives of our study were to determine overall N dynamics for crop residues applied to land under corn grain production under three tillage systems in eastern Canadian conditions, and to see how constituent plant parts contribute to overall patterns of net N immobilization and release. Mesh litterbags (fiberglass screen) containing corn leaves, stems, cobs, or husks were buried or left on the soil surface in plots under no‐till, reduced tillage, or conventional tillage, and retrieved over a 2‐yr period. Residue N dynamics, including depth effects on residue N, differed greatly by residue type. Cobs, husks, and stems all immobilized N at some point. However, N immobilization was counterbalanced or exceeded by simultaneous N release from other residues, and no net N immobilization was observed for the residues overall (all types combined) for the sampling intervals included in our 2‐yr study. Nitrogen dynamics were related to ease of residue decomposition, in turn influenced by residue physical and chemical characteristics as well as by placement depth. Thus cobs immobilized little or no N at any given time because of their slow decomposition, despite very low initial N content. Estimated differences in residue N content between overall tillage systems were relatively small.
Characterization of Iron, Manganese, and Copper Synthetic Hydroxyapatites by Electron Paramagnetic Resonance Spectroscopy
Authors: Sutter B. , Wasowicz T. , Howard T. , Hossner L. R. , Ming D. W.
Published: July 2010

The incorporation of micronutrients (e.g., Fe, Mn, Cu) into synthetic hydroxyapatite (SHA) is proposed for slow release of these nutrients to crops in NASA's Advanced Life Support (ALS) program for long‐duration space missions. Separate Fe3+ (Fe‐SHA), Mn2+ (Mn‐SHA), and Cu2+ (Cu‐SHA) containing SHA materials were synthesized by a precipitation method. Electron paramagnetic resonance (EPR) spectroscopy was used to determine the location of Fe3+, Mn2+, and Cu2+ ions in the SHA structure and to identify other Fe3+‐, Mn2+‐, and Cu2+‐containing phases that formed during precipitation. The EPR parameters for Fe3+ (g = 4.20 and 8.93) and for Mn2+ (g = 2.01, A = 9.4 mT, D = 39.0 mT and E = 10.5 mT) indicated that Fe3+ and Mn2+ possessed rhombic ion crystal fields within the SHA structure. The Cu2+ EPR parameters (gz = 2.488, Az = 5.2 mT) indicated that Cu2+ was coordinated to more than six oxygens. The rhombic environments of Fe3+ and Mn2+ along with the unique Cu2+ environment suggested that these metals substituted for the 7 or 9 coordinate Ca2+ in SHA. The EPR analyses also detected poorly crystalline metal‐oxyhydroxides or metal‐phosphates associated with SHA. The Fe‐, Mn‐, and Cu‐SHA materials are potential slow release sources of Fe, Mn, and Cu for ALS and terrestrial cropping systems.