bluuebunny/crossref_metadata_2025 huggingface dataset:
Downscaling Monthly Forecasts to Simulate Impacts of Climate Change on Soil Erosion and Wheat Production
Authors: Zhang X.-C. , Nearing M. A. , Garbrecht J. D. , Steiner J. L.
Published: July 2010

Climate change can affect agricultural production and soil and water conservation. The potential for global climate changes to increase the risk of soil erosion is clear, but the actual damage is not. The objectives of this study were to develop a method for downscaling monthly climate forecasts to daily weather series using a climate generator (CLIGEN), and to determine the potential impacts of projected mean and variance changes in precipitation and temperature on soil erosion and wheat (Triticum Aestivum L.) yield. Monthly forecasts for the periods of 1950–1999 and 2056–2085 for the Oklahoma region, projected by a general circulation model (HadCM3), were used. Projected mean and variance changes in precipitation and temperatures between the two periods were satisfactorily incorporated into CLIGEN input parameters derived for the El Reno station, Oklahoma, and future transitional probabilities of precipitation occurrence were estimated as a linear function of historical monthly precipitation. Five climate change scenarios were constructed, and the Water Erosion Prediction Project (WEPP) model was run for each combination of five climate scenarios and three tillage systems. A 50% increase in CO2 resulted in some 26% increase in wheat yield. At that elevated CO2 level, projected decrease in total precipitation decreased surface runoff, soil loss, and wheat yield. However, predicted changes in precipitation variance increased runoff by 15 to 17%, and increased soil loss by 10 and 19% under conservation and conventional tillage, respectively. Predicted increase in mean temperature reduced wheat yield by 31%, and increased soil loss by 40 and 19% under conservation and conventional tillage, respectively. Under the assumed climate change, predicted average soil loss under conventional tillage was about 2.6 times that under conservation tillage and 29 times that under no‐till. With all changes considered, predicted average wheat yield during 2056–2085, compared with the present climate at the present CO2 level, would decrease by 12%; runoff would increase by <7%; and soil loss would increase by <8% in all tillage systems. Overall results indicate that adoption of conservation tillage and no‐till will be effective in controlling soil erosion under projected climate change used in this study.
State‐Space Modeling to Simplify Soil Phosphorus Fractionation
Authors: Shuai Xiufu , Yost Russell S.
Published: July 2010

Soil P can be fractionated by methods such as the Hedley extraction method to help identify and quantify soil P. Measuring the increases in soil P fractions from P fertilizer does not indicate whether external P can control a P fraction because of transfers among P fractions. Similarly, correlations between soil P fractions and plant P uptake do not directly indicate whether a P fraction affects plant P uptake. The objectives of this research were to describe the transformation among fractions, the effect of P fertilizer on P fractions, and the relationship between plant P uptake and P fractions by a state‐space modeling approach, and to minimize the dimension of the state‐space model by introducing concepts of controllability and observability and by implementing the General Decomposition Theorem. A P fraction was said to be controllable if its size can be controlled directly by the amount of external P fertilizer, or indirectly through transformations among P fractions. A P fraction was considered observable if it contributed to plant P uptake directly, or indirectly through transformations among P fractions. The jointly controllable and observable P fractions identified by the General Decomposition Theorem were minimum to describe the measured soil P dynamics in selected soil‐plant systems, while other fractions were redundant in the cases described. Results showed that only strip‐P, inorganic NaHCO3–Pi, organic NaHCO3–Po, and inorganic NaOH‐Pi of the seven fractions were necessary and sufficient to describe the P dynamics in example Mollisol, Vertisol, Ultisol, and Oxisol.
Diagnosis of Sulfur Deficiency in Soybean using Seeds
Authors: Hitsuda Kiyoko , Sfredo Gedi J. , Klepker Dirceu
Published: July 2010

The objectives of this study were to obtain a reliable index for the evaluation of the S nutrition status in soybean [Glycine Max (L.) Merr.] and to identify the critical S level in relation to seed yield and quality. Two Oxisols were used: A‐horizon soil from Serra dos Gerais, and A‐ and B‐horizon soils from Sambaiba in Maranhão State, Brazil. Soybean plants in pots were grown in a greenhouse with the supply of 0 to 80 mg S kg−1 soil. The seed S concentration was a more reliable index of seed yield because of the higher correlation between S concentration and yield. In the plants with visible symptoms of S deficiency, the seeds contained 1.5 g S kg−1, and the seed yield was 60% of the control. Electrophoresis analysis indicated that the critical seed S concentration for deficiency of protein components was 2.0 g kg−1 when the yield was 80% of the control. The S concentration was 2.3 g kg−1 or higher for >90% yield when the composition of the protein components was identical with that in the original seeds obtained under sufficient S fertilization. We classified the S concentration in the seeds as: deficient (S < 1.5 g kg−1), very low (1.5 ≤ S < 2.0 g kg−1), low (2.0 ≤ S < 2.3 g kg−1), and normal (2.3 g kg−1 ≤ S). Because of stable S concentration, easy sampling, and sufficient time for planning of fertilizer application for the subsequent cropping, seed analysis is preferable to leaf analysis.
Preferential Flow Revealed by Hydrologic Modeling Based on Predicted Hydraulic Properties
Authors: Gérard Frédéric , Tinsley Mark , Mayer K. Ulrich
Published: July 2010

Pedotransfer functions have shown a reasonable reliability and accuracy for predicting soil hydraulic properties. However, the contribution of the range of macroscopic features leading to preferential water flow is not readily taken into account. We modified and used the hydrological component of the reactive transport model MIN3P and the neural network‐based code ROSETTA in an attempt to simulate 4 yr of daily measurements of the soil water content in a forest soil covered by Douglas‐fir (Pseudotsuga menziessii Franco). A good fit of the mean measured water contents was obtained during periods of low soil moisture, while the model tended to overpredict water contents during periods of high soil moisture. This behavior is typical for the presence of significant preferential flow. Slightly better results were obtained by using predicted values of the saturated hydraulic conductivity, while the assumption of a water table located at shallow depth increased discrepancies. A good match was obtained by calibration of a simple preferential flow scheme, which was based on the assumption that the retention properties of the porous network control preferential flow. Accordingly, preferential flow seemed to initiate within the capillary pore domain. This causes a much greater sensitivity of the results to the position of the water table than with other schemes that consider pure gravity‐driven flow in large macropores. Knowledge of the functional pore size is needed to ascertain the type of preferential flow scheme to be used.
The Dielectric Permittivity of Calcite and Arid Zone Soils with Carbonate Minerals
Authors: Lebron I. , Robinson D. A. , Goldberg S. , Lesch S. M.
Published: July 2010

Measurement of soil dielectric properties, ε are widely used to estimate water content in soils from remote sensing and from in situ soil sensors such as time domain reflectometry (TDR). The mineral permittivity also plays an important role in geochemical dissolution and precipitation. Models used to estimate water content from soils often assume a value of 5 for the mineral permittivity εs However, calcite (CaCO3), a major constituent of some arid and semi‐arid soils, has a permittivity of 8 to 9, nearly twice the permittivity of quartz (εs = 4.6). We studied four soils, with micaceous mineralogy, but with two soils having approximately 40% calcite. We also measured the permittivity of Iceland Spar calcite (εs = 9.1) and a microcrystalline calcite (εs = 8.3), and use atomistic modeling to account for differences in permittivity based on the crystal density. We found permittivities for our soils to be in the range of 5.8 to 6.6, higher calcite contents resulting in increased permittivity. The estimated permittivity of the calcite in the soils was 7.4 to 7.9, lower than the highly crystalline samples. We estimate, for a soil with a porosity of 0.5 that assuming a permittivity of 5 instead of 6.6 will result in an overestimation of water content of about 1% at saturation. This demonstrates that a large quantity of pedogenic calcite (40%) in soil is unlikely to cause substantial error in the determination of water content using standard calibration equations. However, the lower dielectric permittivity predicted for pedogenic calcite may have consequences for the interpretation and understanding of geochemical processes.
A New Method for the Simultaneous Measurement of pH‐Dependent Cation Exchange Capacity and pH Buffering Capacity
Authors: Oorts K. , Vanlauwe B. , Pleysier J. , Merckx R.
Published: July 2010

The pH dependent cation exchange capacity (CEC) and pH buffering capacity (pH BC) are two crucial properties in soil fertility management of variable charge soils. However, they are rarely measured, since most of the existing methods are cumbersome and time‐consuming. We propose a new method, based on the silver‐thiourea (AgTU) method, for the simultaneous measurement of pH dependent CEC and the pH BC. In general, this method consists of first increasing the pH of the soil to about pH 7 and then gradually acidifying the soil by titrating with HNO3, while measuring pH and CEC after each equilibration. This way, both CEC at different pH values and the pH BC are measured on the same sample, without the multiple washing steps needed in other procedures. Various aspects of the proposed method were tested and the results obtained were compared with the ion adsorption method. The modified AgTU method obtains field relevant results and is suitable for the routine analysis of large numbers of samples.
Cation and Water Content Effects on Dipole Rotation Activation Energy of Smectites
Authors: Logsdon Sally , Laird David
Published: July 2010

In soil science, single frequency permittivity measurements are used to determine soil water content, and single frequency bulk electrical conductivity is used to determine soil salinity. The accuracy of these measurements may be influenced by complex interactions between frequency, temperature, and water that is tightly bound to clay surfaces. The purpose of this study is to determine the effect of temperature, saturating cation, water content, smectite properties, and frequency on electrical properties of humidified clays by analyzing three different activation energies for dipole rotations, which are calculated from the temperature dependence of electrical properties. Four reference smectites saturated with K, Na, Ca, and Mg and equilibrated at relative humidities ranging from 56 to 99% were investigated over a frequency range from 3 × 105 to 1 × 109 Hz. Two of the three activation energies were found to decrease slightly as water content increased. Higher activation energies were found for smectites saturated with Mg and K and lower values for smectites saturated with Na and Ca. Trends for type of clay were variable but appeared to be influenced by both the total water content and the distribution of water between the interlayers and the external surfaces of the smectite quasi‐crystals. Changes in quasi‐crystal orientation induced by thermal cycling were also found to influence the activation energies. The results indicate complex frequency and temperature dependent interactions impact electrical properties of the clays. We conclude that no simple equation will correct for temperature and clay content effects on single frequency measurements of permittivity or bulk electrical conductivity.
Carbon and Nitrogen Dynamics During Incubation of Manured Soil
Authors: Calderón Francisco J. , McCarty Gregory W. , Van Kessel Jo Ann S. , Reeves James B.
Published: July 2010

Denitrification N losses during manure net mineralizable N assays may lead to miscalculation of the manure's N‐supplying capacity. In this study we measured denitrification, manure properties, gas fluxes, nutrient pools, and mineralizable N during laboratory incubation of manured soil. Different dairy manures (n = 107) were added to soil at a rate of 0.1 mg N g−1 Manured and control soils were incubated and sampled weekly for soil mineral N, CO2 flux, and N2O flux. The denitrification enzyme activity (DEA) was measured at the end of the experiment. Weekly N2O and CO2 production increased in the manured soils during the first 3 wk of incubation. There was a positive correlation between added manure C and cumulative CO2 production. Nitrate content increased in all soils throughout the 6‐wk period, but the increase was more marked in the manured soils. In most manured soils, ammonium concentration was initially high then declined rapidly during the first 2 wk. This high net NH4+ decline in the manured soils suggests that N was immobilized during the incubation. Microbial biomass N should be determined during manure mineralization assays to account for all potential manure N sinks. No correlation existed between DEA and N pools or gas fluxes in the manured soils. Manures with negative N mineralization had an average C/N of 19.0, while manures with positive N mineralization had an average C/N of 16.0. On average, denitrification accounted for approximately 5% of the added manure N. Higher proportions of denitrified N were observed in some manures, supporting our hypothesis that N losses through denitrification may be significant in manure mineralizable N assays.
Inorganic and Organic Phosphorus Fertilizer Effects on the Phosphorus Fractionation in Wetland Rice Soils
Authors: Saleque M. A. , Naher U. A. , Islam A. , Pathan A. B. M. B. U. , Hossain A. T. M. S. , Meisner C. A.
Published: July 2010

Long‐term effects of rice (Oryza sativa L.) cultivation with varying nutrient management on soil P fraction are important to understand from soil nutritional and environmental point of view. Soil P fractionation gives an idea about the soil P supplying capacity to plants. The present experiment was conducted to evaluate the effect of different nutrient management in wetland rice on the changes of soil P fraction at different depths. Soil samples from five depths (0–5, 5–10, 10–15, 15–30, and 30–50 cm) were collected from a long‐term experimental field classified as a Chhiata clay loam, hyperthermic Vertic Endoaquept. The field received six treatments for 10 yr: absolute control with no fertilizer applied (T1), one‐third of recommended fertilizer doses (T2), two‐thirds of recommended fertilizer doses (T3), full doses of recommended fertilizers (T4), T2 + 5 Mg cow dung (CD) and 2.5 Mg ash ha−1 (T5), and T3 + 5 Mg CD and 2.5 Mg ash ha−1 (T6). The apparent balance of P compared with the initial P status after 10 yr varied from −115 kg ha−1 under T1 to 348 kg ha−1 under T6 The P fractionation study was conducted over the treatments and soil depth. Treatment and depth had no significant effect on solution P. Larger concentrations of NaHCO3 soluble P, NaOH extracted inorganic P (Pi), and acid P were observed under treatments with organic fertilizers (T5 and T6) than with other treatments at 0‐ to 5‐, 5‐ to 10‐, and 10‐ to 15‐cm depths. The concentrations of NaHCO3–P, NaOH‐Pi and acid P fractions were lowest under T1 and T2 treatments. At 15 to 30 cm or lower soil depths, none of the P fractions were affected by treatments. The change in NaOH organic P (Po) and residual P (extracted with HNO3 + HClO4) with soil depth was not significant, and the differences in these P fractions under the tested P treatments were not large. The depletion of NaHCO3–P and NaOH‐Pi at the 0‐ to 15‐cm depth under control and T2 suggests that the rice plant depends upon these fractions of P. The P depletion profile in wetland rice appears to be confined within the first 15‐cm depth. The mean P uptake by rice showed a polynomial relationship with NaHCO3–P and NaOH‐Pi (average of 0–15 cm) and it was linearly correlated with acid P (0–15 cm).
Phosphorus Dynamics in a Highly Weathered Soil as Revealed by Isotopic Labeling Techniques
Authors: Bünemann E. K. , Steinebrunner F. , Smithson P. C. , Frossard E. , Oberson A.
Published: July 2010

Isotopic labeling techniques have the potential to elucidate soil P dynamics and the fate of P sources added to the soil, but they have rarely been applied to highly weathered tropical soils. We collected soils from two crop rotations [continuous maize (COM; Zea mays L.) and maize‐crotalaria (MCF; Crotalaria grahamiana Wight & Arn.) fallow rotation] in a field experiment in Kenya and incubated them for 9 wk after addition of a plant residue or inorganic phosphorus (Pi), both labeled with 33P and added at 6 mg P kg−1 soil, or after carrier‐free labeling of isotopically exchangeable soil phosphorus (soil IEP). The amount of P and recovery of 33P were determined in resin‐extractable Pi (Presin), microbial P (Phex), and in a 0.1 M NaOH extract of samples from which Presin and Phex had been removed. The Presin increased after addition of Pi, while Phex increased after plant residue amendment, involving considerable microbial uptake of soil P. The recovery of 33P in Presin followed the order added Pi > soil IEP > plant residue, and decreased steadily from 7 to 22% after 1 d to 3 to 5% after 9 wk. The recovery of 33P in Phex remained constant throughout the incubation, being greater after plant residue amendment (15%) than in the other two treatments (4–7%). An additional 66 to 76% of 33P was recovered in the NaOH extract, as much as 27% of which was in organic phosphorus (Po) after plant residue amendment and 2 to 8% in the other two treatments. Similar to P dynamics after plant residue amendment, the comparison of the two rotations indicated a shift toward Phex and Po with increasing microbial activity due to previous fallow biomass incorporation.
Rapid Screening of Soil Properties using Thermogravimetry
Authors: Siewert Christian
Published: July 2010

Organic C, N, clay, and carbonate content are basic soil properties, which are commonly assessed by different analytical methods. This study aimed at utilizing temperature‐induced dynamics of weight losses to determine these parameters simultaneously without losing precision and accuracy. For this purpose, thermogravimetric profiles of 52 soil samples were recorded and compared with C, N, and textural data obtained from conventional analyses using dry combustion and pipette methods. The samples originated from different climatic regions, land‐use systems and parent materials. The results showed that thermal weight losses correlated closely (P< 0.001) with the content of organic C (R2= 0.98), total N (R2= 0.94), clay (R2= 0.87) and CO3–C (R2= 0.99) for mineral soil samples, while no such relationships were found in organic soil horizons. For mineral soils, each soil property correlated with a specific interval of temperature‐induced weight losses. Application of thermogravimetry to independent additional sets of 250 samples confirmed a reliable estimation of organic C, total N, clay and CO3–C of mineral soils. It is concluded that thermogravimetry allows a simultaneous, rapid and reliable screening of these four properties in mineral soils.
Using the Mehlich‐1 Extract to Estimate Soil Phosphorus Saturation for Environmental Risk Assessment
Authors: Beck M. A. , Zelazny L. W. , Daniels W. L. , Mullins G. L.
Published: July 2010

Methods for environmental risk assessment of P loss potential from soils lack uniformity and are generally difficult for routine analysis. Mehlich‐1 extractable P (M1‐P), an approach that is widely used to assess soil P status for plant growth, was used as a soil test P (STP) estimator of the degree of P saturation (DPS) of a soil. The concept of DPS integrates the dominant properties controlling the P sorption‐desorption status of soils. Soil samples from three physiographic regions of Virginia were analyzed for M1‐P and a wide range of other extractable P forms and selected chemical and physical soil properties. The DPS determined by ammonium oxalate (NH4–Ox) extractable P (Pox), Al (Alox), and Fe (Feox), ranged from 2 to 155%. Mehlich‐1 P, with a range of 1 to 1100 mg kg−1 was the most suitable single variable for estimating DPS. However, soil type and properties from the three physiographic regions were sufficiently different that regression models to estimate DPS based on M1‐P were significantly (P < 0.001) different between regions. Addition of other chemical or physical soil properties yielded insufficient improvements to the regression models over the strong relationships (r2 = 0.93, 0.98, and 0.75 for the Ridge & Valley, Piedmont, and Coastal Plain regions, respectively) between M1‐P and DPS. Interpretations/comparisons between studies are often limited by the numerous methods that are used to calculate DPS. We recommend DPS be determined as mmol kg−1 of NH4–Ox extractable P, Al and Fe and calculated as 100 (Pox) (Alox + Feox)−1
Carbon Sequestration in Microaggregates of No‐Tillage Soils with Different Clay Mineralogy
Authors: Denef Karolien , Six Johan , Merckx Roel , Paustian Keith
Published: July 2010

Identification of diagnostic soil organic matter (SOM) fractions and the mechanisms controlling their formation and turnover is critical for better understanding of C dynamics in soils. Enhanced microaggregate formation and stabilization of C due to reduced macroaggregate turnover has been proposed as a mechanism promoting C sequestration in no‐tillage (NT) compared with conventional tillage (CT) systems in temperate soils dominated by 2:1 clay mineralogy. We evaluated the contribution of macroaggregate‐protected microaggregates to total soil organic carbon (SOC) sequestration in NT relative to CT in three soils differing in clay mineralogy: a 2:1 clay‐dominated soil (2:1), a soil with mixed clay mineralogy [2:1 and 1:1] and oxides (mixed), and a soil dominated by (1:1) clay minerals and oxides (1:1). Microaggregates (mM) were isolated from macroaggregates from 0‐ to 5‐ and 5‐ to 20‐cm soil layers. Particulate organic matter (POM) located within the microaggregates (intra‐mM‐POM) was separated from POM outside of the microaggregates (inter‐mM‐POM) and the mineral fraction of the microaggregates (mineral‐mM). In all three soils, total SOC as well as microaggregate‐associated C (mM‐C) was greater with NT compared with CT. Although less than half of the total SOC under NT was associated with the microaggregate fraction, more than 90% of the total difference in SOC between NT and CT was explained by the difference in mM‐C in all three soils. Thus, we identified and isolated a fraction that explains almost the entire difference in total SOC between NT and CT across soils characterized by drastically different clay mineralogy.
Evaluation of Multispectral Data for Rapid Assessment of Wheat Straw Residue Cover
Authors: Sullivan D. G. , Shaw J. N. , Mask P. L. , Rickman D. , Guertal E. A. , Luvall J. , Wersinger J. M.
Published: July 2010

Crop residues influence near surface soil organic carbon (SOC) content, impact our ability to remotely assess soil properties, and play a role in global carbon budgets. Methods that measure crop residues are laborious, and largely inappropriate for field‐scale to regional estimates. The objective of this study was to evaluate high spectral resolution remote sensing (RS) data for rapid quantification of residue cover. In March 2000 and April 2001, residue plots (15 by 15 m) were established in the Coastal Plain and Appalachian Plateau physiographic regions of Alabama. Treatments consisted of five wheat (Triticum aestivum L.) straw cover rates (0, 10, 20, 50, and 80%) replicated three times. Spectral measurements were acquired monthly via a handheld spectroradiometer (350–1050 nm) and per availability via the Airborne Terrestrial Applications Sensor (ATLAS) (400–12500 nm). Overall, treatment separation was influenced by soil water content and percentage of total organic carbon (TOC) of the residue (degree of decomposition). Results showed that atmospherically corrected visible and near‐infrared ATLAS data can differentiate between residue coverages. Similar results were obtained with the handheld spectroradiometer, although treatment differentiation was less consistent. Thermal infrared ATLAS imagery best discriminated among residue treatments due to differing heat capacities between soil and residue. Results from our study suggest airborne thermal infrared (TIR) imagery can be used for crop residue variability assessment within the southeastern USA.
Carbon Storage in Coarse and Fine Fractions of Pacific Northwest Old‐Growth Forest Soils
Authors: Homann P. S. , Remillard S. M. , Harmon M. E. , Bormann B. T.
Published: July 2010

Many assessments of soil C have been restricted to the <2‐mm fraction, but C has recently been identified in >2‐mm fractions of forest mineral soils. Our objective was to determine the importance of the >2‐mm fraction to whole‐soil C pools in Pacific Northwest old‐growth coniferous forests. Seventy‐nine pedons in 18 western Washington and Oregon forests were sampled to a depth of 100 cm. The <2‐mm fraction was separated from the >2‐mm fraction by air‐drying, physically crushing soil, and sieving; C was determined by Leco combustion. The >2‐mm fraction contained up to 46% of the whole‐soil C and averaged 23% for the seven forests that had C in that fraction. Following treatment with sodium hexametaphosphate to disaggregate soil material, up to 20% of whole‐soil C remained in the >2‐mm fraction. Thus, the >2‐mm fraction C appears to be in stable and unstable aggregates, as well as concretions. The whole‐soil C in the surface 100 cm of mineral soil ranged from 30 to 400 Mg C ha−1 Multiple regression analysis indicated this C pool was positively related to available water capacity, annual precipitation, and coarse woody debris (r2 = 0.63 to 0.66, n = 18 forests). Similar results were obtained with only the <2‐mm soil C, which is the basis of previous regional evaluations. This suggests consideration of the >2‐mm fraction does not alter our understanding of the importance of climate and soil texture as controls of soil C pools, but it does affect the quantification of soil C pools in many old‐growth forests in the Pacific Northwest.
Amounts, Forms, and Solubility of Phosphorus in Soils Receiving Manure
Authors: Sharpley Andrew N. , McDowell Richard W. , Kleinman Peter J. A.
Published: July 2010

Continually land‐applying manure at rates exceeding crop removal can change soil P chemistry and increase soil P to levels that are of environmental concern. To assess the effect of long‐term manure application on soil P forms and solubilities, we determined water‐extractable P, Mehlich‐3 P, Hedley‐P fractions, and crystalline Ca‐P minerals in surface soil (0–5 cm) from 20 locations in New York (n = 6), Oklahoma (n = 8), and Pennsylvania (n = 6), which received dairy, poultry, or swine manure (40–200 kg ha−1 yr−1) for 10 to 25 yr. For all untreated and manured soils, the pH averaged 5.9 and 6.6; exchangeable Ca, 0.9 and 6.2 g kg−1; organic C, 15.7 and 32.6 g kg−1; and total P, 407 and 2480 mg kg−1, respectively. As Mehlich‐3 P increased (64–2822 mg kg−1), the proportion that was water extractable (14–3%) declined as exchangeable soil Ca increased (R2 = 0.81). Results suggest that addition of manure to soils shifts P from Al‐ and Fe‐ to Ca‐P reaction products, accounting for the relatively greater Mehlich‐3 but lower water extractability of soil P. This shift has implications to environmental soil P testing. For instance, the fact that Mehlich‐3 P has been shown to overestimate potential losses of P in overland flow from heavily manured soils may be explained by dissolution of Ca‐P minerals not soluble in water.
Agricultural Practices Influence Dissolved Nutrients Leaching through Intact Soil Cores
Authors: Jiao You , Hendershot William H. , Whalen Joann K.
Published: July 2010

Nitrogen and P leaching from agricultural land to ground water poses a threat to water quality, but it may be possible to control dissolved nutrient leaching by choosing appropriate management practices. The objective of this study was to evaluate the effects of agricultural practices on dissolved N and dissolved P leaching from topsoil to subsurface soil after crop harvest. Intact soil cores and small disturbed soil columns were collected from a factorial (tillage × crop × fertilizer source) field experiment, 3 yr after the treatments were established. Soils were leached with synthetic rainwater in the laboratory and nutrient loads (kg ha−1) were calculated. Dissolved N and dissolved P loads were not affected by tillage and were similar following corn (Zea mays L.) (in a continuous corn rotation) and soybean [Glycine Max (L.) Merr.] (in a soybean/corn rotation) production. Soils receiving inorganic fertilizer had a 70% greater nitrate (NO3–N) load and 48% less dissolved reactive P than soils receiving organic fertilizer, suggesting that fertilizing soils with a combination of inorganic and organic fertilizers might be a good way to reduce both NO3–N and dissolved reactive P transport to water systems. The NO3–N load increased as the soil NO3–N concentration increased (R2 = 0.36) while the dissolved reactive P load was positively related to the soil Mehlich‐3 P concentration (R2 = 0.50) and soil P saturation ratio (M3‐PSR) (R2 = 0.55). These results suggest that the leaching of dissolved N and dissolved P compounds is influenced more by the type of fertilizer applied than tillage or cropping practices.
Short‐term Response of Soil Iron to Nitrate Addition
Authors: Matocha C. J. , Coyne M. S.
Published: July 2010

The inhibition of soil Fe(III) reduction by fertilizer NO3− applications is complex and not completely understood. This inhibition is important to study because of the potential impact on soil physicochemical properties. We investigated the effect of adding NO3− to a moderately well‐drained agricultural soil (Sadler silt loam) under Fe(III)‐reducing (anoxic) conditions. Stirred‐batch experiments were conducted where NO3− was added (0.05 and 1 mM) to anoxic slurries and changes in dissolved Fe(II) and Fe(III), oxalate‐extractable Fe(II), and dissolved NO3− were monitored as a function of time. Addition of 1 mM NO3− inhibited Fe(II) production sharply with reaction time, from 10% after 1 h to 85% after 24 h. The duration of inhibition in Fe(II) production was closely related to the presence of available NO3−, suggesting preferential use of NO3− by nitrate reductase enzyme. Active nitrate reductase was confirmed by the fivefold decline in NO3− reduction rates in the presence of tungstate (WO42−), a well‐known inhibitor of nitrate reductase. In addition, NO3−–dependent Fe(II) oxidation was observed to contribute to the inhibition in Fe(II) production. This finding was attributed to a combination of chemical reoxidation of Fe(II) by NO2−– and NO3−–dependent Fe(II) oxidation by autotrophic bacteria. These two processes became more important at a greater initial oxalate‐Fe(II)/NO3− concentration ratio. The inhibitory effects in Fe(II) production were short‐term in the sense that once NO3− was depleted, Fe(II) production resumed. These results underscore the complexity of the coupled N–Fe redox system in soils.
Measurement of Hydraulic Characteristics of Porous Media Used to Grow Plants in Microgravity
Authors: Steinberg Susan L. , Poritz Darwin
Published: July 2010

Understanding the effect of gravity on hydraulic properties of plant growth medium is essential for growing plants in space. The suitability of existing models to simulate hydraulic properties of porous medium is uncertain due to limited understanding of fundamental mechanisms controlling water and air transport in microgravity. The objective of this research was to characterize saturated and unsaturated hydraulic conductivity (K) of two particle‐size distributions of baked ceramic aggregate using direct measurement techniques compatible with microgravity. Steady state (Method A) and instantaneous profile measurement (Method B) methods for K were used in a single experimental unit with horizontal flow through thin sections of porous medium providing an earth‐based analog to microgravity. Comparison between methods was conducted using a crossover experimental design compatible with limited resources of space flight. Satiated (natural saturation) K ranged from 0.09 to 0.12 cm s−1 and 0.5 to >1 cm s−1 for 0.25‐ to 1‐ and 1‐ to 2‐mm media, respectively. The K at the interaggregate/intraaggregate transition was ≈10−4 cm s−1 for both particle‐size distributions. Significant differences in log10K due to method and porous medium were less than one order of magnitude and were attributed to variability in air entrapment. The van Genuchten/Mualem parametric models provided an adequate prediction of K of the interaggregate pore space, using residual water content for that pore space. The instantaneous profile method covers the range of water contents relevant to plant growth using fewer resources than Method A, all advantages for space flight where mass, volume, and astronaut time are limited.
The Soil Physics Contributions of Edgar Buckingham
Authors: Nimmo John R. , Landa Edward R.
Published: July 2010

During 1902 to 1906 as a soil physicist at the USDA Bureau of Soils (BOS), Edgar Buckingham originated the concepts of matric potential, soil–water retention curves, specific water capacity, and unsaturated hydraulic conductivity (K) as a distinct property of a soil. He applied a formula equivalent to Darcy's law (though without specific mention of Darcy's work) to unsaturated flow. He also contributed significant research on quasi‐empirical formulas for K as a function of water content, water flow in capillary crevices and in thin films, and scaling. Buckingham's work on gas flow in soils produced paradigms that are consistent with our current understanding. His work on evaporation elucidated the concept of self‐mulching and produced sound and sometimes paradoxical generalizations concerning conditions that favor or retard evaporation. Largely overshadowing those achievements, however, is that he launched a theory, still accepted today, that could predict transient water content as a function of time and space. Recently discovered documents reveal some of the arguments Buckingham had with BOS officials, including the text of a two‐paragraph conclusion of his famous 1907 report on soil water, and the official letter documenting rejection of that text. Strained interpersonal relations motivated the departure of Buckingham and other brilliant physicists (N.E. Dorsey, F.H. King, and Lyman Briggs) from the BOS during 1903 to 1906. Given that Buckingham and his BOS colleagues had been rapidly developing the means of quantifying unsaturated flow, these strained relations probably slowed the advancement of unsaturated flow theory.
Short‐Term Competition for Ammonium and Nitrate in Tallgrass Prairie
Authors: Dell Curtis J. , Rice Charles W.
Published: July 2010

The availability of N limits productivity in tallgrass prairie. Spring burning is common because it results in greater plant productivity despite reducing net N mineralization. To better explain how burning affects inorganic N availability in tallgrass prairie, the partitioning of15N among plant and soil pools was measured in June and August 1994. Approximately 2.5 μg N g−1soil was injected as either NH4or NO3to a depth of 15 cm within cores in burned and unburned prairie. Cores were removed from the field 6 d after injection, and15N recovery in plant and soil N pools was determined. No more than 14% of the applied15N remained in inorganic form 6 d after application. The largest portion of the applied15N (35–80%) was recovered in the soil organic nitrogen pool (No). Burning significantly increased the immobilization of both NH4and NO3within No, and microbial biomass accounted for ≥50% of the15N recovered in NoAccumulation of15N in plants accounted for ≤35% of the applied15N with a majority recovered from roots. Burning had little effect on15N recovery in plants; however,15N accumulations in roots were significantly greater when NO3was used. Results indicate that immobilization within soil organic matter (SOM) controls the availability of both NH4and NO3to plants. Increased immobilization in soils with burning probably results largely from increased microbial N demand resulting from greater litter inputs with wider C to N ratios. Further research is needed to determine if abiotic mechanisms for N immobilization also significantly influence N availability in prairie soils.
Biochemical Properties of Decomposing Cotton and Corn Stem and Root Residues
Authors: Zibilske L. M. , Materon L. A.
Published: July 2010

Maintaining soil C is especially difficult in hot climates. Information is needed regarding the influence of residue biochemical properties on decomposition in hot, semiarid climates so that management practices can be developed that improve organic matter retention. Litterbags containing stalk or root tissues of senescent cotton (Gossypium hirsutum L.) or corn (Zea mays L.) were placed on the surface or 10 cm below the surface of a fallow Hidalgo sandy clay loam (fine‐loamy, mixed, hyperthermic Typic Calciustoll) near Weslaco, TX, USA (26°9′ N lat., 97°57′ W long.), and were monitored quarterly for 1 yr for changes in mass, water‐extractable C (WEC), water‐ and alcohol‐extractable polyphenolics (WEP and AEP, respectively). Surface‐placed cotton residues retained more mass than when buried, from approximately 80% (surface) to <50% (buried). For corn, retention ranged from approximately 60 to approximately 70% for surface residues to approximately 40% for buried residues. Most mass loss occurred within the first three months. The greatest increases in WEC (approximately 1500 μg C g−1 for corn; approximately 500 μg C g−1 for cotton) and WEP (approximately 175–325 μg g−1) for corn also occurred within the first 3 months. Water‐extractable polyphenolics peaked (about 100 μg g−1) in cotton residues at 6 mo, while corn residues reached a maximum (approximately 300 μg g−1) at 3 months. Over a year, AEP decreased in cotton stem residues, from approximately 5 to 8 to approximately 2 μg g−1 Surface cotton roots maintained approximately 6 μg g−1 after three months. Results illustrated the importance of residue moisture content during decomposition, and indicate that different residues may have different capacities to hold moisture, which may affect the biochemical characteristics and kinetics of decomposition.
Impact of Nitrogen Fertilization and Cropping System on Carbon Sequestration in Midwestern Mollisols
Authors: Russell A. E. , Laird D. A. , Parkin T. B. , Mallarino A. P.
Published: July 2010

Growing interest in the potential for agricultural soils to provide a sink for atmospheric C has prompted studies of effects of management on soil organic carbon (SOC) sequestration. We analyzed the impact on SOC of four N fertilization rates (0–270 kg N ha−1) and four cropping systems: continuous corn (CC) (Zea mays L.); corn–soybean [Glycine max (L.) Merr.] (CS); corn–corn–oat–alfalfa (oat, Avena sativa L.; alfalfa, Medicago sativa L.) (CCOA), and corn–oat–alfalfa–alfalfa (COAA). Soils were sampled in 2002, Years 23 and 48 of the experiments located in northeast and north‐central Iowa, respectively. The experiments were conducted using a replicated split‐plot design under conventional tillage. A native prairie was sampled to provide a reference (for one site only). Cropping systems that contained alfalfa had the highest SOC stocks, whereas the CS system generally had the lowest SOC stocks. Concentrations of SOC increased significantly between 1990 and 2002 in only two of the nine systems for which historical data were available, the fertilized CC and COAA systems at one site. Soil quality indices such as particulate organic carbon (POC) were influenced by cropping system, with CS < CC < CCOA. In the native prairie, SOC, POC, and resistant C concentrations were 2.8, 2.6, and 3.9 times, respectively, the highest values in cropped soil, indicating that cultivated soils had not recovered to precultivation conditions. Although corn yields increased with N additions, N fertilization increased SOC stocks only in the CC system at one site. Considering the C cost for N fertilizer production, N fertilization generally had a net negative effect on C sequestration.
Chemical Composition of Crop Biomass Impacts Its Decomposition
Authors: Johnson Jane M.-F. , Barbour Nancy W. , Weyers Sharon Lachnicht
Published: July 2010

Understanding the interaction between plant components and their subsequent decomposition provides insights on how plant quality differences may influence C sequestration within a given management system. Our hypothesis was that decomposition is a function of biochemical composition when all other variables are constant (e.g., particle size, temperature and moisture). Recognizing the challenges of reconciling laboratory and field studies, this study examined the decomposition dynamics of five selected crops with varying composition under controlled temperature and moisture regimes. Residue materials were partitioned into leaf, stem, and root organs to give a clearer indication of compositional control on decomposition. Plant quality varied among species (alfalfa [Medicago sativa L.], corn [Zea mays L.], cuphea [Cuphea viscosissima Jacq. · Cuphea lanceolata W.T. Aiton], soybean [Glycine max (L.) Merr.] and switchgrass [Panicum virgatum L.]). A two‐component litter decomposition model was used to describe decomposition observed during 498 d. Stepwise multivariate regression indicated initial N concentration, starch, total lignin, and acid‐insoluble ash (AI ash) were the four best predictors (r2 = 0.83) of the rate of active component decomposition (ka); however, initial composition poorly predicted the rate of passive decomposition (kp). The best four‐component model (r2 = 0.43) identified by stepwise multiple regression for kp included AI ash, hemicellulose, N concentration, and C/N ratio. Rate constants are a function of the incubation period, thus making direct comparison among separate experiments difficult. Chemical recalcitrance appears to slow root decomposition; such chemical recalcitrance to decay may partially explain why roots have been found to contribute more C to the SOC pool than surface residues.
Mapping Soil pH
Authors: Brouder S. M. , Hofmann B. S. , Morris D. K.
Published: July 2010

The theoretical profitability of variable rate (VR) lime management has driven adoption of intensive soil sampling strategies used with complex statistical techniques without demonstration of approach efficacy. Our objective was to compare the accuracy of spatially continuous pH and lime requirement (LR) maps derived from commercially used approaches to sampling and LR prediction at unsampled locations. We evaluated point (P) sampling on 0.1‐, 0.4‐, and 1.0‐ha grids and area composite (AC) sampling by 1‐ha grids, soil type (ST), and whole field (WF). Inverse distance (ID) weighting and ordinary kriging were applied to water pH and LR data from 11 fields. Modeling of semivariance identified range parameters of ≤100 m. For intensive P sampling (0.1‐ or 0.4‐ha grids), kriging was occasionally more accurate than ID weighting but mean absolute error (MAE) differences were small (≤0.01 pH units and ≤0.13 Mg lime ha−1), suggesting little practical consequence to prediction method selection. One‐hectare point data were too sparse to produce variograms and applying ID weighting to these data found only small advantages over WF compositing. Lime use was either unaltered or minimally reduced (10%) by 1‐ha P as compared with WF compositing. When compared with WF composites, map prediction efficiencies (PEs) based on mean square error (MSE) analysis ranged from 7 to 51, −13 to 40, and −6 to 54% for ST compositing, 1‐ and 0.4‐ha P sampling, respectively. These results suggest ST compositing remains viable and cost‐effect for pH management, especially where ancillary information exists to verify distinct soil series boundaries.
Soil Properties along Cultivation and Fallow Time Sequences on Vertisols in Northeastern Mexico
Authors: Bravo-Garza Maria R. , Bryan Rorke B.
Published: July 2010

Rain‐fed agriculture in alternation with natural fallow is widespread in semiarid northeastern Mexico, but little information on changes in soil properties, soil degradation, and natural rehabilitation is available. The effects of rain‐fed agriculture and fallow on soil quality indicators on vertisols in a semiarid area near Linares, Nuevo León, were studied. One cultivated time sequence representing 3 to 30 yr of use and one fallow time sequence of 2 to 22 yr were selected. Fifty percent of soil organic carbon (SOC) and 56% of total nitrogen (TN) were lost during the first 4 yr of cultivation, but loss reached approximate equilibrium after 6 yr. The SOC showed 34% recovery and TN showed 62% recovery on sites abandoned for 22 yr. Despite this recovery after 22 yr of fallow, SOC and TN levels reached only 50% of those observed under native vegetation. Water‐stable macroaggregation declined by 14% under cultivation, but increased swiftly during fallow, showing no significant correlation with SOC. The levels of SOC and TN depletion under conventional rain‐fed agriculture observed are very difficult to mitigate by natural fallows in economically‐viable time periods. However, the precise impact of these changes on aggregation properties of these vertisols and the long‐term sustainability of present cultivation–fallow practices is not clear. Further research to determine the precise influence of individual soil organic constituents on physical properties of these vertisols is in progress.
Digitally Mapping Gypsic and Natric Soil Areas Using Landsat ETM Data
Authors: Nield S. J. , Boettinger J. L. , Ramsey R. D.
Published: July 2010

Mapping salt‐affected soils in remote rangelands is challenging. We used Landsat 7 ETM data to facilitate digital mapping of gypsic and natric soil areas in the upper Colorado River drainage. Optimum index factor band combinations were used to explore the scene. Normalized difference ratio models and threshold values were developed by comparing spectral signatures with gypsic and natric soil areas verified in the field. Gypsic soil areas were mapped using the normalized difference ratio of Bands 5 and 7 with a threshold >0.11, probably related to the spectral reflectance of gypsum within a few centimeters of the surface. All sites predicted to be gypsic soil areas were determined to be gypsic by field assessment, and 87% of the field‐observed gypsic soil areas were correctly predicted. Natric soil areas were mapped using the normalized difference ratio of Bands 5 and 4 with a threshold >0.19, possibly related to the co‐occurrence of Fe‐bearing minerals with natric soil areas. Most of the sites predicted to be natric were determined in the field to be natric (82%), but only half of the field‐observed natric areas were correctly predicted, indicating that natric soils are harder to detect spectrally than gypsic soils. While the gypsic model may be transferred to other areas, particularly in the arid Colorado Plateau, transfer of natric models would be difficult. Normalized difference ratio models can be developed for other digital soil mapping areas where land surface features produce differences in Landsat spectral band reflectances.