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Since information islimited regarding N management and tillage options for corn (Zea mays L.) grown on claypan soil in the eastern Great Plains, the objective of this study was to determine the effect of preplant and side‐dress N applications on corn grown in conventional‐ and no‐till systems. The yield penalty for no‐till grown corn was nearly 20% due partially to an 8% stand reduction, but also to lower kernel weight and kernels ear–1 than with conventional till. These yield and yield component reductions with no‐till may be because of lower dry matter production and N uptake throughout the growing season. The general lack of interactions suggest that N management system effects on corn were not influenced by tillage system selection. Fertilizing with N more than doubled corn yields primarily by nearly doubling the number of kernels ear–1, but with additional increases in kernel weight and average number of ears plant–1. Averaged over years, split‐N resulted in up to 15% greater yield, and additional side‐dress N resulted in up to 28% greater yield than when 168 kg N ha–1 was applied only at preplant, with no yield reduction for delaying side‐dress application from V6 to V10. The relationship of relative N uptake to relative corn yield approached a direct 1:1 relationship by R1 (silking). The decision of whether to split‐apply fertilizer N or to add additional N, regardless of tillage system, will likely be influenced by economic factors, but side‐dress N applications may extended to the V10 stage with no yield penalty. Core Ideas: Corn yield penalty was near 20% with no‐till compared with conventional till.Side‐dress N, as split or additional, resulted in greater corn yield than all N preplant.Corn dry matter and N uptake were greater with conventional till than with no‐till.Side‐dress N management resulted in few differences in dry matter and N uptake.Increasing N uptake increased yield primarily by increasing kernels ear−1. [ABSTRACT FROM AUTHOR]

Quantitative next-generation sequencing techniques have been critical in gaining a better understanding of microbial ecosystems. In soils, denitrifying microorganisms are responsible for dinitrogen (N 2) production. The nosZ gene codes for nitrous oxide reductase, the enzyme facilitating the reduction of nitrous oxide (N 2 O) to N 2. The objectives of this research were to: 1) understand how soil depth influences RNA concentration and nosZ gene abundance; 2) assess the spatial dependence of nosZ gene abundance in two claypan soil fields; and 3) compare and evaluate multiple RNA-based sequencing methods for quantifying nosZ gene abundance in soils in relation to dinitrogen (N 2) production. Research sites consisted of two intensively studied claypan soil fields in Central Missouri, USA. Soil cores were collected from two landscape transects across both fields and analyzed for extractable soil RNA at two depths (0–15 cm and 15–30 cm). Measurements of nosZ gene abundance were obtained using real-time quantitative polymerase chain reaction (RT-qPCR), droplet digital polymerase chain reaction (ddPCR), and nanostring sequencing (NS). In both fields, soil RNA concentrations were significantly greater at 0–15 cm depth compared to 15–30 cm. These data indicated low overall soil microbial activity below 15 cm. Due to low quantities of extractable soil RNA in the subsoil, nosZ gene abundance was only determined in the 0–15 cm depth. Sequencing method comparisons of average nosZ gene abundance showed that NS results were constrained to a narrow range and were 10-20-fold lower than ddPCR and RT-qPCR at each landscape position within each field. Droplet digital PCR appears to be the most promising method, as it reflected changes in N 2 production across landscape position. • Soil RNA concentration significantly decreased with depth. • Measurements of the nosZ gene significantly differed between RT-qPCR and ddPCR, and NS. • RT-qPCR and ddPCR appear to be promising methods for nosZ gene estimation from soil samples. • Neither RT-qPCR, ddPCR, or NS measurements of the nosZ gene significantly correlated with N 2 flux. [ABSTRACT FROM AUTHOR]

Core Ideas: Seasonal corn N uptake was greater with ridge‐till than with no‐till.Increasing N fertilizer rate generally increased N uptake.Nitrogen uptake at R4 was greater with banded applications than broadcast in no‐till.Increasing N uptake increased yield, primarily by increasing kernels per ear. Information on N management is limited regarding N uptake and recovery by corn (Zea mays L.) grown on claypan soils in the eastern Great Plains, especially in conservation tillage systems. The objective of this study was to examine the effect of fertilizer N rate (0, 34, 67, 101, and 134 kg ha‐1) applied by surface broadcast, surface band (dribble), and subsurface band (knife) placement methods on N uptake by corn grown in no‐till and ridge‐till systems on a claypan soil. Ridge‐till consistently increased corn N uptake compared with no‐till by 53% early to 20% later during the growing season. Maximum N uptake rate was earlier in the season and greater with ridge‐till than with no‐till, perhaps helping to contribute to increased corn yields. Early in the season, corn N uptake was increased with low N fertilization rates, but not at higher rates. However, as the season progressed, N uptake increased with all rates. Even though the effect of N fertilizer placement on corn N uptake was not consistent during the entire season, by the R4 growth stage, placement did not affect N uptake in ridge‐till but was nearly 20% greater with banded (dribble and knife) applications than with broadcasting in no‐till. At low N rates, knife placement increased N uptake at R4, likely because of improved apparent N recovery, but was unaffected by placement at greater N rates. Improving total N uptake increased relative yield primarily by increasing kernels per ear, with lesser effects due to kernel weight and ears per plant. [ABSTRACT FROM AUTHOR]

Microbial activity within the soil is critical for plant growth and development, and a major determinant of crop performance and yield. Claypan soils are characterized by a dense, impermeable subsoil that impedes root system development. Little is known about soil microbial properties in claypan soils or how microbial activity changes with depth in the soil profile. We explored how management practices mediate changes in soil microbial composition and potential enzyme activities with depth in a claypan soil. The soil microbial biomass and composition were examined through phospholipid fatty acid (PLFA) assay. We found that the soil organic carbon (SOC), microbial biomass, and oxidative enzyme activities declined with depth, while hydrolase activity increased in the upper layer of the claypan. Changes in soil management practices affected the degree of increase in hydrolase activity in subsoils, especially for N-acetyl-β- d -glucosaminidase. No accumulation of SOC in the claypan layer was observed. Contrary to our expectation, soil microbes deeper within the soil profile were phosphorus- and nitrogen-limited rather than carbon-limited. Vertical stratification of measured soil properties was found with an upper layer from 0 to 15 cm, an intermediate layer between 15 cm and approximately 30 cm, and the lowest layer of soils in the claypan below 30 cm. The interaction between clay content and changes in soil factors with depth resulted in an increased potential activity but unaltered microbial composition in the claypan layer. [ABSTRACT FROM AUTHOR]

The effectiveness of vegetative buffer strips ( VBS) for reducing herbicide transport has not been well documented for runoff prone soils. A multi-year plot-scale study was conducted on an eroded claypan soil with the following objectives: (1) assess the effects of buffer width, vegetation, and season on runoff transport of atrazine ( ATR), metolachlor ( MET), and glyphosate; (2) develop VBS design criteria for herbicides; and (3) compare differences in soil quality among vegetation treatments. Rainfall simulation was used to create uniform antecedent soil water content and to generate runoff. Vegetation treatment and buffer width impacted herbicide loads much more than season. Grass treatments reduced herbicide loads by 19-28% and sediment loads by 67% compared to the control. Grass treatments increased retention of dissolved-phase herbicides by both infiltration and adsorption, but adsorption accounted for the greatest proportion of retained herbicide load. This latter finding indicated VBS can be effective on poorly drained soils or when the source to buffer area ratio is high. Grass treatments modestly improved surface soil quality 8-13 years after establishment, with significant increases in organic C, total N, and ATR and MET sorption compared to continuously tilled control. Herbicide loads as a function of buffer width were well described by first-order decay models which indicated VBS can provide significant load reductions under anticipated field conditions. [ABSTRACT FROM AUTHOR]

Switchgrass ( Panicum virgatum L.) is an attractive bioenergy crop option for eroded portions of claypan landscapes where grain crop production is marginally profitable. Topsoil thickness above the claypan, or depth to claypan (DTC), can vary widely within fields, and little information exists on its impacts on N management of switchgrass. Therefore, a study was conducted at the University of Missouri South Farm near Columbia, Missouri, to determine whether topsoil thickness influenced fertilizer N requirements of switchgrass. Switchgrass was planted in 2009 on main plots with a range of DTC classified as exposed (<8 cm), shallow (8-15 cm), moderate (16-30 cm), and deep (>30 cm) and was harvested annually at postdormancy during 2011 to 2015. Three split-plot treatments were 0, 67, or 101 kg N ha applied annually in May, and a fourth was three intercropped native legumes as the N source. Across years, the legume treatment apparently supplied no N because it produced the same or less switchgrass yield than the nonfertilized treatment. Topsoil proved valuable as switchgrass yield, nutrient removal, and profit usually increased as DTC increased. Fertilization with 101 kg N ha on exposed, shallow, or moderate DTC and 67 kg N ha on deep DTC was required to obtain the highest biomass yield, but it also increased nutrient removal. Strikingly, profit across years was negative for the legume treatment and highest with no fertilizer on all DTC classes. Therefore, improvements are needed before intercropped legumes are profitable, and N fertilization may be needed only periodically to maximize switchgrass profit on claypan soils. [ABSTRACT FROM AUTHOR]

Organic crop production is dependent on tillage for weed control, but because tillage can lead to decreased levels of soil organic carbon (SOC) alternative management needs to be explored. This study was conducted in Boone County, Missouri, in 2012 to 2014 to determine the effects of three organic production systems and four poultry compost rates on crop yield and SOC on a claypan soil. The production systems included tillage wiThno cover crop, tillage wiTha mowed and incorporated cover crop, and no-till wiTha crimped cover crop in a wheat (Triticum aestivum L.)-corn (Zea mays L.)-soybean (Glycine max L.) rotation. Cover crops included cereal rye (Secale cereale L) and hairy vetch (Vicia villosa L.). Compost rates were 0, half the recommended rate, the recommended rate, and 1.5 times the recommended rate. Achieving cover crop biomass sufficient for weed suppression was a challenge when soil fertility declined during the study. Corn yield was reduced 30% in 2013 in no-till plots compared to tilled although plant populations were nearly equal, indicating that N immobilization may be significant in crimped cover crops. When there was adequate soil moisture and weed control from the cover crop, soybean grown under organic no-till was competitive wiThtilled treatments. Optimum timing of cover crop crimping for acceptable weed control was more successful in a soybean system compared wiThcorn. Organic no-till in this study was more successful in soybean and wheat than in corn, when the cover crop biomass was sufficient to suppress weeds. [ABSTRACT FROM AUTHOR]

Conversion of annual grain crop systems to biofuel production systems can restore soil hydrologic function; however, information on these effects is limited. Hence, the objective of this study was to evaluate the influence of topsoil thickness on water infiltration in claypan soils for grain and switchgrass ( Panicum virgatum L.) production systems. The experiment was performed at the University of Missouri South Farm (38°54′N, 92°16′W) on a Mexico silt loam (Vertic Luvisols) soil. Since 2009, plots were planted with either switchgrass or a corn ( Zea mays L.)-soybean (Glycine max (L.) Merr.) rotation. Infiltration rates were measured using ponded infiltrometers during two years (2014 and 2015) under switchgrass and grain crop management each with two levels of topsoil thickness (0 and 37.5 cm). Physically-based Parlange and Green-Ampt infiltration models were used to estimate saturated hydraulic conductivity ( K s ) and sorptivity ( S ) parameters. Switchgrass planted on degraded soil (shallow topsoil treatment) resulted in greater K s , S , q s (quasi-steady infiltration rate) and K fs (field-saturated hydraulic conductivity) values than with row crop management for both 2014 and 2015 measurement years. Results for selected 24-hour mean frequency (11.8, 14.2, and 16.2 cm) storms showed that switchgrass production systems enhanced estimated water infiltration, reduced estimated runoff, and decreased estimated time from water ponding to end of ponding compared with row crop management. Switchgrass is recommended to be planted on degraded soils especially in claypan landscapes for improved water use. [ABSTRACT FROM AUTHOR]

Assessment studies of conservation efforts have shown that best management practices were not always implemented in the most vulnerable areas where they are most needed. While complex computer simulation models can be used to identify these areas, resources needed for using such models are beyond reach for most water resources managers. Soil and water conservationists need simple, spatially explicit tools such as the USDA-NRCS's Soil Vulnerability Index (SVI) to evaluate the inherent vulnerability of soils and the risk they pose to water quality when used for row crop agriculture. In this study, the SVI was evaluated in the Goodwater Creek Experimental Watershed (GCEW), a claypan watershed in Missouri, using three methods: professional judgment, comparison to the Conductivity Claypan Index (CCI) developed specifically for claypan soils, and comparison to model results. Factors affecting the critical areas identified by each method were assessed and classified areas were compared. Slope and depth to claypan had the most variability in GCEW and were found to be influential in determining area classification by each index. While the original definition of SVI included the soil type representative slope from the USDA SSURGO database, slope values provided by a Digital Elevation Model (DEM) improved the index usefulness by classifying visibly degraded and non-degraded areas in different categories. High and moderately high vulnerability areas identified with SVI, CCI and model results with DEM slopes were consistent and matched professional judgment. Additional testing of SVI is recommended in areas characterized by soils of different permeability and under different climates. [ABSTRACT FROM AUTHOR]

Prairie restoration has received increased public attention in recent years for its ecosystem services. The objective of this study was to evaluate effects of prairie restoration on soil hydraulic properties as compared to native prairie (NP), grass and row-crop management. Soil cores (76 mm diam. × 76 mm long) from six replicate locations were sampled to a 60-cm depth at 10-cm intervals from two prairie treatments, a continuous no-till treatment (NT), a long-term timothy grass ( Phleum pratense L.) treatment (TM) and a row-crop (RC) treatment. The NP has never been tilled and the restored prairie (RP) was established in 1993. All treatments have Mexico silt loam (fine, smectitic, mesic, Vertic Epiaqualfs) soil. Bulk density, saturated hydraulic conductivity (K sat ), soil water retention and pore size distribution were determined. In-situ K sat was measured using a constant head permeameter with five replications. Bulk density was significantly lower for NP than all treatments. Bulk density was significantly lower for the 0 to 10 cm depth for all treatments, and the 10 to 30 cm depth recorded the highest values. The in-situ K sat of RP was lower than other treatments. The first horizon had the highest value for this parameter for all treatments. NP had significantly higher laboratory measured K sat , and it was almost four times higher than RP. The 0 to 10 cm depth of all treatments had significantly higher values for laboratory K sat than other depths and the 50 to 60 cm showed the lowest K sat . NP had the highest macroporosity and fine-mesoporosity, while RP had the highest microporosity. NP had significantly higher water retention at saturation while RP had the highest water retention for soil water pressures of − 33 kPa, − 100 kPa and − 1500 kPa. Soil water retention was significantly higher in NP for − 0.4 kPa to − 10 kPa soil water pressures; at − 20 kPa NP, RP and RC had significantly higher water retention. The NP treatment had higher soil water content than the other treatments for the 0 to 10 cm, 10 to 20 cm, 20 to 30 cm and 50 to 60 cm depths at soil water pressure of − 20 kPa. The 30 to 40 cm and 40 to 50 cm depths of RP had higher soil water content at all soil water pressures. Results imply that prairie restoration influences some hydraulic properties in claypan soils; however, it is unlikely to achieve the original prairie soil characteristics due to the prior erosion of the top soil. [ABSTRACT FROM AUTHOR]

Thousands of eroded-soil hectares in the U.S. Midwest have been planted to Miscanthus × giganteus as an industrial or bioenergy crop in recent years, but few studies on factors affecting crop establishment have been performed on these soils. The objective of this study was to quantify how both rhizome quality and depth of soil from the surface to the first argillic horizon (or depth to claypan (DTC 1 1 DTC—depth to claypan or argillic horizon. )) affected M. × giganteus establishment. Rhizome quality (i.e., mass, length, diameter, viable buds, score), emergence, growth, and winter survival were measured on rhizomes planted in 2013 at Columbia and 2014 at Centralia, Missouri on clay loam soils with a range of DTC. Rhizome emergence and early tillering slightly increased as DTC increased, but these effects on growth diminished as the season progressed. Rhizome emergence and growth were more influenced by some metrics of rhizome quality; the odds of a rhizome emerging increased by 25 and 40% with each 1 cm and 1 bud increase in rhizome length and active bud count, respectively. Furthermore, late tiller counts, basal circumference, and end-of-season biomass increased as rhizome length and mass increased. Winter survival could not be estimated as well as emergence, but the odds of survival across sites increased by 5% with each 1 cm increase in rhizome length. When DTC was categorized as soil erosion class or landscape position, only the backslope at Centralia caused greater M. × giganteus growth than other positions. These findings demonstrate the resiliency of M. × giganteus for early growth and establishment on even the most degraded parts of the claypan soil landscape and indicate that propagating larger rhizomes will improve establishment. [ABSTRACT FROM AUTHOR]

In this study, unconsolidated-undrained (UU) shear strengths of a clayey soil that is subject to saturation separately by using vacuum saturation method and falling head method were investigated. In the study, a soil with CL class according to Unified Soil Classification System was used. The soil samples prepared by being compacted in a rigid-wall permeameter mechanism were subject to a saturation process for periods varying from 1 week to 4 weeks. In the saturation by using falling head method, maximum 4m hydraulic load was applied to the samples. In saturation by using vacuum method, minimum - 70 kPa vacuum was used. After the saturation process, the samples were subject to UU type triaxial tests. Depending on the saturation method and duration, a decrease of approximately 2 - 3 times was observed in UU shear strength parameters (cu and Φu) of the samples, which are subject to the saturation process, compared to the unsaturated samples. In the samples compacted with Standard Proctor Energy (SPE), strength parameters obtained under vacuum for one week were lower compared to samples saturated for 4 weeks by using the method of saturation by gravity. In the samples compacted with Modified Proctor Energy (MPE), vacuum method did not give a successful result. [ABSTRACT FROM AUTHOR]

Previous studies have shown that once compacted, forest soils often recover slowly over many decades to pre-disturbed levels for soil properties such as bulk density or penetrometer resistance. This study was conducted to evaluate the effects of selected harvesting techniques on soil physical and hydraulic properties. The effects of logging roads, log landing areas, and logged areas on soil properties of water retention, saturated hydraulic conductivity (K Sat ), pore-size distributions, and bulk density were investigated on harvested sites within the Mark Twain National Forest in Callaway County, Missouri, USA on claypan landscape with a moderately well-drained Keswick soil (fine, smectitic, mesic Aquertic Chromic Hapludalfs). Soil cores (7.6 cm by 7.6 cm) were removed in four 10-cm depth increments. Bulk density was significantly greater (P < 0.01), and K Sat was significantly lower (P < 0.01) under the logging road and log landing areas as compared to the logged area treatment. No statistical differences in bulk density and K Sat values occurred among treatments at the deepest sampling depth (30 to 40 cm). For the 0 and − 0.4 kPa soil water pressures, water retention was 14% greater and 9% greater for the logged areas versus the logging road and log landing areas averaged across all soil depths, respectively. For the macropores (> 1000 μm diameter) and coarse mesopores (60 to 1000 μm diameter) combined, values were 131% greater for the logged area compared to logging road and log landing areas within the 0 to 10 cm depth. From this study, the methods used in the logged area appear to have caused small changes to soil physical and hydraulic properties; however, significant changes to these properties occurred for logging road and the log landing areas. [ABSTRACT FROM AUTHOR]

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Sustainable grain crop production on vulnerable claypan soils requires improved knowledge of long-term impacts of conservation cropping systems (CS). Therefore, effects of CS and landscape positions (LP) on corn (Zea mays L.), soybean [Glycine max (L.) Merr.], and wheat (Triticum aestivum L.) production were evaluated from 1991 to 2010 on a claypan soil in Missouri. Replicated treatments were three CS (2-yr mulch till corn-soybean [MTCS], 2-yr no-till corn-soybean [NTCS], and 3-yr notill corn-soybean-wheat-cover crop [NTCSW]) and three LP (summit, backslope, and footslope). Corn yield was equivalent among CS on the summit, 13% higher for NTCS and NTCSW on the backslope, and 14% lower for NTCSW on the footslope. Soybean yield was 8% higher on the summit, 24% higher on the backslope in NTCS and NTCSW, and 12% higher on the footslope in NTCSW than MTCS. Corn yield was more stable in NTCS and NTCSW than MTCS and increased in stability from the footslope to summit. Soybean yield was less stable in NTCS and NTCSW than MTCS and LP effects on stability were similar to corn. The coefficient of variation (CV) of corn yield across years was 10% points lower in NTCS and on the footslope, and of soybean yield was 10% points lower at the footslope and summit. Wheat production was not affected by LP. Results indicate that conservation systems oft en can maintain grain crop productivity equal to, increase yield stability above, and reduce yield variability below those of a conventional system on claypan soils. [ABSTRACT FROM AUTHOR]

Installing subsurface tile drain systems in poorly drained claypan soils to improve corn (Zea mays L.) yields could potentially increase environmental phosphorus (P) loss through the tile drainage system.The objectives of the study were to quantify the average concentration and loss ofortho-P in tile drain water from a claypan soil and to determine whether managed subsurface drainage (MD) could reduce ortho-P loss in tile water compared with free subsurface drainage (FD). Flow-weighted ortho-P concentration in the tile water was significantly lower with MD (0.09 mg L-1) compared with that of FD (0.15 mg L-1). Ortho-P loss in the tile water of this study was reduced with MD (36 g ha-1) by 80% compared with FD (180 g ha^1). Contrary to previous research, reduced ortho-P loss observed over the 4-yr study was not solely due to the reduced amount of water drained annually (63%) with MD compared with FD. During the spring period, when flow was similar between MD and FD, the concentration of ortho-P in the tile water generally was lower with MD compared with FD, which resulted in significantly less ortho-P loss with MD. We speculate that MD's ability to conserve water during the dry summer months increased corn's uptake of water and P, which reduced the amount of P available for leaching loss in the subsequent springs. [ABSTRACT FROM AUTHOR]

With poorly-drained claypan soils in the midwestern United States, it is common to have wet soil conditions in the spring and dry soil conditions in the summer. Management practices that can improve or mitigate the effects of excessive wet and dry soil conditions are essential to obtain maximum corn (Zea mays L.) yield potential. The objective of the 4-yr study was to determine if subsurface drainage (free drainage [FD] or managed drainage [MD]) with polymer-coated urea (PCU) could increase corn yield compared to an application of non-coated urea (NCU) without drainage (ND) in a claypan soil. Corn grain yields were low over the 4-yr study due to extreme wet conditions in 2010 that delayed planting and mild to extreme summer drought conditions in 2011 to 2013. Averaged over 2010 to 2013, corn grain yields ranged from 4.76 to 5.75 Mg ha-1. Averaged over 2010 to 2013, the presence of drainage (FD or MD) increased corn yield (15-21%) compared to ND when NCU was applied. In the absence of drainage, PCU increased corn grain yields 20% compared to NCU, which indicated that PCU mitigated the high N loss potential in a wet soil environment. Managed drainage averaged a 4% increase in corn yield compared to FD. Corn yield increases with drainage compared to ND were limited over the 4 yr of this research; however, greater corn yield benefits from drainage of claypan soils might occur in years with greater overall yield potential. [ABSTRACT FROM AUTHOR]

Continuous corn (Zea mays L) production during dry years combined with high N fertilizer rates can have a high potential for NO3--N loss through tile drainage water. Claypan soils can further increasethe potential for NO3--N loss through tile drainage water due to the claypan layer that restricts N leaching below the tile drains. The objective of this 4-yr study was to determine whether use of managed subsurface drainage (MD) in combination with a controlled-release N fertilizer could reduce the annual amount of NO3--N loss through tile drainage water compared with free subsurface tile drainage (FD) with a noncoated urea application. Due to dry conditions over the summer and fall months, MD reduced the annual amount of water drained by at least 73% compared with FD in two of the four crop years. Low N loss and reduced corn N uptake possibly resulted in carry-over N and high soil N concentrations throughout the study, which may have limited the effect of N fertilizer source on annual NO3--N loss in the tile drainage water. Use of MD reduced annual NO3--N loss in the tile drainage water by 78 to 85% in two of the four years. High NO3--N loss reduction with MD compared with FD was largely due to dry growing season conditions in combination with wet conditions over the noncropping period. [ABSTRACT FROM AUTHOR]

Starting in 1971, stream flow and climatologie data have been collected in the Goodwater Creek Experimental Watershed, which is part of the Central Mississippi River Basin (CMRB) Long-Term Agroecosystem Research (LTAR) site. Since 1992, water quality and socio-economic data have complemented these data sets. Previous modeling efforts highlighted the challenges created by the presence of a claypan. Specific changes were introduced in the Soil and Water Assessment Tool (SWAT) (i) to better simulate percolation through and saturation above the claypan and (ii) to simulate the spatial and temporal distributions of the timing of field operations throughout the watershed. Our objectives were to document the changes introduced into the code, demonstrate that these changes improved simulation results, describe the model's parameterization, calibration, and validation, and assess atrazine [6-chloro-N-ethyl-N'-(1-methylethyl)-1,3,5-triazine-2,4-diamine] management practices in the hydrologie context of claypan soils. Model calibration was achieved for 1993 to 2010 at a daily time step for flow and at a monthly time step for water quality constituents. The new percolation routines ensured correct balance between surface runoff and groundwater. The temporal heterogeneity of atrazine application ensured the correct frequency of daily atrazine loads. Atrazine incorporation by field cultivation resulted in a 17% simulated reduction in atrazine load without a significant increase in sediment yields. Reduced atrazine rates produced proportional reductions in simulated atrazine transport. The model can be used to estimate the impact of other drivers, e.g., changing aspects of climate, land use, cropping systems, tillage, or management practices, in this context. [ABSTRACT FROM AUTHOR]

Long-term monitoring data from agricultural watersheds are needed to determine if efforts to reduce nutrient transport from crop and pasture land have been effective. Goodwater Creek Experimental Watershed (GCEW), located in northeastern Missouri, is a high-runoff-potential watershed dominated by claypan soils. The objectives of this study were to: (i) summarize dissolved NH4-N, NO3-N, and PO4-P flow-weighted concentrations (FWC), daily loads, and yields (unit area loads) in GCEW from 1992 to 2010; (ii) assess time trends and relationships between precipitation, land use, and fertilizer inputs and nutrient transport; and (iii) provide context to the GCEW data by comparisons with other Corn Belt watersheds. Significant declines in annual and quarterly FWCs and yields occurred for all three nutrient species during the study, and the decreases were most evident for NO3-N. Substantial decreases in first- and fourth-quarter NO3-N FWCs and daily loads and modest decreases in first-quarter PO4-P daily loads were observed. Declines in NO3-N and PO4-P transport were attributed to decreased winter wheat (Triticumaestivum L) and increased corn (Zeamays L) production that shifted fertilizer application from fall to spring as well as to improved management, such as increased use of incorporation. Regression models and correlation analyses indicated that precipitation, land use, and fertilizer inputs were critical factors controlling transport. Within the Mississippi River Basin, NO3-N yields in GCEW were much lower than in tile-drained areas, but PO4-P yields were among the highest in the basin. Overall, results demonstrated that reductions in fall-applied fertilizer and improved fertilizer management reduced N and P transport in GCEW. [ABSTRACT FROM AUTHOR]

Goodwater Creek Experimental Watershed (GCEW) has been the focus area of a long-term effort to document the extent of and to understand the factors controlling herbicide transport. We document the dataseis generated in the 20-yr-long research effort to study the transport of herbicides to surface and groundwater in the GCEW. This long-term effort was augmented with a spatially broad effort within the Central Mississippi River Basin encompassing 12 related claypan watersheds in the Salt River Basin, two cave streams on the fringe of the Central Claypan Areas in the Bonne Femme watershed, and 95 streams in northern Missouri and southern Iowa. Details of the analytical methods, periods of record, number of samples, study locations, and means of accessing these data are provided. In addition, a brief overview of significant findings is presented. A key finding was that near-surface restrictive soil layers, such asargillic horizons of smectitic mineralogy, result in greater herbicide transport than soils with high percolation and low clay content. Because of this, streams in the claypan soil watersheds of northeastern Missouri have exceptionally high herbicide concentrations and relative loads compared with other areas of the Corn Belt. [ABSTRACT FROM AUTHOR]

Flow monitoring in Goodwater Creek Experimental Watershed started in 1971 at three nested watersheds ranging from 12 to 73 km². Since then, runoff or stream flow has been measured at 14 plots, three fields, and 12 additional stream sites ranging from 0.0034 to 6067 km² in the Central Mississippi River Basin. Long-term data sets are important to document the changes resulting from anthropogenic and natural drivers. The data set presented here documents discharge across a range of catchment sizes in an area known for its high runoff potential. It constitutes the flow database of the Central Mississippi River Basin site of the Long-Term Agricultural Research network. Like the other sites of this network, data are accessible through the STEWARDS web interface (www.nrrig.mwa.ars.usda.gov/stewards/stewards. html). Here we (i) describe the data collection methods, (ii) document the data available at plot, field, and watershed scales, and (iii) provide the main characteristics of discharge. General characteristics of discharge per unit area for different cropping system management systems show that in this claypan soil setting, management and tillage of row crop systems do not affect surface flow during the growing season (April-October). Data from fields and stream sites show the dampening of peak flow values and lengthening of storm hydrographs caused by mixed land uses and longer times of concentration. Overall, stream flow accounts for a third of the precipitation, of which 80% is from surface runoff and 20% is from groundwater. [ABSTRACT FROM AUTHOR]

Long-term effects of alley cropping on soils in the temperate zone are not widely known. Management, landscape, and soil depth effects on soil physical and biological properties were examined in a silver maple (Acer saccharinum L.) no-till corn (Zea mays L.)- soybean (Glycine max L.) rotation established in 1990 in northeast Missouri. Soils from crop alleys and tree rows were collected along transects traversing upper to lower landscape positions at three depths. Fluorescein diacetate hydrolase (FDA), β-glucosidase, β-glucosaminidase, and dehydrogenase activities were measured. Soil bulk density, aggregate stability, carbon (C), nitrogen N), and enzyme activities decreased with soil depth in alley and tree rows except for glucosaminidase. Soil physical and biological parameters did not differ significantly between alley and tree row. Landscape position effects were not significant for management or depth. Tree establishment improves soil quality in the crop alley as the system matures with improvements extended throughout the soil profile. [ABSTRACT FROM PUBLISHER]

Summary Fuzzy rainfall–runoff models are often used to forecast flood or water supply in large catchments and applications at small/field scale agricultural watersheds are limited. The study objectives were to develop, calibrate, and validate a fuzzy rainfall–runoff model using long-term data of three adjacent field scale row crop watersheds (1.65–4.44 ha) with intermittent discharge in the claypan soils of Northeast Missouri. The watersheds were monitored for a six-year calibration period starting 1991 (pre-buffer period). Thereafter, two of them were treated with upland contour grass and agroforestry (tree + grass) buffers (4.5 m wide, 36.5 m apart) to study water quality benefits. The fuzzy system was based on Mamdani method using MATLAB 7.10.0. The model predicted event-based runoff with model performance coefficients of r 2 and Nash–Sutcliffe Coefficient (NSC) values greater than 0.65 for calibration and validation. The pre-buffer fuzzy system predicted event-based runoff for 30–50 times larger corn/soybean watersheds with r 2 values of 0.82 and 0.68 and NSC values of 0.77 and 0.53, respectively. The runoff predicted by the fuzzy system closely agreed with values predicted by physically-based Agricultural Policy Environmental eXtender model (APEX) for the pre-buffer watersheds. The fuzzy rainfall–runoff model has the potential for runoff predictions at field-scale watersheds with minimum input. It also could up-scale the predictions for large-scale watersheds to evaluate the benefits of conservation practices. [ABSTRACT FROM AUTHOR]

Preplant-applied, urea-based fertilizer management in high-residue, no-till ( NT) corn ( Zea mays L.) is challenging because of potential N loss due to cool, wet conditions in the spring and dry conditions during the summer months. Field research evaluated the effects of polymer-coated urea ( PCU) application timing, placement and cropping system on urea release for corn and determined corn yield response to PCU on claypan soils following wheat ( Triticum aestivum L.) cropping systems [reduced-till corn following wheat, no-till corn following wheat with double-cropped ( DC) soybean [ Glycine max ( L.) Merr.] and no-till corn following wheat with a frost-seeded red clover ( FSC) ( Trifolium pratense L.) cover crop]. Urea release from PCU was <35 % from fall through winter ( November- January) and <20 % for early preplant ( February- March) applications until 1 April. By 1 August, less urea was released in some instances from surface applications of PCU following FSC or DC soybean, but release was generally greater than in the absence of soil. No-till corn following DC soybean or FSC had yields that were 1.01-1.32 Mg ha−1 greater when grown with PCU compared to urea at 168 kg N ha−1. Grain yields were similar within no-till cropping systems with PCU, anhydrous ammonia and sidedressed urea ammonium nitrate ( UAN) at 168 kg N ha−1. Farmers should recognize that high yields may not be obtained if PCU rates are reduced by 50 % (84 kg N ha−1) in high-residue ( DC soybean or FSC), no-till production systems. Several N sources such as PCU, anhydrous ammonia and sidedressed UAN worked similarly in high-residue, no-till systems, although no differences between N sources were observed in a reduced-tillage system. [ABSTRACT FROM AUTHOR]

In the U.S. Corn Belt, claypan soils are vulnerable to both erosion and transport of unincorporated herbicides. Thus, there is a need to identify tillage practices that can achieve a balance between herbicide transport and soil erosion for these soils. The objectives of this research were to compare the effect of three tillage systems on sediment and atrazine transport in surface runoff for a claypan soil and to compare their agronomic utility. The tillage treatments were: (1) rotary harrow with atrazine incorporated to ~5 cm (RH), (2) no-till without incorporation (NT), and (3) minimum till with atrazine incorporated to ~10 cm (MT). Three main tillage plots were established on a Leonard silt loam (2% to 3% slopes), a typical claypan soil series. For each treatment, two sets of runoff subplots, with three replicates each, were established within the main plots. Runoff was generated with a rainfall simulator at an average rate of 27 mm h-1. Runoff samples were collected at unequal time intervals from 1 to 90 min after runoff initiation and analyzed for total suspended sediment (TSS) and dissolved-phase atrazine concentrations. The RH treatment had significantly lower mean TSS concentrations and load (0.25 g L-1 and 67 kg ha-1) than MT (0.58 g L-1 and 155 kg ha-1), but it did not significantly increase erosion compared to NT (0.16 g L-1 and 42 kg ha-1). The RH treatment also significantly decreased atrazine concentrations and relative loads compared to NT, but it did not significantly increase atrazine transport compared to ME. Average atrazine concentrations (in µg L-1) and relative loads (as a percentage of applied) were: 2100 and 22.2%for NT, 850 and 10.6% for RH, and 405 and 6.4%for MZ. The RH treatment also resulted in comparable or better grain yield than the other treatments. Results indicated that the RH treatment successfully managed the trade-off between erosion and atrazine transport and, thus, holds promise as a best management practice for claypan and related restrictive layer soils. [ABSTRACT FROM AUTHOR]

Poorly drained claypan soils can increase the importance of tillage and N management for corn (Zea mays L.) production. Field research in 2008, 2009 and 2010 (high rainfall years) near Novelty, MO (40° 1' N, 92° 11' W) sought to determine the effect of polymer-coated urea (PCU) placement [strip-tillage (ST) deep banded and no-till (NT) broadcast] and application timing (fall, early preplant and preplant) on red clover (Trifolium pratense L.) biomass and corn response compared to non-coated urea (NCU) and anhydrous ammonia (AA) in the presence and absence of nitrapyrin a nitrification inhibitor. Strip-tillage reduced clover dry weights 20% in 2008 and 2009 and early preplant ST reduced dry weights 40 to 45% in 2010 compared to NT. Corn plant population was 8,100 to 8,400 plants ha-1 greater with ST compared to NT. Preplant applications of AA plus nitrapyrin, AA, ST placement of PCU and NCU increased grain yields 1 to 1.2 Mg ha-1 compared to fall applications of these fertilizer sources. Fall and preplant ST placement of PCU increased grain yields 1.2 Mg ha-1 compared to NCU. Strip-till placement of PCU and NCU increased yields 2.1 to 3.2 Mg ha-1 over broadcast applications of these fertilizer sources. Strip-till placement of PCU synergistically increased yield over NCU and broadcast applications of PCU or NCU due to increased stands and possibly due to better plant utilization of the banded N fertilizer utility. [ABSTRACT FROM AUTHOR]

Development of effective management practices to maximize corn (Zea mays L.) production is important in poorly drained claypan soils due to their relatively low yield potential and vulnerability for environmental N loss. The objective of this 3-yr study, conducted at one location was to determine whether an N management system with strip-till (ST) and deep banding placement of polymer-coated urea (PCU) could produce greater corn yields than no-till (NT) systems with broadcasted non-coated urea (NCU) or injected anhydrous ammonia (AA) with or without nitrapyrin with fall, early pre-plant, or pre-plant N applications. The experiment was a split-plot design with N application dates as the main plot and eight N management systems (N source and tillage/N placement) as subplots. Nitrogen sources of PCU, NCU, and a non-treated control (NTC) were used in conjunction with NT/surface broadcast and ST/deep band placement practices. Anhydrous ammonia was injected into a NT soil with or without nitrapyrin. Injecting AA into a NT soil with nitrapyrin at pre-plant produced at least 2 Mg ha-1 greater corn yields than any of the management systems with a fall application during three wet years. When N was applied in the fall or at early pre-plant, ST/deep banding of PCU and NCU produced yields similar to NT/injected AA with or without nitrapyrin. Strip-tillage with deep banding of urea fertilizers may be a viable, high yielding alternative N management system in poorly drained claypan soils when tillage and N applications are done in fall. [ABSTRACT FROM AUTHOR]

Vegetative filter strips (VFS) have long been promoted as a soil conservation practice that yields many additional environmental benefits. Most previous studies have focused primarily on the role of vegetation and/or soil physical properties in these ecosystem services. Few studies have investigated the soil microbial community of VFS. Therefore, we examined potential differences in soil microbial community characteristics of claypan soil planted to VFS with differing vegetation and a traditional row-crop system in a maize-soybean rotation. Samples were tested for soil microbial function and community structure using dehydrogenase and fluorescein diacetate (FDA) hydrolysis enzyme assays and phospholipid fatty acid (PLFA) analysis, respectively. The grass VFS soil exhibited the greatest dehydrogenase activity levels and FDA activity was greater in the grass and agroforestry (i.e., tree-grass) VFS soils relative to the cropland soil. The PLFA analysis revealed community structural differences underlying these functional differences. The agroforestry VFS soil was characterized by a greater proportion of total bacteria, gram-negative bacteria, anaerobic bacteria and mycorrhizal fungi than the cropland soil. The grass VFS soil shared some characteristics with the cropland soils; but the grass VFS supported greater mycorrhizal fungi and protozoa populations. This work highlights differences in soil microbial function and community structure in VFS relative to cropland soil 12 years post VFS establishment. It also enhances our fundamental knowledge regarding soil microorganisms in VFS, which may aid in explaining some ecosystem services provided by VFS (e.g., decomposition of organic agrichemicals). [ABSTRACT FROM AUTHOR]

Soil organic carbon (SOC) plays an important role in soil aggregation, yet the exact nature of this relationship is not well understood. The objectives of this study were to (i) evaluate relationships among field-moist and air-dried macroaggregate stability (WSAFM and WSAAD, respectively), cold water-extractable organic C from whole soil and the particulate, adsorbed and occluded (PAO) fraction, and associated soil properties, (ii) compare properties of the PAO fraction to those of whole soil, and (iii) evaluate the effects of conservation management practices, including grass vegetative filter strips (VFS), agroforestry VFS, and no-till, plus landscape positions on these variables. Soil samples were collected in 2007 from an agroecosystem established on claypan soils located in Missouri. This study found that cold water-extractable organic C and aggregate-associated organic C were more highly correlated with WSAAD (r ≥ 0.74) than SOC, suggesting that these organic C fractions may play an important role in aggregate stability. In addition, less degraded water-extractable organic C (as indicated by a greater C/N ratio) was preferentially concentrated in the PAO fraction (C/N = 10.6) relative to whole soil (C/N = 4.2). Further, macroaggregation and accumulation of less degraded organic C (in solid and water-extracts) was enhanced under grass VFS and agroforestry VFS relative to no-till. Overall, this study found that macroaggregate stability, cold water-extractable organic C, and the PAO fraction served as effective early indicators of soil C change in the soil studied. [ABSTRACT FROM AUTHOR]

This study was undertaken to assess the importance of stream bank erosion to the total in-stream sediment of two agricultural watersheds within the Central Claypan Areas. The objective of this research was to determine the effect of stream order, adjacent land use, and season on strean1bank erosion rates. Thirty-four study sites were established in 2007 and 2008 within Crooked and Otter Creek watersheds, two claypan watersheds located in northeastern Misso uri. At each site, field assessments of severely to very severely eroding bank length were determined along 300 to 400 m (984 to 1,312 ft) stream reaches. A factorial experimental design was implemented with four land uses (crop, forest, pasture, and riparian forest), three seasons, and three stream orders (1st, 2nd, and 3rd). Each treatment was replicated three times for each stream order, except for the cropped 3rd order treatment as only one suitable treatment site could be found. Streambank erosion was measured using erosion pins, which were installed in randomly assigned plots that included at least 20% of the eroded bank length within each site. The effect of dififerent seasons was assessed by measuring the length of the exposed pins three times per year (March,July, and November) . The bulk density and carbon and nitrogen content of bank material were also determined. Sediment loss rates showed that season and the three-way interaction between season, land use, and stream order were highly sigtlificant. Erosion rates were consistently higher in the winter months than spring/ sununer and fall seasons; however, the sigtlificant three-way interaction precluded a simple interpretation of the seasonal effect. Soil nutrient concentration data showed that forest sites had significantly lower C and N concentrations than other land uses. At the watershed scale, bank sediment accounted for 79% to 96% of the total in-stream sediment and 21% to 24% of the total N exported from the study area. These results indicate that streambanks are the dominant source of sediment and a significant source of N in these streams. Therefore, improved management of riparian areas to decrease streambank erosion would result in significant water quality improvement in streams of the Central Claypan Areas in northeastern Missouri . [ABSTRACT FROM AUTHOR]

The Central Claypan region is an important agricultural production contributor in the U.S. Midwest. Because of the tendency for grain yield fluctuations caused by water stress, however, claypan soils may have potential for conversion from grain to grass production in support of biomass energy markets and conservation programs. This study examined the economic potential of transitioning from grain to perennial switchgrass (Panicum virgatum L.) production on claypan soils using comparative break- even analysis. Partial budgets for a corn (Zea mays L.)-soybean [Glycine max (L.) Merr.] rotation and a perennial switchgrass cropping system were developed. Yield data from research plots with varying topsoil depths defined by the underlying claypan layer were used to establish yield expectations as affected by topsoil depth. Switchgrass yield projections for the claypan region were simulated with the Agricultural Land Management Alternatives with Numerical Assessment Criteria (ALMANAC) model. Comparative breakeven prices for two switchgrass cultivars ranged from US$65 on marginal, eroded soils to US$124 Mg-1 on soils with >27cm of topsoil. Breakeven yields with a biomass price of US$40 Mg-1 would require yield increases of up to 450% for lower yielding cultivars. The switchgrass cultivar Kanlow holds the most promise for biomass production on claypan soils; with an average projected yield of 12.56 Mg ha-1, breakeven prices fall to around US$60-80 Mg-1 for marginal soils with <15cm of topsoil. Based on these projections, perennial switchgrass shows potential to compete with conventional grain crops at reasonable yield levels on eroded soils in the Central Claypan region. [ABSTRACT FROM AUTHOR]

To solve the problem of inhomogeneous distribution of Kang's surface temperature and poor indoor thermal comfort, this paper proposes a method to incline the Kang board. By the numerical simulation of grounded Kang and elevated Kang with different oblique degree of Kang board, it is found that when the claypan thickness at the head/end of the Kang is 80/20 mm, the Kang has the best heating effect. [ABSTRACT FROM AUTHOR]

Abstract: Information is lacking on nutrient runoff losses from poultry wastes and commercial fertilizers from claypan soils such as those found in southeastern Kansas. The objectives of this study were: (i) to compare field-scale surface runoff losses of nutrients from turkey (Melleagris gallopavo) litter manure and fertilizer and (ii) to compare the influence of tillage incorporation of turkey litter with no tillage on nutrient losses in surface runoff. The experiment was conducted from 2005 through spring 2008 near Girard, KS. The soil was a low-slope Parsons silt loam overlying a claypan B horizon. A high litter rate (N-based) resulted in high flow-weighted concentrations of N and P in runoff, and also resulted in carry-over P losses. N losses were inorganic and organic, whereas P losses were mainly the soluble, ortho-P form partially influenced by low sediment losses. Nutrient losses from fertilizer-only applications were usually lower than from N-based and similar to P-based turkey litter applications. Incorporation appeared to reduce nutrient losses in runoff, but was not always significant. A high litter rate built up soil P levels, and annual P runoff losses appeared to accelerate when soil P values exceeded 30mgkg−1 in a 0–15cm sample. [Copyright &y& Elsevier]

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A study evaluated corn (Zea mays L.) hybrids (Asgrow785, DKC61-73, DKC63-42, LG2642, and Kruger2114) and water management systems (nondrained, nonirrigated (NDNI); drained, nonirrigated (DNI) with subsurface drain tiles 6.1 and 12.2m apart; drained plus subirrigated (DSI) with tiles 6.1 and 12.2m apart; nondrained, overhead irrigated (NDOHI)) on yields, plant population, and grain quality from2008 to 2010. Precipitation during this study was 36 to 283mmabove the past decade. Planting date was delayed 18 d in the nondrained control in 2009, and additional delayed planting controls were included this year. Grain yields were similar in the 6.1- and 12.2m-spaced DNI and DSI systems in 2008 and 2010, but plant population increased 74% and yields were 3.1Mg ha-1 greater with DSI at a 6.1m spacing compared to 12.2m in 2009. At a 6.1m spacing, DNI or DSI increased yield 1.1 to 6.6Mg ha-1 (10 to over 50%) compared to NDNI or NDOHI soil. High yielding hybrids achieved similar yields with DNI, while NDNI DKC63-42 had 1.2Mg ha-1 greater yields compared to DKC61-73. A 6.1m spacing for DNI claypan soils is recommended for high yielding corn production. [ABSTRACT FROM AUTHOR]

Abstract: In agroecosystems, compaction-induced changes in soil physical properties may significantly affect soil microbial activity, especially N-related processes. The objective of this study was to determine the effect of soil compaction on soil microbiological properties related to N in a claypan soil amended with poultry litter (i.e., Turkey (Meleagris gallopavo) excrement mixed with pine shavings as bedding) and cropped to corn (Zea mays L.). In a laboratory incubation, a silt loam soil was compacted to four bulk density levels (1.2, 1.4, 1.6 and 1.8mgm−3) amended with and without poultry litter and incubated at 25°C for 28d. In a field experiment conducted in 2001 and 2002, a Mexico silt loam claypan soil was amended with litter (0 and 19mgha−1), left uncompacted or uniformly compacted and planted to corn or left fallow. In the incubation study, soil compaction reduced microbial biomass N (MBN) and soluble N (Sol N), but increased microbial C:N ratio and soil β-glucosaminidase activity. Added litter increased Sol N and soil β-glucosaminidase activity in the laboratory. Under controlled soil water content and temperature, all soil microbiological properties had a linear relationship with soil bulk density (r 2 =0.63**–0.90***). In the field, the compaction effect on all the measured soil microbial properties was less pronounced. The field observation also showed that litter-amended soil had higher MBN, Sol N and soil β-glucosaminidase activity compared to unamended soil in both compaction treatments, regardless of fallow and cropped plots. Under field conditions, MBN and microbial C:N ratio significantly correlated with soil water content (r =0.49*** and −0.32***, respectively), while soil β-glucosaminidase activity was correlated with total soil organic C (r =0.39***). The results showed that N-related soil microbiological properties were sensitive to changes induced by soil compaction, while beneficial effects of litter addition may mitigate some compaction effects on these soil properties. [Copyright &y& Elsevier]

Abstract: Conservation management practices including upland vegetative filter strips (VFS) and no-till cultivation have the potential to enhance soil carbon sequestration and other ecosystem services in agroecosystems. A modified two-factor analysis of variance (ANOVA) with subsamples was used to compare SOC and TN on a concentration, soil volume and soil mass basis in claypan soils planted to different conservation management practices and as a function of landscape position. The three conservation management practices (no-till cultivation, grass VFS and agroforestry VFS) and four landscape positions (summit, shoulder, backslope and footslope) investigated were compared 10years after VFS establishment in a no-till system planted to maize (Zea mays. L.)–soybean (Glycine max (L.) Merr.) rotation. Two soil depth increments (0–5cm and 5–13cm) were modeled separately to test for treatment effects. In the surface layer, mean SOC concentration was significantly greater in the VFS soils compared to no-till. On a soil volume or mass basis, no significant differences in SOC stocks were found among treatment means. Concentration and mass based TN values were significantly greater in the grass VFS relative to no-till in the surface layer. A rapid slaking stability test, developed to separate particulate, adsorbed and occluded organic carbon (PAO-C) and nitrogen (PAO-N), showed that VFS soils had significantly greater mean PAO-C and PAO-N concentrations, soil volume and soil mass based stocks than no-till. In addition, comparison of SOC:TN and PAO-C:PAO-N ratios suggest reduced decomposition and mineralization of SOC in the PAO fraction. No significant treatment effects were detected in total or PAO soil fractions in the subsurface layer or among landscape position in either depth increment. Study results emphasize the need to compare soil carbon and nitrogen stocks on a soil volume and/or soil mass basis using bulk density measurements. Additionally, the rapid PAO separation technique was found to be a good indicator of early changes in SOC and TN in the systems studied. Overall, this research indicates that grass VFS may sequester TN more rapidly than agroforestry VFS and that a greater proportion of SOC and TN may be stabilized in VFS soils compared to no-till. [Copyright &y& Elsevier]

Abstract: Parametric and non-parametric depth functions have been used to estimate continuous soil profile properties. However, some soil properties, such as those seen in weathered loess, have anisotropic peak-shaped depth distributions. These distributions are poorly handled by common parametric functions. And while nonparametric functions can handle this data they lack meaningful parameters to describe physical phenomena in the depth distribution of a property such as a peak, an inflection point, or a gradient. The objective of this work is to introduce the use of asymmetric peak functions to model complex and anisotropic soil property depth profiles. These functions have the advantages of providing parameters, which quantify or describe pedogenic processes. We demonstrate the application of the Pearson Type IV (PIV) and the logistic power peak (LPP) functions to high resolution soil property depth profiles measured by diffuse reflectance spectroscopy in a claypan soil landscape of Northeastern Missouri, USA. Both peak functions successfully fit clay, silt, and pH data for an example soil profile from a summit landscape position (R2 =0.90 for pH and 0.98 for silt and clay). The LPP function was further demonstrated to fit clay depth distribution for a shoulder, backslope, footslope, and a depositional landscape position (R2 =0.98, 0.96, 0.96, 0.91). Relationships between the fitted parameters of these profiles were useful to describe landscape trends in their morphological features and show promise to continuously describe pedogenic processes in three dimensions. Peak functions are a useful companion to high-resolution soil profile data collected by sensors and their combined use may allow more intensive mapping and better explanation of soil landscape variability. [Copyright &y& Elsevier]

Integrated water management systems using drainage plus subirrigation (DSI) have reduced nitrate-loading of drainage water flow and may increase soybean [Glycine max (L.) Merr.] yield. Shallow drain tile depths and narrow spacings are recommended for claypan soils. Field research (2003-2006) evaluated the effects of drainage (DO) and DSI on planting date and the effects of DO and DSI at 6.1 and 12.2 m spacings on soybean yield compared to nondrained (ND) and nondrained delayed planting (NDDP) controls on claypan soils. Soybean were planted up to 17 d earlier with DO or DSI systems. Plant populations were reduced 29 to 52% in the nondrained control due to poor drainage in 3 of the 4 yr. Grain yield, water applied through the DSI system, and water level depth were similar at a 6.1 or 12.2 m drain tile spacing. Average yield increase with DSI at 6.1 and 12.2 m spacings was 12 to 29% (410-910 kg ha-1) while DO at the same spacings increased yield 9 to 22% (300-710 kg ha-1) compared to ND or NDDP controls. In a dry year (2005), drainage plus subirrigation increased yield up to 1200kg ha-1 compared to DO. Plant population variability at harvest was lower with the DO or DSI systems compared to ND or NDDP controls. Yield variability over the 4 yr was lower with DSI compared with DO or ND controls, which was affected by the spring-summer precipitation regimes and is important to farmers for a more predictable soybean marketing strategy. [ABSTRACT FROM AUTHOR]

Abstract: Changes in soil physical characteristics induced by soil compaction may alter soil microhabitats and, therefore, play a significant role in governing soil microorganisms and their activities. Laboratory incubation and field experiments (in 2001 and 2002) were conducted to investigate the effect of soil compaction on soil microbiological properties in a claypan soil amended with poultry litter and cropped to corn (Zea mays L.). In both laboratory and field studies, moderate soil compaction increased total soil organic C, β-glucosidase activity, microbial biomass C (MBC), and microbial functional diversity, but decreased soluble organic C (Sol C). However, more severe soil compaction imposed in the laboratory caused an adverse effect on these soil microbiological properties, except for Sol C. Turkey (Meleagris gallopavo) litter application and cropping significantly increased soil β-glucosidase activity, MBC, Sol C and microbial functional diversity, partly due to inputs of labile C substrates from both litter and crops. Overall, modification of soil microhabitat by compaction could change soil microbial growth and activity in relation to C and shift soil microbial functional diversity; however, the positive effects of litter addition and cropping could overcome the compaction effect on these soil microbiological properties. [Copyright &y& Elsevier]

The article presents a study on the use of vegetative buffer strips (VBSs) to reduce herbicides and veterinary antibiotics losses from agroecosystems in the U.S. It mentions the experiment of three VBS designs and one continuous cultivated fallow control in triplicate which was conducted to assess effectiveness in reducing herbicide and antibiotic transport for claypan soils. The VBS designs include tall fescue, tall fescue with a switchgrass hedge barrier, and native vegetation. The findings suggest that all VBS significantly reduced the transport of dissolved and sediment-bound atrazine, metolachlor, and glyphosate in surface runoff by more than 70%.

Abstract: Soil compaction decreases soil pores are important for root growth as well as infiltration of water and nutrients. A study was conducted to evaluate the effects of soil compaction on macropore parameters measured using X-ray computed tomography (CT). Macropore parameters included number of pores, number of macropores (>1000μm diam.), number of coarse mesopores (200 to 1000μm diam.), porosity, macroporosity, coarse mesoporosity, area of largest pore, pore circularity, and fractal dimension of macroporosity. A field experiment was conducted on Mexico silt loam (fine, smectitic, mesic Vertic Epiaqualfs) with field treatments including four replicates of uniformly Compacted (C) and Non-Compacted (NC) plots arranged in a randomized complete block design. Soil cores (76.2mm diam. by 76.2mm long) were removed from three selected depths (0 to 10cm, 10 to 20cm, and 20 to 30cm). Cores were scanned using a medical X-ray CT scanner with four scans taken in each sample at 15mm spacing starting at 25mm from the core surface. Images were analyzed using Image-J software. The C treatment was found to increase bulk density by 8% (1.34 to 1.45gcm−3) and decrease saturated hydraulic conductivity by 69% (47.1 to 14.6cmhr−1). CT-measured number of pores decreased by 71%, number of macropores by 69%, and coarse mesopores by 75% with the C treatment used in the study. Compaction was also found to significantly decrease CT-measured porosity and macroporosity by 64%. Differences between treatments for the parameters were most pronounced in the upper 10cm; differences between treatments were not significant below 20cm. A regression equation with CT-measured macroporosity, area of largest pore and porosity explained most of the variability in saturated hydraulic conductivity (R 2 =0.79). Efforts should be made to minimize soil compaction due to its harmful effects on soil pores and subsequent challenges for plant root growth and enhanced runoff of water and nutrients. [Copyright &y& Elsevier]

The midwestern United States has >4 million ha of claypan soils. These soils often require special management because of poor infiltration, drainage, and available water supply. This study was conducted to quantify the hydro- logic balance of a claypan soil and determine the effect of tillage on water balance components. It was part of an ongoing project in Labette County, Kansas, in which no-till and chisel tillage plots had been maintained since 1995. A sorghum [Sorghum bicolor(L.) Moench]-soybean [ Glycine max (L.) Merr.} rotation was initiated in 2003, with both crops grown each year in a randomized complete block design. The plots in sorghum were instrumented to measure water content throughout the profile. Precipitation and evapotranspiration (ET) were determined at the field scale. Soil hydraulic properties and water content data were used to estimate drainage. Runoff was determined as the residual in this water balance, Evaporation from chisel tillage was up to 1 mm d-1 greater than that from no-till during the early season. This resulted in differences in surface water content and runoff. These effects were limited to the early season, however, so that the water balance for the full growing season was not significantly affected by tillage. Drainage from the claypan soil was negligible. The 2006 crop year had 23.5 cm of ET, a value greater than the in-season precipitation. The 2007 crop year had 33.5 cm of ET, a value less than the in-season precipitation. With limited drainage and storage in the claypan, 37.5 cm of runoff occurred in 2007. [ABSTRACT FROM AUTHOR]

Various land management decisions are based on local soil properties. These soil properties. include average values from soil characterization for each soil series. In reality, these properties might be variable due to substantially different management, even for similar soil series. This study was conducted to test the hypothesis that for claypan soils, hydraulic properties can be significantly affected by long-term soil and crop management. Sampling was conducted during the summer of 2008 from two fields with Mexico silt loam (Vertic Epiaqualfs). One field has been under continuous row crop cultivation for over 100 years (Field), while the other field is a native prairie that has never been tilled (Tucker Prairie). Soil cores (76 × 76 mm [3.0 × 3.0 in]) from six replicate locations from each field were sampled to a 60 cm (24 in) depth at 10 cm (3.9 in) intervals. Samples were analyzed for bulk density, saturated hydraulic conductivity (Ksat), soil water retention, and pore-size distributions. Values of coarse (60 to 1,000 μm [0.0024 to 0.039 in] effective diameter) and fine mesoporosity (10 to 60 μm [0.00039 to 0.0024 in] effective diameter) for the Field site (0.044 and 0.053 m3 m-3 [0.044 and 0.053 in3 in-3]) were almost half those values from the Tucker Prairie site (0.081 and 0.086 m3 m-3 [0.081 and 0.086 in3 in-3]).The geometric mean value of Ksat was 57 times higher in the native prairie site (316 mm h-1 [12.4 in hr-1]) than in the cropped field (5.55 mm h-1 [0.219 in hr-1]) for the first 10 cm (3.9 in) interval. Differences in Ksat values were partly explained by the significant differences in pore-size distributions. The bulk density of the surface layer at the Tucker Prairie site (0.81 g cm-3 [50.6 lb fr-3]) was two-thirds of the value at the Field site (1 .44 g cm-3 [89.9 lb ft-3]), and was significantly different throughout the soil profile, except for the 20 to 30 cm (7.9 to 12 in) depth. These results show that row crop management and its effect on soil loss have significantly altered the hydraulic properties for this soil. Results from this study increase our understanding of the effects of long-term soil management on soil hydraulic properties. [ABSTRACT FROM AUTHOR]

Abstract: While the effects of landscape position (LP) and management practices on soil compaction have been documented as individual factors, limited understanding exists of their interactions. Such understanding is needed to prevent site-specific compaction and to better optimize soil management practices using precision agriculture principles and technologies. The objective of this investigation was to quantify, for a typical claypan soil [Epiaqualfs (USDA); Stagnic Luvisols (WRB)], the impacts and interactions of crop management system and LP on soil compaction as quantified by cone index (CI) and CI-related variables. Cone penetrometer measurements were collected in 2004 at three claypan soil LP (summit, backslope, and footslope) for four different cropping systems [CS; mulch tillage corn (Zea mays L.)-soybean [Glycine max (L.) Merr.] (MTCS), no-tillage corn–soybean (NTCS), no-tillage corn–soybean–wheat (Triticum aestivum L.) (NTCSW), and conservation reserve program (CRP)] that had been in place for more than a decade. Soils were sampled at the same time for soil water content (WC) and soil bulk density (BD) measurements. Mean differences for response variables were examined using F-protected (P ≤0.05) LSD values. Cone index averaged over soil depth differed by CS and LP. At the footslope position, CI for the NTCSW CS measured ∼2.0MPa in the upper 25cm of soil, and was notably greater than the other management systems. This outcome was attributed to the footslope staying wetter for a longer period during the spring and early summer because of un-removed cover crop plant residues. Wetter soils resulted in vulnerability to compaction during planting and spraying operations. Compaction on CRP was predictably less than the grain CS at all LP because farm machinery traffic only occurred on this system with bi-annual weed mowing during the mid-summer. These findings help bring to light where in claypan soil landscapes certain types of grain crop management will cause significant compaction. These areas could be targeted for further soil strength testing and then, when necessary, appropriate compaction remediation actions. [Copyright &y& Elsevier]

Field research (2003-2005) evaluated the effect of wheat row spacing (19 and 38 cm) and cultivar on double-cropped (DC) soybean response, 38-cm wheat on relay-intercrop (RI) response, and wheat cultivar selection on gross margins of these cropping systems. Narrow-row wheat increased grain yield 460 kg ha-1, light interception (LI) 7%, and leaf area index (LAI) 0.5 compared to wide rows, but did not affect DC soybean yield. High yielding wheat (P25R37) with greater LI and LAI produced lower (330 kg ha-1) soybean yields in an RI system than a low yielding cultivar (Ernie). Gross margins were $267 ha-1 greater when P25R37 was RI with H431 Intellicoat (ITC) soybean compared to Ernie. Gross margins were similar for monocrop H431 non-coated (NC) or ITC soybean, P25R37 in 19- or 38-cm rows with DC H431 NC soybean, and P25R37 in 38-cm rows with RI H431 ITC soybean in the absence of an early fall frost. [ABSTRACT FROM AUTHOR]

Abstract: The rapid transport of water and solute through desiccation soil cracks can lead to crop water and nutrient stress as well as ground and surface water contamination. The objectives of this research were to determine (1) soil surface crack area, (2) fractal dimension of crack edges (D1), and (3) mass fractal dimension (D2) and lacunarity of soil surface cracks. Photographs were used to record in situ soil cracking in a Mexico silt loam (fine, smectitic, mesic Vertic Epiaqualf) at two locations for three sampling dates. Photographs of the cracks were digitized and an algorithm was developed to determine crack area, and the fractal dimension and lacunarity of the digitized images. Location 1 produced 7% crack area, a mass fractal dimension (D2) of 1.44, and a crack edge fractal dimension (D1) of 1.08. Location 2 produced 25% crack area, a mass fractal dimension (D2) of 1.64, and a crack edge fractal dimension of 1.08 (D1). Lacunarity curves as a function of box size for crack boundary fractal dimension were more variable at location 2. Soil profile moisture content and texture analysis indicated the presence of an argillic horizon at the 20-cm depth at Location 1 while at Location 2 the argillic horizon was exposed to the soil surface. Photographic image analysis techniques and fractal analysis appear to distinguish differences in crack area and patterns which may be useful in characterizing soil cracking. [Copyright &y& Elsevier]