Claypan Soil Research Articles

Incorporating Pesticide Transport into the WEPP Model for Mulch Tillage and No Tillage Plots with an Underlying Claypan Soil

<abstract><title><italic>Abstract.</italic></title> Best management practice (BMP) tools that provide site-specific water quality assessment with limited input data are needed to assist soil and water managers as they work to target BMP placement and reduce dissolved and sediment bound pesticide loss from agricultural landscapes. BMP effectiveness largely depends on accurate characterization of dominant regional hydrologic processes. However, most BMP tools are region specific in their characterization of hydrology (e.g., most models capture either infiltration excess runoff or saturation excess runoff but cannot predict a combination of the two). In this study, we develop and couple a pesticide transport module with the Water Erosion Prediction Project (WEPP) model (v2012.8). The WEPP model realistically simulates infiltration excess and saturation excess runoff as well as dissolved pesticide loss from hillslopes in the Goodwater Creek Experimental Watershed (GCEW) in northeastern Missouri. Simulated runoff and dissolved atrazine concentrations were compared to observed data from mulch till (MT) and no till (NT) plots in the GCEW. The timing of runoff predicted by WEPP coincided well with observed events and simulated flow magnitudes were between minimum and maximum observations for replicate plots. Event-based Nash-Sutcliffe Efficiencies (NSE) are 0.84 and 0.79 for MT and NT runoff simulations, respectively. Both simulations and observations showed little difference in total growing season (planting to harvest) runoff between MT and NT. Event-based dissolved atrazine loads are well predicted for MT and NT with NSEs of 0.59 and 0.71, respectively. Consistent with observations, seasonal NT atrazine losses were greater than losses from MT plots. While this study only focuses on dissolved pesticide transport from the base of hillslopes using MT and NT conservation practices, the WEPP pesticide transport module is capable of predicting both dissolved and sediment bound pesticide loss from each section of the hillslope (i.e., top-slope, mid-slope, and toe-slope) for a wide range of BMPs. However, further field data are needed to evaluate these aspects of the model.

Agricultural Policy Environmental eXtender Simulation of Three Adjacent Row‐Crop Watersheds in the Claypan Region

The Agricultural Policy Environmental Extender (APEX) model is used to evaluate best management practices on pollutant loading in whole farms or small watersheds. The objectives of this study were to conduct a sensitivity analysis to determine the effect of model parameters on APEX output and use the parameterized, calibrated, and validated model to evaluate long-term benefits of grass waterways. The APEX model was used to model three (East, Center, and West) adjacent field-size watersheds with claypan soils under a no-till corn ( L.)/soybean [ (L.) Merr.] rotation. Twenty-seven parameters were sensitive for crop yield, runoff, sediment, nitrogen (dissolved and total), and phosphorous (dissolved and total) simulations. The model was calibrated using measured event-based data from the Center watershed from 1993 to 1997 and validated with data from the West and East watersheds. Simulated crop yields were within ±13% of the measured yield. The model performance for event-based runoff was excellent, with calibration and validation > 0.9 and Nash-Sutcliffe coefficients (NSC) > 0.8, respectively. Sediment and total nitrogen calibration results were satisfactory for larger rainfall events (>50 mm), with > 0.5 and NSC > 0.4, but validation results remained poor, with NSC between 0.18 and 0.3. Total phosphorous was well calibrated and validated, with > 0.8 and NSC > 0.7, respectively. The presence of grass waterways reduced annual total phosphorus loadings by 13 to 25%. The replicated study indicates that APEX provides a convenient and efficient tool to evaluate long-term benefits of conservation practices.

Corn Yield Response to Timing of Strip‐Tillage and Nitrogen Source Applications

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.

Corn yield response to polymer and non-coated urea placement and timings

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.

Grain Sorghum Nutrient Uptake and Yield Following Turkey Litter and Fertilizer Applications on a Claypan Soil

Grain Sorghum Nutrient Uptake and Yield Following Turkey Litter and Fertilizer Applications on a Claypan Soil

Relationships Among Water Stable Aggregates and Organic Matter Fractions Under Conservation Management

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.

Microbial community diversity in agroforestry and grass vegetative filter strips

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).

Comparative Breakeven Analysis of Annual Grain and Perennial Switchgrass Cropping Systems on Claypan Soil Landscapes

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 breakeven 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 &gt;27 cm 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 &lt;15 cm 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.

Nitrous Oxide Emissions from Claypan Soils Due to Nitrogen Fertilizer Source and Tillage/Fertilizer Placement Practices

Poorly drained soils can potentially have large amounts of applied fertilizer N lost through denitrification which can be a major contributor to soil nitrous oxide (N2O) emissions. These soil N2O emissions due to agricultural practices are significant because they contribute to global warming and ozone depletion. The objectives of this research were to quantify the effects of tillage/fertilizer placement (i.e., no‐till/surface broadcast and strip‐till/deep banded) and N fertilizer source [i.e., non‐coated urea (NCU), polymer‐coated urea (PCU), nontreated control] on soil N2O emissions from corn (Zea mays L.) production over the 2009 and 2010 growing seasons in a poorly drained claypan soil in Northeast Missouri. Averaged over 2009 and 2010, no significant differences were observed in cumulative soil N2O emissions, between treatment plots with NCU (5.21 kg N2O‐N ha−1) and PCU (5.48 kg N2O‐N ha−1). Soil N2O losses represented between 2.8 and 3.0% of annual fertilizer N applied, respectively. Strip‐till/deep banded N placement emitted 28% less N2O (0.2 kg N2O‐N) per Mg grain produced (P = 0.0284) compared to that of no‐till/surface broadcasted N. Impacts of alternative management practices on soil N2O losses may also need to consider changes in agricultural production to allow producers to decide which practices are best suited to balance their production and environmental goals.

Nutrient losses in field-scale surface runoff from claypan soil receiving turkey litter and fertilizer

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.

Corn Hybrid Response to Water Management Practices on Claypan Soil

A study evaluated corn (Zea maysL.) 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 12.2 m apart; drained plus subirrigated (DSI) with tiles 6.1 and 12.2 m apart; nondrained, overhead irrigated (NDOHI)) on yields, plant population, and grain quality from 2008 to 2010. Precipitation during this study was 36 to 283 mm above 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 12.2 m-spaced DNI and DSI systems in 2008 and 2010, but plant population increased 74% and yields were 3.1 Mg ha−1greater with DSI at a 6.1 m spacing compared to 12.2 m in 2009. At a 6.1 m spacing, DNI or DSI increased yield 1.1 to 6.6 Mg 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 1.2 Mg ha−1greater yields compared to DKC61-73. A 6.1 m spacing for DNI claypan soils is recommended for high yielding corn production.

Phosphorus and nitrogen losses in relation to forest, pasture and row-crop land use and precipitation distribution in the midwest usa

Little information is available comparing the influence of land use and precipitation on the control of phosphorus (P) and nitrogen (N) losses from agricultural watersheds in claypan soils. Eight watersheds with varying proportions of row-crop, pasture, forest, and grass filter strip condition were examined for three consecutive years to evaluate effects of land use and precipitation on P and N losses from row-cropped watersheds. Total P (TP) and total N (TN) losses were inversely related to the percentage of forest and pasture cover. Forest (n=2), pasture (n=3), row-crop (n=2), and row-crop grass filter strip (n=1) land use types had mean annual TP losses of 0.43, 0.90, 3.82 and 1.30 kg•ha-1•yr-1, respectively and mean annual TN losses of 2.02, 4.34, 29.25 and 12.31 kg•ha-1•yr-1, respectively. During the 3-year study, the respective land use types lost 0.36, 0.64, 13.99 and 7.26 kg NO3-N•ha-1•yr-1. Runoff events on row-cropped watersheds resulted in significantly greater TP, TN, and NO3-N losses than those from pastured and forested watersheds. Stream nitrate-N concentrations averaged 0.39, 0.50, and 2.56 mg•L-1 for forest, pasture, and row-crop land use types, respectively. During the study, 136% of the long-term average precipitation in 1998 caused significant nutrient losses in all watershed categories and the variability within a land use type was larger than in years with below long-term rainfall. The study results emphasize the incorporation of perennial vegetation such as vegetative buffers, grass/conservation reserve program areas, and grass filter strips or other perennial vegetation as a long-term option for effective control of nutrient losses in runoff from agricultural watersheds.

Assessment of soil organic carbon and total nitrogen under conservation management practices in the Central Claypan Region, Missouri, USA

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 10 years after VFS establishment in a no-till system planted to maize ( Zea mays. L.)–soybean ( Glycine max (L.) Merr.) rotation. Two soil depth increments (0–5 cm and 5–13 cm) 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.

Soil microbial biomass nitrogen and β-glucosaminidase activity response to surface compaction and poultry-litter application in a claypan soil

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 1.8 mg m −3) amended with and without poultry litter and incubated at 25 °C for 28 d. In a field experiment conducted in 2001 and 2002, a Mexico silt loam claypan soil was amended with litter (0 and 19 mg ha −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.

Soybean Yield Response to Pyraclostrobin and Drainage Water Management

Although pyraclostrobin {carbamic acid, [2,[[[1‐(4‐chlorophenyl)‐1H‐pyrazol‐3‐yl]oxy]methyl]phenyl]methoxy‐,methyl ester} has been used to protect soybean [Glycine max (L.) Merr.] from foliar diseases, its interaction with drainage water management (DWM) systems was unknown. Field research during two wet years (95 to 97 mm greater than the past decade) evaluated the effects of pyraclostrobin application timing (R3, R5, R3+R5, and R3+R5+lambda‐cyhalothrin) and DWM system (nondrained and drainage only [DO] or drainage plus subirrigation [DSI] at 6.1 and 12.2 m drain tile spacings) on soybean yield, grain quality, and severity of Septoria brown spot (SBS) (Septoria glycines) and frogeye leaf spot (FLS) (Cercospora sojina). Grain yields increased 18 to 22% with DO or DSI at 6.1 and 12.2 m spacings compared to a nonfungicide treated, nondrained control. In the absence of drainage, pyraclostrobin with or without lambda‐cyhalothrin increased yields 20 to 27% compared to the nondrained, nonfungicide treated control. The combination of DWM and pyraclostrobin increased grain yields up to 36%. Pyraclostrobin plus lambda‐cyhalothrin at R3+R5 increased yield 8 to 12% except with DO at 12.2 m compared to similar nonfungicide‐treated DWM systems. A DWM and pyraclostrobin interaction was detected for grain oil and protein concentration, but differences were minimal. Pyraclostrobin with or without lambda‐cyhalothrin reduced severity of SBS and FLS 2 to 8% depending on the year, but DWM did not affect severity of these diseases. The greatest synergistic yield increase on a claypan soil occurred when foliar disease management and DWM systems were used together in years with higher than normal rainfall.

Peak functions for modeling high resolution soil profile data

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 (R 2 = 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 (R 2 = 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.

Soybean Response to Drainage and Subirrigation on a Claypan Soil in Northeast Missouri

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 1200 kg 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.

NITROGEN, PHOSPHORUS, AND POTASSIUM EFFECTS ON GRAIN SORGHUM PRODUCTION AND STALK ROT FOLLOWING ALFALFA AND BIRDSFOOT TREFOIL

Grain sorghum [Sorghum bicolor (L.)], grown on the often infertile claypan soils of the eastern Great Plains, requires attention to soil fertility. Experimental objectives were to determine the effects of phosphorus (P) and potassium (K) fertility levels, N application, and legume residual on grain sorghum production and stalk rot. Following alfalfa and birdsfoot trefoil, first-year sorghum yield was 7 Mg ha−1 and not affected by N fertilizer. In subsequent years, yield increases due to N were less than 20%. Sorghum yield increased at low P and K rates, especially with nitrogen (N) fertilization and was greater following birdsfoot trefoil than following alfalfa. In 1995 when fertilized with N, lodging and stalk rot severity were increased by P and reduced by K. In 1996, stalk rot severity was reduced by K fertilization. Grain sorghum, grown after legume crops, required minimal levels of P and K, especially when N fertilizer was added.

Reducing Herbicides and Veterinary Antibiotics Losses from Agroecosystems Using Vegetative Buffers

Multiple species vegetative buffer strips (VBSs) have been recommended as a cost-effective approach to mitigate agrochemical transport in surface runoff derived from agronomic operations, while at the same time offering a broader range of long-term ecological and environmental benefits. However, the effect of VBS designs and species composition on reducing herbicide and veterinary antibiotic transport has not been well documented. An experiment consisting of three VBS designs and one continuous cultivated fallow control replicated in triplicate was conducted to assess effectiveness in reducing herbicide and antibiotic transport for claypan soils. The three VBS designs include (i) tall fescue, (ii) tall fescue with a switchgrass hedge barrier, and (iii) native vegetation (largely eastern gamagrass). Rainfall simulation was used to create uniform antecedent soil moisture content in the plots and to generate runoff. Our results suggested that all VBS significantly reduced the transport of dissolved and sediment-bound atrazine, metolachlor, and glyphosate in surface runoff by 58 to 72%. Four to 8 m of any tested VBS reduced dissolved sulfamethazine transport in the surface runoff by more than 70%. The tall fescue VBS was overall most effective at reducing dissolved tylosin and enrofloxacin transport in the runoff (>75%). The developed exponential regression models can be used to predict expected field-scale results and provide design criteria for effective field implementation of grass buffers. Our study has demonstrated that an optimized VBS design may achieve desired agrochemical reductions and minimize acreage removed from crop production.

Soil microbial activity and functional diversity changed by compaction, poultry litter and cropping in a claypan soil

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.