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Chan R.,University of Missouri | Baffaut C.,Cropping Systems and Water Quality Research Unit | Thompson A.,University of Missouri | Sadler J.,Cropping Systems and Water Quality Research Unit
Catena | Year: 2016

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. © 2016.

Sheridan A.H.,University of Missouri | Kitchen N.R.,Cropping Systems and Water Quality Research Unit | Sudduth K.A.,Cropping Systems and Water Quality Research Unit | Drummond S.T.,Cropping Systems and Water Quality Research Unit
Agronomy Journal | Year: 2012

Active-light crop canopy sensing for corn (Zea mays L.) N fertilizer rate decisions typically include measurements of N-sufficient plants as a reference. When producers use multiple hybrids in one field, the question is raised of whether an N-sufficient reference is needed for each hybrid. The objective of this research was to assess the impact of sufficiently N-fertilized, similar-maturing corn hybrids on crop-reflectance measurements. Eleven similar-maturing hybrids were selected from three sites in 2008 and eight hybrids from two sites in 2009. When the corn was about 10 cm tall and on 3 to 5 d intervals canopy reflectance, leaf chlorophyll, and plant height measurements were obtained. Results were classed into two growth periods based on crop height: 20 to 70 cm and 71 to 120 cm. In three of the four growing periods assessed corn hybrid had no significant effect on reflectance. In 2008, reflectance for corn 71 to 120 cm tall was affected by hybrid; however the effect was minor leading to an average N rate recommendation difference of 10 kg ha -1. More pronounced differences occurred among hybrids for leaf chlorophyll measurements, resulting in differences in N fertilizer recommendations of 55 kg ha -1. Reflectance differences among similar maturing hybrids would have minimal impact on N fertilizer recommendations. Models were also developed to represent typical upper and lower values for various vegetative indices as a function of corn height. These models can help guard against using questionable data when assessing N-sufficient corn. © 2012 by the American Society of Agronomy, 5585 Guilford Road, Madison, WI 53711.

Chu B.,University of Missouri | Anderson S.H.,University of Missouri | Goyne K.W.,University of Missouri | Lin C.-H.,University of Missouri | Lerch R.N.,Cropping Systems and Water Quality Research Unit
Vadose Zone Journal | Year: 2013

Two soils with different vegetative management were evaluated for sorption and leaching of an antibiotic. The antibiotic was bound more tightly and leached less in soils from agroforestry than cropland management. Results will benefit managers by providing evidence in support of vegetative buffers as a practice to mitigate antibiotic transport. Knowledge of veterinary antibiotic (VA) transport and persistence is critical to understanding environmental risks associated with these potential contaminants. To understand mobility of sulfamethazine (SMZ) and sorption processes involved during SMZ transport in soil, batch sorption experiments were conducted and column leaching experiments were performed with repacked soil columns containing silt loam soils collected from cropland (Crop) and an agroforestry (AGF) vegetative buffer system. Bromide (Br-) was applied as a nonreactive tracer to characterize the flow of water. Radio-labeled (14C) SMZ with or without 150 mg L-1 of manure-derived dissolved organic carbon (DOC), was added as a pulse and leaching of the compounds was monitored for 21 d. Sulfamethazine concentration in the leachate was monitored using a liquid scintillation counter and high performance liquid chromatography analysis confirmed absence of SMZ degradation product in the leachate. Breakthrough curves of SMZ and Br- were constructed for each column. Bromide breakthrough curves were fitted with a convection/dispersion based transport equilibrium model with no sorption, whereas SMZ breakthrough curves were fitted with multisite sorption chemical nonequilibrium transport models with linear or Freundlich sorption components. Results indicated that the three-site model containing two reversible sites (one instantaneous and one kinetic) and one irreversible site coupled with the Freundlich sorption component (3S2R-Freu-irrev model) best described SMZ transport through the columns with model efficiencies of 0.998, 0.994, and 0.991 for AGF, AGF + DOC and Crop soils, respectively. No difference or small difference between fitted sorption parameters, such as the linear sorption coefficient (Kd), Freundlich sorption coefficient (Kf), and Freundlich nonlinearity parameter (A/), and those obtained from equilibrium sorption experiments was observed. Data from equilibrium sorption experiments and column transport experiments suggested that the AGF soil was able to retain a larger quantity of SMZ than the Crop soil, and DOC had little effect on SMZ sorption or leaching. Greater SMZ retention by the AGF soil compared to the Crop soil suggests that vegetative buffers may be a viable means to mitigate VA loss from agroecosystems. © Soil Science Society of America 5585 Guilford Rd., Madison, WI 53711 USA. All rights reserved.

Roberts D.F.,Mississippi State University | Ferguson R.B.,University of Nebraska - Lincoln | Kitchen N.R.,Cropping Systems and Water Quality Research Unit | Adamchuk V.I.,McGill University | Shanahan J.F.,DuPont Pioneer
Agronomy Journal | Year: 2012

Integrating soil-based management zones (MZ) with crop-based active canopy sensors to direct spatially variable N applications has been proposed for improving N fertilizer management of corn (Zea mays L.). Analyses are needed to evaluate relationships between canopy sensing and soil-based MZ and their combined potential to improve N management. The objectives of this study were to: (i) identify soil variables related to in-season crop canopy reflectance and yield and use these variables to delineate MZ for N fertilizer management; and (ii) compare corn yield response to different N fertilizer treatments for different MZ. Eight N rates (0-274 kg N ha-1 in 39 kg ha-1 increments) were applied in replicated small plots across six irrigated fields in 2007 to 2008 throughout central Nebraska. Soil variables evaluated for MZ delineation included: apparent soil electrical conductivity (ECa), soil optical reflectance, and landscape topography. Crop response to N was determined via active sensor assessments of in-season canopy reflectance (chlorophyll index, CI590) and grain yield. Relationships between soil and topography data and crop performance were evaluated, with selected soil variables used to delineate two MZ within four of the six fields. Economic benefits to N application according to soil-based MZ were observed in fields with silty clay loam and silt loam soils with substantial relief and eroded slopes. Sensor-based algorithms may need to be adjusted according to MZ to account for differences in crop N response. © 2012 by the American Society of Agronomy.

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