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Nov-Dec 2005
November/December 2005: Volume 60, Number 6
Table of Contents
Features
Picture This!
How to help landowners "picture" the conservation plan you are proposing.
By Gary Bentrup and Gary Wells
Conservation Districts Connect
An award winning Conservation District shares their view on their importance in their community.
By Erin Meyer
"Worlds Underfoot" Soil Exhibit
A proposed soil exhibit at the Smithsonian museum in Washington, D.C. could educate millions of people about different types of soil and their complexities.
By Paul Kamps
Departments
Homefront
Column by the Soil and Water Conservation Society’s Executive Director, Craig A. Cox.
Raise Your Voice
Letters to the Editor
Going Retro – Celebrating 60 Years of the JSWC
A year long celebration comes to an end.
Viewpoint-Precision Conservation
NRCS Chief Bruce Knight
Notebook
Conservation News You Can Use
Conservogram
The Soil and Water Conservation Society in Action
Research Section:
Special Section:
Research Section
Watershed management, structural characteristics, information processing, and cooperative strategies in conservation organizations
(Full text appears in the Journal of Soil and Water Conservation, Vol. 60, No. 6)
S. Low and T. Randhir
ABSTRACT: This study focuses on evaluating organizational characteristics, the role of watershed-based planning, biodiversity protection efforts, and cooperative strategies in conservation organizations using a mail-out survey. The goal is to get more insights into interrelationships between variables and to summarize the interrelationships for organizational improvement and research. Descriptive statistics and structural equation modeling (path analysis) are used. There existed paths of influence among structural variables of an organization. Cooperation, volunteerism, publicity, leadership, and better funding opportunities were identified as key factors important for the success of an organization. Administrative leadership, funding, information management, and collaboration were identified as four elements of an organizational framework that were necessary for assessment, reorganization, and design of new organizations. There exists opportunities for more interaction with public and for coordination of efforts at a watershed scale. Education and incentive policies are suggested to improve conservation organizations.
Keywords: Cooperative strategies, information processing, path analysis, structural characteristics, watershed organizations
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Evaluation of stormwater from compost and conventional erosion control practices in construction activities
(Full text appears in the Journal of Soil and Water Conservation, Vol. 60, No. 6)
L.B. Faucette, C.F. Jordan, L.M. Risse, M. Cabrera, D.C. Coleman, and L.T. West
ABSTRACT: Soil erosion is considered the biggest contributor to nonpoint source pollution in the United States according to the U.S. Environmental Protection Agency and the federally mandated National Pollution Discharge Elimination System. Soil loss rates from construction sites can be 10 to 20 times that of agricultural lands. The use of surface applied organic amendments has been shown to reduce runoff and erosion, however, with the exception of animal manure, little research has focused on nutrient loss from these amendments. Four types of compost blankets, hydroseed, silt fence, and a bare soil (control) were applied in field test plots. Treatments were seeded with common bermuda grass. A rainfall simulator applied rainfall at an average rate equivalent to the 50 yr hr-1 storm event (7.75 cm hr-1). Three simulated rain events were conducted: immediately after treatment application, at three months when vegetation was established, and at one year when the vegetation was mature. After three months, the compost generated five times less runoff than hydroseed with silt fence, and after one year, generated 24 percent less runoff. All treatments proved better than the control at reducing solids loss. Total solid loads were as much as 3.5 times greater from hydroseed and silt fence compared to the composts during the first storm, and as much as 16 times greater during the second storm. Materials high in inorganic nitrogen (N) released greater amounts of nitrogen in storm runoff; however, these materials showed reduced N loss over time. Hydroseeding generated significantly higher total phosphorus (P) and dissolved reactive P loads compared to compost in storm runoff during the first storm event.
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A southeastern piedmont watershed sediment budget: Evidence for a multi-millennial agricultural legacy
(Full text appears in the Journal of Soil and Water Conservation, Vol. 60, No. 6)
C.R. Jackson, J.K. Martin, D.S. Leigh, and L.T. West
ABSTRACT: A sediment budget was developed for a representative rural southeastern Piedmont watershed to estimate the relative importance of various sediment sources, particularly the contribution of agricultural sediments introduced to stream systems during the cotton-farming era (approximately 1820 to 1930 A.D.). The Murder Creek basin containing Monticello, Georgia was chosen because: 1) forestry and agriculture were and continue to be dominant land uses;
2) a U.S. Geological Survey (USGS) gage provided flow and suspended sediment records; and
3) the creek discharges into the Lake Sinclair reservoir (constructed 1949 to 1953), which could be used as a bedload sediment trap. Sediment rating curves, reservoir sediment deposition, and the Water Erosion Prediction Project (WEPP) and Universal Soil Loss Equation (USLE) erosion models were used to estimate suspended sediment export, bedload export, unpaved road erosion, and other surface erosion, respectively. Depths of historical agricultural sediment deposits were measured in stream cutbanks and floodplain auger holes. Historical row-crop agriculture led to floodplain deposition of a nearly-uniform 1.6 m (5.3 ft) of sediment, equivalent to 12.2 cm (0.40 ft) of topsoil over the watershed. The mass of cotton-farming sediments in valley storage was extremely large compared to current sediment export rates. At present sediment export rates, it would take six to ten millennia to remove all of the cotton-farming sediment in storage. This study suggests that the unstable streambanks, mobile sandy streambeds, and turbid conditions characteristic of modern Piedmont streams are largely a legacy of poor farming practices in the late 1800s and early 1900s. Estimated sediment exports exceed estimates of current inputs, and floodplain accretion rates and streambank conditions suggest streams have been in a state of net sediment export over the last 50 years.
Keywords: Erosion, fluvial geomorphology, sedimentation, sediment budgets, water quality
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Effect of cover crops established at time of corn planting on phosphorus runoff from soils before and after dairy manure application
(Full text appears in the Journal of Soil and Water Conservation, Vol. 60, No. 6)
P.J.A. Kleinman, P. Salon, A.N. Sharpley and L.S. Saporito
ABSTRACT: Phosphorus (P) runoff from agricultural soils is a concern due to eutrophication. The simultaneous corn and cover crop system was developed by U.S. Department of Agriculture’s Natural Resources Conservation Service (USDA-NRCS) for dairy farms in the northeastern United States, where short growing seasons have limited fall seeding of cover crops. The simultaneous corn and cover crop system uses post-emergence imidazolinone herbicides to allow for simultaneous seeding of cover crops with silage corn. Trials were established at two locations in the Cannonsville Reservoir watershed, New York, part of New York City’s drinking water supply system, to assess the effects of this cover cropping system on water quality. Rain simulations (60 mm hr-1) were conducted to evaluate the initial 30 minutes of runoff from small (1 x 2 m; 3 ft x 7 ft) plots before and after surface application of dairy manure (50 or 100 kg total P ha-1 ; 45 or 89 lb P ac-1). Corn yields from plots interseeded with red clover compared most favorably with the conventionally cropped controls, with no significant differences in yields noted between the two treatments at either location. Prior to dairy manure application, losses of P in runoff were primarily a function of erosion. Because all cover crops increased ground cover (up to 81 percent greater than the control), total P loads in runoff were significantly lower from cover cropped plots (averaging 10 mg per plot) than from conventionally cropped controls (averaging 39 mg per plot). At the same time, suspended solids loads averaged 25.3 g (1 oz) from the control plots and 5.9 g (0.2 oz) from the cover crop plots. Despite concern that release of soluble P from the cover crops could enrich dissolved reactive P in runoff, dissolved reactive P losses from the simultaneous corn and cover crop system were generally not different from conventionally-cropped silage corn losses. Application of manure obscured cover crop/conventional silage corn treatment differences with regard to P runoff, with dissolved reactive P becoming the dominant form of P in runoff due to contributions of readily soluble P in manure. Because runoff P losses were already high from unmanured conventional silage corn plots, application of manure did not significantly increase P losses from some of the conventional silage corn treatments. Results highlight the agronomic and water quality benefits of the simultaneous corn and cover crop system, particularly when implemented with red clover.
Keywords: Corn, cover crops, erosion, manure, phosphorus, runoff
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Development and sensitivity of a method to select time- and flow-paced storm event sampling intervals for headwater streams
(Full text appears in the Journal of Soil and Water Conservation, Vol. 60, No. 6)
K.W. King, R.D. Harmel, and N.R. Fausey
ABSTRACT: Water quality research and monitoring programs often form the basis from which related legislation is derived. Yet, no standard, protocol, or method is available for guiding the selection of a water quality sampling strategy for runoff from fields and small watersheds. The objective of this study was to develop a methodology that provides guidance in the selection of a water quality sampling strategy for headwater streams (drainage areas less than 2500 ha; 6,177 ac). The developed method is based on the dimensionless unit hydrograph and relationships of measured pollutant concentrations to discharge hydrographs. The methodology was designed for storm events with a specific return interval and a selected acceptable level of error in pollutant load. Nine input parameters (hydraulic length, watershed slope, curve number, drainage area, runoff coefficient, 10-year, one hour precipitation amount, 100-year, one hour precipitation amount, 10 year, 24 hour precipitation amount, and recurrence interval) were used to develop the design hydrograph. Both time- and flow-paced sampling techniques were considered. A global sensitivity analysis of the method indicated that time-paced sampling was primarily sensitive to parameters included in the time of concentration calculation (hydraulic length, watershed slope, and curve number). Flow-paced sampling showed some sensitivity to all nine input parameters. An example application illustrates the utility of the method. Use of the method should facilitate the selection of water quality sampling strategies for field and small watershed scale studies and aid in budgetary planning for sample collection and analysis. The measurements taken based on the recommended sampling strategy will provide more confidence in the pollutant storm load estimates.
Keywords: Concentrations, hydrographs, pollutant loads, water quality
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Relationship between thermal ground-water and environmental genesis of wetlands: The case of the Prats de Sant Sebastià, northwestern Mediterranean margin
(Full text appears in the Journal of Soil and Water Conservation, Vol. 60, No. 6)
M. Vehí, J. Bach, C. Roqué, and R. Linares
ABSTRACT: The Prats de Sant Sebastià wetland is located in Caldes de Malavella, on the northeast of the Iberian Peninsula. Several zones with anomalously high ground conductivity have been identified at this site. As a result of local high salinity, rare, highly specialized plant species grow in this area. The geophysical data to 6 m depth show saline soil concentrations in a north-south direction. The hydrogeological setting of the wetlands provides an insight into soil genesis and the origin of the wetland environment. It was deduced that discharging groundwater from underlying hydrogeothermally deposited salts produced and maintains soil salinity in the wetland. The locality is little known, and until now, there were few hydro-geological data available.
Keywords: Caldes de Malavella (northwestern Mediterranean margin), groundwater flow, salinization, thermal saline springs, wetlands
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Special Section
Precision conservation in North America
Special section introduction
(Full text appears in the Journal of Soil and Water Conservation, Vol. 60, No. 6)
J.A. Delgado, C.A. Cox, F.J. Pierce, and M.G. Dosskey
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Soil organic carbon maintenance in corn (Zea mays L.) and soybean (Glycine max L.) as influenced by elevation zone
(Full text appears in the Journal of Soil and Water Conservation, Vol. 60, No. 6)
D.E. Clay, C.G. Carlson, S.A. Clay, J. Chang, and D.D. Malo
ABSTRACT: Landscape processes may impact the amount of carbon (C) required to maintain soil organic C levels. The objective of this study determined the influence of elevation zones on soil organic C maintenance and C-budgets. Research conducted between 1995 and 2003 in a 160 ac (65 ha) east-central South Dakota field measured spatial and temporal biomass [corn (Zea mays) and soybean (Glycine max)] production and changes in soil organic C and 13C isotopic discrimination (?). Results from this study showed that: 1) data collected through precision farming practices (yield and grid soil samples analyzed for soil organic C) can be used to determine soil organic C maintenance requirements; 2) the corn - soybean rotation may not return enough biomass-C to maintain soil organic C levels at all landscape positions; 3) calculated maintenance rates were dependent on the approach used to estimate below ground biomass; 4) footslope areas had higher maintenance rates than summit/shoulder areas; and 5) 1.84 percent and 1.21 percent soil organic C measure in 1995 (SOC95) were mineralized annually in elevation zones less than 527.3 and greater than 527.3 m, respectively. To maintain soil organic C levels, areas where mineralization is high (footslopes) will require higher biomass-C additions than areas where soil organic C mineralization is low (shoulders). The potential benefits of increasing biomass-C additions to footslope areas at the expense of summit/shoulder areas must be balanced against the potential effects on erosion.
Keywords: Biomass for energy production, carbon sequestration, stable C13 isotope discrimination, carbon sequestration, sustainable agriculture
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Establishing conservation buffers using precision information
(Full text appears in the Journal of Soil and Water Conservation, Vol. 60, No. 6)
M.G. Dosskey, D.E. Eisenhauer, and M.J. Helmers
Abstract: Conservation buffers, such as filter strips and riparian forest buffers, are widely prescribed to improve and protect water quality in agricultural landscapes. These buffers intercept field runoff and retain some of its pollutant load before it reaches a waterway. A buffer typically is designed to have uniform width along a field margin and to intercept runoff that flows uniformly to it. However, spatial analysis of field conditions and runoff patterns indicate that more runoff is likely to flow to some locations along a field margin than to others which can substantially limit a buffer’s effectiveness. We propose that precision conservation, the use of precision spatial information, technologies, and procedures to implement conservation practices, can be used to improve the design of buffers and ensure their effectiveness. Precision conservation can integrate detailed landscape data with mathematical models in a geographic information system. We can then analyze spatial patterns of runoff and design variable-width buffers that precisely match the needs of every location along a waterway. Greater cost of precision conservation is offset partly by greater water-quality benefit from each acre of buffer. Many of the required data sources and modeling components already exist, substantial improvements are possible that can produce even greater conservation efficiency.
Keywords: Buffer design, filter strip, precision agriculture, precision conservation, riparian buffer, water quality
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Identifying spatial patterns of erosion for use in precision conservation
(Full text appears in the Journal of Soil and Water Conservation, Vol. 60, No. 6)
J.A. Schumacher, T.C. Kaspar, J.C. Ritchie, T.E. Schumacher, D.L. Karlen, E.R. Venteris, G.W. McCarty, T.S. Colvin, D.B. Jaynes, M.J. Lindstrom, and T.E. Fenton
Abstract: The application of site-specific conservation practices requires knowledge of spatial patterns in fields. This study evaluated two methods of delineating soil erosion patterns in a central Iowa field. First, soil erosion rates of individual grid based samples were estimated using soil displacement of cesium-137 (137Cs). Second, tillage and water erosion were estimated using the topography-driven Water and Tillage Erosion Model (WATEM). The tillage erosion map showed soil loss in convex shoulder positions and soil accumulation in concave footslope and toeslope landscape positions. Alternately, water erosion was associated with slope severity and slope length on backslopes. When the tillage and water erosion map patterns were combined a good correlation with the 137Cs soil erosion pattern was graphically and statistically exhibited. Study results suggest that tillage erosion be included with water and wind erosion estimates when developing spatial maps that reflect a field’s erosion history. Spatial maps depicting a field’s erosion history and the primary processes affecting erosion could be used for site-specific implementation of conservation practices such as cover crops, organic matter additions, and no-till, which could be targeted at specific erosion processes.
Keywords: Erosion, precision agriculture, soil conservation, tillage
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Applying spatial analysis for precision conservation across the landscape
(Full text appears in the Journal of Soil and Water Conservation, Vol. 60, No. 6)
(Full Text PDF)
J.K. Berry, J.A. Delgado*, F.J. Pierce, and R. Khosla
ABSTRACT: Although new technologies such as precision farming will contribute to increasing yields per unit area, similarly soil and water conservation will be instrumental in maintaining these increases in productivity while reducing environmental degradation, off-site transport, and water pollution. Initially, ‘precision conservation’ was defined as the integration of spatial technologies such as global positioning systems (GPS), remote sensing, and geographic information systems (GIS) and the ability to analyze spatial relationships within and among mapped data. Surface modeling, spatial data mining and map analysis are three broad approaches that can be used to analyze layers of information to help develop and implement management practices that contribute to soil and water conservation in agricultural and natural ecosystems. In this paper, we expand the definition of precision conservation to a developing science that uses the new spatial technologies to link a system from a site specific location, to a field, to a set of fields (farm) to a regional scale. We also expand our discussion based on the status of precision conservation as it was shown by twenty six precision conservation papers presented at the 2004 Soil Science Society of America annual meeting. We propose that precision conservation will be a key science to contribute to the sustainability of our biosphere in this century.
Keywords: Agricultural sustainability, geographic information systems, global positioning systems, precision conservation, precision farming
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Opportunities for conservation with precision irrigation
(Full text appears in the Journal of Soil and Water Conservation, Vol. 60, No. 6)
E.J. Sadler, R.G. Evans, K.C. Stone, and C.R. Camp
ABSTRACT: Precision agriculture has mostly emphasized variable-rate nutrients, seeding, and pesticide application, but at several research sites, variable-rate irrigation equipment has been developed to explore the potential for managing irrigation spatially. The modifications to commercial machines are relatively straightforward, but costly; thus economic analyses have not been positive at current grain price: water cost ratios. However, with increased attention to conservation of water during drought, with increased contention for environmental, recreational, municipal, and industry use, or with regulatory constraints, conclusions regarding profitability or desirability of variable-rate irrigation may change. The objectives of this paper are to: 1) define and describe site-specific irrigation, 2) discuss the opportunities for conservation using site-specific irrigation, 3) present case studies from production and research fields that illustrate these opportunities, and 4) discuss critical research needs to fully implement precision irrigation and thus realize these opportunities for conservation. The opportunities for conservation discussed include situations where non-cropped areas exist in a field for which irrigation can be turned completely off, situations where a reduced irrigation amount provides specific benefits, and finally, situations where optimizing irrigation amount to adapt to spatial productivity provides quantitative benefits. Results from the case studies provide estimates of the potential for water conservation using precision irrigation that range from marginal to nearly 50 percent in single years, and average from eight to 20 percent, depending on the previous irrigation management strategy employed. Critical research needs include improved decision support systems and real-time monitoring and feedback to irrigation control.
Keywords: Site-specific irrigation, spatial variation, water conservation
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Potential use of precision conservation techniques to reduce nitrate leaching in irrigated crops
(Full text appears in the Journal of Soil and Water Conservation, Vol. 60, No. 6)
J.A. Delgado and W.C. Bausch
ABSTRACT: There is a continuing need to develop advanced nitrogen (N) management practices that increase N use efficiencies and reduce nitrate-nitrogen (NO3-N) leaching. Our goal was to evaluate the use of geographic information systems (GIS), global positioning systems (GPS), modeling and remote sensing for reducing residual soil NO3-N and NO3-N leaching in a center-pivot irrigated corn (Zea mays L.) field. Specific objectives were: 1) to determine if productivity zones delineated using precision agriculture technologies could also correctly identify unique areas within corn fields that differed in residual soil NO3-N and NO3-N leaching potential; and 2) evaluate the potential to use remote sensing of crop productivity to reduce NO3-N leaching losses. This study was conducted in northeastern Colorado during the 2000 and 2001 growing seasons in a 70 ha (173 ac) center-pivot irrigated commercial cornfield. For the first objective, initial and final soil samples after harvesting were collected at known locations in high, medium and low productivity areas across this field. For the second objective initial and final soil samples after harvesting were collected in a low productivity area where “in season” N management was conducted based on remote sensing data. Crop yields and total N were determined on plant samples located at the soil sampling coordinates. The N reflectance index was used to determine the “in season” N application. Remote-sensing-based N fertilization treatment occurred whenever the mean N reflectance index was lower than 0.95 and/or more than 50 percent of the area had an N reflectance index less than 0.95. For both studies, the nitrate leaching economic analysis package and GIS were used to evaluate NO3-N leaching losses. We found that GIS, GPS, and modeling technologies can be used to identify and simulate the spatial residual soil NO3-N patterns. Productivity zones delineated using precision agriculture technologies identified areas within corn production fields that differed in residual soil NO3-N and NO3-N leaching potential. This spatial variability was negatively correlated with the soil texture (P<0.001), having lower residual soil NO3-N on the lower productivity sandier areas, which also had a higher NO3-N leaching potential. The N Reflectance Index method can maximize the synchronization of “in season” N applications with corn N uptake needs to increase N use efficiencies and reduce NO3-N leaching losses by 47 percent when compared to traditional practices (P<0.0001).
Keywords: Corn, GIS, GPS, nitrate leaching, nitrogen, nitrogen management, NLEAP, precision conservation, remote sensing
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Variation in soil properties and crop yield across an eroded prairie landscape
(Full text appears in the Journal of Soil and Water Conservation, Vol. 60, No. 6)
S.K. Papiernik, M.J. Lindstrom, J.A. Schumacher, A. Farenhorst, K.D. Stephens, T.E. Schumacher, and D.A. Lobb
ABSTRACT: Intensive tillage moves large quantities of soil, resulting in a pattern of soil redistribution where topsoil is depleted from convex slope positions and deposited in concave positions. In these experiments, the variation in erosion estimates, properties of the surface soil, and crop yield (four years) were determined in an undulating landscape that is subject to annual moldboard plowing. Results indicated that areas with high tillage erosion (shoulder slope positions) had high inorganic carbon contents in the surface soil due to the incorporation of calcareous subsoil material. Wheat yields in 2000, 2001, and 2003 were lowest in these areas, demonstrating yield reductions of 50 percent or more. Conversely, wheat yields were highest in areas in which soil translocation by tillage and water results in a net deposition of soil (depressions). These areas had a deeper A horizon, and the surface soils had higher organic carbon contents, lower pH and lower inorganic carbon contents. Soybean yields in 2002 did not show a strong dependence on location within the landscape. These results indicate that the observed variation in crop yield in undulating landscapes may be significantly influenced by removal of topsoil through repeated intensive tillage, and point to opportunities for landscape restoration to reduce yield losses.
Keywords: Erosion, precision agriculture, spatial variability, tillage erosion
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Precision conservation for co-management of carbon and nitrogen on the Canadian prairies
(Full text appears in the Journal of Soil and Water Conservation, Vol. 60, No. 6)
D.J. Pennock
ABSTRACT: Agriculture is targeted to make a substantial contribution to Canada’s greenhouse gas reduction targets under the Kyoto Protocol. To achieve a net reduction in emissions any gains in soil organic carbon storage cannot come at the expense of enhanced nitrous oxide emissions from the soil. In non-level agricultural landscapes of the Canadian Prairies the potential for significant soil organic carbon gain due to adoption of soil conserving practices is greatest on convex upper slope positions, which have experienced major losses of soil organic carbon due to cultivation. The potential for soil organic carbon gain in lower slope positions is limited due to their high soil organic carbon contents, but targeted wetland and riparian vegetation restoration programs could lead to significant above ground carbon gains. Several studies have shown that emissions of nitrous oxide from lower slope positions are significantly higher than the convex slope positions, and that improvements in nitrogen fertilizer use efficiency through site-specific management has the potential to significantly reduce nitrous oxide (N2O) emissions from these positions. Because of the close relationship between landform position and the key carbon and nitrogen processes, quantitative landform segmentation procedures can be used to delineate precision conservation management zones in these landscapes. Site-specific management practices such as reduced or no-till, seeding to grass, wetland restoration, and site-specific nitrogen (N) management can then be implemented to simultaneously increase soil organic carbon stores on eroded upper slope segments while preserving existing stores of soil organic carbon and reducing N2O emissions from lower slope segments. Close cooperation between precision conservation professionals and agronomists is required to ensure that information required by producers is available to guide them in their decision making and implementation of precision conservation for co-management of carbon and nitrogen.
Keywords: Carbon sequestration, greenhouse gas, Kyoto Protocol, landform segmentation, nitrous oxide
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Nitrogen fertilizer management based on site-specific management zones reduce potential for nitrate leaching
(Full text appears in the Journal of Soil and Water Conservation, Vol. 60, No. 6)
J.A. Delgado, R. Khosla, W.C. Bausch, D.G. Westfall, and D.J. Inman
ABSTRACT: Although nitrogen (N) is an essential nutrient that is a key component of intensive irrigated agricultural systems, its management to maximize yields and reduce losses to the environment is difficult. One reason is due to the spatial and temporal variability that affect residual soil nitrate-N (NO3-N) and NO3-N leaching potential. The objective of this study was to evaluate the potential of N fertilization prescriptions based on site-specific management zones to reduce NO3-N leaching losses. We mapped site-specific management zones based on soil color from aerial photographs, topography, and the producer’s past management experiences that reflect spatial soil variability. We used the Nitrate Leaching and Economic Analysis Package (NLEAP) model to assess the benefits of N management based on site-specific management zones. Nitrate leaching was variable across management zones with the highest leaching occurring in the low productivity zone. This study found that productivity zone is an important spatial factor in determining NO3-N leaching potential since site-specific management zones characterized the variability of factors that affect NO3-N leaching. As the N fertilizer rate is increased by productivity zone the rate of NO3-N leaching increased faster for the low productivity zone creating a “higher leaky zone.” Since we found that a factor other than N is limiting yields, a better N management practice is to apply N accounting by realistic maximum yields to avoid over-fertilization, to reduce NO3-N leaching losses during the growing season and residual soil NO3-N that is available to leach during the non-growing season. Furthermore, this study demonstrates that spatially variable N management based on productivity zones produces less NO3-N leaching than uniform strategies while maintaining maximum yield. We estimated that by using a Site Specific Management Zone we cut NO3-N leaching losses by 25 percent during the first year after a site-specific management zones nutrient management plan.
Keywords: Corn, nitrate leaching, nitrogen, nitrogen management, NLEAP, site-specific management zones, water conservation
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Development of a conservation-oriented precision agriculture system: Water and soil quality assessment
(Full text appears in the Journal of Soil and Water Conservation, Vol. 60, No. 6)
R.N. Lerch, N.R. Kitchen, R.J. Kremer, W.W. Donald, E.E. Alberts, E.J. Sadler, K.A. Sudduth, D.B. Myers, and F. Ghidey
ABSTRACT: A comprehensive approach to achieving sustained crop productivity and profitability requires implementation of conservation systems that simultaneously consider soil and water quality. The objectives of this study were to: 1) assess long-term surface and groundwater quality in a conventionally managed field; 2) assess long-term changes in soil quality under a conventional management field; and 3) use this assessment to support development of the precision agriculture system presented in the companion paper. The study site was a 36-ha (89 ac) field in the Central Claypan Area of northeastern Missouri. The field was managed in a corn-soybean rotation using mulch tillage and soil incorporated fertilizer and pre-emergence herbicide inputs for 13 years (1991 to 2003). In general, agrichemical leaching to groundwater was minimal, but the existing management system negatively impacted the quality of surface runoff in five of the nine years reported. Preliminary spatial assessment indicated that the northern half of the field has been the main source of herbicides, nutrients, and sediment transported in surface runoff from this field. Topsoil loss and, therefore, decreased depth to the claypan from historic erosion of the field was a key soil quality indicator related to limitations in crop productivity. Spatial variability in soil loss over the last 150 to 200 years controls the soil quality, water quality, and crop productivity patterns currently observed within this field. Therefore, spatial variability in soil erosion, or a surrogate measure such as depth to claypan, serves as a useful basis for the development of a comprehensive precision agriculture system.
Keywords: Precision agriculture system, runoff, soil erosion, soil quality, spatial variability, topsoil depth, water quality
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Development of a conservation-oriented precision agriculture system: Crop production assessment and plan implementation
(Full text appears in the Journal of Soil and Water Conservation, Vol. 60, No. 6)
N.R. Kitchen, K.A. Sudduth, D.B. Myers, R.E. Massey, E.J. Sadler, R.N. Lerch, J.W. Hummel, and H.L. Palm
ABSTRACT: From site-specific crop and soil information collected from a Missouri claypan soil field for over a decade (1993 to 2003), we implemented a precision agriculture system in 2004 with a goal of using site-specific management practices to improve farming profitability and conserve soil and water resources. The objectives of this study were to: 1) show how precision crop and soil information was used to assess productivity, and 2) document the development of the precision agriculture system plan for implementation on the field, relying on this productivity assessment and conservation opportunities. The study field was uniformly managed from 1991-2003, during which time variability in soil and landscape parameters and yield were measured, and causes of yield variation were determined. Profitability maps were created from yield maps and production records. Because erosion has degraded the topsoil on shoulder and side slope positions of major portions of this field, corn-soybean management practices have rarely been profitable in these shallow topsoil areas. We prioritized these and other results, and developed the precision agriculture system plan. The plan, described in detail, is aimed at increasing profitability while improving water and soil quality.
Keywords: Precision agriculture system, profitability mapping, site-specific management, topsoil depth, yield limiting factors
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Soil management system and landscape position interactions on nutrient distribution in a Coastal Plain field.
(Full text appears in the Journal of Soil and Water Conservation, Vol. 60, No. 6)
K.S. Balkcom, J.A. Terra, J.N. Shaw, D.W. Reeves, and R.L. Raper
ABSTRACT: Soil nutrient concentrations vary with soil management system and landscape position, but limited information exists describing these interactions within a heterogeneous field. A three year experiment was conducted to evaluate pH, phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), and zinc (Zn) concentrations at three depths, 0 to 5 cm, 5 to 15 cm, and 15 to 30 cm (0 to 2 in, 2 to 6 in, and 6 to 12 in), and three landscape positions, summit, sideslope, and drainageway, in a 9 ha (22 ac) field containing four different management systems. Management systems consisted of a conventional (chisel plowing/disking in-row subsoiling with no cover crops) and conservation tillage system (in-row subsoiling with cover crops) with or without dairy bedding manure. Soils ranged from Aquic to Typic Paleudults. Manure applications increased pH and nutrient concentrations in the soil surface at 0 to 5 cm (0 to 2 in) of conventional and conservation tillage systems, with highest values measured in conservation tillage. Landscape position affected soil pH and P concentrations; however, depth and landscape position interactions were observed for soil pH, P, and K concentrations. The lowest soil pH and P concentrations were measured from the sideslope position, while K concentrations did not exhibit consistent distributions across landscape positions. Future soil testing of Coastal Plain fields to account for erosion of the landscape may help direct future sampling methodology and interpretations for nutrient management.
Keywords: Conservation tillage, conventional tillage, dairy manure, stratification
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Impacts of landscape attributes on carbon sequestration during the transition from conventional to conservation management practices on a Coastal Plain field
(Full text appears in the Journal of Soil and Water Conservation, Vol. 60, No. 6)
J.A. Terra, D.W. Reeves, J.N. Shaw, and R.L. Raper
ABSTRACT: Field-scale experiments on degraded soils comparing management systems would facilitate a better understanding of the soil organic carbon (C) landscape dynamics associated with transition to conservation systems. We assessed the effects of soil management practices and terrain attributes on soil organic C in a 9 ha (22.2 ac) Alabama field (Typic and Aquic Paleudults). Treatments were established in strips across the landscape in a corn (Zea mays L.)-cotton (Gossypium hirsutum L.) rotation. Treatments included a conventional system (chisel plowing/disking without cover crops) with or without dairy manure, and a conservation system (no-till and cover crops) with and without manure. A soil survey, topography, soil electrical conductivity, initial soil organic C and soil texture were used to delineate management zones or clusters. After one rotation cycle (30 months), averaged across 240 positions distributed over the entire field, no-till or conventional tillage + manure increased soil organic C (0 to 5 cm; 0 to 2 in depth) by ~50 percent compared to conventional tillage (7.34 and 7.62 vs. 5.02 Mg ha-1; 3.28 and 3.40 vs. 2.24 t ac-1, respectively); but no-till+manure increased soil organic C by 157 percent. Initial soil organic C content was the most common correlated variable with soil organic C changes (DSOC) across the landscape for all treatments and conservation systems had greater soil organic C increases relative to conventional systems at low soil quality landscape positions. Our results show the potential to sequester C using high-residue producing conservation systems and manure is scale dependent, and may be higher than previously expected for degraded soils in the southeastern United States.
Keywords: Carbon sequestration, conservation systems, dairy manure, landscape variability, soil management, soil organic C, terrain attributes
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Spatially distributed assessment of short- and long-term impacts of multiple best management practices in agricultural watersheds
(Full text appears in the Journal of Soil and Water Conservation, Vol. 60, No. 6)
C.S. Renschler and T. Le
ABSTRACT: Best management practices (BMPs) are a critical tool for preventing or mitigating the degradation of water quality caused by soil erosion. However, currently available assessment models are primarily designed for use over and, therefore, are only valid over these particular spatial and temporal scales. This study investigates the feasibility of combining three models that were designed for use at different spatial scale into a single assessment tool that allows for more detailed, spatially-explicit assessment of BMPs over both short (four to eight years) and longer (100 year) time scale. The three models evaluated were: 1) the Water Erosion Prediction Project (WEPP) model for hillslope and small watershed up to 260 ha (642 ac); 2) the Geospatial interface for WEPP (GeoWEPP), which utilizes geographic information system (GIS) or precision farming datasets of topography, soils, and landuse to automatically derive WEPP model input; and 3) a linked GeoWEPP-SWAT model, which injected WEPP model output as point sources into the Soil and Water Assessment Tool (SWAT). The linked GeoWEPP-SWAT model provides a mechanism for applying the WEPP model to larger watershed scales beyond the validity of its channel routing algorithms. This paper summarizes the challenges, validity, and opportunities of this modeling approach for BMP assessment in large watersheds.
Keywords: BMP, GeoWEPP, scale, SWAT, WEPP
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An overview of precision conservation in Canada
(Full text appears in the Journal of Soil and Water Conservation, Vol. 60, No. 6)
T.W. Goddard
ABSTRACT: While some precision farming technologies have already been adopted in Canada, the concept of precision conservation presents new opportunities for viewing and analyzing spatial agricultural data. The extreme diversity of agricultural conditions across the country needs to be accounted for and addressed. Landscape analysis is a tool that can be used to facilitate precision conservation. We have documented soil and crop properties related to landforms and are starting to develop stochastic and risk based modeling approaches to better manage agricultural systems. Precision conservation has the potential to facilitate a variety of emerging environmental applications including traceability or identity preservation systems, environmental regulations for farm practices and evaluation of better management practices.
Keywords: Canada, enviornmental risk, overview, precision agriculture, precision conservation
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Erosion probability maps: Calibrating precision agriculture data with soil surveys using logistic regression
(Full text appears in the Journal of Soil and Water Conservation, Vol. 60, No. 6)
T.G. Mueller, H. Cetin, R.A. Fleming, C.R. Dillon, A.D. Karathanasis, and S.A. Shearer
ABSTRACT: Soil surveys provide information about the location of eroded areas across landscapes, but not at a scale that may be necessary for land use planning, precision agriculture, and conservation management. The objective of this paper was to determine whether site-specific information and logistic regression could be used to improve the spatial resolution of soil surveys. This study was conducted on fragipan soils developed from loess in a western Kentucky agricultural field. Information about the presence and severity of erosion was obtained from a highly detailed first-order soil survey and less detailed second-order county soil surveys. Digital terrain attributes (slope, length-slope factor, wetness), reflectance (visible, red-NIR, and NIR), soil electrical conductivity, and direct contact electrical conductivity were used as regressor variables. Binary variables were assigned a value of one if they were located in eroded map phases and if slope values were greater than or equal to two percent. For all other cases they were assigned values of 0. Stepwise multiple logistic regression was used to develop models that were used to map probability that substantial soil erosion had occurred in the past. The resulting probability maps were remarkably similar for both survey orders indicating that this approach was robust to soil map unit inclusions and classification errors. Erosion probability maps created using the second order soil survey matched in many cases with the boundaries of the first order survey. Our results demonstrated that precision agriculture technologies and logistic regression analysis could potentially be used to improve the value and utility of existing second order soil surveys. Soil and water conservation, management, and planning will be more effective and economical if these methods can be adapted for soils in other regions of the United States.
Keywords: Conservation, electrical conductivity, erosion remote sensors, terrain analysis
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