Showing papers in "Journal of Soil and Water Conservation in 2005"

Opportunities for conservation with precision irrigation

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.

A southeastern piedmont watershed sediment budget: Evidence for a multi-millennial agricultural legacy

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.

Variation in soil properties and crop yield across an eroded prairie landscape

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.

The effect of socioeconomic factors on the adoption of best management practices in beef cattle production

Abstract: Factors affecting cattle producers9 adoption of best management practices (BMPs) are examined using probit analyses. Results show that in situations such as when the farm includes more enterprises, the farmer has had contact with Natural Resources Conservation Service personnel at least once within the past year, the farmer holds a college bachelor9s degree, the percentage of income from beef cattle production is higher, or the operation includes hilly land, the likelihood of BMP adoption is greater. Having a greater number of other agricultural enterprises and having a greater percentage of income from the cattle operation were significant factors in the adoption of companion practices. Results of this study suggest changes in formulating future environmental policies associated with pasture-based beef cattle production.

Establishing conservation buffers using precision information

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.

A tool for estimating best management practice effectiveness for phosphorus pollution control

Abstract: A best management practice (BMP) tool was developed as a part of an effort to address the phosphorus (P) pollution and associated eutrophication problem affecting the Cannonsville Reservoir, part of the New York City water supply system. P reaching the reservoir is thought to emanate from runoff from the surrounding farms, mainly as a result of manure spread on these farms. Efforts to address the problem have involved implementation of BMPs on the watersheds; however, the effectiveness of these practices is not known. This study establishes a means of estimating BMP effectiveness, based on data available in the literature, and develops a tool that allows users to obtain BMP effectiveness estimates for their respective site soil and slope conditions. The tool offers stand-alone capabilities and has the potential to be linked to a GIS. An example is presented to illustrate tool application for effectiveness-based BMP selection, with a focus on a farm within the New York City watersheds.

Evaluation of stormwater from compost and conventional erosion control practices in construction activities

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 a 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.

Applying spatial analysis for precision conservation across the landscape

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.

Development of a conservation-oriented precision agriculture system: Water and soil quality assessment

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 in a conventionally managed 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.

Potential use of precision conservation techniques to reduce nitrate leaching in irrigated crops

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

Development of a conservation-oriented precision agriculture system: Crop production assessment and plan implementation

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.

Assessment of groundwater use by wheat (Triticum aestivum L.) in the Luancheng Xian region and potential implications for water conservation in the northwestern North China Plain

Abstract: Agricultural sustainability in China, especially in the North China Plain, is highly dependent on water resource availability. Land management has changed dramatically in this region since the 19709s when a more intensive practice of winter wheat (Triticum aestivum L.) and summer corn (Zea mays L.) in one-year rotation started causing excessive exploitation of groundwater to meet crop water needs for high yield productivity. Over fifty percent of the area in the northwestern region of the North China Plain is irrigated using groundwater. Over ninety percent of Luancheng Xian county is in a groundwater-irrigated winter wheat—corn rotation. In addition the irrigation management practices, agricultural management practices, soil textural classes (mostly loam soils) and climate are similar throughout the Northwestern North China Plain and the Luancheng Xian county. Our objectives were to identify whether land use is a factor contributing to groundwater table decline in Luancheng Xian county of the North China Plain and to use long term small plot studies from 1998 to 2002 to evaluate the potential of limited irrigation based on wheat stage of growth as a viable water-saving practice to reduce consumptive use and stabilize the groundwater table. Assessment of groundwater resources for the Luancheng Xian county found that groundwater levels have been dropping at a rate of 0.8 m yr−1 (31.52 in yr−1) (P

Polyacrylamide Use for Erosion and Turbidity Control on Construction Sites

Abstract: Streams and lakes adjacent to construction sites are often heavily impaired by sediment and turbidity coming from areas of exposed soil. A study was conducted to determine if the application of polyacrylamide (PAM) can reduce erosion and runoff turbidity on moderate to steep slopes at construction sites. The test sites were three North Carolina Department of Transportation construction sites in the Piedmont and Coastal Plain. Two PAM products were applied at recommended rates (10.5 and 1.5 kg ha−1; 9.3 and 1.3 lb ac−1) and one half the recommended rates (5.2 and 0.76 kg ha−1; 4.6 and 0.68 lb ac−1) with and without grass seeding and straw mulching. Runoff volumes, turbidity levels, and eroded sediment data were collected after natural rain events. On a 50 percent fill slope, turbidity and sediment loss were significantly decreased with application of seed/mulch but not PAM alone. PAM applied on the seed/mulch treatment did not have statistical effects compared to the seed/mulch alone. Erosion rates of up to 43 t ha−1 were recorded for one storm on bare soil; seed/mulch reduced this by 83 percent. On a 20 percent cut slope, PAM significantly (P

Nitrogen fertilizer management based on site-specific management zones reduces potential for nitrate leaching

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 (NO 3 -N) and NO 3 -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 NO 3 -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 NO 3 -N leaching potential since site-specific management zones characterized the variability of factors that affect NO 3 -N leaching. As the N fertilizer rate is increased by productivity zone the rate of NO 3 -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 NO 3 -N leaching losses during the growing season and residual soil NO 3 -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 NO 3 -N leaching than uniform strategies while maintaining maximum yield. We estimated that by using a Site Specific Management Zone we cut NO 3 -N leaching losses by 25 percent during the first year after a site-specific management zones nutrient management plan.

Effect of cover crops established at time of corn planting on phosphorus runoff from soils before and after dairy manure application

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 Agriculture9s 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 City9s 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 × 2 m; 3 ft × 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.

Spatially distributed assessment of short- and long-term impacts of multiple best management practices in agricultural watersheds

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.

Tillage effects on rainfall partitioning and sediment yield from an ultisol in central Alabama

Abstract: Coastal Plain soils in the Southeast have been intensively cropped, traditionally managed under conventional tillage practices, and are susceptible to erosion. Conservation tillage systems have significant potential as a management tool for row crop production, especially on sandy surface soils of the Coastal Plain because they reduce soil loss and conserve water. We quantified rainfall partitioning and sediment delivery from a Plinthic Paledudult-Typic Hapludult soil complex (loamy sand surface) located in the Coastal Plain region of Alabama managed under conventional- and no-till systems for 10 years. Conventional till and no-till treatments were evaluated with and without surface (Black Oat, Avena strigosa Schreb.) residue (0-9600 kg ha−1) and with and without paratilling (non-inversion subsoiling to 40 cm). Field plots (∼60 m2) represented eight treatment combinations, two tillage treatments (conventional till, no-till), two residue management treatments, residue removed or left in place (+R), and two non-inversion, deep tillage treatments, paratilled, non-paratilled, with each treatment combination replicated four times. Two 1-m2 rainfall simulator plots were established on one tillage-residue-deep tillage treatment replicate. Each 1-m2 plot received 2 h of simulated rainfall (50 mm h−1). Runoff and sediment delivery were continuously measured from each flat, level-sloping 1-m2 plot (slope = 1 percent). No-till plots had at least two times less runoff and four times less sediment delivery compared to conventional till plots. Runoff was greatest for conventional till, residue removed, non-paratilled plots (58 percent of the rainfall amount), and lowest for no-till, residue left in place, paratilled plots (4 percent of the rainfall amount). About 42 percent of the rainfall infiltrated in the conventional till, residue removed, non-paratilled plots (worst-case scenario) compared to about 96 percent for the no-till, residue left in place, paratilled plots (best-case scenario), resulting in only 2.8 days of water for crop use in conventional till, residue removed, non-paratilled plots and 6.9 days of water for crop use in no-till, residue left in place, paratilled plots (2.5-fold difference). Removing residue resulted in 18 percent more runoff as a rainfall percentage (18 percent less infiltration) for no-till plots and 25 percent more runoff (25 percent less infiltration) for conventional till plots, and accounted for 38 to 76 percent of the differences in runoff and sediment transported from no-till and conventional till plots. For conventional till and no-till plots, removing surface residue increased sediment yields by 1.5 and 7 times. Paratilling resulted in 10 percent less runoff as a rainfall percentage (10 percent more infiltration) for no-till plots and 26 percent less runoff (26 percent more infiltration) for conventional till plots. Compared to non-paratilled conventional till and no-till plots, paratilling caused runoff rates to increase at a slower rate, and increased steady-state runoff rates by 40 percent and 400 percent, respectively. Paratilling reduced bulk density (0 to 12 cm) and soil strength 0 to 50 cm) by at least 15 percent compared to non-paratilled treatments. Combining residue management and paratilling through conservation tillage in row-crop agriculture in the Coastal Plain region of Alabama reduces runoff and soil loss for conventional till and no-till systems by improving soil properties and maintaining infiltration, resulting in increased estimates of plant available water.

Identifying spatial patterns of erosion for use in precision conservation

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 field9s erosion history. Spatial maps depicting a field9s 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.

Measurement and simulation of herbicide transport from the corn phase of three cropping systems

Abstract: Soils that naturally have a significant runoff component because of low permeability, such as claypans or steep slopes, are especially susceptible to herbicide losses in runoff. For these soils, seasonal losses as impacted by management practices are not well quantified. The objectives of this study were to evaluate the effect of three cropping systems on herbicide loss in surface runoff and develop a model that calculates herbicide concentration. Cropping System 1 (CS1) was a mulch tillage corn-soybean rotation system with herbicides surface applied then incorporated. Cropping System 2 (CS2) was a no-till corn-soybean rotation system with herbicides surface applied and not incorporated. Cropping System 5 (CS5) was a no-till corn-soybean-wheat rotation system with split herbicide application in 1997 and 1999 and no incorporation. The study was conducted on 0.37 ha (0.92 ac) plots equipped with flumes and automated samplers. During each runoff event, runoff volumes were measured, and water samples were collected at equal flow increments and analyzed for atrazine [2-chloro-4-ethylamino-6-isopropylamino-s-triazine] and metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethy/acetamide]. Averaged over years, atrazine and metolachlor losses from CS2 were 2.2 and 1.6 times those from CS1, respectively. Atrazine loss to surface runoff from CS1, CS2, and CS5 accounted for 1.6, 2.5, and 5.7% of the total atrazine applied, respectively. Metolachlor loss to surface runoff accounted for 1.8, 2.0, and 2.0% of the total applied for the three cropping systems. Herbicide concentrations were extremely high in the first runoff event measured after application, particularly when it occurred within a few days after application. A generalized model was developed to account for the effects of time after application, runoff volume, and application rate on herbicide concentration in runoff. Overall, the study showed that accounting for incorporation, split application, runoff volume, and timing of runoff events relative to the day of application can increase the confidence in calculations of the amount of herbicide transported to surface runoff.

Trends in phosphorus fertility of New York agricultural land

Abstract: Monitoring of soil test phosphorus (STP) levels over time is essential for the evaluation of fertility management practices. Our objectives were to (1) assess the current soil P fertility status of New York at state, regional, county, and farm level, (2) determine statewide and regional trends over the past 40 years, and (3) investigate the impact of soil test phosphorus trends on fertilizer needs for typical corn-alfalfa/grass rotations. A 1995 to 2001 dataset (119,326 soil samples analyzed for Morgan extractable P) from the Cornell Nutrient Analysis Laboratory was analyzed and compared with published data from 1957-58, 1977-78, 1981, and 1982, and unpublished data from 1985 to 95. Mean statewide P levels remained constant from 1957 to 1980 (26 to 29 percent high or very high in P), but steadily increased after 1980. Currently, 47 percent of the soil samples test equal to or higher than the critical agronomic soil test phosphorus for field crops (4.5 mg kg−1 or 9 lbs ac−1 Morgan extractable P). The highest soil test levels occur in vegetable production regions on Long Island and the highly productive dairy, vegetable and fruit areas in Western New York while the greatest increases over time took place in the dairy-dominated northern and northeastern regions. As these soils reach progressively higher P levels, fertilizer P needs for New York will diminish but more attentive management is needed to ensure that environmental thresholds are not exceeded.

Field evaluation of three phosphorus indices on new application sites in Texas

Abstract: Phosphorus (P) indices were developed to address nonpoint source P losses from agricultural fields; however, only limited information on P index performance at the field- and watershed-scale is available. Evaluation of P indices is necessary to provide the basis of modification and improvement of their usefulness as P management tools. In this study, the ability of the Texas P index to estimate P loss potential was evaluated by comparison with measured annual P loads over three years on four new pasture and six new cultivated litter application sites in the Texas Blackland Prairie. The Arkansas and lowa P indices were also evaluated. The Texas and lowa versions were able to provide reasonable estimates of P loss potential as illustrated with significant linear relationships (p

Trends in recent reservoir sedimentation rates in Southwestern Ohio

Abstract: Soil erosion rates on U.S. cropland are declining. This decline can be expected to have two effects on sediment yield: 1) an overall decrease in sediment yield; and 2) an increasing importance of channel erosion relative to upland sediment sources. Here we examine recent sedimentation rates in 12 reservoirs in two southwest Ohio counties to determine whether sedimentation rates are declining, and whether there is evidence for a shift to channel sediment sources. One of the two counties is primarily urban with high local relief, while the other is primarily agricultural with low relief. In each case a large range of reservoir sizes was studied ( 70 km2 drainage area or 24 mi2). Previous sediment surveys are available for some of the reservoirs studied. Measured sedimentation rates range from 1200 m3 km−2 yr−1 ( 2.5 mi−2 yr−2). Sedimentation rates are generally higher in the urban county than the agricultural one. Comparison of recent (since ∼1980) sedimentation rates with those from the mid-20th Century indicate that sedimentation rates are declining in the agricultural county, presumably as a result of improved soil conservation practices, while those in the urban county remain high. In the agricultural county sedimentation rates follow the normal pattern of decreasing sedimentation per unit drainage area with increasing drainage area, indicating that the channel systems in the area are likely functioning as sediment sinks. In contrast, in the urban county there is no decrease in sedimentation rate with increasing drainage area, indicating that the channels in that landscape are functioning as efficient conduits and/or net sediment sources. These trends highlight the need to update our reservoir sedimentation databases to determine whether the trends are local or widespread.

Testing a spatially distributed sediment delivery model (SEDD) in a forested basin by cesium-137 technique

Abstract: The aim of the paper is to validate the sediment delivery distributed (SEDD) model for estimating hillslope sediment yield estimates using net soil erosion values obtained by the cesium-137 technique. The cesium-137 technique provides spatially-distributed measurements useful to verify the predictive capability of a distributed sediment yield model. The application of the cesium-137 technique requires a calibration procedure to convert measurements of 137Cs inventories to estimates of net soil erosion rates. Rainfall and sediment yield data from 1978 to 1994 in a small Calabrian basin forested with eucalyptus trees, were initially used to calibrate, at mean annual temporal scale, the SEDD model applicable both at the morphological unit and basin scale. Then, estimates of net soil erosion were obtained using a mass balance model and the spatial distribution of cesium-137 inventories. The reliability of the mass balance model was verified by comparing the basin net soil erosion value obtained by 137Cs measurements against the mean annual value of sediment yield measured at the basin outlet. Finally a good concordance between calculated mean annual hillslope sediment yield and the corresponding net soil erosion values was proved at the scale of both the single morphological unit and the entire basin. In conclusion, the cesium-137 technique and the mass balance model confirmed the validity of the internal functioning of SEDD model.

Effects of curve number modification on runoff estimation using WSR-88D rainfall data in Texas watersheds

Abstract: The purpose of this study was to evaluate variations of the Natural Resources Conservation Service (NRCS) curve number method for estimating near real-time runoff for naturalized flow, using high resolution radar rainfall data in Texas watersheds. This study was undertaken in an attempt to provide more accurate runoff estimates to watershed and water resource managers for planning purposes. Stage Ill Weather Surveillance Radar 1988 Doppler (WSR-88D) precipitation data, obtained from the West Gulf River Forecast Center, was used as the precipitation input for runoff estimates in this study. The study areas consisted of dominant or homogenous land use and were characterized by naturalized flow. Findings indicate that the use of a dry antecedent soil moisture condition curve number value and a reduced initial abstraction coefficient (la) in the NRCS curve number equation produced the most statistically significant comparison between observed and estimated runoff in nine out of ten watersheds. The combined comparison for all events in these nine watersheds produced a coefficient of efficiency (COE) of 0.70, with a slope of 0.78 and an r2 of 0.77. Overall, the results of this research suggest that, although further improvements can be made for improved runoff estimation, the use of modified inputs to the NRCS curve number equation in conjunction with WSR-88D radar rainfall data could be useful in producing runoff estimates for Texas in real-time.

Precision conservation for co-management of carbon and nitrogen on the Canadian prairies

Abstract: Agriculture is targeted to make a substantial contribution to Canada9s 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.

Impacts of landscape attributes on carbon sequestration during the transition from conventional to conservation management practices on a Coastal Plain field

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 (SOC) 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.

Mapping surface soil organic carbon for crop fields with remote sensing

Abstract: The organic C concentration of surface soil can be used in agricultural fields to vary crop production inputs. Organic C is often highly spatially variable, so that maps of soil organic C can be used to vary crop production inputs using precision farming technology. The objective of this research was to demonstrate the feasibility of mapping soil organic C on three fields, using remotely sensed images of the fields with a bare surface. Enough soil samples covering the range in soil organic C must be taken from each field to develop a satisfactory relationship between soil organic C content and image reflectance values. The number of soil samples analyzed in the three fields varied from 22 to 26. The regression equations differed between fields, but gave highly significant relationships with R2 values of 0.93, 0.95, and 0.89 for the three fields. A comparison of predicted and measured values of soil organic C for an independent set of 2 soil samples taken on one of the fields gave highly satisfactory results, with a comparison equation of % organic C measured + 1.02% organic C predicted, with r2 = 0.87.

Development of an agricultural land evaluation and site assessment (LESA) decision support tool using remote sensing and geographic information system

Abstract: The general trend in North America, which is agriculturally based, have indicated that prime agricultural lands are being constantly lost to natural hazards such as soil erosion, land degradation, and especially through human activities such as urban development. In order to control and manage these prime agricultural lands, there is a need for improved agricultural land evaluation methods. Lately, a combination of geospatial technologies (GST) such as remote sensing, geographical information systems (GIS), and the global positioning system (GPS), and land evaluation methods such as Land Evaluation and Site Assessment (LESA) have shown to be promising tools for land evaluation. Even though numerous studies have demonstrated the importance of integrating land evaluation models with GIS, few studies have combined the popular LESA model with GIS to provide a decision support tool for mangers. The goal of the study is to develop a decision support tool for agricultural land evaluation using geospatial technologies and a LESA model in Black Hawk County, Iowa. Currently, the county is using an Excel-based land evaluation and site assessment system, which lacks a spatial context even though land evaluation factors are spatial in nature. In order to develop a decision support tool, LESA criteria, and relevant data for these criteria were collected from different sources. Then, these data were analyzed using ERDAS IMAGINE and ArcGIS software. Finally, a decision support tool was developed by customizing ArcGIS software using Visual Basic Application. The results of the study found that soil productivity, development potentials, and farmland are the major factors in the LESA model in this county. The decision support tool developed in this study is easy to use, accurate, combines spatial and non-spatial data, and saves time and money for the planners in the county over traditional methods.

Nutrient management planning: Is it the answer to better management?

Abstract: Agricultural nutrient management is an important part of water resources protection strategies, especially in the upper Midwest. In Wisconsin, nutrient management plans are thought to reduce the excess application of agrichemicals, such as nitrogen and phosphorus, on cropland. A survey of 127 farmers, representing 90 percent of the farmers in two northeastern Wisconsin watersheds where nutrient management plans had been extensively promoted documented the application of nitrogen (N) and phosphorus (as P2O5) and the extent to which those farmers follow nutrient management plans. Results indicate that farmers with nutrient management plans do apply lower rates of total N and P2O5 compared to farmers without plans, however, the existence of a plan does not necessarily lead to the elimination of excess nutrient applications. Furthermore, there is minimal difference between public agency plans and those supported by the private sector in Wisconsin. Results from this study are useful in developing more effective public policy, and especially conservation programs that encourage the adoption of nutrient management plans.

Erosion probability maps: Calibrating precision agriculture data with soil surveys using logistic regression

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 sitespecific 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.