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Journal of Soil and Water Conservation RSS feed -- current issue1941-3300January/February 2020Journal of Soil and Water Conservation0022-4561Journal of Soil and Water Conservationhttp://jswconline.org/icons/banner/title.gif
http://jswconline.org
http://jswconline.org/cgi/content/short/75/1/1?rss=1
The Soil Vulnerability Index (SVI) was developed by the USDA Natural Resources Conservation Service (NRCS) to classify inherent vulnerability of cropland soils based on field sediment and nutrient transport resulting from surface runoff and leaching. The primary purpose of the SVI is to aid conservation planners in more rapidly assessing managed lands and inherent resource concerns. The index is based on hydrologic soil group, slope, and soil erodibility for cultivated cropland soils, with the addition of percentage rock fragments and organic matter when considering leaching. Although the SVI is intended for use throughout the United States, its development was based on the physiographic and rainfall characteristics of the Upper Mississippi and Ohio-Tennessee River basins. The purpose of this study was to evaluate the SVI in areas both in and outside of the area for which it was developed. Thirteen different watersheds were selected to conduct this evaluation. Vulnerability classifications using the SVI were compared with those from on-site experts' knowledge and with model simulations using local data. Four companion papers in this special collection discuss SVI classification based on the effects of land slope, artificial drainage, sediment and nutrient loads, and vulnerability assessment using hydrologic simulation models. Using results from the various sites, the objective of this paper was to synthesize the interpretation of the value and applicability of SVI vulnerability classification to sediment and nutrient loss across various physiographic regions and suggest where improvement in the SVI could be made.
]]>2019-12-23T14:45:59-08:00info:doi/10.2489/jswc.75.1.1hwp:resource-id:jswc;75/1/1Soil and Water Conservation Society2020-01-01Special Research Section: Soil Vulnerability Index751111
http://jswconline.org/cgi/content/short/75/1/5A?rss=1
2019-12-23T14:45:59-08:00info:doi/10.2489/jswc.75.1.5Ahwp:resource-id:jswc;75/1/5ASoil and Water Conservation Society2020-01-01Features7515A12A
http://jswconline.org/cgi/content/short/75/1/12?rss=1
Soil erosion and nutrient loss from surface runoff and subsurface leaching are critical problems for cultivated land. Conservation initiatives show a persistent need for field-scale cropland vulnerability assessments to inform farm management options and prioritize efforts at watershed or regional scales. The Soil Vulnerability Index (SVI) was developed by USDA's Natural Resources Conservation Service (NRCS) to assess inherent vulnerability of cropland to surface runoff and leaching using readily available soil and topographic inputs: hydrologic soil group, slope, erodibility K-factor, coarse fragments, and organic carbon (C). The SVI has been evaluated in a few watersheds but requires further evaluation across a wider range of physiographic and climatic conditions. The objective of this study was to evaluate the ability of the SVI to correctly identify vulnerability class based on slope, digital elevation model (DEM) resolution, hydrologic soil group, and soil erodibility across 13 of USDA's Conservation Effects Assessment Project (CEAP) watersheds. The SVI classification was consistent with model output classification with a similarity rate of more than 70% when the SVI component corresponded to the primary route of loss for nutrients or sediment. Results showed that SVIs were consistent with local scientific expertise about the site vulnerability to runoff and leaching, and were particularly useful in areas with mixed slopes and hydrologic soil groups. In watersheds with uniform C or D hydrologic soil groups, the SVI was primarily driven by slope. In these cases, it was important to use a digital elevation map with 10 m resolution or higher to more finely distinguish vulnerability. In areas with uniform slopes and hydrologic soil group, and in areas with uniformly steep slopes, the SVI was not able to identify fields with greater or lower vulnerability than others. In these cases, vulnerability assessments required additional factors: depth of restrictive layer, clay content, slope length, and landscape position. While the SVI was able to categorize vulnerability correctly in mixed soil and slope conditions, findings from this project highlight the need for incorporating DEM-sourced slope and other factors like depth of restrictive layer, clay content, slope length, and landscape position into the SVI to ensure that the SVI is applicable to the broad range of geomorphic conditions found in the United States.
]]>2019-12-23T14:45:59-08:00info:doi/10.2489/jswc.75.1.12hwp:resource-id:jswc;75/1/12Soil and Water Conservation Society2020-01-01Special Research Section: Soil Vulnerability Index7511227
http://jswconline.org/cgi/content/short/75/1/13A?rss=1
2019-12-23T14:45:59-08:00info:doi/10.2489/jswc.75.1.13Ahwp:resource-id:jswc;75/1/13ASoil and Water Conservation Society2020-01-01Features75113A19A
http://jswconline.org/cgi/content/short/75/1/20A?rss=1
2019-12-23T14:45:59-08:00info:doi/10.2489/jswc.75.1.20Ahwp:resource-id:jswc;75/1/20ASoil and Water Conservation Society2020-01-01Research Introduction75120A22A
http://jswconline.org/cgi/content/short/75/1/28?rss=1
The USDA Natural Resources Conservation Service (NRCS) has proposed the Soil Vulnerability Index (SVI) as a standard tool to classify inherent soil vulnerability of cropland to loss of sediment and nutrients by runoff and leaching. The tool uses soil properties and topography, and does not consider crop management, except for the presence of artificial surface or subsurface drainage. For artificially drained cropland, SVI vulnerability to runoff remains unchanged but vulnerability to leaching is raised by two classes out of four to reflect the increased risk of nitrate (NO3) transport. The SVI was reviewed within different contexts, but there is a need for SVI evaluation when artificial drainage is present. Thus, the objectives of this evaluation were to (1) evaluate SVI vulnerability to runoff and leaching for artificially drained cropland, and (2) propose changes to the SVI ruleset based on the findings of Objective 1. The SVI was evaluated for eight sites with artificial drainage located in regions ranging from Idaho to Maryland. Seven sites were watersheds ranging in size from 600 to 113,600 ha, with 44% to 84% cropland consisting of row crops or small grains. The eighth site consisted of six fields ranging from 7 to 30 ha in size. Consistency between SVI vulnerability, hydrologic processes that take place on the landscape, and outcomes such as crops grown were examined, using the accumulated experience and knowledge of the coauthors of this paper. Overall, SVI vulnerability to runoff and leaching was consistent with earlier research for sites with artificial subsurface drainage unless rainfall intensities were greater than they are in the Upper Mississippi and Ohio-Tennessee River basins. SVI vulnerability to leaching was greater than expected in case of surface drainage. In addition, complex soil map units can cause incorrect vulnerability classification at field scale. At the watershed or regional scale, the leaching component should be considered both with and without artificial drainage so that the causes of the vulnerability (permeable soils or artificial drainage) can be distinguished.
]]>2019-12-23T14:45:59-08:00info:doi/10.2489/jswc.75.1.28hwp:resource-id:jswc;75/1/28Soil and Water Conservation Society2020-01-01Special Research Section: Soil Vulnerability Index7512841
http://jswconline.org/cgi/content/short/75/1/42?rss=1
The Soil Vulnerability Index (SVI) was developed by the USDA Natural Resources Conservation Service (NRCS) to identify inherent vulnerability of cropland to runoff and leaching. It is a simple index that relies on the SSURGO database and can be used with basic knowledge of ArcGIS. The goal of this study was to investigate a relationship between constituent (sediment and nutrient) loadings and fraction of the watershed in each SVI class. The SVI maps were developed for each of the seven subwatersheds of the Mark Twain Lake watershed in Missouri, which were similar in soil conditions and climatic variability. The SVI assessment was performed by investigating if the distribution of the SVI for cropland in each subwatershed could help explain measured 2006 to 2010 sediment and nutrient loads better than crop distribution alone. Regression analyses were performed between annual loads of sediment and nutrients exported from the watersheds and a composite number that included either cropland distribution alone, or cropland distribution combined with the SVI. Coefficients of determination and p-values were compared to assess the ability of land use and SVI distributions to explain stream loads. Integrating the SVI in the land cover variable improved the ability to explain constituent loads in the watersheds for sediment, total nutrients, and dissolved nitrogen (N). Regression results with and without the SVI were identical for dissolved phosphorus (P), potentially indicating that SVI was not indicative of dissolved P transport at the current site. Overall, the application of the SVI at watershed scale was not perfect, but acceptable at correctly identifying cropland of greatest vulnerability and linking with transported constituent loads.
]]>2019-12-23T14:45:59-08:00info:doi/10.2489/jswc.75.1.42hwp:resource-id:jswc;75/1/42Soil and Water Conservation Society2020-01-01Special Research Section: Soil Vulnerability Index7514252
http://jswconline.org/cgi/content/short/75/1/53?rss=1
There is an increasing need to quickly and accurately identify areas where agricultural conservation practices can provide the greatest reduction in nutrient and sediment runoff. Geographic information systems (GIS)-based tools and indices are promising for identifying critical areas that are significant contributors of nonpoint source pollution loads with limited data. One such tool, the Soil Vulnerability Index (SVI), is tested here in Beasley Lake and Goodwin Creek watersheds in Mississippi. The SVI runoff component results are compared against aerial images and long-term land use histories in the watershed to determine if a higher SVI score is related to visibly degraded land or land removed from cultivation. SVI results are also compared to sediment yield estimates generated with the Annualized Agricultural Non-Point Source pollution model (AnnAGNPS) to determine the degree of agreement. The SVI runoff score demonstrated agreement with imagery and land use histories in both watersheds. The SVI categories and corresponding AnnAGNPS-predicted sediment yield also had moderate agreement, with 45% and 68% of watershed area in agreement in Beasley Lake and Goodwin Creek watersheds, respectively. In general, the tool is a quick way to assess spatial areas potentially contributing to nonpoint source pollution, which can then be combined with field-based knowledge and/or imagery to provide valuable insight for placement of conservation practices.
]]>2019-12-23T14:45:59-08:00info:doi/10.2489/jswc.75.1.53hwp:resource-id:jswc;75/1/53Soil and Water Conservation Society2020-01-01Special Research Section: Soil Vulnerability Index7515361
http://jswconline.org/cgi/content/short/75/1/62?rss=1
Natural resource advisors operate at a natural resource-climate nexus that presents opportunity for utilization of regionally relevant climate science and tools to support climate smart decision making among land managers. This opportunity, however, may be underutilized. In thousands of county offices across the country, USDA field staff with the Natural Resources Conservation Service (NRCS) and Farm Service Agency (FSA) interface with farmers on a daily basis to provide conservation technical assistance, farm loans, and disaster recovery assistance. In this study, we conducted a survey of NRCS field staff (n = 1,893) and a similar survey of FSA field staff (n = 4,621) to determine the following: (1) how concerned USDA field staff are with both general and specific climate and weather threats and their effect on agriculture and forestry, (2) what available climate and weather resources staff are currently using, (3) how these factors relate to USDA field staff's confidence and interest in playing the role of climate advisor, and (4) the differences that exist between NRCS and FSA field staff related to these research questions. We found that many USDA field staff are concerned about climate change in general and about several specific impacts, but fewer are confident in their ability to support land managers in addressing these impacts. Additionally, increased concern about climate threats was related to higher levels of climate and weather resource use and an increased desire to play the role of climate advisor, but was also related to lower levels of self-reported ability to play that role. These findings can be used to inform appropriate application of professional development opportunities and creation of tools and resources to improve professional uses of weather and climate information.
]]>2019-12-23T14:45:59-08:00info:doi/10.2489/jswc.75.1.62hwp:resource-id:jswc;75/1/62Soil and Water Conservation Society2020-01-01Research7516274
http://jswconline.org/cgi/content/short/75/1/75?rss=1
Water availability, use, and quality in dispersed rural communities in a rural watershed within the Chilean Coastal Range were investigated through participatory research involving the local community, also called "citizen science." Research included the quantification of recharge water and water use at the household level; monitoring of water quality of streams, community water intakes, and household faucets; and the determination of land use and water quality interactions. A group of mainly women along with the children of three local rural elementary schools were involved in the principal aspects of the research, from design to implementation and remediation options. The study area receives considerable, but highly variable, rainfall, and the hydrogeological setting does not offer enough interannual natural storage to cope with increasing demand and variable water viability. Our results also showed that chemical quality of the water is relatively good, except for the high concentration of iron (Fe; >0.3 mg L–1), manganese (Mn; >0.1 mg L–1), and turbidity (>5 nephlometric turbidity units [NTU]). From the microbiological point of view, the water is of poor quality. The low water quality could be related to the lack of maintenance of water collection systems, nonmaintenance of septic tanks, animal traffic, and low coverage of associated riparian vegetation. In the present approach the involvement of children in research helped to stimulate the improved management of both land and water resources by the community, and this practice could be applied in small rural watersheds in developed or developing countries.
]]>2019-12-23T14:45:59-08:00info:doi/10.2489/jswc.75.1.75hwp:resource-id:jswc;75/1/75Soil and Water Conservation Society2020-01-01Research7517590
http://jswconline.org/cgi/content/short/75/1/91?rss=1
Corn (Zea mays) grown in the southern Piedmont requires 200 to 280 kg nitrogen (N) ha–1 annually and requires up to 0.87 cm of water per day, making groundwater systems susceptible to nitrate (NO3–) leaching. A perennial white clover (Trifolium repens L.) living mulch (LM) system may reduce NO3-N leaching by using legume N to replace mineral N, though little information is available on such a system in the southern Piedmont. Therefore, a HYDRUS-1D model was used to simulate water and NO3-N flux in three cover crop systems. Cereal rye (Secale cereal L.) (CR), crimson clover (Trifolium incarnatum L.) (CC), and a white clover LM were fertilized with 280, 168, and 56 kg N ha–1. The HYDRUS-1D model was calibrated and validated with observed water contents and NO3-N data that were collected over two years. Water and NO3-N flux models were created for each treatment and evaluated using coefficient of determination, percentage bias, and index of agreement, and showed good agreement to observed data. Nitrate leaching below 1 m in 2015/2016 was 23.5, 12.7, and 21.4 kg ha–1 for the CC, LM, and CR treatments, respectively, but was less than 1 kg ha–1 for all treatments in 2016/2017 due to prolonged drought. Differences in leached NO3-N among treatments were attributed to variation in mineral N application rate and NO3-N uptake by cover crops. Overall, results suggest that the use of a perennial LM system may reduce NO3-N leaching when compared to annual CC and CR cover crop systems.
]]>2019-12-23T14:45:59-08:00info:doi/10.2489/jswc.75.1.91hwp:resource-id:jswc;75/1/91Soil and Water Conservation Society2020-01-01Research75191102
http://jswconline.org/cgi/content/short/75/1/103?rss=1
Much attention has been paid to the effects of multiple soil conservation and soil health practices on the mean yield of the subsequent crop. Much less research has focused on the variability of crop yields over time or space. Yield stability reported in standard deviation, mean absolute deviation, or coefficient of variation can be an important measure of risk for producers. Risk reduction has economic value, and understanding the effect of tillage and other soil conservation practices on yield risk is relevant to farm financial management and crop insurance risk assessment. We used data from test plots in a corn (Zea mays L.)–soybean (Glycine max L.) rotation, spanning from 2003 to 2011 to assess differences in yield stability over time and space. In this experiment, each plot was randomly assigned to a treatment of no-till with no cover crop (NTNC), no-till with an annual ryegrass (Lolium multiflorum Lam.) cover crop (NTCC), or a control group using conventional tillage with no cover crop (CTNC). The statistical analysis made three relevant comparisons: (1) NTCC versus NTNC, (2) NTNC versus CTNC, and (3) NTCC versus CTNC. The analysis also included separating temporal and spatial variation using a time-first approach from the literature, followed by testing for differences between groups. We employed a standard deviation ratio test, Levene's test, and coefficient of variation t-test. Additionally, analysis of temporal volatility was conducted using ordinary least squares regression and associated t-tests in a method similar to a stock beta, a technique commonly accepted in finance to measure the volatility of an investment. We propose this as a new method in analyzing the temporal volatility in crop yields. We found that no-till reduced average temporal yield variation in corn, and that cover crops reduced average spatial variation in corn. These results were robust over multiple statistical tests. Using the beta coefficient methodology proposed in this paper, we found in both corn and soybeans that NTNC and NTCC had lower temporal yield volatility relative to a benchmark yield from the CTNC group. However, the beta coefficients were, in most cases, not statistically significant. The results of this study suggest that both no-till and cover crops may help reduce yield risk for Midwestern farmers while reducing soil and nutrient loss.
]]>2019-12-23T14:45:59-08:00info:doi/10.2489/jswc.75.1.103hwp:resource-id:jswc;75/1/103Soil and Water Conservation Society2020-01-01Research751103111
http://jswconline.org/cgi/content/short/75/1/112?rss=1
A rise in global temperature has been observed since the 1980s. The objective of the study was to understand the winter wheat (Triticum aestivum L.) responses and yield performances to the changing climate. The study was performed using growing degree day (GDD) model and regression analysis method. Wheat data (1940 to 2016) were obtained from the Southern Regional Performance Nursery (SRPN) experiments at Bushland, Texas. Wheat genotypes were divided into three groups: Kharkof as a check cultivar, the highest yielding cultivar for each year, and all other cultivars. Climate data were obtained from USDA Agricultural Research Service at Bushland and the National Oceanic and Atmospheric Administration. Temperatures between 1940 and 2016 showed a curvilinear trend with a significant rise since 1980. Mean temperature during wheat growing season (September 15 to June 15) increased at a rate of 0.35°C per decade since 1980. Consequently, seasonal GDD and extreme degree days (EDD) increased at a rate of 69°C d and 19°C d per decade. From 1940 to 2016, wheat heading date has shifted earlier by 16 days for dryland wheat and 11 days for irrigated wheat. Maximum and minimum temperatures in March and April had a negative relationship with heading date, while precipitation had a positive relationship with heading date for both dryland and irrigated wheat. Early heading may have benefits for heat escape but also has the disadvantage of reducing precipitation prior to heading—a loss of 25 mm when heading shifted earlier by 16 days for dryland wheat. The five-year moving average yields increased steadily from about 1960 to 1980, plateaued until the late 1980s, and then declined significantly. However, average genetic yield gains were 505 kg ha–1 under dryland and 1,671.4 kg ha–1 under irrigated conditions for all new cultivars during 1940 to 2016. Yield trends for all three cultivar groups had similar patterns over the years. Increase in maximum temperature, frequencies of maximum temperature greater than or equal to 31°C, and minimum temperature during grain filling period had significant negative effect on grain filling days and yield (except for minimum temperature under dryland conditions). Precipitation during the vegetative growth (November, January, and March) and grain filling (May) had a significant positive effect on dryland wheat yields, but only the January precipitation had significant effect on wheat yield under irrigated conditions. The study indicated that the rising temperature and shifting precipitation timings as a result of early heading are less favorable conditions for winter wheat production in the US southern High Plains.
]]>2019-12-23T14:45:59-08:00info:doi/10.2489/jswc.75.1.112hwp:resource-id:jswc;75/1/112Soil and Water Conservation Society2020-01-01Research751112122
http://jswconline.org/cgi/content/short/75/1/123?rss=1
The Midwest is well known for agriculture, and Iowa is a leader in corn (Zea mays L.) and soybean (Glycine max [L.] Merr.) production. Fertilizers and chemical pesticides used to increase crop production can adversely affect the soil and water health. Midwest farmers also produce livestock and graze cattle on pastureland that can lead to excessive surface runoff and soil erosion. Establishing vegetative filter strips (VFSs) along the edge of farmland is one of the best management practices (BMPs) to reduce nutrient and sediment loss. However, studies have revealed that the classic VFS design along the length of an agricultural field does not adequately address nonuniform flow through the buffer. New designs are being researched to increase the efficiency of the VFS. In order to accurately implement new design strategies, the runoff flowpaths into the VFS need to be accurately modeled. This research assesses the performance of existing established VFS buffers of selected sites by modeling and analyzing the flow accumulation from the field into the VFS using geographic information system (GIS) and light detection and ranging (LiDAR) derived digital elevation model (DEM) 5 x 5 m data. This study also employed the new coefficient of flow interception (CFI) approach that improves the process of identifying areas where flow is concentrated and designing more efficient filter strips to account for concentrated runoff. In this study, the performance of VFS in three sites was evaluated by developing and using the CFI. Among the three sites, site 1 had very poor efficiency and no flow passes through the VFS, site 2 had low efficiency, and site 3 had excellent efficiency.
]]>2019-12-23T14:45:59-08:00info:doi/10.2489/jswc.75.1.123hwp:resource-id:jswc;75/1/123Soil and Water Conservation Society2020-01-01Research751123129