To appropriately place soil conservation measures, locating the most vulnerable areas prone to soil erosion is required. Available tools to locate vulnerable areas are tedious to use and time-consuming, and most water erosion estimations are based on empirical models with limited applicability. The present study takes advantage of two large-scale soil and water conservation tools available for the Midwest U.S.: the Daily Erosion Project (DEP) and the Agricultural Conservation Planning Framework (ACPF).In this study, we will showcase a recently developed large scale modeling approach implemented in the Midwest U.S. that currently downscales DEP from Hydrologic Unit Code (HUC) 12 (~90 km2) average estimation of hillslope runoff and soil loss into a much finer resolution, a field and pixel scale. The DEP uses the Water Erosion Prediction Project (WEPP) and simulates hundreds of thousands of hillslopes across the Midwest, covering the wide range of factors including topography, climate, soils and land use and management.This presentation will introduce the newly developed quantitative soil erosion assessment tool (named OFEtool - Overland Flow Element tool) that uses geographic information systems (GIS) and a physical-based model with real climate data (DEP). The OFEtool analyzes a watershed and groups areas with similar attributes, such as slope, soil type, land use, and management practices (information provided by the ACPF). Following watershed analysis, the tool uses DEP simulations to obtain average hillslope soil erosion or deposition rates for these grouped characteristics. Finally, it associates and assigns these rates to the respective areas within the watershed.The current version of the tool is used by the ACPF to locate the most vulnerable fields across the watershed for conservation planning scenarios to prioritize interventions in fields and specific areas with the highest erosion rates. The applicability of the tool will be shown for the state of Iowa (approximately 145,746 square kilometers). Preliminary results corroborate spatial variability of soil erosion within watersheds and Major Land Resource Areas (MLRA). The presentation will also provide new insights into the main factors governing soil erosion in Iowa (climate, soils, topography, land use and management). ReferencesGelder, B., Sklenar, T., James, D., Herzmann, D., Cruse, R., Gesch, K., & Laflen, J. (2018). The Daily Erosion Project – daily estimates of water runoff, soil detachment, and erosion. Earth Surface Processes and Landforms, 43(5), 1105–1117. https://doi.org/10.1002/esp.4286Daily Erosion Project. (n.d.). Retrieved January 9, 2024, from https://www.dailyerosion.org/Tomer, M. D., Porter, S. A., James, D. E., Boomer, K. M. B., Kostel, J. A., & McLellan, E. (2013). Combining precision conservation technologies into a flexible framework to facilitate agricultural watershed planning. Journal of Soil and Water Conservation, 68(5). https://doi.org/10.2489/jswc.68.5.113Agricultural Conservation Planning Framework. (n.d.). Retrieved January 9, 2024, from https://acpf4watersheds.org/

A new frontier of conservation planning capacity utilizing innovative decision support tools has emerged. Extension professionals play an important role in using these new data and tools to achieve conservation and water quality outcomes. Here, we detail the application of two conservation planning tools: Agricultural Conservation Planning Framework (ACPF) and Financial and Nutrient Reduction Tool (FiNRT). Tools like these are increasingly being used to guide conservation efforts in agricultural landscapes; provide information regarding potential resource concern; and offer valuable data about outcomes from best management practice (BMP) placement. Extension professionals’ use of such tools could enhance conservation implementation and outcomes.

Most irrigation pumps used in Nigeria are imported. Consequently, the challenges farmers faced in using these pumps include but not limited to the following; priming before operation, relatively low-capacity delivery at low head and high price which is often time not affordable by peasant farmers. The objective of this research was to develop an axial flow pump with locally sourced materials and affordable by farmers for small to medium scale irrigation in Nigeria. The design of the pump for the study was adopted from an existing and functioning axial pumping machine, developed by Agricultural Machinery and Mechatronics Department, Kasetsart University, Thailand. The pump was fabricated at the workshop of National Centre for Agricultural Mechanization (NCAM), Ilorin, Nigeria. Diesel fuel was used in powering the pump because of higher torque deliverable. The developed pump based on its capacity can be used to irrigate one hectare in one hour at 16.2 mm depth of water using 2000 rpm at 1m head and 9.6 mm depth of water using 1000 rpm at 3 m head. The maximum water discharge of 162 m3/h (45 l/s) was at 1m using a speed of 2000 rpm with water to fuel delivery of 124.29 l/s. The maximum water discharge of 162 m3/h (45 l/s) was at 1m using a speed of 2000 rpm with water to fuel delivery of 119.57m3/L. And the least water discharge of 59.30 m3/h (28 l/s) and water delivery per fuel was 41.0m3/L at 3 m head at 1000 rpm. Therefore, the developed pump operates best at lower head of 1m featuring a 3kW prime mover. The developed pump based on its capacity can be used to irrigate one hectare in one hour at 16.2 mm depth of water using 2000rpm at 1m head and 9.6 mm depth of water using 1000rpm at 3m head at a moisture content of 45% on a sand-loamy soil. Statistical analysis reveals relationships between pump speed, head, fuel consumption, and various performance indicators. The centrifugal pumps were found to produce lower discharge than axial flow pumps at different water heads evaluated. Comparative economic analysis demonstrates the pump's superiority over conventional centrifugal pumps in terms of water-fuel delivery efficiency and operational cost. This study introduced a locally modified axial flow pump as a practical, cost-effective, and efficient solution to irrigation challenges faced by small and medium-scale farmers in Nigeria. This pump has higher capacity delivery, spare parts are readily available at local market, it is appropriate for use where the irrigation head requirements are low and large volumes of water is required to be lifted at low pressure, it is appropriate where water can be lifted from rivers and canals and then directed to farmers' fields for irrigation. It is also applicable in rice farm flooding and flood drainage. This type of pump is good for flood (surface) irrigation system, which include furrow, border, basin irrigation and uncontrolled flooding in loamy and clay soils for rice production and sugarcane productions. The pump's adoption and economic viability positions it as a potential catalyst for increased food production, income, and food security in the country.

Many crop fields in the United States Corn Belt continue to erode at rates in excess of soil regeneration leading to sediment being transported from farms to adjacent surface water and degrading wildlife habitat. To reduce or eliminate sediment loss, vegetative filter strips can be established perpendicular to the hillslope and at the edge -of -field to intercept and filter surface runoff transporting sediment. The filter strips can be planted with native prairie vegetation to filter sediment out of runoff as well as establishing high quality habitat. A long-term study at Neal Smith Wildlife Refuge Farm in central Iowa found that with as little as 10% of a field converted to prairie filter strips, sediment discharge from fields could be reduced up to 95%. To improve our understanding of prairie filter strips and erosion processes over a broader range of landscapes, this study was conducted at six farm sites throughout Iowa. Following a paired treatment approach, each farm site was broken into two different subcatchments; one subcatchment was fully cropped (control) while the other had a portion of the field sown with native prairie vegetation. Each subcatchment had an H -flume installed to sample runoff water and determine the total suspended sediment (TSS) load and a rain gauge to monitor rainfall amount, frequency, and duration. Between 2016 and 2021, subcatchments with prairie strips median TSS load was 89.5% lower (95% CI, 69.2% to 96.4%, p < 0.001) than the control subcatchments. In fields when corn was planted, the subcatchments with prairie strips had significantly lower TSS discharged, with a median TSS load 97.6% less (95% CI, 92.1% to 99.3%, p < 0.001) compared to the control subcatchments. The TSS loads were significantly influenced by the amount of rainfall (p < 0.001) despite the treatment. To investigate effects of seasonality and rainfall amount, the data set was parsed out based on the growing season of the dominant cropping system. There was no prairie strip effect during the primary growing months (PGS) (May to August); however, outside of the primary growing months (OPGS) (March to April and September to November) the prairie strip subcatchments median TSS load was 96.1% less (95% CI, 82.5% to 99.1%, p < 0.001) than the controls. The significant interaction of crop planted with prairie strip treatment and the differences between PGS and OPGS suggest that prairie strips have the capacity to reduce sediment leaving a field when they are the most vulnerable to effects of splash erosion (i.e., low ground cover and higher rainfall amount). Climate change models predict that areas like Iowa will continue to trend toward higher frequency and intensity rain events, so the compounded benefits of prairie planted in cropped fields could promote biodiverse landscapes that increase resilience to predicted effects from climate change during parts of the year when the land is more susceptible to erosion.

Agriculture continues to be one of the most important sources of nonpoint source pollution to surface water bodies. Consequently, it is critical to identify and prioritize high-contributing agricultural fields and sub-field areas for reducing soil erosion and sediment delivery by implementing best management practices (BMPs). Current erosion risk assessment tools are either complex modelling approaches or rely on a simplified reality and generalized assumption. The Daily Erosion Project (DEP) is a daily estimator of precipitation, hillslope runoff, detachment and soil loss covering similar to 630 000 km(2) across the Midwest United States. These estimations are reported daily and publicly at the hydrologic unit code 12 watershed resolution (approximately 100 km(2)). The main objective of this study was to develop a new tool (named Overland Flow Element tool [OFEtool]) that downscales the watershed scale of DEP to estimate average runoff and soil displacement within a field, helping to locate erosive hotspots at multiple scales. We also demonstrated the applicability of OFEtool in Bennet Creek-Sugar Creek in East Central Iowa (the United States) and compared its results with other erosion vulnerability tools such as the Soil Vulnerability Index for Cultivated Cropland (SVI-cc) and a GIS-based Revised Universal Soil Loss Equation (RUSLE). The same erosion risk classes and ranges (low, moderate, moderately high and high) were implemented for all indexes. The advantages of the OFEtool compared to the SVI-cc and RUSLE models are related to the use of an event-based modelling approach, such as DEP, with updated soil loss estimates based on temporal changes in climate inputs and land use and management. The OFEtool uses a 6-year time frame and a more up-to-date field inputs, while RUSLE provides a long-term average and SVI-cc only considers soil and topographical factors for risk assessment. Results indicated that the spatial distribution of vulnerable fields (and parts of the fields) followed a similar trend as other tested indices. However, the risk level associated with each tool differed (SVI-cc > RUSLE > OFEtool). These differences could arise from intrinsic disparities within the tools (inputs, timing, processes considered, assumptions). While currently limited to the DEP domain and relying on the DEP random sampling scheme, further research is warranted to validate the tool at other Midwest locations and ensure it captures the watershed's landscape variability (combination of terrain, soil, land use and management) required to identifying critical erosion hotspots.

Changing precipitation patterns associated with a changing climate result in altered rainfall erosivities that have direct impacts on soil erosion rates. Informed by observed climate change impacts on precipitation, three scenarios were run with the WEPP soil erosion model to assess changes in soil erosion estimates relative to the Daily Erosion Project (DEP) 2007-2020 baseline results over Iowa, USA. Unlike other studies which obtained results via statistical adjustment through a weather generator, these results were obtained via explicit adjustment of two-minute interval precipitation intensities. These scenarios found more than a 2% increase in average annual soil loss compared to the baseline for every 1% increase in precipitation intensity (Figure 1), a 0.7% increase in soil loss for every one day shift earlier in precipitation timing, and an 8% increase in soil loss for every additional 25 mm h-1 storm added during the spring season. Evidence suggests climate change impacts on precipitation characteristics affecting soil erosion must be considered a priority in planning conservation practices to maintain and/or improve soil health.

We have developed an add-on tool for use with the Agricultural Conservation Planning Framework (ACPF) that features a multistate financial analysis and field-scale nitrogen (N) reduction tool for use when analyzing different ACPF conservation scenarios. Financial and expected field-scale N loss data are used to calculate total long-term cost and cost effectiveness of various conservation plans. Unique to the ACPF Financial and Nutrient Reduction Tool is the ability to identify individual treatment areas for each practice evaluated, allowing users to create combinatorial conservation planning scenarios drawing from multiple ACPF-identified conservation practices. Financial data account for direct long-term annualized costs for best management practice (BMP) installation and management in Iowa and Minnesota. Opportunity costs of BMPs that retire cropland are spatially determined according to weighted-average crop productivity indices and land rent relationships. The tool quantifies the N requirements for each field, based on 6-yr land-use data, and evaluates the proportion of N likely to be lost from the field as nitrate load via leaching. Financial analyses that can be accomplished by using the ACPF are illustrated in case study watershed scenarios in Iowa and Minnesota. In Iowa, featured scenarios range from 26 to 31% reduction in total nitrate, for a total cost between US$0.580 million and $2.3 million per year, respectively. In Minnesota, example scenarios range from 28 to 51% total nitrate reduction, for total costs of $1.7 million to $2.1 million per year. Tradeoffs in BMP selection related to N reduction outcome and cost are also demonstrated.

THE NEED FOR TARGETED AGRICULTURAL CONSERVATION The 2008 Gulf of Mexico Hypoxia Action Plan was developed in response to national water quality impairments that were largely caused by agricultural land uses within and around the US Corn Belt (Alexander et al. 2008; Mississippi River Gulf of Mexico Watershed Nutrient Task Force 2008). The plan prompted states to create nutrient reduction strategies to achieve a 45% reduction in total nitrogen (N) and total phosphorus (P) loads into the Mississippi River, and thereby alleviate the hypoxic zone in the Gulf of Mexico (Mississippi River Gulf of Mexico Watershed Nutrient Task Force 2008). Similar to other state strategies, the Iowa Nutrient Reduction Strategy (INRS) promotes the widespread and voluntary adoption of best management practices (BMPs) to achieve nutrient reduction goals. The INRS establishes goals of 41% and 29% reductions in total N and total P, respectively, from nonpoint sources from a 1980 to 1996 baseline (Iowa Department of Agriculture and Land Stewardship et al. 2017). These goals are largely dependent on regional conservation funding and infrastructure to inform and incentivize BMP adoption at individual farm scales (Zimmerman et al. 2019a).

Abstract Riparian buffers can improve water quality, but watershed‐scale evaluations of riparian buffering opportunities are rare. A landscape discretization tool called riparian catchments, part of the Agricultural Conservation Planning Framework (ACPF) version 3, was applied to evaluate functional riparian settings for 32 headwater watersheds representing three major land resource areas (MLRAs) in Iowa. Riparian settings of 250‐m length were classified based on height above channel and upslope contributing area to show where to place buffers primarily designed to intercept runoff, treat nitrate in shallow groundwater, and/or protect streambanks. Riparian zones found below small riparian catchments were common, typically occupying >50% of streambank lengths in MLRA 103 (northern Iowa) and MLRA 108 (southeast Iowa). In these settings, narrow (6–10 m wide) buffers provide a buffer/contributing area ratio of >0.02 to filter surface runoff, while providing streambank protection. This similarity occurred despite these two MLRAs having contrasting landscapes. Whereas the narrow buffers suggested are associated with ditches and flat terrain in MLRA 103, they occur below short slopes along streams that have well dissected the watersheds in MLRA 108. In MLRA 104 of east‐central Iowa, headwater alluvial streams often had broad low‐lying riparian zones, where wide buffers (>25 m) may be placed to help mitigate nitrate transport in shallow groundwater. The ACPF riparian catchments approach enabled cross‐watershed analyses of riparian settings, while providing spatial data to inform watershed‐scale riparian planning efforts.

Predicting ephemeral gully (EG) location is essential for many land management decisions and for accurate application of widely used soil erosion models. Topographic indexes are widely used for identifying EG head locations, even though the calibration of the topographic index models limits their use for broad scales. The objective of this research was to test the accuracy and usability of grid order in predicting EG head locations at the regional scale compared to other topographic indexes commonly used for this purpose. Three hundred fifty-three EGs in eight watersheds located within different landforms (Major Land Resource Areas) in Iowa, USA, were visually digitized, georeferenced, and analyzed using 3-meter LiDAR-derived elevation datasets and orthoimages. The location prediction accuracy, spatial location prediction error stability, and the variation of grid order critical threshold (CT) values were compared to predictions from four commonly used topographic indexes, specific contributing drainage area (As), Compound Topographic Index (CTI), Stream Power Index (SPI), and a variation of Stream Power Index (AS2). Results indicate that using As, CTI, SPI, and AS2 to identify flow length upstream from predicted EG head locations would require careful calibration for each watershed or substantial errors in prediction accuracy would occur. In contrast, the accuracy of using grid order was acceptable at the regional scale even without model calibration with Nash Sutcliff Efficiency estimates ranging from 0.29 to 0.59; the distance between surveyed and predicted EG head locations was within 20 m for all studied EGs. The grid order value of 4 was the best CT value when the slope gradient was less than 10%, and 3 for steeper slopes. These results could be easily applied for different landforms across wider areas. The result of this research supports the prediction of EGs using automated systems without calibration at a broad scale where quality DEMs are available.

Predicting ephemeral gully (EG) location is essential for erosion modeling because it helps confine portions of the hillslope segment above locations that gully and channel soil loss processes dominate. In the Water Erosion Prediction Project (WEPP), the prediction of EG occurrence location influences the model results by shorting or expanding the flow path, which the hillslope erosion modeling relies on. This research aimed to analyze the sensitivity of EG locations prediction accuracy on WEPP model output within the framework of the Daily Erosion Project (DEP) at the regional scale. DEP is a near real-time estimator of precipitation, soil detachment, hillslope soil loss, and water runoff using WEPP as the erosion model. The above estimations are conducted on randomly selected and spatially distributed flowpaths, and the means are reported at the HUC12 watershed level. The flowpaths are identified based on Digital Elevation Model (DEM) grid cell and D8 connectivity to adjacent cells. A flow path starts at a cell such that all adjacent cells are at a lower elevation, that is, no other adjacent cell directs flow into it and ends when sufficient flow concentration and soil conditions occur that channel erosion processes dominate soil loss where usually EGs occurrence. In this research, the DEP flowpaths, down to and including ephemeral gully heads, were surveyed in 8 HUC12 watersheds distributed in 8 different Iowa MLRAs using high-resolution imagery in-field measurement. A grid order model was used as a method for EG location prediction. The sensitivity of accuracy of EG location prediction on WEPP/DEP soil detachment, hillslope soil loss, and water runoff model output was explored at hillslope, watershed, and regional spatial scale with both extreme rainfall events and yearly average erosion modeling. This research will allow a more clear understanding of EG prediction influence on erosion modeling and help improve the accuracy of erosion modeling by using WEPP / DEP.

Precision conservation planning tools can use high-resolution data to identify conservation practice-placement options for watershed improvement plans. Use of these tools across multiple watersheds could help to identify regional conservation strategies. This study evaluated practice-placement options determined using the Agricultural Conservation Planning Framework (ACPF) ArcGIS tools for controlled drainage (CD), contour buffer strips (CBS), water and sediment control basins (WASCOBs), and grassed waterways (GWWs) across 32 headwater hydrological unit code (HUC)12 watersheds in Iowa. The watersheds represented three Major Land Resource Areas (MLRAs) and four Agro-Hydrologic Landscape (AHL) classes, with four watersheds randomly chosen from each of eight combined MLRA-AHL landscape groupings. Placement options for the practices identified using the ACPF were quantified by watershed as densities (km km−2 of cropland) for GWWs, counts of proposed practice locations per square kilometer for CBS and WASCOBs, and as fractions of tile-drained land for CD. The influence of the landscape groupings on practice-placement densities among watersheds was tested using analysis of variance and contrast comparisons. Significant differences were found that led to nuanced interpretations. Differences attributed to slope steepness were captured by AHL classes, while differences attributed to slope shape and convergence were best captured by MLRA, which better segregated the watersheds based on landscape age and stream dissection. Grassed waterway placements showed minor differences among MLRAs but provided data to better inform the choices that ACPF users can make when running the GWW tool. The MLRA/AHL landscape classifications could be used together to develop effective regional conservation strategies using precision planning tools.

T he online database Sustaining the Earth's Watersheds–Agricultural Research Data System (STEWARDS), was developed in a six year project by a team from several USDA Agricultural Research Service (ARS) locations to deliver weather, hydrology, and water quality data to the public. Launched as part of the Conservation Effects Assessment Project (CEAP; Mausbach and Dedrick 2004), the timeline started with 2002 to 2003's Conception and Agency commitment, extended through July 7, 2007's, beta release with three watersheds, to the 2007 to 2008 public release and population with other data and watersheds (Steiner et al. 2008). In fact, the database continues to grow, adding between 1 and 2 million data records a year. At the decadal anniversary of public availability, the authors set out to examine the impact STEWARDS has had on the scientific community, conservation programs, and the general public. Data in STEWARDS were collected by a number of USDA ARS locations, some of which have documented the various data collection efforts in the literature. The six regional watersheds established after authorization by Senate Bill 59 (USDA 1959) all have database documentation paper series published. Marks (2001) introduced …

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.

The size and density of concentrated animal feeding operations have grown significantly over the past twenty-five years, raising concern over the ability of the surrounding landscape to sustainably handle the byproducts of animal agriculture. A novel geographic information system program was developed to spatially model the application of manure nutrients to proximal agricultural fields. Nutrient losses during storage and field application were accounted for to determine the amount of manure sourced nitrogen available annually for land application. By-field nitrogen requirements were estimated using six-year crop rotations and commonly used guidelines on fertilizer recommendations for agronomic crops. Three different nitrogen fertilizer recommendation approaches, ranging from economically optimized rates on the low end to yield goal-driven rates on the high end, were modeled to gauge the sensitivity of the analysis approach to varying nitrogen application rates. For each fertilizer N rate, three manure haul distance scenarios were modeled, allowing for manure travel distance to be capped at distances unique to each livestock type. Lastly, commercial nitrogen fertilizer sales data were combined with manure sourced nitrogen estimates to assess statewide agricultural nitrogen application. Results indicated minimal (<5%) over-application from manure alone when applied at recommended rates and using the haul distances specified. However, regardless of which application rate guidelines were used, combined manure and commercial fertilizer nitrogen exceeded statewide crop requirements (110%–155%). This suggests that significant application of nitrogen above recommended rates is likely occurring. Information on commercial fertilizer application at the field level is sparse, precluding greater understanding of the relative contribution of manure and commercial sources. Despite this knowledge gap, additional focus should be placed on cumulative nitrogen application in areas with dense animal concentrations. Adequate crediting of all nitrogen sources, including the recognition of manure as a valuable fertilizer resource, presents the opportunity for substantial producer cost savings and potential widespread reduction in the contamination of water resources.

The saturated riparian buffer (SRB) is a new and cost-effective conservation practice that diverts agricultural tile drainage toward subsurface discharge within riparian buffers to achieve nitrate (NO3-N) removal. Conservation planners want to understand the potential role of the SRB practice for reducing NO3-N loads from tile-drained agricultural watersheds. The Agricultural Conservation Planning Framework (ACPF) includes a tool for identifying riparian zones where the SRB practice can be installed with minimal risks of unintended consequences (i.e., crop inundation and streambank failure). Watershed assessment of the potential role for SRBs, however, must identify where SRB-suited sites can actually receive drainage from tile-drained fields. This study compared the extent of SRB-suited riparian sites among 32 Iowa watersheds, and estimated the proportion of each watershed that was tile drained and located above SRB-suited riparian zones. Results showed the extent of sites suited for SRBs did not significantly differ among three Major Land Resource Areas (MLRAs) in Iowa, from which the selected watersheds were randomly chosen. Most watersheds had suitable sites along 30% to 70% of streambank lengths, where tile drainage from 15% to 40% of the watershed areas could be diverted, based on estimated extents of tile drainage above suitable sites. Therefore, the SRB has an important potential role for water quality improvement in many tile-drained watersheds in Iowa. However, the SRB practice is not readily designed for treating drainage from headwater catchments, which frequently con:prised more than 30% of watershed areas in headwater streams of north central Iowa (MLRA 103), where tile drainage is extensive.

Spatial partitioning is a classic hypothesis to explain plant species coexistence, but evidence linking local environmental variation to spatial sorting, demography and species' traits is sparse. If co‐occurring species' performance is optimized differently along environmental gradients because of trait variation, then spatial variation might facilitate coexistence. We used a system of four naturally co‐occurring species of Clarkia (Onagraceae) to ask whether distribution patchiness corresponds to variation in two environmental variables that contribute to hydrological variation. We then reciprocally sowed Clarkia into each patch type and measured demographic rates in the absence of congeneric competition. Species sorted in patches along one or both gradients, and in three of the four species, germination rate in the ‘home’ patch was higher than all other patches. Spatially variable germination resulted in the same three species exhibiting the highest population growth rates in their home patches. Species' trait values related to plant water use, as well as indicators of water stress in home patches, differed among species and corresponded to home patch attributes. However, post‐germination survival did not vary among species or between patch types, and fecundity did not vary spatially. Synthesis. Our research demonstrates the likelihood that within‐community spatial heterogeneity affects plant species coexistence, and presents novel evidence that differential performance in space is explained by what happens in the germination stage. Despite the seemingly obvious link between adult plant water‐use and variation in the environment, our results distinguish the germination stage as important for spatially variable population performance.