Tamie L. Veith

Integrated watershed- and farm-scale modeling framework for targeting critical source areas while maintaining farm economic viability

Quantitative risk assessments of pollution and data related to the effectiveness of mitigating best management practices (BMPs) are important aspects of nonpoint source pollution control efforts, particularly those driven by specific water quality objectives and by measurable improvement goals, such as the total maximum daily load (TMDL) requirements. Targeting critical source areas (CSAs) that generate disproportionately high pollutant loads within a watershed is a crucial step in successfully controlling nonpoint source pollution. The importance of watershed simulation models in assisting with the quantitative assessments of CSAs of pollution (relative to their magnitudes and extents) and of the effectiveness of associated BMPs has been well recognized. However, due to the distinct disconnect between the hydrological scale in which these models conduct their evaluation and the farm scale at which feasible BMPs are actually selected and implemented, and due to the difficulty and uncertainty involved in transferring watershed model data to farm fields, there are limited practical applications of these tools in the current nonpoint source pollution control efforts by conservation specialists for delineating CSAs and planning targeting measures. There are also limited approaches developed that can assess impacts of CSA-targeted BMPs on farm productivity and profitability together with the assessment of water quality improvements expected from applying these measures. This study developed a modeling framework that integrates farm economics and environmental aspects (such as identification and mitigation of CSAs) through joint use of watershed- and farm-scale models in a closed feedback loop. The integration of models in a closed feedback loop provides a way for environmental changes to be evaluated with regard to the impact on the practical aspects of farm management and economics, adjusted or reformulated as necessary, and revaluated with respect to effectiveness of environmental mitigation at the farm- and watershed-levels. This paper also outlines steps needed to extract important CSA-related information from a watershed model to help inform targeting decisions at the farm scale. The modeling framework is demonstrated with two unique case studies in the northeastern United States (New York and Vermont), with supporting data from numerous published, location-specific studies at both the watershed and farm scales. Using the integrated modeling framework, it can be possible to compare the costs (in terms of changes required in farm system components or financial compensations for retiring crop lands) and benefits (in terms of measurable water quality improvement goals) of implementing targeted BMPs. This multi-scale modeling approach can be used in the multi-objective task of mitigating CSAs of pollution to meet water quality goals while maintaining farm-level economic viability.

Precision feeding and forage management effects on phosphorus loss modeled at a watershed scale

Delaware County and the Cornell Cooperative Extension of Delaware County of New York State have initiated a farm-scale precision feed management (PFM) program to reduce soil-phosphorus build-up and phosphorus (P) losses to the Cannonsville Reservoir, a major supply source of New York City drinking water. The PFM program includes strategies that more precisely balance dairy cattle dietary P requirements with actual P intake and that improve on-farm forage production and utilization in the animal diet. The goal of the PFM program is to reduce manure P concentration, feed nutrients importation, P imbalance problems, and soil-P build-up while maintaining farm profitability. In this study, several PFM strategies were evaluated with respect to controlling P losses and soil-P build-up at both field and watershed scales using the Soil and Water Assessment Tool (SWAT) model. Using the SWAT model, manure with reduced P concentration was applied to cropland while grass-forage crop productivity was increased through N fertilizer application. The SWAT model simulation revealed decreased particulate phosphorus and soluble phosphorus losses by 22% and 13%, respectively. Predicted reductions of average particulate phosphorus and soluble phosphorus losses at the watershed outlet were 16% and 13% respectively, over a three-year period, compared to the baseline (conditions before changes were implemented). Model results also demonstrated an appreciable decrease in field-level soil-P during the growing season, indicating increased soil-P uptake by the improved grass-forage. For the growing season, reductions for predicted active and labile P pools were 11 and 5 mg kg-1 (0.02 and 0.01 lb tn-1), respectively, compared to the baseline. The corresponding reductions in field-level soil P were equivalent to 8% and 7% for labile and active P pools, respectively. Overall, the PFM strategies were found to have a potential for reducing soil-P build-up and P losses both at field and watershed levels. Performing a model-based environmental evaluation of farm management strategies at a watershed level helps to integrate farm management planning (the smallest management unit) into watershed level planning. Also, evaluating farm management strategies at a watershed scale provides valuable and comprehensive information for assessing the potential for long-term, cost-effective, and permanent reduction of P loss from dairy agriculture to the Cannonsville Reservoir.

Cannonsville Reservoir and Town Brook watersheds: Documenting conservation efforts to protect New York City's drinking water

The Cannonsville Reservoir watershed is a major component of the unfiltered New York City water supply system. The voluntary, incentive-based Watershed Agricultural Program is a collaborative effort among producers, federal, state, and local organizations to address the problem of phosphorus loading effects on water quality through implementation of whole-farm plans. The effectiveness of selected conservation practices, including stream-bank fencing, precision feeding, and the use of cover crops with silage corn (Zea mays L.) are being evaluated. Simulation models have been developed and improved to evaluate the effectiveness of individual conservation practices and better assess animal agriculture and manure management practices. Conservation practices implemented through the Watershed Agricultural Program are resulting in lower phosphorus loading from nonpoint sources in the watershed. Future efforts need to identify the most cost-effective conservation practices and extend our knowledge of watershed quality protection beyond the boundaries of the Cannonsville Reservoir watershed.

Assessing manure management strategies through small-plot research and whole-farm modeling

Plot-scale experimentation can provide valuable insight into the effects of manure management practices on phosphorus (P) runoff, but whole-farm evaluation is needed for complete assessment of potential trade offs. Artificially-applied rainfall experimentation on small field plots and event-based and long-term simulation modeling were used to compare P loss in runoff related to two dairy manure application methods (surface application with and without incorporation by tillage) on contrasting Pennsylvania soils previously under no-till management. Results of single-event rainfall experiments indicated that average dissolved reactive P losses in runoff from manured plots decreased by up to 90% with manure incorporation while total P losses did not change significantly. Longer-term whole farm simulation modeling indicated that average dissolved reactive P losses would decrease by 8% with manure incorporation while total P losses would increase by 77% due to greater erosion from fields previously under no-till. Differences in the two methods of inference point to the need for caution in extrapolating research findings. Single-event rainfall experiments conducted shortly after manure application simulate incidental transfers of dissolved P in manure to runoff, resulting in greater losses of dissolved reactive P. However, the transfer of dissolved P in applied manure diminishes with time. Over the annual time frame simulated by whole farm modeling, erosion processes become more important to runoff P losses. Results of this study highlight the need to consider the potential for increased erosion and total P losses caused by soil disturbance during incorporation. This study emphasizes the ability of modeling to estimate management practice effectiveness at the larger scales when experimental data is not available.

Improving Daily Water Yield Estimates in the Little River Watershed: SWAT Adjustments

Researchers are assessing the beneficial effects of conservation practices on water quality with hydrologic models. The assessments depend heavily on accurate simulation of water yield. This study was conducted to improve Soil and Water Assessment Tool (SWAT) hydrologic model daily water yield estimates in the Little River Experimental Watershed (LREW) in South Georgia. The SWAT code was altered to recognize a difference in curve number between growing and dormant seasons, to use an initial abstraction (Ia), of 0.05 S rather than 0.2 S, and to adjust curve number based upon the level of soil saturation in low-lying riparian zones. Refinements were made to two SWAT input parameters, SURLAG and ALPHA_BF, from a previous set of calibration parameters. The combined changes improved the daily Nash-Sutcliffe model efficiency (NSE) from 0.42 to 0.66 for water yield at the outlet of the 16.9 km2 subwatershed K of the LREW for the ten-year period 1995 – 2004. Further calibration of the SURLAG coefficient yielded the largest improvement of five alterations and changing Ia effected the next largest improvement. Over the 10-year investigation period, the model predicted annual average water yield within 1% of measured streamflow and deviation between observed and simulated values for stormflow was = 2.2%. Annual daily NSEs for each of the ten years were improved; for two years affected by seasonal tropical storm events, NSEs were changed from negative to positive values. The results of this study support the adjustment of the Ia ratio in the runoff curve number and suggest that additional changes to SWAT would improve water yield prediction for southern Coastal Plain locations.

Pastureland Conservation Effects Assessment Project: Status and expected outcomes

The Conservation Effects Assessment Project (CEAP) is a multiagency scientific effort to quantify environmental outcomes of conservation practices applied to private agricultural lands. The program is anticipated to help shape future conservation policies, programs, and practices. The integrated landscape approach will focus on enhanced ecological resilience and sustainable agricultural production, both of which are essential to maintaining livelihoods and meeting global food needs (Nowak and Schnepf 2010). Principal components of CEAP include (1) detailed syntheses of scientific conservation literature; (2) a national assessment of conservation effects on ecosystem services; and (3) detailed investigations of conservation practices at various scales, including paddock, landscape, and water-shed levels. The CEAP effort on grazing lands began in rangeland in 2006 (Weltz et al. 2008) with a synthesis of the scientific literature on key rangeland conservation practices (Briske forthcoming). A CEAP effort on pastureland, primarily in the eastern and central United States, began in 2008. A literature synthesis documenting the science behind key conservation practices (Nelson forthcoming) revealed that scientific support exists for most conservation practices on pastureland, but critical knowledge, data, and technology gaps remain, including the following: Comprehensive assessments of effects of grazing management on a broad suite of…

Exploring economically and environmentally viable northeastern US dairy farm strategies for coping with rising corn grain prices

In 2008, corn grain prices rose

Seasonal Manure Application Timing and Storage Effects on Field- and Watershed-Level Phosphorus Losses

115/t of DM above the 2005 average. Such an increase creates tight marginal profits for small (<100) and medium-sized (100 to 199) dairy farms in the northeastern United States importing corn grain as animal feed supplement. Particularly in New York State, dairy farmers are attempting to avoid or minimize profit losses by growing more corn silage and reducing corn grain purchases. This study applies the Integrated Farm Systems Model to 1 small and 1 medium-sized New York State dairy farm to predict 1) sediment and P loss impacts from expanding corn fields, 2) benefits of no-till or cover cropping on corn fields, and 3) alternatives to the economic challenge of the current farming system as the price ratio of milk to corn grain continues to decline. Based on the simulation results, expanding corn silage production by 3% of the cultivated farm area increased sediment and sediment-bound P losses by 41 and 18%, respectively. Implementing no-till controlled about 84% of the erosion and about 75% of the sediment-bound P that would have occurred from the conventionally tilled, expanded corn production scenario. Implementing a conventionally tilled cover crop with the conventionally tilled, expanded corn production scenario controlled both erosion and sediment-bound P, but to a lesser extent than no-till corn with no cover crop. However, annual farm net return using cover crops was slightly less than when using no-till. Increasing on-farm grass productivity while feeding cows a high-quality, high-forage diet and precise dietary P levels offered dual benefits: 1) improved farm profitability from reduced purchases of dietary protein and P supplements, and 2) decreased runoff P losses from reduced P-levels in applied manure. Moreover, alternatives such as growing additional small grains on marginal lands and increasing milk production levels demonstrated great potential in increasing farm profitability. Overall, it is crucial that conservation measures such as no-till and cover cropping be implemented on new or existing corn lands as these areas often pose the highest threat for P losses through runoff. Although alternatives that would likely provide the largest net profit were evaluated one at a time to better quantify their individual impacts, combinations of these strategies, such as no-till corn plus a minimum-till cover crop, are recommended whenever feasible.

The Promise, Practice, and State of Planning Tools to Assess Site Vulnerability to Runoff Phosphorus Loss

Timing of manure application to agricultural soils remains a contentious topic in nutrient management planning, particularly with regard to impacts on nutrient loss in runoff and downstream water quality. We evaluated the effects of seasonal manure application and associated manure storage capacity on phosphorus (P) losses at both field and watershed scales over an 11-yr period, using long-term observed data and an upgraded, variable-source water quality model called Topo-SWAT. At the field level, despite variation in location and crop management, manure applications throughout fall and winter increased annual total P losses by 12 to 16% and dissolved P by 19 to 40% as compared with spring. Among all field-level scenarios, total P loss was substantially reduced through better site targeting (by 48-64%), improving winter soil cover (by 25-46%), and reducing manure application rates (by 1-23%). At the watershed level, a scenario simulating 12 mo of manure storage (all watershed manure applied in spring) reduced dissolved P loss by 5% and total P loss by 2% but resulted in greater P concentrations peaks compared with scenarios simulating 6 mo (fall-spring application) or 3 mo storage (four-season application). Watershed-level impacts are complicated by aggregate effects, both spatial and temporal, of manure storage capacity on variables such as manure application rate and timing, and complexities of field and management. This comparison of the consequences of different manure storage capacities demonstrated a tradeoff between reducing annual P loss through a few high-concentration runoff events and increasing the frequency of low peaks but also increasing the annual loss.

Analyzing Within-County Hydrogeomorphological Characteristics as a Precursor to Phosphorus Index Modifications

Over the past 20 yr, there has been a proliferation of phosphorus (P) site assessment tools for nutrient management planning, particularly in the United States. The 19 papers that make up this special section on P site assessment include decision support tools ranging from the P Index to fate-and-transport models to weather-forecast-based risk calculators. All require objective evaluation to ensure that they are effective in achieving intended benefits to protecting water quality. In the United States, efforts have been underway to compare, evaluate, and advance an array of P site assessment tools. Efforts to corroborate their performance using water quality monitoring data confirms previously documented discrepancies between different P site assessment tools but also highlights a surprisingly strong performance of many versions of the P Index as a predictor of water quality. At the same time, fate-and-transport models, often considered to be superior in their prediction of hydrology and water quality due to their complexity, reveal limitations when applied to site assessment. Indeed, one consistent theme from recent experience is the need to calibrate highly parameterized models. As P site assessment evolves, so too do routines representing important aspects of P cycling and transport. New classes of P site assessment tools are an opportunity to move P site assessment from general, strategic goals to web-based tools supporting daily, operational decisions.