Elsevier

Soil and Tillage Research

Volume 101, Issues 1–2, September–October 2008, Pages 78-88
Soil and Tillage Research

Modeling the impacts of soil management practices on runoff, sediment yield, maize productivity, and soil organic carbon using APEX

https://doi.org/10.1016/j.still.2008.07.014Get rights and content

Abstract

Simulation models are increasingly used to analyze the impact of agricultural management at the watershed-scale. In this study, the Agricultural Policy/Environmental eXtender (APEX) model was tested using long-term (1976–1995) data from two watersheds (W2 and W3) at the USDA Deep Loess Research Station near Treynor, Iowa. The two watersheds were cropped with continuous corn (Zea mays L.) and managed with conventional-tillage at W2 (34.4 ha) and ridge-till at W3 (43.3 ha). The monthly runoff and sediment yield were calibrated for the two watersheds during 1976–1987 by adjusting the curve numbers, curve number index coefficient, RUSLE C factor exponential residue and height coefficients, and erosion control practice factor for grassed waterways. Soil organic carbon values in the top 0.15 m soil layer were calibrated for the two watersheds in 1984 by adjusting the microbial decay rate coefficient. Model validation was conducted from 1988 to 1995. The calibrated model was able to reasonably replicate the monthly and yearly surface runoff and sediment yield for both watersheds for the validation period, with Nash–Sutcliffe efficiencies (EF) larger than 0.62 except for the EF of 0.41 for monthly sediment yield comparison at W3. The errors between the predicted and observed means were all within ±6% for runoff and sediment yield; predicted soil organic carbon in the 0.15 m soils in 1994 were within 10% of the observed values for both watersheds. The percentage error between the predicted and observed average corn grain yields was −5.3% at W2 and −2.7% at W3 during the 20-year simulation period. Scenario analyses were also conducted to assess the benefits of ridge-till over conventional-tillage. Over the 20 years, the predicted benefit of ridge-till versus conventional-tillage on surface runoff reduction was 36% in W2 and 39% in W3, and about 82–86% sediment yield reduction in both watersheds. The cumulative soil organic carbon losses from sediment were reduced about 63–67%. The long-term benefit of ridge-till over conventional-tillage was also quantified as a minimum corn grain yield increase of 3.8%. The results of this study indicate that APEX has the ability to predict differences between the two tillage systems. The modeling approach can be extended to other watersheds to examine the impacts of different tillage systems.

Introduction

Agriculture is the primary focus of water quality and erosion control in the U.S. Agricultural practices affect water quality/quantity, crop productivity, and soil quality. Various incentives and education efforts to prevent the loss of nutrient-rich topsoil have resulted in the reduction of erosion from U.S. croplands and Conservation Reserve Program land by 32% between 1982 and 1997 (USDA-NRCS, 1997). Field monitoring is often used to evaluate and acquire knowledge of the impacts of management practices on productivity and environment. However, field research can be prohibitively costly and time consuming to perform across all possible landscape, climate, management practice, and cropping system combinations (Chung et al., 1999, Davis et al., 2000). Monitoring studies conducted at a watershed-scale are difficult to replicate in the way that traditional plot-scale research is designed, in order to compare responses of alternative management practices using only field observations. However, computer simulation models provide an efficient and effective alternative for evaluating the effects of agricultural practices on soil and water quality at the watershed level.

Simulation models have been extensively applied to study the impacts of agricultural management practices. Examples of such applications include predicting soil erosion effects associated with alternative land uses at a northwestern China watershed using the Agricultural Policy/Environmental eXtender (APEX) model by Wang et al. (2006a), quantifying the impacts of conservation tillage, strip intercropping, and other practices for two watersheds in central Iowa, USA using the Soil and Water Assessment Tool (SWAT) model (Vache et al., 2002), and analyzing the effectiveness of agricultural BMPs for sediment reduction in the Mississippi Delta using AnnAGNPS (Yuan et al., 2002). These and other models vary in complexity and flexibility, and provide different capabilities in representing agricultural systems and subsequently quantifying the impact of these systems over a range of climate, soil, and landscape conditions. Many models simulate BMPs using simple removal fractions, which do not allow in-depth depictions of different management practices.

The APEX model (Williams and Izaurralde, 2006) is a farm/small watershed and BMP model that simulates extensive land management (Borah et al., 2006). APEX is an extended and expanded version of the Environmental Policy Impact Climate (EPIC) model (Williams, 1990, Izaurralde et al., 2006). The field scale model, EPIC, has been extensively tested and applied for a wide variety conditions in the U.S. and other regions (e.g., China, Austria) as described in Gassman et al. (2005) and has also been applied at a global scale (Liu et al., 2007). APEX is based on state-of-the-art technology taken from several mature and well-tested models. For example, the soil carbon cycling submodel was developed following the approach used in the Century model Parton et al., 1993, Parton et al., 1994 as reported by Izaurralde et al. (2006), the pesticide component was derived from the Groundwater Loading Effects of Agricultural Management Systems (GLEAMS) model (Leonard et al., 1987), and the plant competition component was originally developed in the Agricultural Land Management Alternatives with Numerical Assessment Criteria (ALMANAC) model (Kiniry et al., 1992).

APEX can provide a consistent approach for evaluating various land management strategies at scales ranging from field to farm to small watersheds. It is a continuous simulation model that runs typically on a daily time-step. The individual field simulation uses the functions originally developed in EPIC, which simulate hydrology, erosion/sedimentation, weather, soil temperature, crop growth/plant competition, nutrients, pesticides, and agricultural management such as nutrient management, tillage operations, alternative cropping systems and irrigation. In addition to the EPIC functions, APEX has components for routing water, sediment, nutrients, and pesticides across complex landscapes and channel systems to a watershed outlet. APEX also has groundwater and reservoir components. APEX can also be configured for simulating the effects of buffers, filter strips, grassed waterways, intensive grazing scenarios, land application of manure removal from livestock feedlots, and other structural conservation practices. The flexibility of APEX has led to its adoption within the Conservation Effects Assessment Project (CEAP) for national assessment, which is designed to estimate the benefits obtained from USDA conservation programs at the national level (Mausbach and Dedrick, 2004). APEX has continued to be expanded and refined to reflect the knowledge advance in multiple areas of agriculture ranging from soil physics to micrometeorology and agricultural management. However, continuous testing and validation against as much field-specific data as possible is needed, to provide increased confidence in supporting ongoing APEX applications such as the CEAP national assessment and for guidance in selecting most suitable parameters to depict different management systems (Chung et al., 1999).

Long-term watershed studies dating back to the mid-1960s at the Deep Loess Research Station near Treynor, Iowa provide excellent data for testing simulation models and exploring management alternatives. The Treynor watersheds represent the Deep Loess hills region (Major Land Resource Area 107) which covers about 4.9 million ha in western Iowa and northwestern Missouri (USDA-NRCS, 2006). Short and/or long-term evaluations of different combinations of cropping systems and conservation practices have been reported for the Treynor watersheds in many studies including Alberts and Spomer (1985), Burwell et al. (1974), Cambardella et al. (2004), Karlen et al. (1999), Moorman et al. (2004), Kramer et al. (1999), Schuman et al. (1973), Steinheimer and Scoggin (2001), Steinheimer et al., 1998a, Steinheimer et al., 1998b, Thomas et al. (2004), Tomer et al. (2005), and Chung et al. (1999). These studies were conducted using descriptive, statistic, autoregressive, or simulation methods, indicating collectively that the Deep Loess hills are vulnerable agricultural landscapes where soil and crop management practices can impact water quality/quantity and soil quality. However, no long-term model-based scenario analyses have been performed for the Treynor watersheds, which provide the ability to isolate the effects of management practices on flow, sediment, and nutrient losses.

This study builds on the previous research performed for the Treynor watersheds, especially the application of EPIC by Chung et al. (1999), by incorporating both model testing and scenario analyses. The EPIC and APEX models share a mostly common parameter set, and thus the previously developed EPIC parameters were also used in the APEX simulations reported here to the extent possible. However, enhanced methods of simulating tillage and the Universal Soil Loss Equation (USLE) crop management “C” factor (Wischmeier and Smith, 1978) are used in APEX (and latest EPIC versions), versus the EPIC model used by Chung et al. (1999). Accounting for grassed waterways present in the watersheds was also performed in this study which allows for assessment of sediment losses at the watershed outlets, which Chung et al. (1999) could not evaluate. Thus, specific attention is focused on the effects of tillage, C factor calculations, and sediment delivery in the current study. The main objectives of this study were: (1) to calibrate and validate APEX using the long-term (1976–1995) field study data from two Treynor watersheds (conventional-tillage versus ridge-till), and (2) to quantify the long-term benefits of ridge-till versus conventional-tillage on runoff, sediment yield, crop, and soil organic carbon by conducting scenario analyses.

Section snippets

Model description

APEX is a physically based and continuous daily time-step model that was developed to predict the impact of various land management strategies on water supply and quality, erosion and sediment yield, soil quality, plant productivity and pests in whole farm/small watershed. A watershed can be subdivided into multiple subareas to assure that each subarea is relatively homogeneous in terms of soil, slope, land use, management, and weather. APEX has components for routing water, sediment,

Model calibration

The APEX monthly surface runoff and sediment yield calibrations were performed for 1976–1987 for both W2 and W3 by adjusting the model parameters that have significant effects on runoff (CN2 and curve number index coefficient) and sediment (RUSLE C factor exponential residue and height coefficients and PEC) (Table 3). The APEX model was set up for batch run, in which W2 was run first followed by running W3 using the same APEX parameter file. This guarantied that the same adjustment of model

Conclusions

Agricultural tillage influences the partitioning of precipitation into surface runoff and infiltration. Conservation tillage systems which leave more crop-residue on the soil surface can effectively reduce water and sediment loss. The APEX model was applied to estimate the long-term effects of ridge-till versus conventional-tillage in two watersheds at the USDA Deep Loess Research Station near Treynor, Iowa. The model was calibrated and validated with reasonable accuracy. Scenario analyses

Acknowledgements

This work was funded by the USDA-NRCS Resource Inventory Assessment Division, through the CEAP (Conservation Effects Assessment Project), and by the USDA CSREES Consortium of Agricultural Soils Mitigation of Greenhouse Gases. The authors acknowledge Mr. Robert Jaquis of the USDA-ARS National Soil Tilth Laboratory in Ames, Iowa for providing the Treynor watershed experiment data sets.

References (54)

  • D.K. Borah et al.

    Sediment and nutrient modeling for TMDL development and implementation

    Trans. ASABE

    (2006)
  • R.E. Burwell et al.

    Quality of water discharged from two agricultural watersheds in Southwestern Iowa

    Water Resour. Res.

    (1974)
  • S.W. Chung et al.

    Validation of EPIC for two watersheds in Southwest Iowa

    J. Environ. Qual.

    (1999)
  • D.M. Davis et al.

    Modeling nitrate leaching in response to nitrogen fertilizer rate and tile drain depth or spacing for southern Minnesota

    USA J. Environ. Qual.

    (2000)
  • Gassman P.W., Williams, J.R., Benson, V.W., Izaurralde, R.C., Hauck, L., Jones, C.A., Atwood, J.D., Kiniry, J.,...
  • D. Ginting et al.

    Corn yield, runoff, and sediment losses from manure and tillage systems

    J. Environ. Qual.

    (1998)
  • G.H. Hargreaves et al.

    Reference crop evapotranspiration from temperature

    Appl. Eng. Agric.

    (1985)
  • Hershfield, D.M., 1961. Rainfall frequency atlas of the United States for durations from 30 minutes to 24 hours and...
  • N. Kannan et al.

    Development of a continuous soil moisture accounting procedure for curve number methodology and its behaviour with different evapotranspiration methods

    Hydrol. Process.

    (2008)
  • D.L. Karlen et al.

    Field-scale watershed evaluations on deep-loess soils: 1. Topography and agronomic practices

    J. Soil Water Cons.

    (1999)
  • Kramer, L.A., Grossman, R.B., 1992. Tillage effects on near surface soil bulk density. ASAB paper 92-2131. ASAE, St.,...
  • L.A. Kramer et al.

    Field-scale watershed evaluations on deep-loess soils: II. Hydrologic responses to different agricultural land management systems

    J. Soil Water Conserv.

    (1999)
  • J.R. Kiniry et al.

    A general process-oriented model for two competing plant species

    Trans. ASAE

    (1992)
  • J.M. Laflen et al.
  • R.A. Leonard et al.

    GLEAMS: groundwater loading effects of agricultural management system

    Trans. ASAE

    (1987)
  • S.D. Logsdon et al.

    Field-scale watershed evaluations on deep-loess soils: III. Rainfall and fertilizer N use efficiencies

    J. Soil Water Conserv.

    (1999)
  • J.M. Mausbach et al.

    The length we go: measuring environmental benefits of conservation practices in the CEAP

    J. Soil Water Conserv.

    (2004)
  • Cited by (0)

    View full text