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Title: Apex simulation: environmental benefits of agroforestry and grass buffers for corn-soybean watersheds

item SENAVIRATNE, ANOMAA - University Of Missouri
item UDAWATTA, RANJITH - University Of Missouri
item Baffaut, Claire
item ANDERSON, STEPHEN - University Of Missouri

Submitted to: ASA-CSSA-SSSA Annual Meeting Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: 6/26/2013
Publication Date: 11/3/2013
Citation: Senaviratne, A., Udawatta, R.P., Baffaut, C., Anderson, S.H. 2013. Apex simulation: environmental benefits of agroforestry and grass buffers for corn-soybean watersheds [abstract]. ASA-CSSA-SSSA Annual Meeting. 92-18.

Interpretive Summary:

Technical Abstract: The Agricultural Policy Environmental Extender (APEX) model is used to simulate the effects of vegetative filter strips on runoff and pollutant loadings from agricultural watersheds. A long-term paired watershed study under corn (Zea mays L-soybean [Glycine max (L.) Merr.] rotation with agroforestry (grass+trees), and grass upland buffers (4.5 m width), in Northeast Missouri, has shown 11-35 percent measured reduction in sediment and nutrient loads. The objective of this study was to calibrate and validate the APEX model for the study watersheds, find optimum buffer dimensions and placement locations, and evaluate the effects of a cover crop. ArcAPEX and APEX0604 versions were used for the simulations. The simulated corn and soybean yields were within ±13 percent and ±27 percent of the measured yields, respectively. The agroforestry, grass buffer, and control watershed models were calibrated (1998 to 2001) and validated (2002 to 2008) for daily event-based runoff with r2 and Nash-Sutcliffe Coefficients (NSC) values of 0.7-0.8 and 0.6-0.7, respectively. The event-based total phosphorous (TP) loads were calibrated and validated well with r2 and NSC ranging 0.7-0.8 and 0.6-0.7, respectively. The sediments and total nitrogen were not calibrated. The simulated grass and agroforestry buffers reduced average annual runoff by 4 percent and 5 percent, and TP by 13 percent and 45 percent TP, respectively. An increase in buffer widths to 5.5 and 7.5 m did not effectively change runoff or TP loads. Placement of buffers in backslope positions was more effective for reducing runoff and TP loads in the agroforestry watershed. Simulation of a winter cover crop reduced TP loadings by 15 percent to 24 percent. The calibrated and validated APEX model may be used to simulate various management scenarios to determine environmental benefits of buffers.