Software / WinAPEX

WinAPEX is a whole farm (small watershed) production-risk management model designed to help agricultural practitioners optimize crop management and maximize production and profit, to identify limitations to crop yield, and to identify best management practices that minimize the impact of agriculture on soil erosion and water quality at the farm and field level. It is a windows-based application of the APEX (Agricultural Policy/ Environmental extender) model originally developed by the Texas Agricultural Experiment Station that simulates the interaction of natural resources (soil, water, climate) and crop management practices to estimate impacts on harvested crop yield, soil properties, soil erosion, profitability, and nutrient/pesticide fate on a whole farm scale.

Download WinAPEX for APEX v.1501 (October 2016)

*NOTICE: If you are currently using WinAPEX 1501, the development team has released an update for this model on 18 May 2016. Please email us at if you have any problems with downloading the new file. The release includes a vital update to the Biological Mixing Efficiency process within the model. The update balances the rate of biological mixing with WinAPEX 1501’s daily time step in comparison to mechanical mixing. If you are already working with a calibrated version of this model, you can fix the same issues by updating the Parm29 file by changing the Biological Mixing Parameter so that the default = 0.001 and range = 0.0001 – 0.01.

Crop Management Simulations

  • Fertilization: N and P (mineral, manure)
  • Planting date, crop maturity, crop type, and rotation sequence
  • Cover crop and double cropping systems
  • Irrigation: sprinkler, furrow, flood, buried and surface drip
  • Plant population and row spacing
  • Tillage/residue management
  • Pesticide fate
  • Pasture and forage utilization by livestock and wildlife

Special Features

  • It contains a watershed builder subroutine in which users can delineate individual field (subarea) attributes including upland slope, soil characteristic, cropping system, land condition, routing reach and channel characteristics, livestock activity, and one or more weather stations.
  • Attributes can be edited for alternative analyses and comparisons of farm and field losses.
  • In addition to terracing and contour farming, the user is able to create buffer strip subareas within existing fields to determine the impact on runoff and erosion.
  • Information is saved, sorted and can be edited at the farm and field level.
  • Control Table Editor is used to customize control parameters for each farm including years of simulation, beginning year of simulation, channel and floodplain geometry, PET equation, etc.
  • Subarea file is used to customize each field including auto-irrigation and auto- fertilization strategies among numerous other field level control parameters. This file controls management, land condition, soil and hydrologic parameters of each field.
  • Generates daily weather from monthly statistics if daily weather data is missing.
  • Stand-alone utility to download and update daily weather records to current day from the web or user collected/supplied daily records.
  • Yearly/monthly/daily data output at the farm and field level to ACCESS tables enabling manipulation of data within EXCEL.


  • Identify best management practices for site-specific climate and soil variation to minimize cropping impact on soil erosion, water quality, and runoff.
  • Identify production constraints and alternative practices to maximize yield, profit, and production efficiency.
  • Determine fertility/nutrient needs and nutrient and pesticide fate.
  • Determine El Nino/La Nina impacts on productivity and alternative production practices.

Databases Included

  • Weather: 20+ years of observed daily maximum and minimum temperature and precipitation and monthly statistics from selected National Weather Service Class 1 or coop weather sites to operate weather generator
  • All NRCS Soils 5, Management Unit Use Files by County
  • Pesticides, Fertilizers and Equipment
  • Management: sequential farming operations by cropping system: crop, tillage (conventional, reduced and no-till), and water application (irrigation versus dryland)
  • Crops simulated: U.S. field crops, forages, perennials, rangeland, forests, sugarcane, and vegetables


Field (subarea) level

  • Stresses
  • Crop yield
  • Water
  • Nutrient
  • Non-point losses
  • Pesticide fate and losses

Farm (watershed) level

  • Runoff and erosion
  • Nitrogen and phosphorus losses
  • Carbon sequestration/loss
  • Pesticide fate