How We Do It

We use a mechanistic cropping systems model, weather forecasting, and in-season soil and crop measurements from 20 site-crop-management replicated treatments across Iowa.

We set up model calibrations for all experimental sites before the season begins.  We then add historical, current, and forecasted weather to drive the calibrations to simulate historical, current, and future field events.  Meanwhile, we measure everything we can at the field sites and check the model against these measurements.  We then publish the results (simulated and measured data) on the website.  

At the end of the season, we perform a scenario analysis by making changes to the model, such as adjusting the amount of fertilizer, seed, plant spacing, or even precipitation.  Then we evaluate what would have led to a greater yield, less environmental influence, and more economic gain.

The weather modeling includes a synthesis of actual and historical weather data together with short (3 days; NDFD) and long term forecasted weather data (>90 days; CFS). 

The APSIM modeling platform

The Agricultural Production Systems sIMulator (APSIM) is used to synthesize soil-crop-weather information and create in-season forecasts for crop yields and soil water-nitrogen and end-of-season evaluations and scenario analysis. The APSIM model simulates crop growth and development, soil water and N balances that includes water/nitrate leaching to tile drainage and GHG emissions on a daily basis. The yield predictions account for water and nitrogen limitations but not weeds, insects and diseases. Within APSIM, crop growth models are coupled with soil-environmental modes and thus interactions between crop and soil variables are explicitly considered. The model operates on a daily time step.

The crop models simulate crop phenology, morphology, physiology and biomass production and partitioning. Water and nitrogen stresses on crop growth and development are simulated using a supply/demand approach. The model can simulate potential, water-limited and water-nitrogen-limited production situations.

To simulate soil water in each layer APSIM runs a water balance that includes the following processes: precipitation, runoff, soil water evaporation, plant transpiration, water flow in tile drainage, water leaching from the bottom of the soil profile and capillary rise of water to the soil profile from groundwater table.

Soil organic carbon and nitrogen cycling is simulated in each layer and a number of processes are considered: soil N mineralization, residue N immobilization, nitrification, denitrification, N20 and CO2 emissions, NO3-N leaching to tile drainage, NO3-N leaching from the bottom of the profile, atmospheric N deposition and N fixation for soybean.

Additional details about the APSIM models can be found here: www.apsim.info and in the following key references: Keating et al. (2003) and Holzworth et al. (2014).

Studies testing the performance of the APSIM model in the USA (click on the link to see the paper or the figure)

Reference Model processes tested
Archontoulis et al. 2014 Agronomy J

 

Soil water, soil nitrate, soil N mineralization, manure application, soil temperature, phenology, leaf area index, biomass production, grain yields response to N, leaf nitrogen concentration, root mass, triticale-corn double cropping systems


 

Archontoulis et al. 2014
Env. Modeling & Software

 

Temperature x photoperiod interactions on soybean development, soybean flowering, start grain filling, maturity days, grain yields, soybean varieties


 

Dietzel et al. 2016
Global Change Biology

 

Crop rotations, cover crops, biomass production, crop yields, soil temperature, soil water, subsurface tile drainage, crop growth, soil nitrate, root N concentration, soil-root CO2 emissions, water use efficiency


 

Basche et al. 2016
Agr. Ecos. & Envrionment

 

Cover crops, biomass production, crop yields, soil organic carbon, soil water


 

Archontoulis et al. 2016
GCB–Bioenergy

 

Biochar, soil organic carbon, nitrogen cycling, soil pH, soil CEC, soil bulk density, crop yields, corn residue


 

Archontoulis et al. 2016
Inter. Crop Model. Conf.

 

Corn and soybean, biomass and grain growth, soil nitrate


 

Archontoulis et al. 2015
ASA meeting

 

Soil nitrate, soil water, soil temperature, groundwater table, corn and soybean yields, biomass production and partitioning, crop phenology, yield gaps,


 

Malone et al. 2007
Geoderma J

 

Corn and soybean yields, cover crops biomass, cover crops N concentration, subsurface tile drainage, subsurface NO3-N leaching


 

Martinez–Feria et al. 2016
Field Crops Research J

(accepted)

 

Corn yields, corn and rye cover crop biomass production, rye CN ratio, rye root and shoot biomass, tile drainage, N leaching


 

Puntel et al.
In prep/under review

 

Corn yield – N relationships, economic optimum N rate, crop rotations, soybean yields, soil organic carbon


 

Unpublished or in preparation for publication  

CROP: phenology, leaf area index, specific leaf area, biomass and grain accumulation, biomass partitioning to stems/leaf/organ/root, grain number and size, corn yields, leaf/stem/grain/cobs/roots N concentration, N uptake by plant tissue, plant counts, root depth and mass, soybean N fixation, crop sequence: corn/soybean, corn-corn, corn vs rye cover crop

SOIL: nitrate and ammonium, water and temperature, groundwater, subsurface drainage and N leaching, N2O emissions, soil organic carbon