Experimenting

Nitrogen (N), required by all living organisms, can limit crop yield, but too much can cause pollution. Use this simulation model to track nitrogen as it cycles from the atmosphere (or fertilizer) to soil to crops, and out to streams or back to the atmosphere.

Here’s the challenge: Can you manage the agricultural system for crop production without negative impacts for nitrate run-off to streams and greenhouse gas production?

By the Law of Conservation of Mass, the total N mass in the system, summed across all the stocks, is constant. However, because N cycles, the amount within each individual stock can change. We can use this principle to experiment with how to maximize the desirable stocks (Yield, Soil Organic N), and minimize the undesirable stocks (nitrous oxide, ~20% of total denitrification, and N loss to Streams).  The user can design experiments to test hypotheses about the effects of cropping system, management, and climate change on N cycling by manipulating the variables described above. Over the course of multiple model runs, the user can collect data from the model output to evaluate their hypotheses about effects of climate change and management on N cycling in an agricultural setting.

Hypothesis testing about management factors.

Use the model in ‘Lab’ mode, to test hypotheses by comparing output from a baseline run with a run in which you have changed only one parameter, e.g., fertilizer addition or management.

Follow these steps:

1. Identify the parameters for the baseline run for your experiment (i.e., Cropping System, Fertilizer, Management).  
2. Identify the parameter you need to change in the second run to be able to test the specific hypothesis.
3. What output data on stocks do you need to record to make comparisons that will allow you to evaluate the hypothesis?
4. What other stocks should you look at to determine other, perhaps unintended effects of the change made in the parameter?

Examples of Hypotheses to test:

Note: In all cases, the singled changed parameter is highlighted in yellow, the response variable in green.

H1: Planting continuous corn with N fertilizer at 270 in spring increases Yield.

Results:

H2: Planting perennial Alfalfa increases Soil Organic N stocks.

Results

H3: Planting a corn-soybean rotation (N fertilizer = 180 in spring) with management of 'Cover Crop' reduces N stocks in 'N Stream'. What is the significance of this?