How is agriculture production affected？

[Tonyzhao610]

In terms of agricultural productivity growth, the documentation mentions changes in yield due to increased fertilizer usage or endogenous irrigation. However, the file FAO_ag_CROSIT.csv only contains two parameters, IRR_lo/hi and RFD_hi/lo, which represent the yield change rates for irrigated and rain-fed crops, respectively. So, how is the change in yield due to fertilizer application reflected?
Thank U！

[pkyle]

The interpretation of the assumptions and the model is a bit subjective. I am aware that there is documentation saying that the high yielding technologies have higher fertilizer application rates. This is true if fertilizer application rates are understood to be per unit land area. However in the representation in the model, the inputs to agricultural production are land, water, and fertilizer, and they are represented per unit crop output. Per unit crop output, and within any nest, the fertilizer input-output coefficients of the representative low yielding technology and high yielding technology are the same.
The way that I interpret the existing set of assumptions is that all crop production requires an exogenous input of nitrogen. Repetitive cycles of crop production and harvest entail a net nitrogen export from any unit of land that exceeds atmospheric nitrogen deposition, and any indigenous soil nitrogen will be depleted after several cycles of this practice. The model only tracks synthetic nitrogen at this time. Really the key assumption that we are making in the existing approach is that the fertilizer recovery efficiency (NUE in the literature) is the same for a low-yield system as it is for a high-yield system.
Within any nest (region / basin / crop / irrigation level), the low-yield and high-yield representative production technologies are defined based on the observed yields plus or minus in exogenous percentage, defined in constants.R:

aglu.MGMT_YIELD_ADJ <- 0.2       # Yield multiplier that goes from the observed yield to the "high" and "low" yields: observed plus or minus observed times this number.

[Tonyzhao610]

Thank you for your professional and detailed response, it's very helpful to me!