Is evapotransporation accounted for in climate models? Is evapotransporation accounted for in climate models, or is it considered so insignificant that it's not considered?  

Could additional crops being planted within the last 100 to 50 years account for additional moisture in the air now?

Sorry, here's some more background.  I recently attended a conference in which there were 2 speakers, one from NOAA and another from the USACE, that both came to the same conclusion that our atmosphere is becoming more 'wet'.  In particular the NOAA scientist compared the last 50 years to the fifty years prior to that.  So by comparing the last fifty years to the 50 years prior to that it looks like the atmosphere is becoming wetter.  I just wonder, if there were more crops in the ground in the last 50 years, what impact that would have on the climate becoming wetter.

I have done some googling on this matter and am finding mostly information on how a changing climate may effect evapotransporation but not vice versa.  I also checked out the USDA website for acres planted over time and I'm not finding much further back that a decade or so.
Now most models include changes in evapotranspiration, it is usually grouped together with a few other factors (like draining wetlands) under the heading "Land Usage"  

Now the question does "Could additional crops being planted within the last 100 to 50 years account for additional moisture in the air now" the answer is no, not by itself.

To get more moisture into the air long term you need the air to be warmer, otherwise it just rains it out. Another issue is different crops affect evapotranspiration in different ways. For instance irrigation induced evapotranspiration, likely the largest evapotranspiration effect, may actually have a cooling effect, by increasing cloud cover and precipitation. Lastly land usage is only a small impact not counting the increased greenhouse gas emission it can cause.