I would assume evaporation is directly correlated with the surface area the water is spread on. Spreading water on farmland as opposed letting the water flow naturally into the Great Salt Lake is going to increase the effective surface area of the water.
Additionally, plants are pretty effective at pulling water out of the ground and releasing it into the air, so the agriculture aspect increases evaporation as well.
Both go back to the same place though. It doesn't matter if the water evaporates, or trickles down to groundwater, it's the same. If it evaporates it goes to the clouds, and then comes back down as rain, and eventually back into the groundwater.
The real problem is the water that is shipped out in the crops. That's why people say that Isreal is exporting all its water in the form of watermelons.
I would assume evaporation is directly correlated with the surface area the water is spread on. Spreading water on farmland as opposed letting the water flow naturally into the Great Salt Lake is going to increase the effective surface area of the water.
Additionally, plants are pretty effective at pulling water out of the ground and releasing it into the air, so the agriculture aspect increases evaporation as well.