Ag planes are designed to carry heavy loads, as a matter of fact, it's almost impossible to do any weight and balance on them.
When you take off with a load, depending on outside temp and alt., etc., you flying just above stall 'till you get some load off. The FS agplanes also have a very high angle of incedence, so that when your flying 5 feet over a crop, your fusilage is actually pointing down for visibility, while the wing is more or less horizontal. Remember, I'm not an aeronautical engineer, I just "Kick the tire and light the fire"