In the country, there just seems to be more mud, dirt, and grass that gets tracked in. Maybe it's because in town, I had St. Augustine grass and it literally made a carpet of my lawn. Mud was never tracked in. Also, I didn't make daily trips to the barn, since my back yard was the size of a postage stamp and cows and goats weren't allowed. 
So here is a recipe of sorts for a shampoo that works nicely in your carpet steam cleaner. I like it better than the cleaner you buy specifically for steam cleaners and it leaves the carpet nice and soft.
1-2 scoops of oxyclean powder (depending on the amount of stains you have)
1/4-1/3 c. of liquid Tide
hot water to fill the cleaner
I go over the carpets twice. If you take the time and go over the carpets the second time with only hot water you will find that your cleaning lasts longer. I have heard that the soap residue left after cleaning attracts dust and dirt and that rinsing will prevent that.
Blessings,
Mrs. P