People who drive across Iowa sometimes ask "what's that smell?" The cute answer is money, but the real answer is manure. Iowa has 20 million hogs and their manure is a high value fertilizer when it is properly applied to the soil in the right season.
That is the job of the commercial nutrient applicators that run machines that apply thousands of gallons of manure per acre, primarily on corn stubble in the fall. The Department of Natural Resources requires a manure management plan that brings the livestock producer and the crop farmer together, both benefitting from the nitrogen and phosphorous in the effluent.
The liquid is incorporated on most fields, but knifed in on highly erodible land.
The major challenge is the odor, which is a part of livestock production across the state, but for those who see the value of livestock and crops in rural areas, the system is working.