Are these really alternatives to fertilizers? I think not. Although these adaptations may help improve nutrient use efficiency of crops (that amount of the nutrient pool in the soil that crops take up), aside from legume nodules they fail as fertilizer alternatives due to conservation of mass, which here can be stated as “nutrients exported from a field must be replaced by an equal import of nutrients.” Nutrients are not created in the field through any mechanism, natural or not. Even nitrogen from legumes is imported from the air. None of these so-called alternatives to synthetic fertilizers create nutrients. They exist to help plants survive (not thrive) in the nutrient limited conditions found in natural ecosystems. Since farmers strive to eliminate such nutrient limitations in their fields, these mechanisms are not so helpful, and they are often switched off when high levels of nutrients are available.

Manure markets tend to be highly localized. In some areas, manure carries enough value as fertilizer that crop producers are willing to pay to receive it; in other areas, livestock producers must pay other farmers to take the manure. About 20 percent of the dairy and hog manure that is removed from farms is sold, as is 36 percent of broiler litter.17 About 60 percent of the hog and broiler manure that is removed from farms is given away for no exchange of money. Prices for manure are determined by the quantities produced in an area relative to the amount of nearby cropland, the mix of crops grown, and the cost of transporting manure. With production shifting to large livestock operations, which are coming under increasing pressure to reduce nutrient applications to their own land, we can expect to see increased manure removals

Conclusions liquid hog manure application was the largest user of energy in this study, mainly due to fuel consumption the most energy efficient system in this study was the grazing system with no manure applied grazing systems were more energy efficient than hayed systems beef production on unmanured land was more energy efficient than on manured land however, beef production on manured land is still more efficient than beef production on land where synthetic fertilizers are applied, even if manure is applied only to P-removal rates