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.