fertilizer: Any substance that isadded to soil in order to increase itsproductivity. Fertilizers can be of naturalorigin, such as composts, or theycan be made up of synthetic chemicals,particularly nitrates and phosphates.Synthetic fertilizers canincrease crop yields dramatically, butwhen leached from the soil by rain,which runs into lakes, they also increasethe process of eutrophication.Bacteria that can fix nitrogen aresometimes added to the soil to increaseits fertility; for example, intropical countries the cyanobacteriumAnabaena is added to rice paddiesto increase soil fertility.
