Nitrogen is generally available to plants in only two forms: ammonium and ________.
Biological nitrogen fixation is accomplished by symbiotic ________ living in mutualistic association with plants.
Nitrogen can be returned to the atmosphere when certain bacteria convert it from nitrate into nitrogen gas, which is a process called ________.
Microbial decomposition of organic matter results in NH4+ production through a process called ________.
Nearly all of the phosphorus in terrestrial ecosystems comes from the ________ of calcium phosphate minerals.
___________ develop as a result of incomplete decomposition of organic matter in swamps and marshes.
The process of ____________ produces a form of nitrogen that is easily lost from soil through leaching.