Declare your variable in the beginning of your script if you know you're gonna test it later. Don't give it a value at this point. A declared variable that has not been assigned a value will have the value 'null'. Use the === compare operator to check whether the variable is really boolean false. The == operator is not reliable as a value of 0 will also evaluate to false. (Basically, the === asks whether variable are of same value AND datatype!).
Nitrogen Fixation. Nitrogen fixation refers to the conversion of atmospheric nitrogen gas (N 2 ) into a form usable by plants and other organisms. Nitrogen fixation is conducted by a variety of bacteria, both as free-living organisms and in symbiotic association with plants. Because it is the principal source of the nitrogen in the soil, nitrogen that plants need to grow, nitrogen fixation is one of the most important biochemical processes on Earth.
This process is called nitrogen fixation. Nitrate and nitrite are two of the nitrogen compounds that are used by plants and animals and eventually return to the air as nitrogen gas. Nitrate and nitrite can also be produced in the body. In nature, plants utilize nitrate as an essential nutrient. Bacteria in soil and plants use oxygen to change nitrite into more stable nitrate, which can be converted back to nitrite by other bacteria when oxygen is lacking. â¢ Animal wastes and nitrogen-containing fertilizers increase concentrations of nitrate in the environment.