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.
Irrigating the ground after you add fertilizer helps it penetrate the soil. Supplying your plants with nitrogen ensures that they can sustain healthy growth and fend off harmful pests and diseases. There are several methods you can use to replace nitrogen in the soil that each have specific benefits and drawbacks. Performing a soil test before you begin adding nitrogen to the soil provides an accurate assessment of how much nitrogen your soil needs.