Carboxyl groups have an electronegative oxygen atom double bonded to a carbon atom. This carbon-oxygen bond is very polar and the fact that its a double bond increases the polarity of the bond.
PEA agar, also referred to as Phenylethyl Alcohol Agar is a medium  used by microbiologists to grow microorganisms. The ingredient that  supplies nitrogen is casein. Making the world better, one answer at a time.
A rule of thumb is that a 1.25 pounds of. nitrogen per acre is fixed for every bushel of peas (field pea has a standard bushel weight of 60 pounds) produced per acre. For example, a field pea crop of 40 bushels per acre will fix 50 pounds of nitrogen per acre.