I understand that by adding Nitrogen to my water my Lucerne plants will grow better. Firtsly, is this correct? Secondly, if so, I further understand that I must add/mix Ammonia (NH3) and nitric acid (HNO3) to form nitrogen which is added to the water, is this correct? However I understand that these two (Ammonia (NH3) and nitric acid (HNO3)) is highly corrosive, therefore would this corrode my irrigation system or damage my lucerne crops, rather than increase the growth? Help will be appreciated!
Ammonia and nitric acid can be considered corrosive materials (though the real question would be "corrosive towards which material?"). The thing here is that ammonia and nitric acid are corrosive for strictly opposite reasons: ammonia is a base and nitric acid is an acid. So in a mixture of 1 equivalent(1) of ammonia and 1 equivalent(1) of nitric acid, both effects will cancel and the resulting mixture is no longer corrosive.
You do not create nitrogen (with such a mixture) for your lucerne, but you provide it with a form of nitrogen(2) which can be transformed by bacteria before being absorbed by your plant. Though, you do not want to mix ammonia and nitric acid because it is dangerous. As Mithoron said, you would better buy the product.
The chemistry and biology of soils are extensively (?) studied nowadays because it appears that monoculture exhausts soils and an agroecological approach can drastically outperform the monocultures we employ in western world.
(1) This requires a bit of calculations.
(2) Use of the term "nitrogen" can be very misleading as it can describe the "nitrogen gas" which composes 80% of our atmosphere (but is quite inert) or any source of nitrogen atoms for a plant.