What do you mean by nitrogen? Isn't nitrogen gas harmless? Or do you mean nitrogen in solid stuff, like fertilizer? Then "emit" would be a strange word, that's usually associated with gasses.
Nitrogen gas is harmless, but various nitrogen compounds can cause air and water pollution. In the air the main issue is nitrogen oxides, called NO
x, but farming is not a very significant source; there used to be much more of them in the air from industrial pollution, but pollution controls have reduced this to a minor problem. Although ammonia and nitrates used in farming can break down and release NO
x over time, they are highly water-soluble and so tend not to stay resident in the soil long enough, so the main issue with farming is runoff. Under some circumstances there are worries about groundwater quality, but the main concern driving laws is the effect it has on fishery production - the extra fixed nitrogen washing into surface waters tends to drive growth of large amounts of algae which can deplete other nutrients from the water, especially when they decay, which consumes oxygen and can lead to "dead zones".
Fixed nitrogen in soil isn't a major issue either; extremely heavy application can make the soil acidic but this is rarely a problem except in drought conditions when there is nothing at all to transport the nitrate away. For the same reason, dry conditions are also when the breakdown into NO
x is greatest, which obviously removes it from the soil, although I understand it can't be too dry because the microbes responsible need to, you know, be able to live. (Acidic soil also suppresses them.) For example, those dry valleys in California are often said to be where NO
x emissions from farming are highest, although of course even there it's nothing compared to the industrial emissions of a few decades ago.