Perhaps you could drum up some interest around a petition by listing all the benefits of that site remaining a farmland including--but not limited to--all breeding, wintering and resident birds with their conservation status meticulously listed, photos and all (as in: 'x endangered species breed/winter/live in...'; the more, the better--apart from your own experience and knowledge you may use information from online birding platforms if there are any checklists limited to the site in question). You could also mention all the leisure and other activities taking place in that area as an argument for the status quo (simply be creative and make it look convincing--you know best). Then, perhaps print a few copies to put at a local library, community centre, school, the like. Also--obviously--don't forget to check if you have some natural allies in the neighbourhood already--a local (chapter of a) wildlife conservation charity, birdwatching club (well) or residents association--who could help you further your cause. No experience on my side, but that's what I would do (and I did give it some thought some time ago when I wanted to make sure I would be able to anticipate a similar development close to where I live just in case it ever occured--it never did, so just a dry run, after all). Ah, and all the best!