[zeratul]

Why don't you try 10-fold CV (http://en.wikipedia.org/wiki/Cross-validation_%28statistics%...) - the graph might drastically change. Here is example how to do it: https://onlinecourses.science.psu.edu/stat857/book/export/ht...

If precision & recall monotonically go down when increasing NN then it means you don't have enough training data.