Answer:
Maintain a riparian "buffer" between her fields and the stream is a good method for preventing the fertilizer into the stream.
Step-by-step explanation:
Nitrogen in the nitrate form is highly mobile means can move from one place to another so a barrier like riparian "buffer" is a good method which prevents the movement of nitrates into the stream by converting nitrate into nitrogen through denitrification process while the phosphate is immobile so it doesn't move into the stream.