He says farmers may be able to better control the amount of nitrate fertilizer they put on fields.

他说农民们也许能控制投放到田地里的氮肥量。

Aaron Packman is a professor of Civil and Environmental Engineering at Northwestern University. He says farmers may be able to better control the amount of nitrate fertilizer they put on their fields.

亚伦•帕克曼（Aaron Packman）是美国西北大学土木与环境工程学教授，他说农民们也许能控制投放到田地里的氮肥量。