Abstract: Soil pot experiments and hydroponic culture conducted with La, Nd, and Ce on wheat, rapeseed, soybean, and rice were carried out. The result informed the maximum threshold of optimal and poisonous application amount and medium concentration of the elements, as well as the elements contained in crop leaves, stems, and roots. The experiments also showed that the threshold was closely related with crop growth.

Key words: county-level agricultural leading industry, eco-fitness, assessment index.