free iron in soil

例句：

1. 1.The plant's roots need to absorb free iron in the soil for growth.
   植物的根需要吸收土壤中的自由铁以促进生长。
2. 2. The researcher found that the amount of free iron in the soil could affect the growth of plants.
   研究者发现，土壤中自由铁的含量会影响植物的生长。
3. 3. The farmer used fertilizers to increase the amount of free iron in the soil for better crop yields.
   农民使用肥料来增加土壤中自由铁的含量，以提高农作物产量。