Feed your friends

Plant roots release different nutrients like sugars, amino acids, and other substances to feed helpful fungi and bacteria in the soil, but also other organisms in soil such as nematodes, earthworms, and protists. These microbes also help plants by providing important nutrients like nitrogen and phosphorus, and they protect the plants from drought and harmful germs. 

Mycorrhizal fungi have helped plants grow since they first moved onto land. These fungi are crucial for 80% of plants in nature and are even used as a natural fertilizer in farming. The tiny "roots" of mycorrhizal fungi, called hyphae, grow into small cracks in the soil. They can unlock phosphate (a key nutrient) from minerals and deliver it to plants. 
Plants make their own food using sunlight and carbon dioxide, which turns into sugars. These sugars travel from the leaves, down the stem, and into the roots, where they feed the mycorrhiza. Since mycorrhizal fungi can’t make their own sugars, they rely on the plant. This kind of relationship, where both organisms benefit, is called symbiosis.

Legumes like clover, soybeans and peas can work with bacteria that turn nitrogen into a form plants can use. This helps the plant grow. Legumes also provide protein-rich foods that can replace meat or eggs.  
These plants have nodules on their roots where the bacteria live. The plant makes a protein called leghemoglobin to keep oxygen from interfering with the bacteria’s job. The bacteria depend on the plant for food and protection.  
There are likely many more helpful plant-bacteria and plant-fungi relationships that could be used in farming. By using them as biological fertilizers, we could reduce the need for chemicals, making farming more sustainable.