Some chemical fertilizers harden the soil and reduce aeration. Nitrate of soda is a typical offender. In yearly applications of this fertilizer, plants use up much of the nitrate but little of the soda. This keeps piling up in the soil, and combines with carbon to form carbonate of soda (washing soda). Where large amounts of nitrate of soda are used, the soil can become so hard that it can be cultivated only after a rain.

Some chemical fertilizers harden the soil and reduce aeration. Nitrate of soda is a typical offender. In yearly applications of this fertilizer, plants use up much of the nitrate but little of the soda. This keeps piling up in the soil, and combines with carbon to form carbonate of soda (washing soda). Where large amounts of nitrate of soda are used, the soil can become so hard that it can be cultivated only after a rain.

Being heavy, it requires aeration. In its natural state it will contain no earthworms (ants and tunneling gophers aerate it for the native vegetation).