Sweetening a soil is another way of saying reducing its acidity. It has three benefits.
First, lowered acidity increases the range of plants you can grow. The nearer a soil is to neutral the greater the number of different plants that will flourish in it.
Next, as the soil becomes less acid, some of the essential plant foods – nitrogen, phosphorus, potassium, sulphur and calcium -become more readily available, and plants will therefore grow stronger and healthier.
Third, reduced acidity encourages beneficial soil microorganisms to operate more effectively and to multiply better. Under acid conditions, soil bacteria are sluggish so that a lot of unrotted organic matter can build up in the soil, and with it an increased risk of soil-borne diseases.