When soil has good tilth, it is soft, porous and easy to work and crumbles easily into fine pieces. Water penetrates the soil better and the soil also holds more water. Tilth prevents the formation of hard crusts on the soil's surface. It allows plants to put out larger root systems easily. When there is lots of air in the soil, microorganisms flourish and speed mineral release.
Good tilth allows delicate seedlings to get a good start.
Unfortunately, using only chemicals for soil improvement results in a rapid loss of humus, the food source for soil microorganisms. These tiny creatures do more for soil than tons of chemicals ever could. Nitrogen stimulates humus-consuming bacteria. Adding chemical fertilizers to the soil causes bacteria to consume two or three times the amount of humus it would ordinarily. Once this has occurred, life level in the soil drops, new soil particles are not broken down as rapidly and the plants become dependent on chemicals.