How to improve clay soil without digging?

Clay and sand are mended by plants with strong taproots: they open up clay and build organic matter and moisture in sand. Perennials: lucerne and white clover (where a garden will go, leave them 2 years, then mow), perennial lupin (it self-seeds). Annuals: runner beans (roots like carrots, and without supports they cover the ground against weeds), sunflower, mustard. Don't dig up daikon or oilseed radish: let the root rot in the ground and leave a channel. Leave everything you cut on top: it is compost in place. Never dig wet clay.