Green manure

Green manuring is a way of increasing humus in soil. It can take up nitrogen but releases it again. It is particularly good on light or sandy soil that tends to lose humus easily, as the green manure can be sown in late summer or early autumn and turned down in winter or early spring to leave manure for the following growing season.

Any green manure is beneficial: mustard, clover, ryegrass, phacelia, winter vetch etc., the main thing is they add humus in readily accessible form.

This can also be achieved by spreading and digging in compost, but green manure is good if you have not got enough compost, and it has no weed seeds, as compost generally does.