Once the vegetables have been harvested the soil can be left bare until it is time to prepare for planting in the following Spring. Alternatively you could plant a cover crop which will have a number of advantages that will lead to an improvement of the soil. I came across an article by Mike McGroarty which I found on his Free Plants website which explains why planting a cover crop is a really good idea.
Cover crops are fast-growing small grains, grasses or legumes that are generally planted in the fall and tilled under in the spring to improve soil. Cover crops are used to increase the amount of organic matter in the soil, prevent erosion, fix nitrogen in the soil, reduce the number of weeds in the garden, and provide habitat for beneficial insects. The specific needs of the soil and the results you wish to achieve will determine which cover crops should be grown to improve the soil in your garden.
Cover crops that are tilled in to improve the condition of soil are sometimes referred to as green manure. Legumes such as mammoth red clover, crimson clover, hairy vetch or bell beans will fix nitrogen in the soil while adding organic matter when they are tilled under in the spring.
New Zealand White Clover, also known as Dutch White Clover, is a low-growing legume that can be planted between rows as a living mulch. This multi-tasking cover crop will provide a nice path between the rows for you to walk on while it keeps weeds down and adds nitrogen to the soil, and its flowers will attract pollinators to your garden. The following spring, the clover can be tilled under and crops planted where the clover had been. Replant the clover in the rows where crops were grown the previous year for a simple form of crop rotation.
See more at Free Plants