Nurse crop.
Nurse Crop
A shelter crop. A quick growing, hardy crop sowed thinly along with a tender, slower growing crop in order to give shelter from harsh conditions during the early stages of growth. The Nurse crop is then killed or harvested before the main growing season leaving the desired crop to grow away. For example: winter sown oats, taken as silage in the spring, may be used to nurse field crops and birch is used to shelter timber trees for the first twenty years of their life.