A full rotation system includes beds that are "resting" or that are growing green manure crops like broad beans, peas, alfalfa or lupins which actually put nitrogen back into the soil. When they get big enough, you chop em down and either dig them in or let them rot down into mulch over the bed. This obviously takes time, but it's a tried and true way to maintain your soil quality over time. Using legume-based straws like pea straw and lucerne hay shortens the time needed but costs more and adds less nitrogen than a grown mulch.