Let me explain maybe not so scientifically. Soil is like a bank account. You have deposits and withdrawals and at a minimum you want the account to stay in balance but would prefer the account to build up. Our crops make withdrawals, especially heavy feeders like corn. Today we mostly make deposits thru fertilizer and other chemicals added to the soil. Fail to make proper deposits and the crop is greatly reduced or fails. There are all sorts of ways where one can make deposits naturally and keep the soil account in balance. Rotation of crops, where you don't plant the same crop in the same plot over & over helps. Companion planting, such as the native American three sisters garden help, where the pole beans, a legume, add nitrogen back into the soil to help feed the corn. Allowing plots to stay unused for a year allows nature to rebuild the soil. Then cover crops, green manure, greatly help to build up that soil account. Most are legumes, so they take nitrogen from the air & store it in the ground. Their roots and above ground growth add nutrients and organic matter back into the soil as they decompose. Those same roots and above ground growth protect the soil from being washed away from the winter & spring rains. Keep in mind, these garden plots don't have a cover of grass to hold the soil in place. Short term cover crops, green manure, do that.
IMO, such natural gardening practices make perfect sense even today but will be life saving during an extended crisis. Another benefit from these green manures is that they help provide food for the wild game, during a time of year where little else grows. Around here farmers use a lot of clover, hairy vetch and winter peas in their fields. They especially use the winter peas when they want to feed the deer during the winter as they keep growing even when the temp drops to 10 degrees. My winter peas grow during the fall and early winter, stay pretty static during the cold winter and then have a huge rush of growth in the spring.
Here is one of my beds where I am cutting the winter peas.
And now in that bed, I'm planting tomatoes with my trusty Hori Horo knife & the dead peas will provide mulch and will slowly break down & add nutrients back into the soil. Note other bed with winter peas.
Random pics of winter peas... green manure.