Most gardeners and farmers will plan to rotate their crops, meaning cycle the land between the principle families of plants. This is largely unnecessary for several reasons.
Some folks rotate because they believe that the plants eat different foods and that by rotating them through, it gives the soil time to rejuvenate one kind of food while another kind of food is consumed. This is patently wrong, and casual observation will demonstrate that all plants eat the same things: soil, water and sunshine. If you are still unconvinced, try planting the same crop over and over again in the same soil, feeding the soil nutrition through tillage and manure, and you will see that they will not die for starvation. Or, examine the nearest potted plant: it has been eating the same soil for even years at a time.
Another reason given for the insanity of rotation is that it reduces disease. Founded on the primitive understanding that some diseases affect just one or two families of plants, and that the continual presence of those plants in the soil will lead to large populations of the disease causing miroorganisms, it ignores basic sanitary science developed in the early 18th century. Sanitation is achieved not through sterilization (a science developed in the 19th century), but through a competition of various microorganisms. A balanced microecosystem is one that presents no danger to the macroorganisms. A chief example is found in your body’s own natural defenses: most of your immune system is not you, but the friendly bacteria, viruses, retroviruses and fungi that live on and in you, eating those bad microorganisms that would cause you disease. When disease organisms increase in population, the defense organisms respond, and eat their way to your safety, defending their host (you).
In soil, this is achieved through tillage. By feeding the soil air and otherwise increasing the biodiversity of the soil, a multitude of organisms develop. The use of manure, green or animal, aids in this because it encourages the diversity of organisms that eat not your plants, but the manure itself. Some farmers will intercrop to increase diversity, a wiser practice than rotation – microorganisms reproduce very quickly, and before your season is out, they have already adapted to the monoculture of whatever family you are planting this year. A few seconds after your plants put out roots they know what kind of plants you have in the ground, and if it was cabbage family last year and is now spinach family, the spinach disease organisms will nearly instantly take advantage of it - if it weren’t for the beneficial organisms in the soil keeping them in check.
Another reason given to rotate crops is to add nitrogen to the soil. Plants do not add nitrogen to soil. Some plants encourage the microorganisms that deposit nitrogen into the soil, but human beings (most of whom are not plants) can encourage the nitrogen making organisms better than plants by stirring the soil with tillage: more than 16kg per hectare can be produced by tilling dirt without any crop or manure added in. This is more than enough to support most grains, very hungry crops indeed.
So stop spinning around and put in aisles, you’ll dance better going in straight lines up and down with your favorite tillage equipment, whether it is shovels and mattocks, or ox and plow, or a tractor!