Ghost patterns occur when the image from a design from a previous year has been literally burnt into the field by solar radiation from the sun.
The now radiated ground which was exposed has retained the shape as a result of UV radiation in the ground.. This in turn affects the next crop in varying degrees some will be more pronounced than others depending on how long the design and the ground was exposed to the sun.
The seed from the next crop will not grow in the contaminated ground for at least a year as it requires time for the solar radiation to dissipate. You can plow it and move it about but the imprint of the design is retained by the radiation that is now present thus holding the shape for the next year! The soil is not so much affected but rather the ground rock below it. That is why it can be plowed and the shape will still be there!
The solar radiation will destroy most of the soil nutrients once it has been plowed in the previous shape of the design the year before thus the seed will not germinate so you end up with a ghost from the past! It is worth noting that if you took a soil sample from the affected area and tested its nutrient content etc. you would find an almost sterile area or a reduced nutrient content in the shape of the design. This can also cause the crop to be a slightly different colour due to reduced nutrient etc. This of course at this stage will only be temporary and usually dissipates after a year or so. However due to global warming and the reduction of the ozone in the upper atmosphere this effect will become more pronounced as the ozone depletes further.