Stripes

 Skunks have them. A sergeant wears them. Even a road sports various stripes. But soybean fields?

 This isn't the first year I've noticed our local soybeans fields are often striped.There are rows of beans which are a rich rust color and others which look faded to a pale gray. The lines usually follow rows though there are some erratic patterns, too. Usually the change between the two shades is abrupt.
 So, since inquiring minds (mine mostly) want to know, I posted the question and these pictures on my Facebook account. Besides blaming aliens ("plant stripes instead of plant circles"), the answers I got were these:

•  It's potassium depletion in the soil.
•  When fertilizer or weed killer was applied, it wasn't done evenly.
•  The stripes are the result of drainage tiles buried in the fields.
•  It's caused by the way the beans were planted or the field plowed.
•  There's a couple different types of beans planted.

 The striped effect is quite noticeable. When the sun is shining especially, some wide rows are richly brown and others are of an almost sickly gray.
 Yesterday I walked into a field and examined the plants up close. I see no difference as to their maturity, the angle of the stalks or where the beans are placed. The plants look identical but for their color.

 The answer I'm leaning to is that this is the difference between species of beans. Is this done purposely for pollination? It is actually a lovely patchwork effect. If I get a definitive answer - or a preponderance of one answer - I'll post the results. In the meantime, I welcome comments from the Internet.