To me, the color looks good.  

You might want to pull plant tissue samples and send them to a lab, to see if it shows something up. 

Have you soil sampled recently?  If not, pull a soil sample and send it along as well.

Fertility-wise, if I had to guess, I wonder if it is low in Phosphorus. I'm thinking that deficiency in phosphorus would show up as short, stunted plants.  

I would also take a shovel - or a tractor hoe - and dig a hole and see what the soil moisture profile is - down 3 feet if you can.   

My first impression is the soil is too dry.  But the thought of phosphorus then also occurred to me.  

I would look at these two avenues first.

edit: if you have a field that looks good, maybe take a plant tissue sample and soil sample in the field that looks good, as well as this field. Then you can compare the two sets of results.

or if you can see parts of this field that looks better - take plant and soil samples from the better parts of this field, and from the poorer areas of this field.  Then, again, compare the results from good and poorer areas.