I can see some areas marked as not to be sprayed (on left) and some areas to be sprayed (on right). Assuming this is spraying of insecticide, the plants growing on the field on the  right should grow better than those on the left (not sprayed) because cotton is susceptible to many insect pests which need to be controlled by insecticide. . If the colours are depicting soil fertility, there are differences in fertility and that may be the reason for the uneven growth of cotton plants.

I assume the cottons have the same genotypes with same planting density, and same treatments (if any). Then, beside soil fertility as mentioned by Ranjith, I also saw one part (green) are grown near a river (water source) and the other part (red) are grown towards inland. This may be a factor too.

Could you tell us which part grow faster?

In addition to the biotic stress, such as attacks from insect pests, all abiotic stresses should be considered since they can also limit plant growth.

You should also consider that the exposition of plants within the same plot/field can affect plant growth for example.

dear dr. Maher Ibrahim ,if you are really after it to know, study this feature in random  block design with a small block area (two squire meter is enough) with replicates, make sure before sowing that your seeds are genetically homogenous. 

Assuming that "to be (or not) be sprayed" means that the fields were sprayed or not it's interesting to see in the sprayed areas green spots. Doesn't seem likely that a aerial spraying or ground spraying would produce such a fragmented crop distribution, at least based on visual observation. I guess what I'm trying to say is that a combination of factors seems to be at work.