Uniformity is important in agriculture.
It can make the farmer's life pretty tough when plants in different parts of their field ripen at different times. You can't wait forever for every last plant to ripen - you need to harvest before bad weather sets in or you have to plant your next crop. Inevitably, some plants will fail to ripen (or over-ripen) by the time you get in to harvest.
The streaks of green in the foreground (and along the horizon) are patches of grain that are maturing slower than the majority of the field. I'd bet these patches sit in low spots in the field, where excess water or cool temperatures may have slowed germination, growth or senescence.
Uniformity is an especially sticky problem when the harvest is mechanized. Machines (even if they're horse-drawn) are calibrated to harvest plants of a certain height, toughness and fruit size. Individual plants that fall outside the accepted range may get trampled, missed or dropped.
Plants naturally vary thanks to their environment but breeders do the best they can to keep their releases uniform (and within the range that suits the agronomic practices of the growers). Individual varieties are often planted en masse in "uniformity trials" before they're released to make sure that soil and microclimate differences in different parts of the field have a minimal impact on the final phenotype.