A very common crop that is noted for its many yellow flowers is mustard. Some farmers grow this and harvest the leaves while others harvest just the seeds.
Sunflower? daisy?
Either it's mustard or canola. You could also be referring to sunflowers...
Wattle flowers are yellow.
Vegetable flowers are not all yellow.
Is bomb flowers!
Buckwheat
Primroses are a type of primula with yellow flowers.
Linseed/Flax
if i am correct the marigold has yellow flowers and has "mar" in its name.
Whattle (Acacia so. ) flowers are yellow. There is some variation in the brightness of the flowers between whattle species. Some species have quite bright yellow flowers, whereas others have pale yellow flowers. Some species have very pale flowers which appear to be white, but the most common colour is yellow.
Hummingbirds will visit red flowers and yellow flowers with the same frequency.
Brassica napus is the common farm plant, from whose seed this useful oil is obtained. Brilliant yellow flowers make this crop notable from the roadside.
Brassicas allowed to run to seed will have small yellow flowers.