Surplus
There's so much grain in your mouth you need to use a knife to remove it. Only when there is a surplus can you put that much grain in your mouth.
Imagine seeing so much grain that you can stuff your mouth so full you can't swallow or spit it out. You have to use a knife to remove it. After you get all the grain out, comment on the surplus of grain.
じょう
あまつさえ, あま
None
The surplus is thanks to the hard work of folks like Joe (じょう), the big farmhand. He worked hard to make sure there was a surplus of grain this year.
Remember how Joe made the soil better? Perhaps this is some of that work paying off. Thanks to that and everything else, there is a great surplus.