Edit: english subtitles say „hundreds“ while it is actually „thousand“ in the German version. ~1 minute into https://www.youtube.com/watch?v=DPVKaj9hVcY

Anyone that would use the hypothetical 'kilotonne' would use 'Gg' instead. Agriculture works in tonnes though, not SI prefixed grams, so it would just be 1000t.

(Source: from writing a lot of code for doing conversions and display and things with differently denominated quantities for ag users!)

Edit: it would most likely be written as one thousand tonnes.

A billion grams is unambiguous, because a billion prefix for the regular reader would mean pretty much the same as infinity. The 0.0000001 as the multiplier after billion prefix doesn't discount that, because you still have to read the billion out loud.