Goldman's head of commodities research, Jeff Currie, spoke to CNBC earlier

China US

In a quick interview, Currie noted that:

"There is still a lot of uncertainty about how you would achieve $40 (billion) or potentially even $50 billion of agricultural purchases. A lot of the people I talk to are really skeptical that you can really achieve that number."

For some context, the US had last month reaffirmed that China has pledged to buy a total of $40 billion in farm purchases - although this has not been officially confirmed by the Chinese camp, even ahead of next week's trade deal signing.

The $40 billion figure comes from a $24 billion baseline set out by the 2017 level, plus an additional $16 billion for at least the next two years.

Anyway, back to the interview, Currie also said that:

"To suddenly reach an annual $40 billion figure as soon as this year, there would need to be a big increase in soybean exports - a tricky prospect given a swine fever outbreak that has reduced the number of pigs in China that are typically fattened up on soy beans."

Whatever the case is, we'll soon find out about the details and how firm China's commitment to US farm purchases will really be. As mentioned before, the trade deal signing next week is all but done and dusted now.

The bigger unknown will be the details of the trade deal and how kindly/poorly markets will react once those are disclosed some time after the signing.