In a forecast published before the US and China reached a phase one trade agreement, NAB said Chinese infrastructure investment could provide some support for commodity markets in 2020, but likely not enough to drive prices higher.

"In annual average terms, US dollar commodity prices are forecast to fall by 11.7% in 2020 -with lower iron ore, metallurgical coal and liquefied natural gas (LNG) prices the key drivers," NAB said.

"In 2021, prices are forecast to fall by a further 0.7%."

NAB is forecasting iron ore to fall to US$76 per tonne by mid-2020 and $68/t by year-end for an average of $74/t for the year.

It expects coking coal to average $150/t and thermal coal to average $70/t, with downside risk to the latter forecast.

On a more positive note, gold is expected to rise to above $1500 an ounce for much of 2020.

"We have maintained our year-end 2019 forecasts at $1480/oz, but slightly lowered our forecasts further out: December 2021 is now $1600/oz(compared with $1625 previously)," NAB said.

Base metals are expected to fall in 2020 after a mixed 2019.

"Recent trends have been mixed across the base metals complex, with relatively stable prices for the major metals (copper and aluminium), while prices for nickel, lead and zinc have fallen rapidly since early November," NAB said.

"The demand outlook for metals remains somewhat negative -given the ongoing trade concerns and slowing economic growth in China (the key consumer of base metals)."

While aluminium is expected to remain at around current levels, copper is set to dip from around $6100/t currently to $5750/t.

NAB sees nickel pulling right back to $12,500/t, and zinc rising slightly to $2400/t.