SAO PAULO, April 4 (Reuters) - Indigenous protests and

poor roads have disrupted shipping of Brazil's bumper soybean

crop this week via the river port of Miritituba in the Amazon

rainforest, where global grains traders including Cargill and

Bunge have important operations.

Demand for soy from Brazil, the world's largest producer and

exporter, has surged in No. 1 consumer China as traders brace

for a trade war discouraging Chinese imports of U.S. soybeans.

Miritituba loaded some 15 million tons of soy and corn last

year onto barges bound for larger shipping ports down river,

representing more than a tenth of Brazil's total exports of

those grains. Volumes at the port are expected to rise around

20% this year.

Protesters from the Munduruku people have been blocking a

key stretch of the Transamazonian Highway near Miritituba at

certain hours of the day to pressure Brazil's Supreme Court to

overturn a 2023 law aimed at limiting their land rights.

That has worsened backups along an unpaved five-kilometer

stretch of the road. Trucking group ANATC said the traffic has

left some cargos waiting three days to unload at Miritituba.

AMPORT, which represents the largest firms shipping from the

terminal, said truckers with pre-scheduled access have not

suffered those wait times at the port.

Still, AMPORT President Flavio Acatauassu estimated each

hour of the protesters' blockade prevents at least 12,000 tons

of soybeans from arriving at the terminal.

Via Brasil BR-163, which administers 1,009 kilometers (627

miles) of the highway linking farms in Mato Grosso state to the

river port, said a new access will be built when courts give it

permission to expropriate certain areas.

Frustrations have boiled over into violent episodes between

truckers and Indigenous protesters, according to a statement

from Munduruku representatives.

"Our fight is peaceful, but we have been suffering attacks

and threats from truck drivers, including insults, stone

throwing, gun shots and dangerous driving," they wrote.

Rafael Modesto, a lawyer for the Indigenous Missionary

Council, which argues for Indigenous interests before the

Supreme Court, said the protest reflects fears among native

peoples about losing their lands to an advancing farm frontier.

Brazil's powerful congressional farm lobby has been at odds

with the Supreme Court over a proposed cut-off date for new

reservations on lands where Indigenous people were not living in

1988.

"We believe that, if any proposal that changes the text of

the Constitution goes through, demonstrations like this one may

become more frequent all over Brazil," he said.