CANBERRA, March 4 (Reuters) - Chicago soybean futures extended gains on Monday after last week's three-year lows but plentiful supply from South America and weak U.S. exports limited gains, with speculators still betting on lower prices.
Corn and wheat futures also rose, but with markets well supplied, both contracts were near their lowest since 2020.
The most-active soybean contract on the Chicago Board of Trade (CBOT) was up 0.8% at $11.60 a bushel by 0641 GMT after dropping to $11.29 on Thursday, its lowest since November 2020.
CBOT corn rose 0.8% to $4.28-1/4 a bushel, having slid to $4.04 on Feb. 22, also the lowest since November 2020.
Wheat gained 0.3% to $5.59-1/2 a bushel but was near September's three-year low of $5.40 after prices fell 3.2% on Friday.
A plentiful supply of soybeans from Brazil, corn from the United States and wheat from Russia have prompted speculators to build up huge short positions in all three CBOT contracts.
That has driven prices lower but left the markets vulnerable to bouts of short covering that accelerate upward price moves when they happen.
Brokers StoneX on Friday raised their forecast for Brazilian soybean production -- the harvest of which is underway -- to 151.5 million metric tons but consultants AgResource dropped theirs to 143.92 million metric tons.
Analysts have been mostly downgrading Brazilian estimates in recent weeks but the country is still flush with beans after a record crop last season and is outcompeting the United States in export markets.
StoneX analysts said Brazilian cash prices rose on Friday but that buyers in China, the biggest importer, still preferred Brazilian to U.S. beans.
Argentina, meanwhile, expects a bumper soybean crop, offsetting any loss in Brazilian yields, with the Buenos Aires grains exchange leaving its 52.5 million ton forecast unchanged last week.
Weather conditions are favourable in South America for the time being so no damage to yields is expected, said independent analyst Tobin Gorey.
For corn, StoneX lowered its Brazilian crop forecast to 124.44 million tons and AgResource reduced theirs to 114.94 million tons.
The Buenos Aires grains exchange left its estimate for Argentina's 2023/24 corn harvest unchanged at 56.5 million tons.
Global corn stockpiles are set to reach five-year highs later in 2024, undergoing their largest annual expansion in seven years.
Large speculators trimmed their net short positions in CBOT corn and wheat in the week to Feb. 27 but increased their net short in soybeans.
(Reporting by Peter Hobson; Editing by Rashmi Aich and Sohini Goswami)
