* Soybeans down for second session on U.S. harvest pressure

* Wheat drops after rally, Russian farmers sow 2021 crop in dry soil

SINGAPORE, Sept 29 (Reuters) - Chicago soybean futures lost ground on Tuesday, with the market dropping for six out of seven sessions, as a rapid pace of U.S. harvest pressured prices.

Corn slid after two sessions of gains, while wheat dropped around half a percent.

"U.S. harvest is gaining momentum which is expected to weigh on prices," said Ole Houe, director of advisory services at agriculture brokerage IKON Commodities in Sydney.

The most-active soybean contract on the Chicago Board of Trade (CBOT) fell 0.1% to $9.95 a bushel, as of 0334 GMT, not far from last session's lowest since Sept. 16 at $9.92 a bushel.

Corn gave up 0.3% to $3.65-1/2 a bushel after gaining around half a percent in the last session, while wheat was down 0.5% at $5.47-3/4 a bushel after climbing 1.1% on Monday.

The U.S. soybean harvest was 20% complete as of Sunday, the U.S. Department of Agriculture said in a weekly crop progress report on Monday, ahead of the five-year average of 15% and the average estimate in a Reuters analyst poll of 18%.

The corn harvest lagged slightly as producers focused on soybeans. The U.S. corn crop was 15% harvested, the USDA said, behind the five-year average of 16% and the average analyst estimate of 17%.

Showers in parts of the Midwest on Monday were expected to give way to dry weather for the rest of the week, favouring field work.

Traders were also squaring positions ahead of quarterly grain stocks reports due midweek from the USDA.

Russia badly needs rains to arrive within the next few weeks as its farmers continue sowing the 2021 winter wheat crop in dry soil, agriculture consultancy Sovecon said.

The loading of grains ships in Argentina was affected on Monday by a 24-hour strike by cargo inspectors demanding higher wages and shorter working hours, said Martin Brindici, general manager of the country's private ports chamber.

Commodity funds were net buyers of CBOT corn, wheat and soyoil futures contracts on Monday and net sellers of soybean and soymeal futures, traders said. (Reporting by Naveen Thukral; editing by Uttaresh.V)