BUENOS AIRES, June 8 (Reuters) - Argentina's current soybean harvest is nearing completion with total production expected to reach just 21 million metric tons, a major grains exchange said on Thursday, far below yields from previous years for the country's main cash crop.

Argentina is the world's leading exporter of processed soybeans, as well as a major wheat and corn supplier to global markets, but a historic drought that began last year has slashed by half expectations for the 2022/2023 harvest.

The soybean harvest is nearly 94% complete, according to a report from the Buenos Aires Grains Exchange.

Corn harvest activity tends to intensify as the soybean crop concludes.

In its latest report, the grains exchange said about a third of planted corn has been threshed - the process by which grains are separated from the plant - while production for the cycle is estimated to hit 36 million metric tons.

Meanwhile, wheat planting during the upcoming 2023/2024 harvest suffered delays over the last week due to rainfall in Buenos Aires province, an important agricultural region, according to the grains exchange.

The wheat crop is expected to total 18 million metric tons.

For now, Argentina's wheat farmers have sown nearly 20% of the 6.3 million hectares (15.6 million acres) set out for the grain's cultivation, according to the exchange. (Reporting by Maximilian Heath Editing by Marguerita Choy)