CHICAGO, Feb 27 (Reuters) - Spot basis bids for soybeans delivered to elevators and processing plants around the U.S. Midwest were steady to higher on Thursday following a recent slowdown in farmer selling that tightened supplies in buyers' hands, merchants said.

* Spot corn basis bids were also steady to higher on slow farmer sales and a sharp drop in futures prices at the Chicago Board of Trade.

* Many grain merchants have rolled their spot basis bids to be tied to CBOT May futures ahead of the March delivery period. More buyers are due to roll their bids in the coming days.

* Flat cash prices for soybeans at elevators and processors were steady to nearly 10 cents a bushel higher on Thursday as buyers rolled their bids to May futures. Their basis adjustments only partly offset the May contract's premium over March futures.

* Chicago Board of Trade corn futures fell sharply near midday while soybeans were narrowly mixed. Corn was pressured by a larger-than-anticipated U.S. spring plantings increase forecast by the U.S. Department of Agriculture (USDA) on Thursday.

* Both corn and soy were also anchored by rising trade tensions after U.S. President Donald Trump said steep tariffs on imports from Canada and Mexico would be imposed next week, while tariffs on Chinese imports would be raised. The moves are expected to spark retaliation by the top three export markets for U.S. farm products.

* Chicago Board of Trade May corn futures CK25 were down 11-1/2 cents at $4.82 per bushel near midday on Wednesday. CBOT May soybeans SK25 were down 3/4 cent at $10.40-1/2 a bushel.

Basis values are quoted against CBOT futures in cts/bu:

NOTE: 0 = Option price, UNC = Unchanged, UNQ = Unquoted

NC = Not comparable, DP = Delayed price, N/A = Not available,

F = January, H = March, K = May, N = JulyQ = August, U = September, X = November, Z = December

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LINKS: 0#USCSHGRN-PM

For U.S. forward basis spreadsheets, please click:

CORN/BASIS, SOYA/BASIS, WHEAT/BASIS, MILO/BASIS

- CBOT corn report COR/

- CBOT soybean report SOY/C

- CBOT wheat report WHE/C

- U.S. grain barge freight values BG/US

- U.S. Midwest cash grain PM GRA/PM

- U.S. CIF/FOB Gulf Grain GRA/F

(Reporting by Karl Plume)

((karl.plume@thomsonreuters.com; +1 313 484 5285))