According to NHK(Nippon Housou Kyoukai/Japan Broadcasting Corporation), there has not been any official soil sampling since the nuclear disasters following the 11 March 2011 quake/tsunami.  Tokyo Electric Power Company has done periodic samples, but only within the area of Fukushima Daiichi nuclear compound.

The Japanese Science Ministry is now taking actual soil samples outside the nuclear facility.  What I mean by ‘actual’ is that up ’till now they’ve been conducting soil samples from the air!  NHK didn’t explain how you do soil sampling from the air, but it’s clear the government has realized they need to actually get down on the ground to properly test the soil.

The Science Ministry will join with universities and private laboratories around Japan, to do the soil sampling.  Samples will be taken every 4 square km (2.4 miles) in areas within 80 km (49.7 miles) of the nuclear plant and every 100 square km (62 miles) in areas further away.