According to Official Guinness Records,
The most sword cuts to straw mats in three minutes is 252 and was achieved by Isao Machhi (Japan) on the set of Lo Show Dei Record, in Milan, Italy, on 21 Apr 2011.
For this record, the straw mats were rolled and place vertically on holders ready to be sliced by the participant. Each mat had to be cut between 5 and 10 times. Isao Machii used a Uchigatana, a type of Katana sword with the blade facing upwards.
For a complete list of 2011 records, please visit 2011 Guinness Records in Italy.