An amendment to add that in applying the set aside program to land that has been farmed under summer fallow practices in three of the five years prior to the requirement of a set aside, the Secretary shall consider the effects of a soil erosion and such other factors as he considers appropriate in determining the amount of land to be idled. However, in no case shall farmers be required to idle more than 60 percent of their crop land when included with land already idled by summer fallow practices are in effect. The secretary is to issue rules and regulations defining "summer fallow".