[If] one leased a field from another to sow barley in it, he may not sow it [with] wheat; wheat —- he may sow it [with] barley. Rabban Shimon ben Gamliel prohibits [it]. Grain —- he may not sow it [with] beans; beans —- he may sow [it] with grain. Rabban Shimon ben Gamliel prohibits [it].