Because these are winter rain zones, the land is fallow from spring to autumn. Water retention work is done during the fallow period, and, counting on subterranean water that has been held in this way, winter crops (mainly wheat) are sown in October and, after germination, depend on winter rainfall for growth. Land is divided into fallow land and winter cropland, which are alternated every year, an agricultural method that is called the two-field system.