Fields in the EAA are typically 40 acres (16 ha), on two sides bordered by canals that are connected to larger ones by which water is pumped in or out depending on the needs of the crops. The water level for sugarcane is ideally maintained at 20 inches (51 cm) below the surface soil, and after the cane is harvested, the stalks are burned.[92] Vegetables require more fertilizer than sugarcane, though the fields may resemble the historic hydrology of the Everglades by being flooded in the wet season. Sugarcane, however, requires water in the dry season. The fertilizers used on vegetables, along with high concentrations of nitrogen and phosphorus that are the by-product of decayed soil necessary for sugarcane production, were pumped into WCAs south of the EAA, predominantly to Everglades National Park. The introduction of large amounts of these let exotic plants take hold in the Everglades.[93] One of the defining characteristics of natural Everglades ecology is its ability to support itself in a nutrient-poor environment, and the introduction of fertilizers began to change this ecology.[94]