To prevent this, farmers must apply enough extra water to carry the salt in solution down below the root zone. It is estimated that a million acres of waterlogged high salinity soils will soon require drainage. Fertilizers Agricultural drainage water contains some nitrogen compounds from manmade fertilizers. Crops rarely absorb more than half these nutrients. Of most serious consequence to the Estuary's rivers is probably ammonia, toxic to fish, which results from excess field application of anhydrous ammonia, a common fertilizer.
Ammonia also appears in runoff from dairies and cattle feedlots.
Another problem residue is nitrate. Nitrate-rich water can undergo eutrophication, a rapid choking growth of algae and other aquatic plants. Decomposing plant material then depletes the water of oxygen, killing fish and other animal life. Eutrophication is currently not, however, a serious problem in the Estuary. Pesticides While some pesticides remain in the soil and decompose in a short time, most are more resistant to chemical breakdown and leach into drainage water unaltered.