Synthetic fertilizer accounts for more than a third of the 1.8 million tons of new nitrogen entering California each year, and animal feed accounts for another 12 percent, making agriculture the largest single source of nitrate pollution in the state, according to a new report from the UC Davis Agriculture Sustainability Institute and the University of California Division of Agriculture and Natural Resources.
“Data show that California crops recover, on average, less than half of applied synthetic nitrogen, with some crops capturing as little as 30%,” says the California Nitrogen Assessment. “Similar or even lower nitrogen recovery rates are found when organic nitrogen sources are used.”
The rest ends up in the soil, and eventually the groundwater. Some 419,000 tons of nitrogen leach into groundwater each year, according the report.
“Livestock consume 614,000 tons of nitrogen each year in their feed. Only 25% of that becomes meat or milk for our consumption; the rest is excreted in manure,” says the report. “Much of that manure is reapplied to cropland, where its nitrogen has the potential to leach into groundwater. Some of the nitrogen in manure is released into the air or water or stored in soils.”
In a 2012 report covered by FERN, UC Davis found nearly 10 percent of the 2.6 million people living in the Tulare Lake Basin and Salinas Valley might be drinking nitrate-contaminated water. If nothing was done to stem the problem, the report warned, those at risk for health and financial problems may number nearly 80 percent by 2050.
California produces more than half of the nation’s fruits, nuts and vegetables and 21 percent of its dairy commodities.