Nitrate pollution is one of the more vexing problems facing rural areas in the U.S. and around the world. It is caused over decades as fertilizer, manure and sewage run off into surface water or are leached through the soil into groundwater. High nitrates in drinking water can cause serious health problems in childbirth.
Nitrogen is critical to plant growth, and in particular, to high yields in food production. Many crops remove significant amounts of it from the soil, which must then be replaced each year in order for the crops to produce the following year. Synthetic nitrogen fertilizer is highly soluble in water, so if it’s not used by crop plants, it moves down through the soil and eventually reaches the groundwater.
The state of California recently began an initiative to monitor and regulate the amount of nitrogen used in agriculture. For the first time, farmers in areas with high levels of nitrates in the groundwater must now report all their fertilizer use.
From its inception, organic farming has recognized synthetic fertilizer as a potential pollutant and has prohibited its use. Instead, farmers have to focus on building up the fertility of their soil over the long run using cover crops and compost. Cover crops are grown before and after cash crops, during times that other farmers leave their fields fallow. The roots of these plants simultaneously hold the soil in place during heavy rain and wind while pulling leftover nitrogen out. Because the cover crops are turned back into the soil instead of being harvested, the nitrogen is recycled and made available for the next crop.
Cover crops also return a tremendous amount of carbon to the soil, which encourages the growth of microbes that eat it. As the microbes die, they also make small amounts of nitrogen available to the crops. It’s like a slow-release fertilizer, naturally.
Synthetic fertilizer is not the only potential source of nitrate pollution. Animal manures can also cause pollution. This is why organic farmers use compost instead. The composting process breaks down and stabilizes the nitrates in manure and other waste products. Fresh manure might contain as much as ten percent nitrogen; compost generally has around 2%.
Unfortunately, the State Water Board has gone with a one-size-fits-all regulatory formula that fails to acknowledge the role that cover crops, compost, and other sustainable and organic practices can play in reducing pollution. Instead of giving us credit for reducing nitrate pollution with these practices, the state considers them a source of nitrogen pollution despite study after study showing they reduce the contamination of both ground and surface water.
After years of soil building on our farm, we have found that we need to add less and less nitrogen to grow our crops — and sometimes none at all. Meanwhile, conventional farmers all over the state have begun to grow cover crops and use compost as they have become more widely recognized as environmentally and economically beneficial. The state needs to catch up and recognize them as important solutions to help reduce nitrate pollution.