Organic farming has been found to pollute the groundwater far more than conventional farming in a recent paper in Hydrology and Earth System Sciences. The paper, published this weekend by a group at Ben-Gurion University in Israel studied a group of greenhouses all built at the same time in the same region. All of them had a special groundwater monitor installed when they were constructed in 2008-2009 in similar terrain.
Some of the greenhouses used conventional growing methods and some used organic methods, where the main difference was the method of fertilization. The organic greenhouses used composted manure (dairy cows, poultry and seabird guano) and the conventional greenhouses used drip irrigation containing soluble mineral fertilizers. The total amount of applied nitrogen was similar in both farming methods.
During a 19 month period, they monitored the nitrates found in the vadose zone well below the root systems and just above the ground water. They found a striking difference in nitrate concentration, with the organic greenhouses producing an average of 357 mg/liter and a peak average concentration of 724 mg/liter at a depth of 2.5 meters. The conventional greenhouses produced only about 10% of that, with an average value of only 37.5 mg/liter. The drinking water standard in most countries limits nitrates to less than 50 mg/liter.
In addition, closer to the root zone, the concentrations were reversed with higher nitrogen content in the conventionally farmed greenhouses and lower in the organically farmed greenhouses, meaning that less nitrogen was getting to the plants in the organic greenhouses and filtering down below the root system into the vadose zone where it could pollute the groundwater.
To check their conclusions, they looked at six more greenhouses (3 organic and 3 conventional) where they drilled boreholes to sample the soil. Two of the three organic greenhouses showed the same nitrate pollution, increasing with depth and all of the conventional greenhouses showed much less pollution. The third organic greenhouse fertilized using water extracts of guano and drip fertilization rather composted manure, and was thus more like the conventional greenhouses in nitrate levels.
The whole idea of organic farming has a number of really good principles: notably better soil care using compost and the use of beneficial organisms for pest control. However, organic crops are no more nutritious, and use more frequent pesticide sprayings of kinds of pesticides that may be much more toxic. And organic farms are still only about 0.5% of the total farms in the US by acreage and are not growing rapidly enough to make a significant impact on agriculture in the near future. And of course, yields of organic farms is in general 70% or less than that of conventional farms, which pushes up organic prices.
This groundwater pollution study is quite disappointing for sustainability considerations, but along with Savage’s conclusions on carbon footprint, makes organic farming less persuasive than it once was.
- O. Dahan, “Nitrate leaching from intensive organic farms to groundwater.”
- Marc Gunther, “Organic agriculture not the answer to the world’s food challenges.”
- Why Does Organic Seem Bigger than it is?
- Steve Savage, “Why you probably don’t know that pesticides of changed.”
- Henry Miller, “The myth of organic agriculture.”
- V Seufert, “Comparing the yields of organic and conventional agriculture.”
- M Jensen, “Health biomarkers in a rat model after intake of organically grown carrots.”
- A Trewavas, “Urban myths of organic farming.”
- S Savage, “The shocking carbon footprint of compost.”