Last week a link to Tom Philpott’s article “New research: synthetic nitrogen destroys soil carbon, undermines soil health” showed up on Energy Bulletin, one of my favorite news sites. The article was originally published in Grist.
The article’s title pretty much says it all: a couple of recent (2007, 2009) studies by soil scientists working in Illinois (and a 2009 study by soil scientists in Iowa) support what some very old sources — published before WWII— had claimed, that use of synthetic fertilizers is bad for soil. What’s bad is that the readily available nitrogen speeds up growth of soil bacteria and fungi; as they grow, they do their usual job of decomposing organic matter more quickly, which results in soil with lower organic matter content.
It has been thought that agricultural soils on which plant debris had been left and then turned under would serve as storage for carbon, which could help mitigate climate change, but the new studies suggest that the industrial farms that rely on synthetic fertilizers are not going to be useful as carbon sinks.
In addition, soils that are lower in organic matter drain less well, hold less moisture, hold nutrients less well, and have lowered numbers of nitrogen-fixing bacteria. As the spaces normally held open by organic matter in the soil close because of the loss of that organic matter, the soil compacts and air is squeezed out. Roots need those air pockets, and so do many members of the community of micro- (and not so micro-) organisms that live in the soil.
I’m writing about this for a couple of reasons. The first is that not everyone who reads my blog reads the same websites that I do, so they might have missed this news. The other is that I had just about decided to save some money this year by using some synthetic fertilizer on my veggies. Obviously, I am going to have to change that plan (back to the cotton-seed meal, kelp meal, etc).
I would say that “Ignorance [was] bliss,” but I am glad to be able to avoid harming my garden’s soil. I may have to drive back out to that horse farm for another load of manure, though.
NOTE: The article discussed here is one in a series posted on Grist about soil nitrogen. Tom Philpott has written them all.