Synthetic Nitrogen Fertilizers Deplete Soil Nitrogen‚
Organic nitrogen and carbon exist naturally in soils but in the 1920’s and 30’s, research showed that soluble nitrogen fertilizers actually depleted soil nitrogen. This story changed in the latter part of the 20th century as farmers were told the soluble nitrogen fertilizers actually increased soil nitrogen and carbon levels.
Once again, recent research has returned us to the 20’s pointing out that soluble nitrogen fertilizers (chemical fertilizer) increases the breakdown rate of crop residue (carbon) by soil microorganisms. In other words, organic matter disappears faster if you apply soluble nitrogen fertilizers.
This becomes important for two reasons. The first is that by using soluble nitrogen fertilizers you’re turning your garden soil into a hydroponic experiment with no buffering ability (organic matter and the important carbon exchange co-efficient are directly related to plant health). The second is that this modern research contradicts what marketers have been telling us for half a century now.
The researchers sum up by concluding the long-term consequences of continued reliance on current production practices will be a decline in soil productivity.
Bottom line: for gardeners – increase the use of compost and crop residues in the garden and decrease any reliance on soluble/synthetic fertilizers with soluble nitrogen.
Having said that, I have to wonder if there’s a middle ground where we continue to use soluble nitrogen (fish emulsion etc) for superior crop yields but continue to replenish the soil organic matter as well (keep high levels of organic matter incorporated or as a mulch)
Reference: R.L. Mulvaney (Dept. of Natural Resources and Environmental Sciences, Turner Hall, 1102 S. Goodwin Ave., University of Illinois, Urbana, IL 61801), S.A. Khan, and T.R. Ellsworth, Synthetic Nitrogen Fertilizers Deplete Soil Nitrogen: A Global Dilemma for Sustainable Cereal Production,‚ Journal of Environmental Quality 38(6), November-December 2009, 2295-2314. (American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America, 677 S.