Additional Comments on “Synthetic Nitrogen Fertilizers Deplete Soil Nitrogen: A Global Dilemma for Sustainable Cereal Production,” by R.L. Mulvaney, S.A. Khan, and T.R. Ellsworth in the Journal of Environmental Quality 2009 38:2295–2314

Reply to Additional Comments on “Synthetic Nitrogen Fertilizers Deplete Soil Nitrogen: A Global Dilemma for Sustainable Cereal Production,” by R.L. Mulvaney, S.A. Khan, and T.R. Ellsworth in the Journal of Environmental Quality 2009 38:2295–2314

“…Manure applications stopped at the same time as the high fertilizer N rate started, so the effects are confounded. While it is impossible to conclude unequivocally which change of treatment is responsible for the greater decline in soil N concentration in the HNPK treatment, we suggest that the cessation of organic inputs in manure is a far more plausible explanation.” David et al (2010) concur with our argument. Mulvaney et al (2010) failed to answer this point in their response to our letter to the editor, just as they did when Reid (2008) made the same criticism of the earlier Khan et al (2007) paper.…”

“…David et al (2010) agree with our contention that Mulvaney et al (2009) and Khan et al (2007) were highly selective in their citation of soil C and N data from other long‐term experiments, including those at Rothamsted, and they cite additional examples to support this. We entirely agree with David et al (2010) in their interpretation of this long‐term data, which leads to contrary conclusions from those drawn by Mulvaney et al (2009) and Khan et al (2007) The data cited by David et al (2010) are also in accord with the review of numerous long‐term experiments by Glendining and Powlson (1995) and data from the Broadbalk Experiment at Rothamsted (Glendining et al, 1996). These show, in the vast majority of cases, modest increases in soil N and C following long‐term applications of N fertilizer as compared to soil not receiving N—the complete opposite of the claim by Mulvaney et al (2009) and Khan et al (2007)…”

“…We are pleased that David et al (2010) agree with our criticisms of Mulvaney et al (2009) and Khan et al (2007) The key error made by Mulvaney et al (2009) arose because, in their analysis of data from the Morrow Plots, their “high NPK” treatment (HNPK) had previously received organic manure, in contrast to the NPK and unamended treatments. In Powlson et al (2010) we wrote, “the observation that soil N and C declines in the HNPK treatment were greater than in the unamended and NPK treatments is entirely understandable on the basis of the cessation of manure applications.…”

From Dust Bowl to Dust Bowl: Soils are Still Very Much a Frontier of Science

“…This topic has been the object of a very lively debate over the last few years (see, e.g., Khan et al, 2007;Mulvaney et al, 2010aMulvaney et al, , 2010bDavid et al, 2010;Powlson et al, 2010). A meta-analysis performed by Janssens et al (2010) suggests that the deposition of biologically reactive N from the atmosphere impedes organic matter decomposition, and thus stimulates C sequestration, in temperate forest soils where N is not limiting microbial growth.…”

Reply to Additional Comments on “Synthetic Nitrogen Fertilizers Deplete Soil Nitrogen: A Global Dilemma for Sustainable Cereal Production,” by R.L. Mulvaney, S.A. Khan, and T.R. Ellsworth in the Journal of Environmental Quality 2009 38:2295–2314

“…In responding to David et al (2010), we would first of all point out that most of their allegations have already been addressed in detail by our recent letter to the editor (Mulvaney et al, 2010), which elaborates on information presented in our two papers (Khan et al, 2007; Mulvaney et al, 2009) and a previous letter to the editor (Khan et al, 2008). With regard to their allegation of “selective use of data,” considerable care was taken in the letter by Mulvaney et al (2010) to highlight that our selection criterion followed from the primary research question addressed by our work: “Does synthetic N fertilization increase or decrease soil C or N storage?” As stated previously, this question cannot be adequately addressed by comparing treatment effects from a one‐time sampling; a far better alternative requires a baseline approach with sequential sampling over time of field trials without organic manuring.…”