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.

1526 Journal of Environmental Quality • Volume 39 • July–August 2010 Dear Editor, Recent letters to the editor by both Powlson et al. (2010) and Mulvaney et al. (2010) concerning conclusions reached by Mulvaney et al. (2009) incorrectly cited our results (David et al., 2009). Powlson et al. (2010) indicated our study had results from the Morrow Plots. We did not conduct any sampling of the Morrow Plots and were reporting on long-term changes in a number of nonexperimental fi elds in Illinois on imperfectly drained, conventionally managed Mollisols. We did conclude from the fi elds we sampled that there was little change in soil C (and N) pools from 1957 through 2002 under commonly used rates of synthetic fertilizer, little or no manure application, tile drainage, and a corn and soybean rotation. Th e historical practices that landowners reported to us for these fi elds were similar to the moderate fertility treatment in the Morrow Plots, which also showed little change in soil C and N in Khan et al. (2007). Khan et al. (2007) reported a decline in soil C and N in the high fertility treatment, which does not appear to have been a commonly used practice. Mulvaney et al. (2010) cited David et al. (2009) to support their conclusions that synthetic N fertilization has led to declines in soil C and N. We disagree with their conclusion, as we found no consistent change in soil C and N concentrations or mass to a depth of 1 m between 1957 and 2002, the period of extensive synthetic N fertilizer use. We found declines from the early 1900s to the 1950s, which may have been residual organic matter decay from the initial plowing of Illinois prairie soils or related to the discontinued use of manure with the decline of farm animals, but we concluded that the declines in organic matter were probably completed by the late 1950s (David et al., 2009) before the modern intensive use of synthetic N fertilizer. We did not include Morrow Plot data in our statistical analysis (David et al., 2009) because we thought that the manure history, lack of replication, unknown initial conditions, spatial variation within this fi eld, and small plot size confounded the results. Manure applications are known to greatly aff ect patterns of change in soil organic C and N pools, often for many years. Powlson et al. (2010) rightly pointed out that Mulvaney et al. (2009) did not take “full account” of past changes in manure history on the Morrow Plots. Further, Powlson et al. (2010) noted the selective use of data by Mulvaney et al. (2009) in their literature review of long-term data sets. We agree and specifi cally call attention to aspects of the data from White (1927) and Albrecht (1938) that contradict the interpretations 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