Variable Levels of Biological Activity in Sanborn Field after Fifty Years of Treatment

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

“…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 specifically call attention to aspects of the data from White (1927) and Albrecht (1938) that contradict the interpretations of these studies presented in Mulvaney et al (2009) as well as in the recent letter by the same authors.…”

“…Mulvaney et al (2009) stated that White (1927) and Albrecht (1938) showed that “fertilizer N depletes soil organic matter by promoting microbial C utilization and N mineralization.” In our review of these papers, we find different conclusions. White (1927) did indicate that adding N fertilizer stimulated microbial decomposition that led to an increasing percentage of residue decomposition with increasing fertilization rates.…”

“…Albrecht (1938) used data from continuous wheat plots at the Sanborn fields in Missouri to examine long‐term changes. Mulvaney et al (2009) utilized one plot in their Table 2 that shows that 25 yr of mineral N fertilizer (following a previous 25 yr of the same treatment) led to a decline in soil N from 1.07 to 1.00 g N kg −1 in the upper 18 cm of soil (Table 1).…”

Synthetic Nitrogen Fertilizers Deplete Soil Nitrogen: A Global Dilemma for Sustainable Cereal Production

“…The assertion has often been made that synthetic N fertilization maintains or increases soil organic C (SOC) by enhancing the production of crop residues (e.g., Melsted, 1954; Odell et al, 1984; Mitchell et al, 1991; Havlin et al, 2005). Yet the opposite effect was reported long before the modern era of chemical‐based N management (White, 1927; Albrecht, 1938), which is fully consistent with evidence that mineral N enhances microbial decomposition of plant residues (e.g., Starkey, 1924; Waksman and Tenney, 1928; Tóth, 1977; Reinertsen et al, 1984; Schnürer et al, 1985; Green et al, 1995; Recous et al, 1995; Neff et al, 2002; Mack et al, 2004; Conde et al, 2005; Pikul et al, 2008; Poirier et al, 2009). Such evidence is likewise consistent with the decline of SOC we previously reported in a paper by Khan et al (2007) that documented this trend for numerous baseline data sets involving nitrogen–phosphorus–potassium (NPK) fertilization and a wide variety of geographic regions, cropping systems, and tillage practices.…”

Reply to 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 theJournal of Environmental Quality2009 38: 2295–2314

“…If synthetic N fertilizers are more apt to increase the input than soil storage of C and N, then logic dictates that these fertilizers must be more effective in promoting microbial decomposition as opposed to humification. Years before the modern agricultural era, this effect was linked to soil C and N depletion in long‐term fertilizer trials (White, 1927; Albrecht, 1938) and is no less apparent today as evidenced by long‐term trials in Iowa demonstrating that synthetic N fertilization is more effective for stimulating C decay than residue C input (Russell et al, 2009). Despite the assertion by Powlson et al (2010) to the contrary, the same effect is apparent from numerous data sets summarized in Table 3 of Khan et al (2007a) and Table 2 of Mulvaney et al (2009) and from more recent studies documenting the loss of organic matter from soils fertilized with synthetic N (Schipper et al, 2007; Fening et al, 2009; Poirier et al, 2009; Senthilkumar et al, 2009).…”