We have been preparing a paper regarding on effects of long term tillage practices on soil quality indicators and I come up with a question on potantial mineralizable nitrogen (PMN) values.
PMN is considered as a soil quality indicator that is used to show the effects of human intervene on functioning capacity of soils. As in paper published in SSSAJ (Zobeck, T. M., Steiner, J. L., Stott, D. E., Duke, S. E., Starks, P. J., Moriasi, D. N., & Karlen, D. L. 2015. Soil Quality Index Comparisons using Fort Cobb, Oklahoma, watershed-scale land management data. 79(1), 224-238).
My question is regarding on SCORING CURVE of PMN in Soil Management Assessment Framework (SMAF). The range of the curve is between 2.5 gN/kg to 25 g N/kg which is very high for soils as we understand from the published papers. 25 gN/kg is equal to 2.5% mineralizable nitrogen which is not possible for soils. Since SMAF has been now widely used in all over the world, I believe that either the range used in scoring curve or the unit of the PMN data should be rechecked.
I checked the literature on reported data for PMN values. Sharifi, M., et al. "Evaluation of some indices of potentially mineralizable nitrogen in soil." Soil Science Society of America Journal 71.4 (2007): 1233-1239. reported that the PMN values ranged from 54 to 197 mg N kg−l and represented an average of 6% of the total organic N. They also cited PMN values from many of publised papers as: The measured values for N0 were in the range of N0 values reported by Campbell et al. (1984; 66–185 mg N kg−1), Jalil et al. (1996; 71–278 mg N kg−1) and Curtin and Wen (1999; 71–250 mg N kg−1) for soils of Saskatchewan (heavily manured soils excluded), Milburn et al. (1990; 107–169.8 mg N kg−1) for New Brunswick, and Carter and MacLeod (1987; 44–247 mg N kg−1) for Prince Edward Island; but were at the low end of the range of values reported by Walley et al. (2002; 9–401 mg N kg−1 if a soil bulk density of 1.2 Mg m−3 is assumed) for Saskatchewan and Simard and N’Dayegamiye (1993; 129–1098 mg N kg−1) for Quebec. Many other studies have also reported similar PMN results as in the Sharifi et al. (2007).
The unit of PMN in the above mentioned paper (Zobeck et ak., 2015) is given as gN/kg which should be mg N/kg.
Best Regards. Hikmet
Dr.Hikmet,potentially mineralizable N is usually expressed in unit of mg N/kg soil and I find the same unit in several papers (as cited by you and others).Your argument appears o.k.
Agree units gN/kg look to be incorrect. For your information PMN also used a soil quality indicator in New Zealand (found to be sensitive to changes in land use and management). Look for Papers by G. Sparling and colleagues.
Potentially Mineralizable Nitrogen as an Indicator of Biologically Active Soil Nitrogen
PMN in conjunction with total N or soil C is an effective indicator of organic matter quality. PMN is the fraction of organic nitrogen converted to plant available (or mineral) forms under specific conditions of temperature, moisture, aeration, and time. Determining levels of PMN can provide an estimate of available N in the soil. PMN originates mainly from microbial biomass and plant and animal tissues—the main source of the organic nitrogen pool. It represents the fraction of nitrogen easily decomposable by soil microorganisms and is considered an indirect measure of nitrogen availability during the cropgrowing season (if measured during that period).
A new theory, based on the diffusion of NH4+ ions during incubation, is put forward to predict potentially mineralizable N (No) in soils. Its validity is tested using predicted real No, based on the regression analysis of experimental data and also it is compared with the conventional one-pool exponential model of Stanford and Smith (1972). In all soil samples employed for the test, our new model predictedNo more accurately than the one-pool model. The procedure to calculate No using our model is also easier than for the one-pool model. It is presumed that the accuracy of prediction of our new model could have been further improved, if an average value for the time-variant diffusion coefficient of NH4+ (D), is used for each of the samples separately, because D could vary with the nature and content of organic matter in soils. Therefore, it is concluded that further studies are needed to establish D for soils with different organic matter contents and under different soil conditions. Source ;Soil Biology and Biochemistry, Volume 26, Issue 11, November 1994, Pages 1491-1493
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