This work was carried out to evaluate the statistical properties of eight nonlinear models used to predict nitrogen mineralization in soils of the Southern Minas Gerais State, Brazil. The parameter estimations for nonlinear models with and without structure of autoregressive errors was made by the least squares method. First, a structure of second order autoregressive errors, AR(2) was considered for all nonlinear models and then the significance of the autocorrelation parameters was verified. Among the models, the Juma presented an autocorrelation of second order, and the model of Broadbent presented one of first order. In summary, these models presented significant autocorrelation parameters. To estimate the parameters of nonlinear models, the SAS procedure MODEL was used (SAS). The comparison of the models was made by measuring the fitted parameters: adjusted R-square, mean square error and mean predicted error. The Juma model with AR(2) best fitted for nitrogen mineralization without liming, followed by Cabrera, Stanford & Smith without autoregressive errors, for both with and without soil acidity correction.

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Nonlinear models to predict nitrogen mineralization in an Oxisol

Nitrification is a major pathway of N2O production in aerobic soils Measurements and model simulations of nitrification and associated N2O emission are challenging Here we innovatively integrated data mining and machine learning to predict nitrification rate (Rnit) and the fraction of nitrification as N2O emissions (fN2ONit) Using our global database on Rnit and fN2ONit, we found that the machine-learning based stochastic gradient boosting (SGB) model outperformed three widely used process-based models in estimating Rnit and N2O emission from nitrification We then applied the SGB technique for global prediction The potential Rnit was driven by long-term mean annual temperature, soil C/N ratio and soil pH, whereas fN2ONit by mean annual precipitation, soil clay content, soil pH, soil total N The global fN2ONit varied by over 200 times (0006%-12%), which challenges the common practice of using a constant value in process-based models This study provides insights into advancing process-based models for projecting N dynamics and greenhouse gas emissions using a machine learning approach

https://iopscience.iop.org/article/10.1088/1748-9326/abe4f5/pdf

New approach for predicting nitrification and its fraction of N2O emissions in global terrestrial ecosystems

This paper highlights major activities and achievements in soil science by professors at the University of Alberta (U of A), which provide incredible benefits to society, provincially, nationally, ...

Soil science at the University of Alberta: a century of service to science and society1

Nitrogen mineralization potentials were determined using an undisturbed-soil incubation procedure. The purpose of this study was to evaluate the above-mentioned method as an index of soil nitrogen availability. Undisturbed soil samples (0–150 and 150–300 mm) of a limed (pH 7.3) and an equivalent non-limed (pH 4.9) soil were incubated at 30°C and field water capacity. After every consecutive 10-day period, four samples of each treatment/depth combination were removed, dried and analysed for mineral N content. This was conducted over a period of 60 days. Distinction was made between changes in NH4 + and NO3 - contents of the incubated soil, assuming the NO3 − release represented N release from the soil due to high nitrification rates. The release of NO3 − was depicted by a straight-line regression, where the slope was equal to the rate constant of mineralization (k). The mineralization potential (NO ) was assumed to be the maximum mineral N content obtained in the soil during incubation. Comparing the amoun...

Evaluation of an undisturbed-soil incubation method as an index of soil nitrogen availability in a limed and non-limed soil

Elemental sulphur (S°) dust blew from a sour gas processing plant into coniferous forest in northwestern Alberta. The objectives were to determine the amounts of wind-blown S° deposited on the soil, its effect on soil pH and vegetation, and to find methods of reclamation of the S°-acidified soils. Wind-blown S° apparently did not travel beyond 3 km downwind from the S° source. S° deposition within 200 m of the source had made the soil extremely acid and most of the vegetation was dead. Two acidified soils (pH 1 to 2) were used in greenhouse experiments with treatments including heavy dose of finely-ground CaCO3 (353 t ha−1). Oats and reed canary grass grew well on CaCO3 treated soil, but only with NPK fertilizer. Field experiments gave similar results. A large area (within 650 m) was Luvisolic soil with the litter layer acidified to <pH 3 and most of shrubs and all of mosses were gone. Here the mineral N did not accumulate whether the soil was limed or not and N fertilizer disappeared from the mineral N pool soon after application, indicating immobilization of mineral N by S° oxidation. Natural re-vegetation was extremely slow despite liming, but agricultural species grew provided they received repeated additions of N fertilizer. Farther from the S° source (up to 2.5 km) the moss stratum was dead or dying when the pH of the 0–2.5 cm soil layer was less than 3.6 to 3.9 and buffering capacity of that layer against dilute H2SO4 was especially low. However, mosses were not harmed by application of finely-ground lime.

Acidification of forest soil by elemental sulphur dust

The objective was to determine the effect of liming on the net ammonification and nitrification in the field of 26 acid soils during the first year after application. The soils ranged from pH 4.4 to 6.0 and were limed to a target pH of 6.7. The 26 sites were located in Alberta and northeastern British Columbia. Soils were limed in the spring, fallowed and sampled in the next spring. The content of NH4 +‐N plus NO3 ‐‐N in the 0–15 cm layer of the non‐limed treatments varied from 6 to 48 Hg/g (average of 26), while the limed treatment varied from 14 to 89 μg/g (average of 40). The increase in ammonification was negatively related to soil pH and positively related to soil total N (R=0.66**). The proportion of NH4 +‐N in the mineral‐N varied among the non‐limed samples, but it was not related to soil pH. The same was true among the limed samples. This field study suggests that for at least a year after liming both the increase of mineral‐N, and variation in nitrification, may complicate crop behavior...

P. B. Hoyt

Papers

Ammonification and nitrification of N in acid soils at 26 field sites one year after liming