Nitrogen mineralization in Canadian agricultural soils: a review of methods for quantifying soil nitrogen mineralization potential and estimating growing season nitrogen mineralization

The ability of soils to provide a portion of the nitrogen (N) required by crops through the mineralization of organic matter is of great economic and environmental importance. Knowledge of the N available to crops from all sources is essential to improve fertilizer use efficiency and minimize the adverse effects of N losses on the environment. However, soil net N mineralization potential is seldom measured in routine soil testing procedures. This paper reviews the current methods of measuring net N mineralization provided by laboratories in Canada and discusses potential techniques that could be adopted for routine laboratory use. Soil testing services for measuring soil net N mineralization are limited in Canada, with some provinces lacking any method at all. Most of the currently available methods are biological. While chemical extraction methods may be faster and more cost-effective, only hot water-extractable N is offered as a routine chemical test. Biological methods are generally considered more reliable; however, other chemical extraction methods, such as UV absorbance of NaOH extract at 260 nm, calcium hypochlorite (Ca(ClO) 2 ), and direct-steam distillation with sodium hydroxide, show promise for routine testing due to their simplicity, and relatively strong correlation with N mineralization potential. Near-infrared reflectance spectroscopy is also a promising technique that could be adopted to measure N mineralization potential. This review demonstrates that these tests account for nearly 50% of the variability in plant N uptake or N 0 measured through incubation. While not perfect, they are “good enough” predictors of N mineralization to allow routine quantification of soil N mineralization and improve fertilizer N recommendations.