Relationships Among Soil Mineralizable Nitrogen, Soil Properties and Climatic Indices.

Soil nitrogen (N) mineralization is an important N contributor to crop uptake, however the soil and climatic controls on soil mineralizable N are poorly understood. Samples from 58 sites across Canada were used to evaluate the degree to which variation in size of soil mineralizable N pools can be explained through simple soil properties and climatic indices. Mineralizable N was determined using a 24 wk aerobic incubation at 25 ¢ªC. Potentially mineralizable N (N₀) was estimated by curve-fitting using N mineralized from 2 to 24 wk and Pool I, a labile mineralizable N pool, was determined as the N mineralized in the first 2-wk period. Soil properties were relatively effective predictors of mineralizable N, with sand and soil organic N both explaining 34% of the variability in N₀. Particulate organic matter N and particulate organic matter carbon explained 18 and 14% of the variability in Pool I. Simple climate normals such as mean annual temperature and total annual precipitation were generally poor predictors for N_0, explaining at best 11% of its variability, whereas potential evapotranspiration predicted 23% of the variability in Pool I. The use of re_clim indices, which combine information on soil moisture and soil temperature, improved the prediction capacity of climatic data compared with simple climate normals alone, and explained up to 31% of the variability for N₀. Including soil and climatic parameters in a multiple regression model explained about two-third and one-third of the variability in N₀ and Pool I, respectively. This study demonstrated that a large proportion of the variation in N₀, which is relatively stable over time, can be explained using simple soil properties in combination with re_clim indices whereas the labile Pool I, which is sensitive to recent management, is more difficult to predict.