Relationships among Mineralizable Soil Nitrogen, Soil Properties, and Climatic Indices

Soil N mineralization is an important N contributor to crop uptake; however, the soil and climatic controls on soil mineralizable N are poorly understood. Soil samples from 56 sites across Canada were used to determine the potential to predict the size of mineralizable N pools through simple soil properties and through simple climatic indices and the re_clim indices. Mineralizable N was determined using a 24-wk aerobic incubation at 25 degrees C. Potentially mineralizable N (N-0) 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 N-0 with soil organic N (SON) and sand explaining 40 and 34% of the variability, respectively. Particulate organic matter N (POM-N) and pH explained 18 and 25%, respectively, of the variability in Pool I. Simple climate normals were generally poor predictors of pool size except for potential evapotranspiration (PET), which predicted 24% of the variability in Pool I. The re_clim indices, normally applied to the activity of soil decomposers and applied here for the first time to explain soil mineralizable N pool size variability, performed better than simple climate indices and explained up to 26% of the variation in N-0. By including soil and climatic parameters in a multiple regression model, it was possible to explain about 63 and 40% of the variability in N-0 and Pool I, respectively, across a wide range of arable soils in Canada.