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The Spatial Distribution of Soil Nutrient Availability

Yates, T.T. 2001. M.Sc. Thesis. Dept. Soil Science, University of Saskatchewan, Saskatoon, SK


The objective of this study was to examine the relationship between selected measurements of soil N availability and wheat grain yield along a single transect in a typical Saskatchewan farm field using both biological and chemical methods. In addition, these relationships were examined spatially using landform element classification and geostatistics. Soil N availability was estimated by aerobic incubation, ion exchange membranes, determination of soil inorganic N (NO3-+ NH4+ ), hot KCl extractable N, and N hydrolyzed from organic matter. Soil measurements also included total soil N and C, soil organic C, spring soil moisture and permanent wilting percentage. Wheat grain yields were collected at each sample location. With the exception of inorganic N, soil N availability was related to landscape position in that it increased from upper to lower slope positions. Soil properties with the strongest relationship to landform were organic N hydrolysable, spring soil moisture content, total C, and grain yield, all of which showed significant differences between shoulder and foot-slope positions. Total soil N, soil organic C, and N mineralized over the 16 wk incubation did not show as strong of a landscape relationship. Organic N hydrolysable showed the strongest correlation with grain yield (rs = 0.492, significant to P=0.01) Soil inorganic N was unrelated to landscape position and to grain yield (rs = -0.114, non-significant). Grain yield, organic N hydrolysable, and spring soil moisture were well correlated with the N mineralization that occurred during the first 2 weeks of a long term incubation. This suggests that the rapidly hydrolysable organic N pool may be the most significant source of available N in terms of setting spring wheat yield potential.Geostatistics indicated that organic N hydrolysable, spring soil moisture, total soil C,and wheat grain yield had a geostatistical range between 40 and 60 m. Soil properties with weaker landform distributions had a similar geostatistical range to each other but were much lower, in the order of 5 to 20 metres.