Abstract: A good understanding of the spatial variability of nitrogen in soil is important for the best management of soil nutrients. For this study, Yangzhong City in Jiangsu Province, China, was chosen as the study area. The data were taken from the soil of 99 plow layer samples collected from paddy fields in Yangzhong. The spatial variation characteristics of alkali-hydrolyzable nitrogen (AN) and what affected that variation at a county scale were studied using geostatistics analysis methods and buffer analysis. The results show that:(1) The average content of soil AN in the study area was 114.30 mg·kg^-1, which was at a rich level. (2) Semivariance analysis showed that the soil AN was moderately spatially auto-correlated. (3) Spatial interpolation results showed that the spatial distribution of soil AN in Yangzhong was generally in convex patches; high in the middle and low at sides of the areas. The high-value areas were located mainly in the middle three towns of the study area, and local extreme-value areas appeared near polluted industrial areas and breeding bases. (4) Analysis of the affecting factors indicated that urbanization, soil texture, industrial distribution, and farmer management had a great effect on the spatial distribution of soil AN in the study area. The soil was prone to accumulate alkali-hydrolyzable nitrogen within 1 km of the breeding cooperatives, and the industrial enterprises had significant effects on soil alkaline nitrogen in a range of 600 m (P<0.05).

Key words: soil alkali-hydrolyzable nitrogen, geostatistics, spatial heterogeneity, Yangzhong City