Abstract: By using geostatistics and GIS, this paper studied the spatial distribution of soil nitrogen in the croplands in Shuangliu County of Sichuan Province, China, and analyzed the related affecting factors. There was a moderate spatial correlation between the contents of total nitrogen (TN) and available nitrogen (AN) in the cropland soils, and the spatial correlation distance was 15480 m for TN and 26980 m for AN. The regions with higher soil TN content were mainly in the north of the County, i.e, Jiujiang and Xinxing towns, while those with lower soil TN content were mainly in the southeast of the County, i.e., Hejiang and Sanxing towns. The soil AN content decreased obviously from north to south. The TN and AN contents in the soils developed from grey alluvium were significantly higher than those developed from purplish rock saprolith and old alluvium. Paddy soil had significantly higher contents of TN and AN than yellow soil and purple soil. Terrain condition affected the soil TN and AN contents to different degree, and hilly region had the lowest contents of soil TN and AN. Paddy fields had significantly higher contents of soil TN and AN, compared with dryland and orchards; and the regions with higher soil nitrogen content were applied with obviously higher amount of Nfertilizer, compared to the regions with lower soil nitrogen content.

Key words: nitrogen, spatial distribution, affecting factor, geostatistics, summer maize, sowing depth, seedling trait, root characteristics, grain yield.