Spatial distribution characteristic and its influential factors of soil nitrogen in Chengdu Plain

Nitrogen is a vital nutrient to enhance plant growth .Nevertheless, when nitrogen fertilizer application exceeds the plant demand , nitrogen can leach to ground water and contaminate environment .Chengdu Plain , as one of the agri- cultural bases in China , is confronted with a series of environmental issues which are caused by extensive or irrational use of nitrogen fertilizer .According to the data of soil nitrogen content collected from 117 random grid and hierarchical sam- pling points in topsoil in 2002 , the spatial distribution characteristics and their influential factors of soil nitrogen in Chengdu Plain were analyzed using the software ArcGIS 9.0 with geostatistics, buffer analysis and overlay analysis .The results indicated that the content of soil total nitrogen (TN)and available nitrogen (AN)were 1.29 ±0.50 g/kg and 72.2 ±40.9 mg/kg , respectively .The regions with high TN content (>2.00 g/kg)were mainly distributed in the mid- dle part of Chongzhou , and declined gradually towards to the periphery , presenting a zonal shape .The regions with low TN (<0.85 g/kg)were located in Pixian —Wenjiang and the southwest of Longquanyi .Taking Chongzhou as the cen- ter , the AN content first increased and then decreased towards east and west , and gradually increased towards south and north .Further more , the regions with high TN (>110 mg/kg)were mainly distributed in some parts of Pengzhou , Xin- 植物营养与肥料学报 2007, 13(1):1-7 Plant Nutrition and Fertilizer Science jin and Xindu , while the two lowest value regions (<30 mg/kg)were distributed in the southeast of Chongzhou and some part of Dayi —Qionglai which was near the southwest edge zone of the plain .The analysis of influential factors showed that , regarding four main parent materials of Quaternary System in Chengdu Plain , TN content of grey-brown allu- vium was highly significantly higher than that of Chengdu clay and old alluvium , whereas there was no significant differ- ence observed between the grey-brown alluvium and grey alluvium;TN content of the vegetable and paddy field were both significantly higher than that of flower land and dryland ;Based on statistical data of the nitrogen fertilizer application lately , the N application rate at the regions with high TN and AN contents were obviously higher than that region with low TN and AN .Buffer analysis showed that :at the rural-urban fringe of 3.0 km outside the Chengdu downtown , both TN and AN contents were highly significantly increased with the distance .