| According to the general detailed soil survey data of 1982 and the chemical analysis dataof soil nitrogen content which were from the 117 regional scale sampling points togetherwith 60 field scale sampling points of 2005, the spatial-temporal variation characteristicsof soil nitrogen at regional scale in Chengdu Plain were performed by the softwareArcGIS9.0, such as geostatistics. Also the influential factors of soil nitrogen werediscussed by routine statistical analysis, buffer analysis and overlay analysis, etc., atregional scale and field scale of 2005. Furthermore, the nitrogen equilibrium of differentcrop rotation types were evaluated by the data from the two test plots and other relatedinformation. The main results were as follows.At the regional scale, the content of soil nitrogen presented obvious spatial-temporalvariation characteristics. The results indicated that the content of soil total nitrogen (TN) was1.29±0.50 g kg-1 in 2005, lower than the content in 1982. The highest value regions (＞2.00gkg-1) of TN content were mainly distributed in the middle part of Chongzhou, and then reducedgradually towards both sides, presenting zonal shapes. The lowest value regions (＜0.85g kg-1)were located in Pixian-Wenjiang and the southwest of Longquanyi. Comparing with the TNcontent in 1982, the plain of central and western had decreased in varying degrees exceptChongzhou. As far as soil available nitrogen (AN) was concerned, the content was72.2±40.9mg kg-1, lower than the content in 1982. Taking Chongzhou as the center, the ANcontent first increased and then decreased towards its east and west, and graduallyincreased towards its south and north. Further more, the highest value regions (＞110mgkg-1) were mainly distributed in some parts of Pengzhou, Xinjin and Xindu, while the twolowest value regions (＜30mg kg-1) were mainly distributed in some part of Dayi-Qionglaiwhich was in the southwest edge zone of the plain. Comparing with the AN content in 1982,the decreased area accounting for 92.97％of the total.The influential factors of soil nitrogen were analyzed at both regional and field scale. At theregional scale, TN content of grey-brown alluvium from which soil derived was highlysignificantly higher than that of Chengdu clay and old alluvium among the four main parentmaterials of Quaternary System in Chengdu Plain, however there was no significant differencebetween the grey-brown alluvium and grey alluvium. Buffer analysis showed that, contrary tothat of Puyang-Pihe-Beihe River, soil TN and AN contents of alluvial deposit presented ahighly significant decreasing tendency as the expand of the buffer distance in Jiang'an-JinmaRiver. Moreover, TN content first increased and then decreased in Fuhe River, presentinghighly significant correlation, while AN content decreased before increasing, and then decreased. Among different land use types, TN content of the vegetable plot and paddy fieldwere both significantly higher than that of flower plot and dryland. From the statistical data ofthe nitrogen fertilizer application in recent years, the highest value regions of TN and ANcontents were both obviously higher than that in the lowest value regions. Furthermore, bothTN and AN contents were highly significantly increased as the increase of the distance in therural-urban fringe of 3.0km outside the Chengdu downtown. At the field scale, soil TN contentof alluvial deposit of Fuhe River was significantly higher than that of Jiang'an-Jinma Riverand Pihe River. From upper reach to lower reach of the rivers, TN content of alluvial deposit in0～20cm profile showed a decreasing tendency, but the content first increased and thendecreased in 20～40cm profile. In Jiang'an-Jinma River, alluvial deposit's TN content ofmiddle reach's side banks and lower reach's east bank increased before decreasing, while in thewest river bank of lower reach, TN content showed significant or highly significant increasingtendency. Also, in Pihe River, alluvial deposit's TN content of upper reaeh's north river bankincreased before decreasing, and then increased, but the variation was just the contrary in thesouth river bank. It was also seen that, TN content increased gradually and then decreased as awhole in different directions outside the downtown, except the south which presented anincreasing tendency.Nitrogen equilibrium evaluation of field test from 2003 to 2005 showed that the two testplots were both in surplus condition. Moreover, nitrogen rate and straw residue were theprincipal sources, while crop absorption and loss of N fertilizer were the principal outputpaths. Thus the profit and loss rates were +7.08％and +23.34％in wheat-rice and rape-ricerotation of sandy loam field, and +29.79％and +23.54％in wheat-rice rotation of loamysand field, respectively.
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