Evolution pattern of soil total N content and its distribution in typical hilly red soil regions

Taking Taoyuan city as research target area,the evolution pattern of soil N content and its distribution during the last 13 years(1979—2003) under different land uses in hilly red soil regions was investigated.The results showed as follows: 1) The content of total N of paddy soil in typical area in 2003 was 1.94±0.02 g/kg.This represented a 4.9% increase compared to that in 1990.The main distribution range increased from 1.25—2.00 g/kg(distribution frequency was 59.1%,The same below) in 1990 to 1.50—2.25 g/kg(77.1%)in 2003,showing a tendency from the quasi normal distribution to right excursion distribution on the diagram of curves.2) The content of total N of dry land soil in 2003 was 1.57±0.14 g/kg,which represented a 18.0% increase compared to that in 1990.Main distribution range was 0.75—1.50 g/kg(58.2%—58.8%)both in 1990 and 2003;however,the distribution frequency ranged in 1.50—2.00 g/kg in 2003 was 33.6%,which was 0.9% higher(increased by 60.8%) than that in 1990.The distribution curve shifted from left excursion distribution to normal distribution.3) The content of total N in orchard soil(orange in slope land) was 1.15±0.02 g/kg in 2003,which represented a 9.5% increase compared to that in 1990. Main distribution range in 1990 and 2003 was similarly being 0.75—1.50 g/kg,but the distribution frequency in this range area in 2003 was 88.0%,higher than that in 1990 being 77.8%,the evolution trend of the content of N in orchard soil was similar with that in paddy soil.4)The average total N content of farmland in investigated area was 1.58±0.03 g/kg in 2003,compared to that in 1990,increased by 3.3%.This indicated that the current fertilization and management increased the content of total N in farmland soils steadily in hilly red soil regions.