Baijiang Soil Fertility Changes under Different Land Use Type and Reclamation Years

Baijiang soil of northeast China is one of the main low-yielding soils.It has about 15cm organic matter layer.Below it is the baijiang layer.Taking barren as the control.We studied the fertility changes of Baijiang soil under three land use types(forest land,dry land and paddy field),different reclamation periods(30,40,50years) of dry land with soybean-maize rotation and paddy field in Heilongjiang Province.The results were as follows:Marked changes of acid has taken place on topsoil(0-20cm) of Baijiang soil under different land use types.There was no significant difference in forest soil compared with barren,the pH of barrenforest landpaddy fielddry land.The topsoil pH was lower than that of the subsoil(20-40cm).Compared with barren land,in dry land and paddy field,the organic matter and the total nitrogen declined sharply by 44.17%,44.74%,and 19.92%,18.42%,but increased in the subsoil.Total phosphorus increased slightly by 2.1%,2.8% and 4.1% in forest land,dry land and paddy field,respectively.There was no significant change of total potassium in three soils.The available nitrogen reached the peak in top soil of dry land,so did available phosphorus in paddy field.Compared with barren,and the available potassium in dry land and paddy field declined by 37.8% and 60.8%,respectively.Soil pH in the dry land soil declined by1.0 to 1.1 as reclamation year increasing from 30 to 50 years.After cultivated 30-50 years,in 0~20cm soil the organic matter and total nitrogen decreased by 42.2%-43.8% and 12.0-31.2% in top soil,total phosphorus increased by 1.1%~ 5.5% and the total potassium had a slight change.Available nitrogen and phosphorus increased by 12.3%-42.2% and 77%-195.35%,but available potassium decreased by 38.8%-49.1% in topsoil compared with barren,respectively.With the increasing years of reclamation,the decrease amplitude of organic matter,total nitrogen increased,the increase rate of available N reduced,rate of organic P rose.In 20-40cm soil the organic matter increased.After the Baijiang soil being reclaimed as paddy field for 30-50 years,soil pH decreased by 0.62-0.84unit,soil organic matter decreased by33.16%-59.92%,available nitrogen and available potassium decreased by 24.25%-78.1% and 49.95%-60.7%,and available phosphorus increased by 56.82-281.9%,compared with barren respectively.And the decrease amplitude of organic matter,available K increased,the decrease rate of available N reduced,rate of available P rose with the increasing years of reclamation.In 20-40cm soil the organic matter and available nitrogen increased in the subsoil.