三江平原不同土地利用方式下土壤磷形态的变化

利用Hedley磷(P)分级方法,比较研究三江平原不同土地利用方式（天然湿地、旱田、水田、弃耕地、人工林地）下土壤P形态变化.结果表明,不同土地利用方式下土壤总磷（TP）含量表现为：湿地>林地>旱田>弃耕地>水田.农田土壤的无机磷（TP_i）占TP比重显著高于湿地,有机磷比重则为湿地高于农田,且水田土壤有机磷（TP_o）比重最小,弃耕地和林地之间差别很小.不同土地利用方式土壤活性无机磷含量差异较小,Resin-P含量约为32～36.3 mg·kg^-1,NaHCO₃-P_i含量为33.77～50.42 mg·kg^-1;农田土壤NaOH-P_i和C.HCl-P_i含量高于湿地土壤,特别是水田中NaOH-P_i达152.4 mg·kg^-1,湿地土壤中D.HCl-P_i含量高于农田达84.3 mg·kg^-1,弃耕地和林地介于二者之间,表明弃耕后土壤P的恢复有向天然湿地的状况发展的趋势.开垦使湿地所有形态有机磷含量和比重都大幅下降,其稳定态有机磷C.HCl-P_o下降幅度最大,其在旱田和水田土壤中含量分别仅为湿地中的25.96%和19.26%;弃耕地有机磷含量比重均有增加,但是速度十分缓慢,湿地开垦后土壤P的恢复需要很长时间.不同土地利用方式下土壤P形态存在显著的差异.

Phosphorus Fractions Under Different Land Uses in Sanjiang Plain

Five land-uses type (soybean-filed, rice-field, abandoned cultivation, artificial forest, natural wetland) were obtained before planting and soil P fractions were determined by a modified Hedley fraction method. The result showed that the content of total P (TP) in natural wetland was higher than other soil. While the proportion of total inorganic P (TPi) in TP of farm land soil was higher than that of wetland. Adversely, the proportion of total organic P (TPo) was higher in wetland and least in rice-field. There was no obvious difference between that of abandoned field and artificial forest. The values of labile inorganic phosphorus (labile Pi) under different land-uses were similar. The contents of Resin-P and NaHCO3-Pi varied at a range of 32-36.3 mg x kg(-1) and 33.77-50.42 mg x kg(-1), respectively. The contents of NaOH-Pi and C.HCl-Pi in farmland were higher than those of wetland, especially in rice-field which was 152.4 mg x kg(-1). But for D.HCl-Pi, the content was higher in wetland with the value of 84.3 mg x kg(-1), and the contents of NaOH-Pi, C. HCl-Pi and D.HCl-Pi in abandoned field and artificial forest were in the middle of the above two land use patterns, which indicated that the restoration of soil P in abandoned farmland tended to approach the level of natural wetland. The value and percentage of Po was decreased greatly with the reclamation of wetland, and the decrease of C. HCl-Po was the most significant in all forms of organic P, and its values in soybean-filed and rice-field were only 25.96% and 19.26% of that in wetland. As the time went by the content of Po in abandoned arable land increased with very slow speed, which indicated that the restoration of wetland after reclamation would need a long time. The distribution of soil P in different P fractions has significant difference for the land-use change in Sanjiang plain.