Differences of soil total phosphorus and its 9 fractions between poplar shelterbelts and adjacent farmlands in 14 locations of Northeast China Plain

The difference of soil phosphorus (P) is one of the guidelines for soil nutrient management of farmland shelterbelt forest.In this paper, total 84 soil samples were collected from 14 sites(Fuyu, Lanling, Mingshui, Zhaozhou, Songzhan, Dumeng, Chifeng, Tongliao, Naiman, Siping, Changling, Baicheng, Dehui and Tailai counties) in Northeast China Plain at the depth of 0~40 cm soil layer.The Hedley method modified by Tiessen and Sui was used to determine 9 P components in soil, and the paired T test was used to study the differences of total P and P components between farmland and poplar shelterbelt soil.(1) Soil total P in 14 sites ranged from 122 to 594 mg·kg^-1, with an overall average at 266 mg·kg^-1.In all 9 fractions, the peak was dilute hydrochloric acid inorganic phosphorus (HCl-Pi), contributing 52.7% of the total soil P (TP), followed by sodium hydroxide organophosphorus (NaOH-Po) (14.8%) and concentrated organophosphorus hydrochloride (conc.HCl-Po) (11.2%).Closed state of phosphorus storage (Re-P), concentrated hydrochloric acid inorganic phosphorus (conc.HCl-Pi) and sodium hydroxide inorganic phosphorus (NaOH-Pi) took a proportion of soil total P at 5%~6%, while water soluble phosphorus (H₂O-Pi), sodium bicarbonate inorganic phosphorus (NaHCO₃-Pi), sodium bicarbonate organophosphorus (NaHCO₃-Po) took a proportion ranged from 0.5% to 3%.(2) On average across the 14 sites, the soil total P content in poplar shelterbelt was 20.9% lower than that in the neighboring farmland.In the nine P components, the NaHCO₃-Pi in poplar forest decreased 30.9% compared with the farmland; The proportion of NaOH-Pi to total soil P in 11 out of the 14 sites was lower in poplar forests compared with farmland, and the average in poplar was significantly lower.(3) The HCl-Pi, NaOH-Po, conc.HCl-Po fractions were also the main drivers for soil total P reduction in poplar forests, and the HCl-Pi contributed 54.1% of the total reduction.Our data manifested that poplar afforestation induced soil total P reduction with different reduction among the nine fractions.Soil total P and different fractions varied at over 10-fold in different locations, while only < 2-fold variations were found between farmlands and poplar forests.Our finding highlighted that large area soil P variations from land uses should fully exclude inter-site variations, and our results provide basic data for the evaluation of soil P changes in Northeast China Plain.