Changes In Soil Physical Properties And Its Influencing Factors After Sandy Land Afforestation With Pinus Sylvestris Var. Mongolica

Mongolian pine(Pinus sylvestris var.mongolica)is one of the major tree species for constructing protective plantations in “Three North”(Northwest,North and Northeast of China)areas.The objective of this study was to provide theoretical basis for promotion,regeneration and management of Mongolian pine plantations.Using a combination of field surveys and laboratory analysis,in the Zhanggutai area of Liaoning province,20 forest plantations of Pinus sylvestris var.mongolica in different growth stages(including young forests,mid-aged forests,mature forests,and over-mature forests)and 7 neighboring control grasslands were selected.In this paper,the changes in soil bulk density and fine soil and their influencing factors were studied in the 0–100 cm soil layer of different growth stages after sandy grassland afforestation with Pinus sylvestris var.mongolica.The results showed that after sandy grassland afforestation,the variance coefficient of soil bulk density was 78% in the 0–10 cm soil layer and the variance coefficient in other soil layers ranged from 1.08% to 4.35%.As the stand age increased,the magnitude of soil bulk density decreased gradually in 0–20 and 60–100 cm soil layers,however,the magnitude decreased firstly and then increased after 37 years in 20–60 cm soil layers,and the magnitude in over-mature forests was significantly higher than that in mature forests.Except for the middle-aged forest of Pinus sylvestris var.mongolica,the change of fine soil particle content(particle size<0.05 mm)in 0-10 cm layer increased gradually with the increase of stand age,and there was no significant difference in fine soil particle variation in 10-100 cm layer,while the fine soil particle variation in middle-aged forest was the smallest in all soil layers.The coarse soil particle content(particle size>0.05 mm)in the 60-80 cm soil layer;soil total nitrogen content in 0-10,20-40,and 60-80 cm soil layers;soil total phosphorus content in 0-10,20-60,and 80-100 cm soil layers;and soil total potassium content in 20-40 and 80-100 cm soil layers were significantly negatively correlated with soil bulk density,and the impact of soil total nitrogen and soil total phosphorus content on soil bulk density changes gradually decreased as the soil layer depth increased.However,soil moisture in the 10-20 cm soil layer and soil organic carbon content in the 20-40 cm soil layer were significantly positively correlated with soil bulk density.The change of soil fine particle content was positively correlated with soil water content in10-100 cm layer,and negatively correlated with soil total potassium in 0-10,20-40 cm and80-100 cm layers,and positively correlated with soil organic carbon in 20-60 cm layer.The estimates gradually decreased with the increase of soil depth.There were significant positive andnegative correlations with total phosphorus in 10-40 cm and 80-100 cm soil layers.To sum up,Pinus sylvestris var.mongolica plantation was established on sandy grassland can improve soil particle composition and soil quality.It is suggested that forestation measures such as enclosure and forbidden grazing should be adopted to increase litter accumulation under Pinus sylvestris var.mongolica forests,reduce wind erosion on the surface soil,improve moisture holding capacity,and promote nutrient cycling to accelerate soil formation process and improve soil texture.