| Unscientific unscientific farming methods and excessive reclamation of slope farmland,the black soil layer in Northeast China becomes thinner and soil erosion is serious.In order to curb soil degradation and prevent the aggravation of soil erosion,China began the project of returning farmland to forest in 1999.In order to study the effect of returning farmland to forest project on soil physical and chemical properties and litter water holding capacity in the black soil area of northeast China,the soil and litter under six different returning farmland to forest years of 1 year,5 years,10 years,15 years,20 years and 25 years in Xilaoyeling Forest Farm were taken as the research objects,and the slope farmland(SF)and natural secondary forest(NF)in the same area were taken as the control plots.The physical and chemical properties,litter accumulation and water holding capacity of the two soil layers(0-20 cm,20-40 cm)under the forest after returning farmland to forest were measured.The main results were as follows :(1)The p H values of the two soil layers in 25 a increased from 5.46 and 5.30 to5.94 and 6.43,respectively,which were 5.18 % and 21.32 % higher than those in 1a.Conversion of cropland to forest could improve acidified soil.The contents of soil organic matter,total nitrogen and total phosphorus in the two soil layers showed a trend of increasing first and then decreasing,and tending to the content of natural secondary forest land.The content of topsoil was higher than that of subsurface,which was consistent with the change trend of organic matter.The soil total potassium content was mainly affected by soil texture and soil forming conditions.The highest content of 20 a in the two soil layers was 6.80 g / kg and 6.35 g / kg,respectively.The content changes of topsoil and subsurface were not significant.The content of soil alkali-hydrolyzable nitrogen and available potassium increased first and then decreased,and the content of topsoil was higher than that of subsurface.The content of natural secondary forest in both soil layers was the highest,which was 548.68 mg /kg,12.11 mg / kg and 356.18 mg / kg,7.28 mg / kg,respectively.The content of available phosphorus in the surface layer showed a trend of first increasing,then decreasing and then increasing,with the highest content of 21.24 mg / kg in10 a.Subsurface showed a trend of increasing first and then decreasing,with the highest content of 8.79 mg / kg in 15 a.The implementation of the Grain for Green Project has a significant positive impact on the accumulation of soil organic matter,total elements and available nutrients in the black soil area of Northeast China.(2)MWD,GMD,MWSSA and D of 25 years were 1.79,1.25,0.69 and 0.91 times of 1year,respectively,indicating that soil physical properties were significantly improved under different years of returning farmland to forest.The aggregate size of > 2 mm in25 a was 1.44 times that in 1 a,and the implementation of the Grain for Green Project could promote the composition of large-scale water-stable aggregates in soil under forest.The implementation of the Grain for Green Project optimized soil structure and increased soil aggregate stability.At the same time,the fractal dimension D of soil aggregates in the Grain for Green Project was highly sensitive to soil organic matter content.(3)The litter accumulation was the highest in 25 years(20.59 t / ha).The variation range of maximum water holding capacity was 4.90 – 85.71 t / ha,the maximum water holding capacity in 25 years,the variation range of maximum water holding rate was 216.47 % – 501.54 %,and the maximum value in 10 years.The variation range of effective storage capacity is 2.55 – 71.90 t / ha,and 10 a is the maximum.With the increase of years of returning farmland,the accumulation and water characteristics of forest litter gradually develop in a good direction,which can effectively reduce runoff generation and maintain soil and water. |
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