| This study based on different plantation age and different density of poplar farmland shelter belt in typical black soil area and the derelict land for comparison.We studied the soil physical and chemical properties,including aggregate characteristics and stoichiometric ratio.The soil physical and chemical properties of the poplar farmland shelter belt were evaluated comprehensively.Results indicated that:(1)The water content of abandoned farmland was higher than the water content of the soil under the forest belt of poplar farmland.Poplar farmland shelter belt increased soil moisture consumption,reduces the soil moisture content.The variation of soil water content under the poplar farmland shelter belt was greater than that of the abandoned land.The field moisture capacity and saturated moisture capacity of abandoned farmland were significantly higher than that of each forest belt.The soil saturated water capacity increases first and then increases with the increase of forest age or the density of the forest belt.The soil saturated water content increases first and then decreases with the increase of soil layer and the field moisture capacity decreased,there was no significant difference between different depths.(2)Soil bulk density of soil in abandoned farmland was lower than that of poplar farmland shelterbelt,with the increase of soil depth,the bulk density of abandoned farmland increased significantly,each forest belt increased first and then increased with the increase of depth.The soil bulk density of different density poplar farmland shelterbelts increased with the increase of density.The soil bulk density of Farmland Shelterbelts of different forest age in 0?10cm and 40?60cm decreased with the increase of forest age,0?20cm and 20?40cm increase first and then decrease.(3)Soil Dry-aggregates to aggregate>0.25 mm,accounting for more than 85%,>0.25 mm water stable aggregate was over 70%,with the increase of the density of the forest,it increases first and then decreases.After wet screening,the number of aggregates with larger particle size decreases and the number of aggregates with smaller size increases.All kinds of surface soil aggregate destruction was the lowest,abandoned soil aggregate destruction degree was higher than that of the Farmland Shelterbelts,with the deepening of the soil layer,the PAD of the abandoned farmland increased,and the PAD of the deep soil in the shelterbelt was lower than the abandoned land.Poplar farmland shelterbelts reduce the damage degree of aggregate in deep soil.(4)The average weight diameter(MWD)and geometric mean diameter(GMD)of soil aggregates in poplar farmland shelterbelt with different stand ages and densities were significantly different(P<0.05)less than those in abandoned farmland.Abandoned farmland non water stable soil aggregate fractal dimension is minimum.The soil wet sifting MWD and GMD increased with the increase of forest age in different forest age and different density poplar farmland shelterbelts,there was significant difference between different forest age(P<0.05).With the decrease of the density of the forest belt,there was a significant difference between the different density forest belts(P<0.05).The average weight diameter and geometric mean diameter of surface soil aggregates are the highest.With the increase of depth,the soil aggregates MWD and GMD decreased,and the differences between different depths were significant(p<0.05).The fractal dimension of water stable aggregate increases with the increase of forest age in 0?20cm,20?60cm increases first and then decreases with the increase of forest age,while 0?10 cm,10?20 cm and 40?60cm decrease with the decrease of density,and the 20?40 cm increases with the decrease of density.(5)The soil total carbon,total nitrogen,total phosphorus,hydrolysable nitrogen,and available phosphorus content decreased with the depth of soil layer with different density and different forest age,there was significant difference between different depths(P<0.05)The total carbon content of each forest belt was higher than that of the abandoned land,and the total carbon content increased with the increase of the forest belt density,and the difference between different densities was significant(P<0.05).The total carbon content in 0?10 and 10?20 cm decreased with the increase of stand age,20-40 and 40?60cm increased and there was a significant difference among different ages(P<0.05).The total nitrogen of soil decreased first and then increased with the increase of forest age.It decreased and then increased with the increase of forest belt density,and the difference between different densities was significant(P<0.05).The total phosphorus content of the soil generally increases with age,the total phosphorus content of 0?10cm decreased with the increasing of forest density,10?60cm decreases first and then increases,the difference between different density significantly(P<0.05).The change range of soil carbon and nitrogen ratio was from 6.7?11.95,most of which is lower than the average level of China.The change range of carbon and phosphorus ratio from 31.08?75.7,except the surface layer,was lower than the average level of China.The ratio of carbon and phosphorus to the abandoned land was the lowest,and the highest ratio of carbon and phosphorus was the high density(HD)forest belt.The range of nitrogen and phosphorus ratio varies from 4.43?7.07 to the average level of China.The content of hydrolyzed nitrogen decreased with the increase of density,in 0?10cm and 40?60cm increased first and then decreased with the increase of forest age,in 10?40cm increased with the increase of forest age.The content of effective phosphorus decreased and then increased with the increase of forest age,overall downward trend.The contents of available phosphorus in 0?10cm and 40?60cm decreased with increasing density.10?40cm decreased first and then increased with increasing density.There was a significant difference between different densities(P<0.05).(6)The resule of comprehensive assessment of soil physical and chemical properties show that the KY score was-0.385,LD score was 0.1675,MA,MD score was-0.1025,HD score was 0.499,LA was-0.115,HA score was-0.065.The evaluation score of soil physical and chemical properties under forest belt was obviously better than that of abandoned land.The comprehensive evaluation of soil physical and chemical properties between different forest ages from high to low,HA(36a)>MA(31a)>LA(26a)>KY.HD(1.5 X 1)>LD(3 X 1.5)>MD(2 X1.5)>KY between different density shelterbelts.Long term planting of poplar farmland shelterbelts would not have a negative impact on the physical and chemical properties of soil,but appropriate density should be chosen. |
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