Study On The Characteristic Of Phosphorus Fractions Within Soil Aggregates In Soil Returned From Farmland To Tea

Soil aggregate is considered to be the basic unit of soil structure,which is the supporter of soil nutrient stability and protection Phosphorus is one of the important indexes to evaluate soil fertility.Phosphorus fractions can be transformed into each other.Study on the dynamics of soil phosphorus fractions in soil of returning from abandoned land to tea of hilly region in the Western Sichuan so as to understand the change and effect evaluation during process of ecological restoration is of great importance.Field investigation and laboratory analysis were combined to investigate the phosphorus fraction characteristics and phosphorus storages in soil aggreggates,which were located in Zhongfeng Township,Mingshan County,Ya'an,Sichuan Province,with different ages(2-3,9-10 and 16-17 years old),in response to the returning of farmland to tea,with the control of nearby abandoned land.Focusing on soil aggregates,this research investigated the characteristics of soil phosphorus fraction in response to the returning of farmland to tea,and provided theoretical basis to evaluate the process of the evolution of soil phosphorus fertility and the comprehensive effect of the returning of abandoned land to tea.The main results are as follows:(1)Under the condition of dry sieving,>2 mm particle size was the dominant aggregate..size for all sites,followed by 5-2 mm and<0.25 mm particle size.The conternt of>2 mm particle size accounted for more than 69%of soil aggregates,while the particle size of<0.25 mm accounted for 0.80%-5.46%of soil aggregates.Under the condition of wet sieving,0.5-0.25 mm particle size were the dominant aggregate size in abandoned land,2-3 years of returning from farmland to tea plantations(RT2-3)and 9-10 years of returning from farmland to tea plantations(RT9-10),accounting for 26.55%-33.34%.The particle size of 2-1mm were the least dominant,accounting for 8.74%-9.92%.For the soil of returning from fermland to tea plantations forl6-17 years(RT16-17),the particle sizes of 0.5-0.25 mm,1-0.5 mm and>5 mm were the dominant aggregate size,and the content of<0.25 mm particle size was the least dominant.In terms of micro-aggregates,250-50 ?m particle size was the dominant aggregate size for all sites,with content of 69.46%-76.11%.The<1 mm particle size was the least dominant,accounting for 2.09%-2.86%.Compared with the abandoned land,the content of non-water-stable agregates with>5 mm particle size,>2 mm particle size in soil of RT9-10 and>0.5 mm particle size in soil of RT16-17 showed an increase trend.The non-water-stable aggregates of>5 mm particle size,water stable aggregates of>1 mm particle size and 250-50 ?m particle size increased with the increasing ages.(2)For the non-water-stable aggregates,the Fe-P,Ca-P and moderate labile organic phosphorus mainly distributed in<0.25 mm particle size,which were 91.40-278.77,12.12-56.95 and 97.80-313.29 mg/kg.Al-P and labile organic phosphorus were mainly distributed in soil aggregates of<1 mm particle size,which were significantly higher than other particle size aggregates.O-P in abandoned land mainly existed in soil aggregates of>1 mm and<0.25 mm particle size,while the O-P was mainly existed in<2 mm partcice size of soil returned from farmland to tea.The moderate resistant organic phosphorus distributed evenly in the abandoned land,and mainly distributed in 5-2 mm and<0.5 mm particle size of soil returned from frmland to tea.The highest content of resistant organic phosphorus,which was 22.84-32.40 mg/kg,was noticed in soil aggregates of>2 mm particle size.The content of O-P and moderate resistant organic phosphorus decreased in soil returned from farmland to tea compared with abandoned land.The O-P,Ca-P,moderate labile organic phosphorus and moderate resistant organic phosphorus in each particle size decreased with the increasing ages,while the content of Al-P and Fe-P increased with the increasing ages.The content of each phosphorus fraction in 20-40 soil layer was lower than that in 0-20 cm soil layer.The distribution law of the two soil layers is similar.(3)For water-stable aggregates,the Al-P was 4.26-154.65 mg/kg and mainly distributed in<1 mm particle size.Labile organic phosphorus,moderate resistant organic phosphorus were mainly distributed in<0.5 mm particle size,which were 4.69-11.64 mg/kg,3.16-57.50 mg/kg.Fe-P,resistant organic phosphorus were mainly distributed in>5 mm and 5-2 mm particle size.Moderate labile organic phosphorus was 102.55-239.12 mg/kg and mainly distributed in>5 mm particle size.Besides,O-P distributed more uniformly in soil.The distribution of the two soil layers is simlar.The content of Al-P,Fe-P and moderate labile organic phosphorus increased,while the content of O-P and moderate resistant organic phosphorus decreased,compared to the abandoned land.The content of Al-P,Fe-P and moderate labile organic phosphorus increased,while the content of O-P and moderate resistant organic phosphorus in soil of RT16-17 decreased with the increasing ages.The content of each phosphorus fraction in 20-40 soil layer was lower than that in 0-20 cm soil layer.(4)For the micro-aggregates,the content of Al-P,Fe-P,labile organic phosphorus,moderate labile organic phosphorus and resistant organic phosphorus mainly distributed in<1 ?m.The O-P was 145.06-583.42 mg/kg and mainly distributed in 5-1 ?m and<1?m The Ca-P was 45.66-107.86 mg/kg and mainly distributed in 250-50 ?m and<1?m The distribution of moderate resistant organic phosphorus in different particle sizes is much more uniform.The Al-P,Fe-P and moderate labile organic phosphorus in soil of RT9-10 and RT16-17 increased,while the O-P and moderate resistant organic phosphorus in soil of RT16-17 decreased compared to the abandoned land.The Al-P,Fe-P,Ca-P and moderate labile organic phosphorus increased,while the O-P and moderate resistant organic phosphorus decreased with the increasing ages.The content of each phosphorus fraction in 20-40 soil layer was lower than that in 0-20 cm soil layer.The distribution law of the two soil layers is similar.(5)The greatest storages of all phosphorus fractions in non-water-stable aggregates and water-stable aggregates were observed in>5 mm particle size and 0.5-0.25 mm particle size,respectively.The greatest phosphorus fraction storage in soil micro-aggregates was observed in particle size of 250-50?m.All phosphorus fractions both in non-water-stable aggregates and water-stable aggregates showed the greatest storages in soil of RT16-17 with>5 mm particle size.These results indicated that the storage characteristics of phosphorus fractions were consistent with the distribution of soil aggregates.The storages of each phosphorus fraction in 20-40 soil layer was lower than that in 0-20 cm soil layer.The distribution law of the two soil layers is similar.