| In this paper,32-year-old mixed forests in Jianlagou forest cultivation experimental station of Northeast Forestry University were selected,including Picea koraiensis × Fraxinus mandshurica mixed forest,Pinus koraiensis × Fraxinus mandshurica mixed forest,Larix olgensis × Fraxinus mandshurica mixed forest,Fraxinus mandshurica pure forest,the 21-year-old Fraxinus mandshurica plantations near Jinde village of Maoershan Experimental Forest Farm were selected with four planting densities of 2000 plants·hm-2,2500 plants·hm-2,4400 plants·hm-2 and 10000 plants·hm-2.The contents of K in understory soil were measured,meanwhile,the conversion rate of non-exchangeable K and the stratification ratio of K content are calculated,to analyze the effects of tree species composition and stand density on soil K of Fraxinus mandshurica plantation.The results showed that:(1)The contents of water-soluble potassium,non-special adsorptive potassium,special adsorptive potassium,non-exchangeable potassium,available potassium and effective potassium in soil of Fraxinus mandshurica plantation and Fraxinus mandshurica natural forest were 6.18 mg·kg-1?129.31 mg·kg-1,3.54 mg·kg-1?164.54 mg.kg-1,17.36 mg·kg-1?268.66 mg·kg-1,300.38 mg·kg-1?781.95 mg.kg-1,28.29 mg·kg-1?534.66 mg.kg-1 and 74.17 mg·kg-1?571.78 mg·kg-1.The potassium content of Fraxinus mandshurica plantation was significantly lower than that of Fraxinus mandshurica natural forest.The potassium content of mixed forest of Larix olgensis × Fraxinus mandshurica was the highest,and that of mixed forest of Picea koraiensis × Fraxinus mandshurica was the lowest.The content of potassium in pure Fraxinus mandshurica stands was significantly higher than that in mixed stands of Pinus koraiensis × Fraxinus mandshurica and Picea koraiensis × Fraxinus mandshurica.(2)The contents of water-soluble potassium,non-special adsorptive potassium,special adsorptive potassium,non-exchangeable potassium,available potassium and effective potassium in soil of Fraxinus mandshurica plantation with 4 stand densities were 3.20 mg.kg-1?84.97 mg·kg-1,11.17 mg·kg-1?112.95 mg·kg-1,15.36 mg·kg-1?120.27 mg·kg-1,304.51 mg·kg-1?592.86 mg·kg-1,12.98 g·kg-1?14.11 g·kg-1,38.02 mg·kg-1?291.75 mg·kg-1 and 65.63 mg·kg-1?300.10 mg·kg-1.The potassium contents of the four plantations were arranged in the order of density ?,density ?,density ? and density I from high to low.(3)The contents of non-exchangeable K in different soil layers of four species composition and four stand densities of Fraxinus mandshurica plantation were 300.38 mg·kg-1?589.32 mg·kg-1 and 304.51 mg·kg-1?592.86 mg·kg-1,respectively,both in the mid-range.But the contents of non-exchangeable K in some forest stand and some soil layers were close to the critical value of K deficiency of 300 mg·kg-1.(4)The non-exchangeable K conversion amount and conversion rate in 0?30 cm soil layers of four species composition of Fraxinus mandshurica plantation were the highest in Picea koraiensis × Fraxinus mandshurica mixed forest and the lowest in Larix olgensis ×Fraxinus mandshurica mixed forest.The non-exchangeable K conversion amount and conversion rate of Fraxinus inandshurica plantation in 0?30 cm soil layer of four stand densities were generally highest in density I and lowest in density III.(5)The soil available K of Fraxinus mandshurica plantation in the study area showed obvious surface aggregation and stratification,and the available form K SR1 and SR2 showed different significant differences among the forest stand.In addition to the mixed forest of Larix olgensis × Fraxinus mandshurica,K deficiency occurred in 10?30 cm soil layer in the other three species composition and the four stand densities.Based on the characteristics of soil K in Fraxinus mandshurica plantations with different tree species composition and different stand densities,and combined with the tree growth status,fully considering the diagnosis results of the contents of available K and effective K as well as the conversion status of non-exchangeable K,timely and effectively applying potash fertilizer to Fraxinus mandshurica plantation can improve the soil quality and promote the growth of Fraxinus mandshurica plantation. |
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