湘中丘陵区不同土地利用方式土壤碳氮含量的特征

Soil Carbon and Nitrogen Concentration under Different Land Use in Central Hilly Area of Hunan Province

对湘中丘陵区杉木人工林、油茶经济林、苗圃地、坡耕地、采伐迹地、弃耕地6种土地利用方式下土壤碳氮含量垂直分布特征进行比较分析.结果表明:6种土地利用方式下,土壤有机碳含量的空间垂直分布大体随着土层的深入而降低,按分异程度(变异系数)由大到小的次序为:弃耕地(80.09%)>经济林地(67.21%)>坡耕地(62.41%)>杉木人工林(58.03%)>苗圃地(35.58%)>采伐迹地(25.32%);6种土地利用方式的土壤有机碳加权平均含量(g/kg)从高到低依次为:采伐迹地(9.87)>经济林(9.78)>弃耕地(7.35)>杉木人工林(6.84)>坡耕地(5.48)>苗圃地(5.36);6种土地利用方式的土壤有机碳含量在空间分布上呈极显著差异(F=5.43,p<0.01);土壤全氮含量的空间垂直分布与有机碳相似,按分异程度(变异系数)由大到小的次序为:弃耕地(55.71%)>坡耕地(48.43%)>经济林地(46.22%)>杉木人工林(33.75%)>采伐迹地(20.56%)>苗圃地(19.65%);6种土地利用方式的土壤全氮加权平均含量(g/kg)从高到低依次为:采伐迹地(0.84)>弃耕地(0.80)>坡耕地(0.78)>经济林(0.75)>苗圃地(0.71)>杉木人工林(0.62),且6种土地利用方式的土壤全氮含量在空间水平分布上呈极显著差异(F=4.63,p<0.01);不同土地利用方式下,土壤铵态氮、硝态氮空间垂直分布没有明显的规律性,水解氮空间垂直分布表现为表层较其它土层高;6种土地利用方式的土壤铵态氮含量在空间分布上呈显著差异(F=2.30,p<0.05),硝态氮含量呈极显著差异(F=3.34,p<0.01),水解氮含量无显著性差异(F=1.21,p>0.05);土壤有机碳含量与土壤全氮含量之间均存在极显著线性正相关(R2≥0.84,p<0.01).

A comparative study was made of the vertical distribution characteristics of soll carbon and nitrogen contents of forest plantation, economic forest-land, nursery garden, slope farm land, deforested-land and abandoned land in the central hilly area of Hunan province. The results show that the soil organic carbon content decreased gradually with the increase of soil depth on 6 kinds of land use types and according to the variation coefficient, it went down as follows, abandoned land （80. 09~）〉economic （forestland （67.21%）〉slope farm land （62.41 %）〉forest plantation （58.03%）〉nursery garden （35.58%）〉deforested-land （25.32%A）： that the weighted means of this content were ranked as ： deforested-land （9. 87） 〉economic forest-land （9. 78） 〉abandoned land （7.35） 〉slope farm land （0. 62）〉forest plantation （0. 58）〉nursery garden （0. 36）：and that there existed a highly significant difference among these 6 kinds of land use types （7=5.43, p〈（0. 01） in soil organic carbon content. The results also show that the spatial vertical distribution of soil all-nitrogen content was similar to that of organic carbon and according to the variation coefficient, it was ranked as： abandoned land （55.71%） 〉slope farm land （48. 43^）〉economic forest-land （46. 22%）〉forest plantation （33, 75%）〉deforested-iand （20. 56%）〉nursery garden （19. 65%）; that the weighted means of these contents （g/kg） were as follows： deforested-land （0.84）%〉abandoned land （0.80）%〉slope farm land （0. 78）〉economic forest-land （0.75）〉nursery garden （0. 71）〉forest plantation （0. 62）; and that there also existed a highly significant difference among the 6 kinds of land use types （F=4, 63, p〈0.01） in soil all-nitrogen content. The results further show that the spatial vertical distribution of soil ammonium nitrogen and nitration nitrogen had no obvious variation rule but the distribution of hydrolyzed nitrogen had a higher content in top layer than in other layers, that there likewise existed a difference, highly significant among the 6 kinds of land use types （F=2. 30, p〈0.05） in soil ammonium nitrogen content, significant in soil nitration nitrogen content （F=3.34, p〈0.01） and not significant in soil hydrrolyzed nitrogen content （F=1.21, p〉0. 05）, and that there was a highly significant positive correlation （R^2≥0.84. p〈 0.01） between the organic carbon and the all-nitrogen contents of the 6 kinds of land use types.