宁夏贺兰山、六盘山典型森林类型土壤主要肥力特征

采用野外调查结合室内分析的方法,对该区域典型森林类型下土壤的主要剖面肥力特征进行了研究,并对主要理化指标进行了因子分析.结果表明:受森林凋落物的累积、分解和成土母质、气候条件的影响,贺兰山、六盘山主要森林土壤的剖面肥力具有明显差异.其中,土壤孔隙度(54.50％-72.22％,剖面均值,下同)受有机质影响显著,随土层加深逐渐减小,容重(0.72-1.21 g/cm3)、比重(2.55-2.68 g/cm3)随土层加深显著增大,且六盘山各样地比重大于贺兰山.受有机质归还作用影响,有机碳(24.03-65.37 g/kg)、全N(1.48-3.49 g/kg)、NO3--N(1.88-10.50 mg/kg)、NH4+-N(5.02-11.01 mg/kg)、全P (0.37-1.19 g/kg)、有效P(4.82-13.38 mg/kg)、速效K含量(82.03-244.62 mg/kg)均随土层加深逐渐降低；全K含量(18.92-26.14 g/kg)随土层加深逐渐增大,且六盘山各样地全K含量大于贺兰山.土壤C/N (11.74-19.88)旱现B层＞C层＞A层,且贺兰山各样地C/N大于六盘山.土壤CEC(23.94-40.30 cmol/kg)受有机质的主导作用明显,随土层加深显著减小,pH值(7.09-8.09)、ESP(0.59％-2.47％)及BSP(51.24％-80.57％)均随土层加深逐渐增大,且贺兰山各样地pH值、ESP大于六盘山.粘粒(5.46％-10.20％)、TDS (0.33-1.12 g/kg)及CaCO3(1.44-14.23 g/kg)均未出现明显积聚,且贺兰山各样地TDS、CaCO3含量大于六盘山.因子分析显示,对于该区域各样地土壤的肥力特征,可以应用有机质因子、环境因子和NO3--N因子进行综合描述.其中青海云杉、山杨混交林下土壤的有机质因子得分最高,贺兰山各样地环境因子得分显著大于六盘山,NO3--N因子得分则以小叶金露梅灌丛和华北落叶松天然林最高.

Soil fertility under different forest types in the Helan and Liupan Mountain ranges of Ningxia Province

The main areas of forest in Ningxia Province lie in the Helan and Liupan mountain ranges. These forests have important ecological and economic significance. The fertility of forest soil in these areas has not been systematically studied. The objective of this study was to evaluate soil fertility under six forest types in the Su-Yukou forest zone of the Helan mountain range and in the Xi-Xia and Die-Diegou forest zones of the Liupan mountain range. The natural forest types were Pinus tabulaeformis × Populus davidiana, Picea crassifolia × Populus davidiana, Potentilla parvifolia, and Larix principis-rupprechtii. The planted forest types were Quercus liaotungensis and Larix principis-rupprechtii. Five separate profiles (replications) were sampled in an 'S' pattern for each soil type. The profiles were divided into A, B, and C horizons and then sampled, making a total of 18 soil samples. Soil physical and chemical properties were measured with conventional methods. The results were analyzed using univariate analysis of variance. Differences among forest types and soil horizons were analyzed with Duncan's test (SSR). Soil fertility characteristics were evaluated using principal component analysis. The results indicated significant differences in soil fertility under the six forest types. These differences can probably be attributed to differences in the accumulation and decomposition of forest litter, in soil parent material, or in climatic conditions. Soil porosity ranged from 54.5 to 72.2% and decreased as soil depth increased. Soil bulk density ranged from 0.72 to 1.21 g/cm³ and particle density ranged from 2.55 to 2.68 g/cm³. Soil bulk density and particle density both increased as soil depth increased. Soil particle density in the Liupan mountains was higher than that in the Helan mountains. Soil organic C (24.03-65.37 g/kg), total N (1.48-3.49 g/kg), NO^-₃-N (1.88-10.50 mg/kg), NH⁺₄-N (5.02-11.01 mg/kg), total P (0.37-1.19 g/kg), available P (4.82-13.38 mg/kg), and available K (82.03-244.62 mg/kg) increased as soil depth increased. Total K (18.92-26.14 g/kg) increased as soil depth increased. Total K concentrations were higher in soil from the Liupan mountains than in soil from the Helan mountains. The soil C : N ratio (11.74 to 19.88) tended to be highest in the B horizon followed by the C and A horizons. The cation exchange capacity (23.94-40.30 cmol/kg) decreased as soil depth increased. In contrast, soil pH (7.09-8.09), exchangeable sodium percentage (0.59%-2.47%) and base saturation percentage (51.24%-80.57%) increased as soil depth increased. Clay content (5.46%-10.20%), total dissolved salt, (0.33-1.12 g/kg), and CaCO₃ content (1.44-14.23 g/kg) did not change significantly with soil depth. The soil C : N ratio, pH, exchangeable sodium percentage, total dissolved salt, and CaCO₃ content of soil from the Helan mountains was higher than that of soil from the Liupan mountains. Factor analysis was used to describe soil fertility under the six forest types. Three soil fertility components (organic matter factor, environmental factor, and NO^-₃-N factor) were derived from 14 physico-chemical soil properties. Component scores showed significant differences among the three fertility components under different forest types. The soil under the Picea crassifolia × Populus davidiana forest had the highest component score for the organic matter factor. Soils from the Helan mountain range had the highest component score for the environmental factor, and soil from the natural Potentilla parvifolia and Larix principis-rupprechtii forest had the highest component score for the NO^-₃-N factor.