崩岗侵蚀对土壤速效养分质量分数及化学计量比的影响

Effects of collapse mound erosion on soil available nutrient contents and their stoichiometry ratios

为揭示崩岗侵蚀对土壤速效养分及化学计量比的影响,选取福建省长汀县黄泥坑崩岗群微度、中度和强度崩岗3处为研究对象,测定和分析了0-30 cm土层集水坡面、崩壁、崩积体以及沟道部位的土壤基本物理性质、速效养分及化学计量特征。结果表明：1）随着侵蚀强度的增加,硝态氮和速效磷质量分数表现为强度〉中度〉微度,中度侵蚀崩岗铵态氮质量分数最低,速效钾质量分数最高;从水平方向上,各速效养分质量分数表现为速效钾（AK）〉铵态氮〉硝态氮〉速效磷（AP）;垂直方向上,各速效养分质量分数大致随着土层深度而降低,但同一侵蚀强度内各质量分数差异较小。2）土壤速效氮为铵态氮与硝态氮的总和（AN）,AN/AP比表现为微度〉强度〉中度,微度与中度差异显著（P〈0.05）;AK/AN比为中度〉微度〉强度,中度与强度差异显著（P〈0.05）;AK/AP比为微度〉中度〉强度,微度与中度差异显著（P〈0.05）。3）从集水坡面、崩壁、崩积体至沟道,3种类型崩岗的铵态氮和硝态氮平均值都呈降低的趋势,速效磷逐渐升高,速效钾在崩积体处最低,其他3个部位变化不大;土壤AN/AP、AK/AP比呈降低的趋势,AK/AN比在沟道处最高。4）速效养分化学计量比与砂粒、粉粒、p H和有机质皆密切相关,黏粒、容重和含水率对其影响相对较小。

[ Background] Collapse mound, called ＂ Benggang＂ in Chinese geomorphic pictograph, has been known to describe a kind of erosion phenomenon in hilly and mountainous area among subtropical and fractional tropical climatic zone of south China that gully head collapsed, transported and developed a deep-cut shape, concave-deforming deep-seated failure landform. [ Methods] To reveal the effects of collapse mound erosion on soil available nutrients and stoichiometry ratios, we chose 3 collapse mounds of slight, moderate and strong erosion intensities in Huangniken collapse mound groups of Changtiug County of Southwest Fujian as research object. Soils at 0 - 10 cm, 10 - 20 em and 20 - 30 cm in 4 positions of upper catchment, collapsing wall, colluvial deposit and channel were sampled, and the contents of ammonium N （NH4^＋-N）, nitrate N （NO3-N）, available P （AP） and available K （AK） and related physical-chemical properties, such as mechanical composition, bulk density, water content, and organic matter content were measured, finally, the stoiehiometric characteristics of available nutrients were analyzed. [ Results] The results indicated that： 1 ） With erosion intensity increasing, the contents of NO3 -N and AP occurred in the collapse mound of strong 〉 moderate 〉 slight, and the content of NH] - N was the lowest and AK was the highest in collapse mound under moderate erosion; horizontally, the diminishing order of contents of soil available nutrients were displayed as following： AK 〉 NH]-N 〉 NO3 -N 〉 AP, while the content of each available nutrient decreased vertically as soil depth increasing, and their variance of the same erosion intensity was very little. 2） With different erosion intensities, AN （NH4^＋-N ＋ NO3-N）/AP ratio showed： slight 〉 moderate 〉 strong, and there was significant difference （P 〈 0.05） between slight and moderate collapse mound; AK/AN ratio was in moderate 〉 slight 〉 strong, and there was significant difference （P 〈 0.05） between moderate and strong collapse mound; AK/AP ratio was in slight 〉 strong 〉 moderate, and difference was significant （ P 〈 0.05 ） between slight and moderate. 3） From upper catchment, collapsing wall, colluvial deposit and channel, the averaged content of NH4^＋-N and NO3^--N showed a downward tendency, while AP increased gradually, and AK was the lowest at colluvial deposit, but in 3 other sections they varied slightly under different erosion intensities; meanwhile, AN/AP and AK/AP ratios decreased from slope of catchment area to channel, but the value of AK/AN ratio was the highest at channel. 4） Stoichiometric ratios of soil available nutrients were closely correlated to sand, silt, pH value and organic matter, but they were impacted slightly by the clay, bulk density and water content. [ Conclusions] collapse mound erosion resulted in variation of soil available nutrients and stoichiometry ratios with different layers and position.