毕节地区4大类型土壤的养分含量及土壤C/N值分析

以毕节市耕地地力评价的调查数据为基础,分析了石灰土、粗骨土、紫色土和黄壤4种类型土壤的养分含量及土壤C/N。结果表明,毕节市耕地的土壤有机质、土壤全氮、土壤全钾、土壤速效氮、土壤速效磷、土壤速效钾和土壤C/N均值分别为30.69 g/kg、1.59 g/kg、301.92mg/kg、175.95 mg/kg、19.29 mg/kg、169.79 mg/kg和19.20;其中,黄壤的土壤有机质、全氮和速效氮含量最高,土壤C/N也最大;石灰土的土壤全钾和速效钾含量最高;而紫色土的土壤有机质、全氮、全钾、速效氮、速效磷和速效钾含量最低,土壤C/N也最小。

Mixing Alfalfa Straw and Maize Straw to Enhance Nitrogen Mineralization, Microbial Biomass and Enzyme Activity: A Laboratory Study

The quality of straw affects N release after straw retention. As straw with high C： N ratio could result in N immobilization, additional N is needed to compensate N demand of crops. However, more and more N fertilizers have been applied to the soil to improve crop yields in China, which not only increases production cost but also reduces soil quality. Therefore, reasonable application of N fertilizer becomes a key problem after straw retention. This study aimed to assess the effects of applying maize straw with high quality alfalfa straw on mineral N content, microbial biomass and enzyme activity under controlled conditions. The effect of applying maize straw with alfalfa straw was compared with that of maize straw in combination with N fertilizer under the same C： N ratio （25：1）. The laboratory incubation experiment consisted of four treatments： （1） soil with no addition （CK）; （2） soil amended with maize straw （M）; （3） soil amended with alfalfa straw and maize straw with an adjusted C： N ratio of 25：1 （MM）; （4） soil amended with inorganic nitrogen fertilizer and maize straw with an adjusted C：N ratio of 25：1 （MF）. The results showed that application of maize straw leaded to an N immobilization during the 270 d of incubation. Combined application of alfalfa and maize straw and or mineral N fertilizer alleviates the N immobilization and increase soil mineral N content. Compared to MF treatment, MM treatment prolonged N availability during the incubation. MM and MF treatments increased the soil microbial biomass carbon and nitrogen contents, and soil invertase and β-glycosidase activities. There was no difference between MM and M treatment in soil urease activity. MF treatment had significantly negative influence on soil urease activity compared with M treatment. The amount of added N significantly affected mineral N content, soil microbial biomass and enzyme activity. The mixture of alfalfa straw and maize straw sustains higher level of mineral N content, microbial biomass and enzyme activity as it had high N input compared to maize straw in combination with N fertilizer. It is concluded that alfalfa straw may be a better N source than N fertilizer in alleviating N immobilization caused by maize straw retention.

Preliminary Analysis on Abnormal Granularity Layers of Soil Profile and the Response of Relative Factors in Loess Plateau

[Objective] The paper was to analyze organic carbon content （SOC）, granularity, total nitrogen content （TN）, carbon-nitrogen ratio （C/N）, calcium carbonate content （CaCO3） of 1cm soil profiles in returning forest in Zhifanggou watershed of Ansai County in Loess Plateau, so as to study the changes of physical and chemical properties in abnormal layer of soil reflected with granularity, as well as the physical and chemical responses of soil. [Method] Three quadrats with the size of 10 m×10 m were randomly selected in three sampling plots in Loess Plateau, three profiles in upper, middle and lower slope were excavated, and the samples were collected with interval of 10 cm; the surface layer with the depth of 0-10 cm was divided into two layers of 0-5 and 5-10 cm for sampling, respectively. Eleven samples were collected in each profile with a total of 99 samples. Its organic carbon content, granularity, total nitrogen content, carbon-nitrogen ratio and CaCO3 content were analyzed. [Result] The soil profiles in three sampling sites contained five characteristic layers, including a1, b1, b2, c1 and c2, the content of soil granule with particle size less than 0.02 mm decreased, and those with particle size 0.02 mm increased, the organic carbon content and C/N value （a1, b1, b2, c2） increased, but the increase trend of CaCO3 content was not obvious. [Conclusion] The study shows that the characteristic soil layer is commonly existed in loess region, especially the eroded loess region, which should be paid attention in the research fields of modern soil science and ecology.

我国三种种植制度下农田土壤有机碳、氮关系的演变特征

对34个国家级耕地质量监测点20余年连续监测数据进行了统计分析,旨在探讨常规施肥下我国旱作、水旱轮作和稻田系统土壤碳、氮关系的演变特征。结果表明,1985-2006年,我国常规施肥方式下旱地、水旱轮作和稻田系统表层土壤有机碳和全氮均显著增加,三种种植制度下土壤C/N演变存在一定差异。土壤C/N均值从1985-1990年的9.87上升至2001-2006年的10.32。20年期间,土壤C/N分布在9-11的区间范围内的频率为45%-48%;土壤C/N在7-9区间的分布频率从27.5%减少到14.5%,但在11-13区间的分布频率从15.6%增加到27%,且30%以上的旱地连续监测点土壤C/N呈显著增加趋势。进一步分析表明,土壤C/N与土壤速效磷、速效钾以及磷肥和有机肥的投入量呈显著正相关关系,而与土壤pH值呈显著的负相关关系。表明常规施肥方式中,磷肥和有机肥投入促进了土壤中有机碳和全氮的积累,且对旱地土壤有机碳积累的贡献大于对氮素积累的贡献,是土壤碳、氮关系演变的重要影响因子。

针叶林补阔对土壤有机碳、氮含量的影响

为改善马尾松人工纯林林分结构单一、地力衰退等现象,文章以乡土树种木荷(Schima superb)进行补阔的马尾松木荷混交林分土壤为研究对象,马尾松纯林和木荷纯林做对照,研究马尾松纯林补阔后不同林分土壤全碳、氮含量变化及差异,研究结果表明:(Ⅰ)木荷林具有较高的土壤全碳含量,马尾松木荷混交林次之,马尾松林相对较低,马尾松纯林补植木荷阔叶树后显著提升了土壤全碳含量;(Ⅱ)土壤全氮含量均表现为木荷林>马尾松木荷混交林>马尾松林,表明马尾松林补植木荷阔叶树后提升了土壤N储量;(Ⅲ)马尾松木荷混交林、木荷林的C/N均低于马尾松林,表明马尾松林补植木荷阔叶树后降低了土壤C/N.

华北地区典型农田土壤有机质和养分的空间异质性

华北平原是我国重要的粮食生产基地,研究华北平原土壤有机质及养分的丰缺状况对于区域农业生态系统的可持续性发展具有重要意义。本研究选取华北平原典型农田,通过设置北线、中线、南线3条研究线路,在省域尺度上研究土壤有机质和养分的空间异质性及其平衡状况。结果表明,研究区域内土壤有机质、全氮、碱解氮、有效磷、速效钾平均含量分别为14.0±3.5 g/kg、0.98±0.28 g/kg、76.6±21.6 mg/kg、18.6±9.9 mg/kg,136.1±42.7 mg/kg,除全氮和有效磷外,有机质及其余养分在不同线路间无显著差异。有效磷在靠近黄河、土壤pH值较高的南线上显著偏低。土壤有机质及养分均为中等程度变异,有效磷的变异系数(47.8%)显著高于有机质及其余土壤养分(24.3%～31.6%)。土壤碳氮比介于4.2～14.3间,平均为8.6,低于全国平均水平。土壤有机质和各养分均较1980年有所增加,主要原因可能是华北平原长期以来投入了大量的有机、无机肥。华北平原农田配方施肥应该考虑增施有机肥、减少氮素化肥的投入。

不同生境下氮沉降对土壤N_(2)O通量影响的整合分析

基于在我国开展的66个野外氮沉降模拟试验的290组数据,采用整合分析方法,探究实验样地特征(气候因子、土壤性质)和施氮因素对施氮后土壤N_(2)O通量变化的影响。结果表明:样地的年均降水量、年均温、自然氮沉降量和土壤C/N与施氮后N_(2)O通量增幅呈显著正相关,土壤pH与施氮后N_(2)O通量增幅呈显著负相关。湿地生态系统土壤对施氮最敏感,森林生态系统次之,草原生态系统最小。所有的样地因子中,土壤pH和C/N对施氮后N_(2)O通量变化幅度的影响最大。施加硝态氮后土壤N_(2)O通量增幅最大,施加尿素与铵态氮后N_(2)O通量增幅相当,而施加硝酸铵后N_(2)O通量增幅最小。综上,在准确评估和预测土壤N_(2)O通量对氮沉降的响应时,应综合考虑样地特征及氮源种类的影响。

松嫩平原玉米带土壤碳氮比的时空变异特征

土壤碳氮比(C/N)是土壤质量的敏感指标,是衡量土壤C、N营养平衡状况的指标,它的演变趋势对土壤碳、氮循环有重要影响.通过野外调查、采样和分析,运用地统计学方法和GIS技术,探讨1980～2005年松嫩平原玉米带土壤C/N的时空变化规律.结果表明,1980年和2005年土壤C/N的平均值分别为10.56和12.30.2个时期土壤C/N的空间相关距离分别为196.3 km和51.1 km,呈递减趋势,说明农田管理影响因素的作用在逐渐增强.过去25 a间,有84.88%的土壤面积的C/N呈上升趋势,以西部增加最为显著,德惠和九台市部分地区有所降低.对于不同的土地利用方式,旱田、水田、林地和草地土壤的C/N均呈上升趋势,其中以草地增加最为明显,从1980年的10.03±1.12上升为2005年的12.61±0.87;旱田和水田土壤C/N均高于全国平均水平.土壤C/N的升高表明碳素的增加速度高于氮素,为保持C/N的稳定提高,今后的农业生产中在提高氮素投入水平的同时,应注重碳素的归还水平,大力推广秸秆还田和增施有机肥.