免耕与常规耕作潮棕壤交换性阳离子的剖面分布特征

通过田间定位试验.研究了不同耕作方式对潮棕壤0-100 cm深度6个土层土壤交换性阳离子的影响.结果表明,与常规耕作相比,免耕使土壤表层pH显著增,.而电导率下降;同时,免耕增加了表层土壤可交换性K~+含量,降低了可交换性Na~+含量,但对可交换性Ca~(2+),Mg~(2+)和阳离子交换量没有产生显著影响.相关分析结果表明,可交换性K~+与土壤养分含量没有显著相关性,而可交换性Na~+,Ca~(2+),Mg~(2+)和阳离子交换量与有机质和全氮含量均呈负相关关系.     

黄土区土壤CO2释放及其影响因素研究

研究表明黄土区土壤CO2释放具有一定特殊性。从当日清晨至次日晨土壤CO2释放量呈由高至低再变高的规律,其变化趋势大体与温度变化一致,但时间上有一定滞后性。土壤CO2释放量有明显季节变化,夏季日释放量最高,秋季次之,冬季最低。不同覆被土壤CO2释放量存在差异,裸地释放量较高。CO2释放量对土质变化敏感,致密土壤则释放量小。     

Evaluation and mapping of soil erosion susceptibility: an example from Kenya

Abstract. The erosion susceptibility of the Erosion Research Farm at Kabete Campus was mapped using a qualitative parametric method. A grid soil survey of the 4 ha farm was combined with a map of slope gradients, slope segments being delineated by breaks in slope. Rainfall erosivity and soil erodibility were also measured. Areas with the greatest erosion susceptibility according to this method were those occupying convex slope positions and slopes of more than 30%. Field observations and soil loss measurements generally supported the erosion susceptibility rating map produced by this method. The soil and erosion susceptibility maps were useful for planning erosion control measures and for selecting suitable sites for runoff plot experiments.     

Effects of Oyster Shell Soil Amendmenton Fruit Auality and Soil Chemical Properties in Greenhouse Tomato Acidic Soils

[Objective]The aim was to explore the feasibility of applying oyster shell soil amendment for tomato production in order to determine proper quantity of the soil conditional.[Method]Field tests were performed to research effects of the soil conditioner on tomato yield,quality and soil p H.[Result]The results showed that tomato yield increased in the treatment groups with oyster shell soil amendment.The group SC50 increased the most by 16.5%than the control group.Based on normal fertilization,tomato growth was promoted by the soil amendment,and per tomato weight and lycopene content both improved during peak-fruiting period.Besides,soil p H value was enhanced by the soil amendment also.[Conclusion]It can be concluded that the effect was the best when soil conditioner was applied at 750 kg/hm2.     

Perspectives on soil fertility change: a case study from southern Ethiopia

This paper explores the complexities underlying the apparently simple question—Is soil fertility declining?—for Wolayta in southern Ethiopia, an area famed for its high population densities and extreme pressure on resources. Drawing on extensive field research in the area, the paper examines differing perceptions of soil fertility decline, and attempts to pick apart the range of evidence of changes in soil fertility over time from a variety of different sources, ranging from historical interviews with farmers to fertilizer trials carried out over many years. In contrast to the definitive statements so often made in development policy statements, the actual situation is much less clear. A detailed understanding of soil fertility dynamics is only reached by a farm and field level examination of soil nutrient balances. Differences according to agroecological zone and socio-economic group are evaluated. These results show that soil fertility is indeed declining in some places, for some people and over certain periods, but it is not universal. Indeed, soil fertility is apparently increasing at certain sites. The implications of such findings for development policy and practice are briefly explored. Copyright © 1999 John Wiley & Sons, Ltd.     

Effects of tetracycline on the soil microflora: function,diversity, resistance

Background  Tetracycline is a widely used antibiotic in animal production. Significant amounts of the substance reach the soil via feces, urine and manure application. As tetracycline is a persistent compound with antibacterial activity, its presence in soil may have undesired direct and indirect effects. These have been investigated so far focusing on effects on selected microbial functions. Objectives  The aim of the present study was to obtain comprehensive information on potential effects of tetracycline on the soil microflora under environmentally relevant conditions. The investigations included function and structure of the microbial biocoenosis and the distribution of resistance genes. Methods  Pig manure rich in tetracycline resistance genes was applied to a sandy soil. This soil as well as an unamended soil were additionally treated with several concentrations of tetracycline. The spiked soils were incubated in outdoor lysimeters for several months. Substrate induced respiration, PLFAs, ten selected resistance genes, and the concentrations of tetracycline were determined. Results  The test concentrations, though far exceeding environmental relevance, caused only small effects. An establishment of resistance could not be detected. Applied resistance genes were not detectable at the end of the study even in the presence of added tetracycline. Conclusion  Due to the high sorption capacity of the antibiotic, environmentally relevant concentrations of tetracycline do not seem to cause undesired effects on the soil microflora.     

Fluxes of nitrous oxide and nitric oxide from experimental excreta patches in boreal agricultural soil

Nitric oxide (NO) and nitrous oxide (N₂O) emissions were measured from experimental dung and urine patches placed on boreal pasture soil during two growing seasons and one autumn period until soil freezing. N₂O emissions in situ were studied by a static chamber method. NO was measured with a dynamic chamber method using a NO analyser in situ. Mean emissions from the control plots were 47.6±4.5 μg N₂ON m⁻² h⁻¹ and 12.6±1.6 μg NON m⁻² h⁻¹. N₂O and NO emissions from urine plots (132±21.2 μg N₂ON m⁻² h⁻¹ and 51.9±7.6 μg NON m⁻² h⁻¹) were higher than those from dung plots (110.0±20.1 μg N₂ON m⁻² h⁻¹ and 14.7±2.1 μg NON m⁻² h⁻¹). There was a large temporal variation in N₂O and NO emissions. Maximum N₂O emissions were measured a few weeks after dung or urine application, whereas the maximum NO emissions were detected the following year. NO was responsible on average 14% (autumn) and 34% (summer) of total (NO+N₂O)N emissions from the pasture soil. NO emissions increased with increasing soil temperature and with decreasing soil moisture. N₂O emissions increased with increasing soil moisture, but did not correlate with soil temperature. Therefore we propose that N₂O and NO were produced mainly during different microbial processes, i.e., nitrification and denitrification, respectively. The results show that the overall conditions and mechanism especially for emissions of NO are still poorly understood but that there are differences in the mechanisms regulating N₂O and NO production.