Factors influencing decline in soil pH in Hawaiian Eucalyptus and Albizia plantations

Soil pH declined from 5.9 to 5.0 in 8 years beneath plantations of Eucalyptus saligna (Sm.) in Hawaii. In stands of Albizia falcataria, (L.) Fosberg, the soil pH change was more dramatic, declining from 5.9 to 4.6. We measured several components of soil acidity beneath four mixtures of the two tree species to gain insight on the processes responsible for the decline in soil pH. These components were studied using an empirical method of comparing acid quantity, degree of neutralization (depletion of base cations), and acid strength. The decline in soil pH differed between species as a result of differences in the degree of neutralization of the soil exchange complex; the larger decrease in soil pH under Albizia was produced by greater acidification of the exchange complex. Empirical titration curves suggested that differences in acid strength moderated the divergence in soil pH beneath the species. Had the acids accumulating in the soil under Albizia been as strong as those in the Eucalyptus soil, the difference in soil pH would have been greater. Though the two species had contrasting effects on soil pH, the differences in degree of neutralization, responsible for the pH decline, were small compared with differences in the amount of cations stored in tree biomass. Continued supply of nutrient cations (from weathering or fertilization) will ultimately control both the extent of soil pH decline and the level of productivity sustained by the forest.     

Effects of 'Agri-SC' soil conditioner on soil structure and erodibility: some further observations

Abstract. In field and laboratory experiments the conditioner‘Agri-SC’has shown improvements in the structure of loamy sand soils in east Shropshire, UK. It resulted in statistically significant decreases in soil bulk density values and increases in soil porosity and aggregate stability. Further experiments are in progress on both loamy sand and silt loam soils.     

拖拉机集材对迹地土壤条件及苗木生长影响的研究(Ⅱ)——拖拉机对集材道苗木生长影响的灰色动态分析

履带式拖拉机和轮式拖拉机由于其走行机构的不同,其集材道土壤压实也存在差异,特别衡量土壤压实的两个重要指标——土壤硬度和孔隙度——两种机型不一致。通过对调查测定数据进行计算处理以及用灰色系统理论进行动态分析,结果表明:与轮式拖拉机相比,履带式拖拉机对苗木生长是有利的。     

三峡水库重庆库区移土培肥的效益分析——以云阳县为例

应用前后对比分析法,对三峡水库重庆库区云阳县移土培肥一期与二期工程进行效益分析;得出移土培肥工程将给三峡库区带来巨大的生态效益、经济效益和社会效益的结论;说明该工程不仅能带动库区经济发展,并对其社会及生态环境产生深远影响。     

Root growth conditions in the topsoil as affected by tillage intensity

Many studies have reported impeded root growth in topsoil under reduced tillage or direct drilling, but few have quantified the effects on the least limiting water range for root growth. This study explored the effects of tillage intensity on critical soil physical conditions for root growth in the topsoil. Samples were taken from a 7-year tillage experiment on a Danish sandy loam at Foulum, Denmark (56°30′ N, 9°35′ E) in 2008. The main crop was spring barley followed by either dyer's woad (Isatis tinctoria L.) or fodder radish (Raphanus sativus L.) cover crops as subtreatment. The tillage treatments were direct drilling (D), harrowing 8-10 cm (H), and ploughing (P) to 20 cm depth. A chisel coulter drill was used in the H and D treatments and a traditional seed drill in the P treatment. Undisturbed soil cores were collected in November 2008 at soil field moisture capacity from the 4-8 and 12-16 cm depths.We estimated the critical aeration limit from either 10% air-filled porosity (ε_a) or relative gas diffusivity (D/D₀) of 0.005 or 0.02 and found a difference between the two methods. The critical limit of soil aeration was best assessed by measuring gas diffusivity directly. Root growth was limited by a high penetration resistance in the D and H soils (below tillage depth). Poor soil aeration did not appear to be a significant limiting factor for root growth for this sandy loam soil, irrespective of tillage treatment. The soil had a high macroporosity and D/D₀ exceeded 0.02 at field capacity. Fodder radish resulted in more macropores, higher gas diffusivity and lower pore tortuosity compared to dyer's woad. This was especially important for the H treatment where compaction was a significant problem at the lower depths of the arable layer (10-20 cm depth). Our results suggest that fodder radish could be a promising tool in the amelioration of soil compaction.     

邢台唐山地震对河北平原土壤的影响

对1966年的河北邢台大地震,1976年的唐山大地震的震中区的土壤情况进行调研表明:这两次强震,在烈度6度以上的震区,普遍引起地裂、地面升降、地表形变和喷砂冒水现象。喷砂冒水对该两地土壤的机械组成影响明显,凡经喷砂冒水、掺进砂粒后,耕层土壤质地级别均变动了一个级别;变化最大的是0.25—0.05mm和0.05—0.01mm这两个粒级。滨海区,强震冒出咸水,明显增加了地表土壤溶液的氯化钠含量。在经过多年的农耕区,目前已找不到当时强震对当地土壤类型(指土属、土种)影响的踪迹。     

江西省农田土壤有效硫现状研究

采集了江西１６个县市９种主要母质的６０９个农田耕层土样进行了土壤有效硫含量测定。统计结果表明：平均值为２６．７１ｍｇ／ｋｇ,缺硫和潜在缺硫样点占３９．１０％。按地区分,以赣南、赣东北山区缺硫最严重,有效硫小于１２ｍｇ／ｋｇ的样点占２６．６０％～４４．７０％,其次是丘陵地区,有效硫小于１２ｍｇ／ｋｇ的样点占１０．００％～１９．００％。按母质分,母质中以石英岩、花岗岩发育的土壤最缺,约占５０％～６０％,其次是红砂岩、泥质岩,缺硫为３０％～４０％,这些是江西省急需施用硫肥的土壤。水稻土以黄砂泥田、麻砂泥田、红砂泥田、鳝泥田等土属缺硫面积最多,全省缺硫水稻土面积约为１０３．８万ｈｍ２,约占水稻土面积的３４％。     

庐山山地红壤养分状况研究

为了明确庐山土壤剖面养分状况及各营养元素之间的关系,在庐山红壤分布区挖取土壤剖面观察土壤分层与形态,分析A、B、C不同层次的有机质、氮磷钾及微量元素的含量。结果表明,红壤有机质、速效钾和有效铜含量的变化趋势大致相同,即随着土壤深度的增加而减少。其中,有机质和有效铜含量随土壤深度的增加而下降明显,有机质含量从15.68 g/kg下降至5.67 g/kg,降幅63.84%;有效铜含量从0.52 mg/kg下降至0.06 mg/kg,降幅88.46%。与之相反,有效硼的含量则随着土壤深度的增加而增加,且增幅明显。红壤全氮含量在A、B层之间差异不明显,而在C层中含量较上面2层少,且降幅明显;速效磷的含量则出现了\"高—低—高\"的分布情况。红壤有机质与有效硼、有效铜在各层次中的分布均呈现出线性关系,其中有机质与有效硼成负相关,与有效铜则成正相关。庐山山地红壤养分含量不足,盐基淋失、酸化现象较为明显,各养分含量之间关系密切,本研究为今后的红壤改良提供了参考。     

土壤调理剂在水稻上的施用效果研究

研究土壤调理剂对水稻产量和土壤性状的影响,结果表明：随着土壤调理剂用量的增加,水稻产量和秸秆量随之增加;高量调理剂和低量调理剂处理比不施调理剂处理水稻的千粒重分别增加4．57％和4．39％,分蘖数分别增加28．6％和21．0％;施用土壤调理剂可以提高土壤pH值,增加土壤碱解氮、有效磷含量。