Severe acidifications in acid sulfate soils (ASSs) have occurred worldwide due to sulfuric acidity, which requires sustainable
measures for their reclamation. Accordingly, an incubation study was conducted with the topsoil of two different ASSs (Cheringa
and Badarkhali) to evaluate the effects of basic slag (BS; size <1 mm, pH 9.6, Ca 20.8%, Mg 9.8%, etc.), on reduction of acidity
and changes in exchangeable cations. It is noted that BS is a byproduct of steel industry in Bangladesh and can be collected
almost free of charge. These soils received BS at the rate of 0 (T0), 11 (T1), 22 (T2) and 33 (T3) t ha−1 under various moisture regimes (saturated condition M1,, i.e., 100% moisture content, wetting–drying cycles of 100 and 50% moisture M2, and moisture at field condition M3, i.e., 50%). The impacts of these treatments on some selected parameters in these soils were studied within 180 days of incubation.
The application of BS was found to increase the pH of soils from 3.6 to 5.1 for Cheringa, 3.9 to 5.2 for Badarkhali soils
at the end of incubation. These increments were more striking with the highest doses of BS under saturated moisture conditions
in both of the soils. The ECe of the soils was not much influenced by the application of BS regardless of time. The treatments
exerted significant (P ≤ 0.05) effects on exchangeable cations in different periods of incubation. The striking changes were recorded for the rate
of increments of Ca2+ and Mg2+, which were about 2–3 times higher for Ca and more than 2 times higher for Mg2+ compared with the control after 180 days of incubation. These results suggest that the application of BS not only increased
the Ca2+ to the higher amount than that of the increment of Mg2+ in the soils, but also improved one of the important criteria of Ca2+ and Mg2+ ratio in the soils. 相似文献
Tropical subsoils contain large reservoirs of carbon (C), most of which is stored in soil organic matter (SOM). Subsoil OM is thought to be particularly stable against microbial decomposition due to various mechanisms and its position in the soil profile, potentially representing a long-term C sink. However, few experiments have explicitly investigated SOM stability and microbial activity across several orders of magnitude of soil C concentrations as a function of soil depth. The objective of this study was to evaluate the biological stability of SOM in the upper 1.4 m of tropical forest soil profiles. We did so by measuring CO2 evolution during a 90-day laboratory incubation experiment on a sample set that was previously characterized for C and nutrient concentrations and microbial biomass. We concurrently measured the energy content of SOM using differential scanning calorimetry (DSC) as an index of the energy available for microbial metabolism, with the hypothesis that the biological stability of SOM would be inversely related to the energy contained within it. Cumulative CO2 evolution, mean respiration rates, and the energy density of SOM (energy released during combustion normalized to soil C) all declined with soil depth (P < 0.01). Biological indices of C stability were well correlated with measures of SOM energy. There was no change in the mean respiration rate as a function of depth when normalized to soil C, and a trend toward increased respiration per-unit microbial biomass (P = 0.07). While reduced microbial respiration in subsoils suggests an increase in the biological stability of SOM, we suggest this is driven principally by concurrent declines in energy availability as measured by DSC and the size of the microbial biomass pool. On a per-unit biomass basis, subsoil OM may be as prone to decomposition and destabilization as surface SOM. 相似文献
The IDS (Incubation, Drying and Separation) method was tested on Schinus molle L. seeds collected from Ethiopia in an attempt to sort non-viable from viable seeds. Seeds were incubated for 24 h followed by one, three, four, five, six, nine and twelve hours of drying and then separated in water. All IDS treatments gave 80.5–93.5% germination in the sunken fraction compared with 61% for untreated seeds. The mean germination time of sunken seeds reduced from 11.2 (control) to 8.9–9.2 days (IDS-treated). Specific gravity separation in water of untreated seeds was also tested, and the germination capacity of sunken fraction was 83.5% with a mean germination time of 9.3 days. IDS method can, therefore, be used to enhance both percentage and rate of germination of a seed lot of Schinus molle, which is desirable to produce uniform and vigorous seedlings in the nursery or out in the field. 相似文献
Several authors have reported that nitrification in acid soils may be restricted to microsites having a more favorable pH. The aim of this study was to propose a conceptual model of the functioning of nitrification in hot-spots, and to test it with the experimental data obtained in laboratory conditions using twelve tropical unamended and -amended soils with a wide range of pH (from 4.2 to 6.9). Nitrification was also measured in two selected soils where the pH was adjusted from 3.5 to 6.2. The model characterizes the relationship between the nitrification rates in unamended and -amended soils as a function of pH. It is based upon the assumption that nitrification of the coming from N mineralization occurs in the hot-spot (RNh), and the nitrification of the added occurs in the hot-spot and also in its adjacent surrounding region (RNs). The experimental design was chosen to be able to estimate both nitrification rates. Soil acidity limited nitrification more in -amended soils than in unamended ones. From our approach, this is due to less favorable conditions for nitrification in the region surrounding the hot-spot. The effect of self-induced acidity on nitrification was not noticeable neither in unamended nor in -amended treatments. The model described well three observations made in the experiments: (i) the minimum pH for nitrification to occur was lower for RNh (pH<4.2) than for RNs (pH<4.7), (ii) the RNh/RNs ratio increased with the decrease of pH (from 1.5 at pH 6 to 8.5 at pH 4), and (iii) for a given pH, the RNh/RNs ratio increased with the decrease of the initial pH of the soil. Among the soil parameters determined in this study (i.e. exchangeable Al, EDTA-extractable Cu and Zn, total C and N), only pH was related to nitrification. However, for a given pH, nitrification varied 3-fold among soils, depending upon their initial pH. This suggests that soil pH as determined on bulk soil is not suitable to predict nitrification in each individual soil, because it is not representative of the acidity level within the hot-spot. 相似文献
Efforts to eradicate brucellosis caused by Brucella abortus in the United States began in 1934 as part of an economic recovery program to reduce the cattle population because of the Great Depression and concurrent severe drought conditions. A number of states saw this as an opportunity to reduce the level of brucellosis, which was the most significant livestock disease problem in the US at the time. In 1934 and 1935, the reactor rate in adult cattle tested was 11.5%. In 1954, the magnitude of the brucellosis problem in the United States in terms of economics to the cattle industry and human health prompted Congress to appropriate funds for a comprehensive national effort to eradicate brucellosis. The brucellosis eradication program was designed as a cooperative effort between the federal government, the states, and livestock producers. As the science and technology of brucellosis has developed over the years through research and experience, the eradication program has been modified many times.
As of 31 December 2000, there were no affected cattle herds in the United States. This was the first time in the history of the brucellosis program that the United States had no known brucellosis affected herds. However, brucellosis has a variable, sometimes quite lengthy incubation period, so it is expected that additional affected herds will be disclosed. It is likely that additional affected herds will be disclosed before brucellosis is finally eradicated from cattle. Animal health officials remain prepared to aggressively pursue any newly disclosed affected herds to eliminate the disease as quickly as possible.
The State-Federal Brucellosis Eradication Program has made tremendous progress since its inception. In an eradication program, it is critically important to recognize that, despite all the tools that are available to eliminate the disease, an effective surveillance system is the critical first step that must be in place in order to be successful. It is imperative, not only to be able to find the disease and eliminate it, but to find it before it spreads to susceptible herds. When brucellosis can be identified, contained, and eliminated before spread occurs, eradication can be achieved. 相似文献