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81.
Abstract A method using membrane filters of appropriate pore size, to selectively isolate actinomycetes from a mixed population of soil microorganisms, is described.
The method is based on the ability of actinomycetes to propagate and pass through the pores of filters while bacteria and fungi are retained on the membrane surface. 相似文献
The method is based on the ability of actinomycetes to propagate and pass through the pores of filters while bacteria and fungi are retained on the membrane surface. 相似文献
82.
Influence of soil gas contamination on tree root growth 总被引:1,自引:0,他引:1
Summary Rooted-cuttings and saplings of green ash (Fraxinus lanceolata) and hybrid poplar (Populus spp) were planted on a former municipal refuse landfill and on a nearby nonlandfill control plot. The root systems of four
trees of each species and size were excavated on the landfill plot-two growing in an area where the concentrations of anaerobic
landfill gases were relatively high and two in a relatively low-gas area. Two trees of each species and size were also excavated
on the control. The root systems of both species were significantly shallower on the landfill plot than on the control. Green
ash appeared to avoid the adverse gas environment of the deeper soil layers on the landfill by producing adventitious roots.
Hybrid poplar became adapted in a different manner, by redirecting root growth from the deepter soil layers to the soil surface. 相似文献
83.
Nematodes of three genera (Acrobeloides sp., Aphelenchus avenae, and Scutellonema brachyurum) were induced to coil and enter anhydrobiosis in drying soil of two types: sandy loam and loamy sand. Coiling was studied in relationship to soil moisture characteristics. Coiling and the physiological state of anhydrobiosis occurred before the water in sandy soils reached a water potential of -15 bars. Coiling was maximum at 3-6 bars, depending on the soil type and nematode species. It appeared that induction of coiling and anhydrohiosis were determined by the physical forces exerted by the water film surrounding the nematode, which, for these three species, was 6-9 monomolecular layers of water, rather than the % moisture and relative humidity of the soil per se. 相似文献
84.
J. F. Witty 《Plant and Soil》1979,52(2):151-164
Summary N2-fixation by algae on the Broadbalk continuous wheat experiment was measured over a two year period using the acetylene reduction technique. The plots studied receive spring fertilizer treatments including farmyard manure and combinations of nitrochalk and Na, P, K and Mg which have remained much the same since the experiment started in 1843.Nitrogen applied at 196 kg ha–1 in spring suppressed algal N2-fixation until late in the season but at lower levels (48 kg N ha–1) the denser plant canopy increased both surface moisture and fixation. Herbicide treatment decreased fixation on plots of moderate nutritional status early in the season but had little effect on unfertilised plots where weed cover was sparse. On plots where weed and crop cover was very dense herbicide treatment increased fixation in August.Algal N2-ase activity, assayed by C2H2 reduction, continued throughout the night at a rate which averaged 33% of the midday value. Laboratory experiments indicate that dark fixation is very temperature sensitive and this value may represent a maximum. Algal crust in the field dried to 4.5–6.8% H2O content became active 3 1/2 h after rewetting and reached a steady state after 7 h which represented only 6–22% of that at the previous maximum suggesting that many cells had been killed.In a year with average rainfall algae on plots receiving 48 kg N ha–1 were estimated to fix 25–28 kg N ha–1 and plots without fertiliser 13–19 kg N ha–1. Algal fixation appeared to make a substantial contribution to the continuing fertility of unfertilised plots. 相似文献
85.
Summary Manganese, N and P fertilizers were applied to wheat in field experiments on a soil so deficient in Mn that it caused the wheat to die before heading. Yields of wheat were increased linearly by soil banded Mn to 44.8 kg/ha, giving a yield of 3.03 tonnes/ha. Yields were increased to a lesser extent by foliar-applied Mn and least by soil-broadcasted Mn. Soil N and P appeared to be adequate, yet ammonium sulphate at 56 kg N/ha where applied alone caused a yield of 1.69 tonnes/ha and ammonium sulphate nitrate gave a yield of 0.98 tonnes/ha, the increases being primarily due to the release of Mn to the plants. Calcium nitrate and triple superphosphate were much less effective in releasing Mn. 相似文献
86.
K. S. Kumarasinghe C. Kirda A. R. A. G. Mohamed F. Zapata S. K. A. Danso 《Plant and Soil》1992,139(1):145-147
Ammonium sulphate was applied at the rate of 300 kg N ha–1 with or without the nitrification inhibitor 1-carbamoyl-3(5)-methylpyrazol (4 kg ha–1) to plots measuring 1.5 × 1.5 m. The fertilizer and the inhibitor were washed into the top 15-cm layer of the soil, which was highly calcareous (55% CaCO3), and the plots were kept bare. The process of nitrification was monitored by regular soil sampling. In the absence of the inhibitor, nitrification was completed in three weeks. In the presence of the inhibitor only 10% of applied N was nitrified by the end of the third week and 42% by the end of the eighth week. Average soil temperature at 5–, 10– and 20-cm depth over the first six weeks was 26.0, 24.8 and 24.2°C, respectively. 相似文献
87.
Laboratory experiments have shown appreciable losses of ammonia after injection of anhydrous ammonia into dry and wet soils.
In this study losses of ammonia injected into a moist (tension 10 kPa), dry (tension 160 kPa) and a wet (tension 1.6 kPa)
sandy loam were measured under field conditions using wind tunnels. Losses were insignificant from a moist soil. However losses
from a dry and a wet soil were 20% and 50% of injected ammonia, respectively. From the dry soil, losses of gaseous ammonia
took place within the first hours after injection, which indicates a rapid transport through cracks and voids. From the wet
soil, 20% of the injected ammonia was lost more gradually between 6 h and 6 d. This indicates that upward movement of water
due to evaporation may be the cause of these ammonia losses which proceeded for longer periods. 相似文献
88.
Influence of root diameter on the penetration of seminal roots into a compacted subsoil 总被引:4,自引:2,他引:2
A field experiment was conducted to evaluate the influence of root diameter on the ability of roots of eight plant species to penetrate a compacted subsoil below a tilled layer. The soil was a fine sandy loam red-brown earth with a soil strength of about 3.0 MPa (at water content of 0.13 kg kg-1, corresponding to 0.81 plastic limit) at the base of a tilled layer. Relative root diameter (RRD), which was calculated as the ratio of the mean diameters of roots of plants grown in compacted soil to the mean diameters of those from uncompacted soil, was used to compare the sensitivity of roots to thicken under mechanical stress.Diameters of root tips of plants grown in soil with a compacted layer were consistently larger than those from uncompacted soil. Tap-rooted species generally had bigger diameters and RRDs than fibrous-rooted species. A higher proportion of thicker roots penetrated the strong layer at the interface than thinner roots. There were differences between plant species in the extent to which root diameter increased in response to the compaction. The roots which had larger RRD also tended to have higher penetration percentage.The results suggest that the size of a root has a significant influence on its ability to penetrate strong soil layers. It is suggested that this could be related to the effects which root diameter may have on root growth pressure and on the mode of soil deformation during penetration. 相似文献
89.
Take-all of wheat, caused by Gaeumannomyces graminis var tritici (Ggt), is reduced by ammoniacal fertilizers as compared to nitrate sources. This influence of nitrogen on the disease is only observed on nodal roots at flowering. But soil conduciveness to take-all, as measured in a soil bioassay, is modified earlier. Forty days after nitrogen application at early tillering, the NH4-treated soil became less conducive than the NO3-treated one. When nitrogen applications are done at sowing and at tillering, differences in disease propagation between the two soils are enhanced. Results from four years of experimentation show that when the level of natural soil inoculum is high, disease severity is reduced by ammonium, showing an effect on the parasitic phase of Ggt. At a low level of natural inoculum the effect of the source of nitrogen is mainly observed on the percent of infected plants, indicating that the saprophytic and preparasitic phases are affected. Rhizospheric bacterial populations increase from sowing to tillering, but differences on take-all conduciveness after tillering are not correlated with differences in the amounts of aerobic bacteria or fluorescent pseudomonads isolated from soils treated with different sources of nitrogen. Qualitative changes in fluorescent Pseudomonas spp. populations, like in vitro antagonism, are more likely to explain differences in soil conduciveness to take-all than are quantitative changes in this group. Nevertheless, the introduction of Ggt in a cropped soil leads to a greater increase in fluorescent pseudomonads populations than in total aerobic bacteria.The delay between reducing soil conduciveness and reducing disease in the field with ammonium nitrogen fertilization, the qualitative change of fluorescent pseudomonads populations and the role of necroses in rhizobacteria multiplication, provide information leading to our representation of a dynamic model based on the differentiation of the wheat root system into seminal and nodal roots. 相似文献
90.
Gert Arnold 《Plant and Soil》1992,142(1):41-51
Three-year-old Scots pine (Pinus sylvestris) trees were grown on a sandy forest soil in pots, with the objective to determine their NH4/NO3 uptake ratio and proton efflux. N was supplied in three NH4-N/NO3-N ratios, 3:1, 1:1 and 1:3, either as 15NH4+14NO3 or as 14NH4+15NO3. Total N and 15N acquisition of different plant parts were measured. Averaged over the whole tree, the NH4/NO3 uptake ratios throughout the growing season were found to be 4.2, 2.5, and 1.5 for the three application ratios, respectively.
The excess cation-over-anion uptake value (Ca-Aa) appeared to be linearly related to the natural logarithm of the NH4/NO3 uptake ratio. Further, this uptake ratio was related to the NH4/NO3 ratio of the soil solution. From these relationship it was estimated that Scots pine exhibits an acidifying uptake pattern
as long as the contribution of nitrate to the N nutrition is lower than 70%. Under field circumstances root uptake may cause
soil acidification in the topsoil, containing the largest part of the root system, and soil alkalization in deeper soil layers. 相似文献