The characterization of microporosity in a ploughpan by submicroscopic and quantimet techniques

Ploughpans are usually recognizable in thin sections because of their massiveness (density) when compared with adjacent parts of the soil. When pores can be measured in the ploughpan such massiveness can be documented and compared with the porosity of the underlying soil profile. Such measurements, however, concern only meso- and macropores when done by Quantimet on micrographs obtained with the light microscope. This is due to the thickness of the thin section and the necessity to work with transmitted light. The measurement of the smaller mesopores may also be problematic with the light microscopy—Quantimet technique.

The introduction of backscattered electron scanning images allows to obtain micrographs of a very thin layer and this made it possible to measure micro- and mesopores by Quantimet. If only small magnifications are used, macropores can also be measured.

In the present investigation, micro- and mesopores were quantified by a combination of backscattered electron and Quantimet techniques and the macropores by light microscopy and Quantimet. It was demonstrated that macro- and mesopores were less frequent in a ploughpan than outside, whereas capillary or micropores increased somewhat.     

Effect of tillage and residue management on properties of two coarse-textured soils and on yield of irrigated wheat and groundnut

Changes in soil properties and yield response in relation to tillage and residue management treatments in an irrigated groundnut (Arachis hypogea L.)—wheat (Triticum aestivum, L.) rotation on a sandy soil (1972–1974) and on a sandy loam soil (1974–1976) were evaluated. Tillage treatments (T₁ and T₂) did not cause significant changes in soil properties. Incorporation of crop residues (5 t residue per ha per crop, T₃) caused a substantial increase in organic C, available N, and NaHCO₃ -extractable P contents in the top 15 cm of both soils. Residue management treatments (T₃, T₄ and T₅) showed no significant effect on soil bulk density and exchangeable K. Crop yields under no-tillage (T₁) and conventional tillage (control, T₂) were comparable on sandy soil but on the sandy loam soil, no-tillage yielded significantly lower than conventional tillage. Compared with the control, incorporation of crop residues (T₃) caused higher yields on sandy soil for groundnut and wheat by 34.1 and 47.4%, respectively, and on sandy loam by 17.1 and 7.2%, respectively. Mulching with crop residues conserved soil moisture and reduced maximum soil temperature (1.5–5.3°C in groundnut and 1.5–2.9°C in wheat) but other measured soil properties were not significantly affected. Significant yield increase due to residue mulching (T₄) was observed in sandy soil but it was significantly less than when total crop residue was incorporated (T₃). Increased wheat root-weight density in the top 15 cm soil with residue mulching was not reflected in grain yield. Compared with the incorporation of the total amount of crop residue (T₃), incorporation of half the amount and application of the other half as mulch (T₅) caused lower yields — on sandy soil for groundnut and wheat by 31.5 and 15.7%, respectively, and on sandy loam by 4.8 and 3.6%, respectively.     

Estimation of soil strength properties for critical rooting conditions

Methods to aid in the large-scale testing and characterization of Coastal Plain soils based on their susceptibility to root-limiting strength problems were developed and analyzed. They were basically regression equations modeled after a Taylor series expansion. The equations relate changes of soil strength, bulk density and soil water content between field and “critical rooting conditions”. Once equations wered eveloped from a data set of 426 laboratory samples, critical rooting bulk density was predicted for a separate set of laboratory and field samples. All laboratory samples and appropriate field samples were equilibrated at — 100 kPa soil-water potential. Soils used were sandy Ultisols, which may limit the scope of equations.

In many cases, changes in the water contents were not a significant factor in the prediction of soil strength. This may be a reflection of the limited capabilities of the equations, the uniform equilibration of soil-water potential of the soils, or the fact that the slope of the strength vs. bulk density curve is independent of water content over the range of samples considered. Nevertheless, it does simplify the equations and may suggest that a series of several equations for different soil types would be better than a single equation that requires soil-water content.     

Carbon and nitrogen budgets of nematodes in arable soil

Summary The amounts of C and N that pass through the nematode biomass in four cropping systems, barley without and with N fertilization, grass ley and lucerne, has been estimated. The nematodes were sampled at the field site of a Swedish integrated research project Ecology of Arable Land: The Role of Organisms in Nitrogen Cycling. The nematode biomass was lower (200 mg dry weight m^–2) in the annual (barley) than in the perennial (grass and lucerne, 350 mg dry weight m^–2) crops. For respiration, the nematodes used 4–71 O₂m^–2 year^–1 corresponding to C liberation of 1.3%–2.0% of the carbon input to the soil. A higher relative contribution by bacterial-feeding nematodes to the C and N fluxes and a higher turnover rate of the nematode biomass is an indication of more rapid nutrient circulation in the annual than in the perennial cropping systems.     

High-performance liquid chromatographic determination of strychnine in grain baits.l.

A simple and rapid high-performance liquid chromatographic procedure is described for the determination of strychnine. Grain baits containing strychnine alkaloid are ground, mixed, and extracted by shaking with chloroform. Without further cleanup, extract filtrates are injected directly into a liquid chromatograph. Chromatography is complete within 7 min and peak heights are used for quantitation. Separations were made on a 30 cm times 4 mm id stainless steel column packed with mu Porasil (8-12 mum silica). The eluting solvent was methanol-chloroform (10+90) at a flow rate of 2.0 ml/min. Recovery of spiked samples ranged from 91.5 to 95.2%. Confirmation of strychnine from a commercial sample was made by high resolution mass spectrometry with mass agreement to 1.2 ppm.     

“Laterite profiles” and “lateritic ironstones” on the hawkesbury sandstone,Australia

Laterite profiles in the Sydney area are generally regarded as fossil soils, formed during the Miocene, on a peneplain, under a tropical climate. It is also held that subsequent uplift and dissection destroyed much of this surface together with the laterite profiles. These views are poorly established yet widely accepted. This study demonstrates that there is a very close mineralogic and stratigraphic relationship between the “laterite profiles” and the Triassic Hawkesbury Sandstone, such that the profiles are best regarded as iron rich sandstone units undergoing contemporary near-surface alteration including the mobilization of iron minerals as crystalline solids.     

Availability of Cadmium in some Phosphorus Fertilizers to Field-Grown Lettuce

Although evaluations of the availability of cadmium (Cd) contaminants in phosphate fertilizers have been made, few have examined the transfer efficiency of Cd from fertilizers to plants, especially under field conditions. This 2-year field study determined the transfer of added Cd to lettuce (Lactuca sativa L.) (Royal Green) from a western phosphate rock (PR) and a triple superphosphate (TSP) as affected by liming and rate of fertilizer (or Cd) input. A readily soluble Cd salt, CdCl₂, was included in the study for comparison. The cumulative amounts of Cd added from the fertilizers and CdCl₂ over the 2-year period ranged from 0 to 1440 g ha^–1. Lettuce yield increased with increasing TSP rates, but was unaffected by PR. Significant (P < 0.01) effects of Cd source and rate, lime, and year were found on Cd accumulation by lettuce. The transfer of the added Cd was consistently higher for CdCl₂ than for the fertilizers regardless of lime rate. A contrasting year effect was also found between the two P fertilizers. In the second year of application, the Cd transfer efficiency increased in the soil treated with the PR, but decreased in the soil treated with the TSP. The Cd transfer efficiency for the plant was better measured with DTPA–Cd (r ²= 0.78 – 0.80) or CaCl₂–Cd (r ²= 0.57 – 0.76) than with soil total Cd (r ²= 0.39 to 0.54) across all Cd sources and lime rates. This is because DTPA–Cd or CaCl₂–Cd reflected the influences of the amount of Cd added, Cd source, and lime rate on Cd accumulation by the plant better than did the soil total Cd. Of the amount of Cd added from the fertilizers an average of 1.0% or less was accumulated in the harvested lettuce tissue. Applications of the fertilizers at high rates could result in increased Cd accumulation in the soil over time.     

孔隙结构图像分析中不同试验因素对分析结果的影响

研究了不同试验因素 (包括图像分辨率、土壤切片定向性、分析区域大小等 )对孔隙结构图像分析结果的影响以及试验误差 ,并简要介绍了用于分析土壤孔隙结构的土壤切片及数字图像的制备技术。结果表明 :不同试验因素对分析结果均会产生一定的影响 ,试验误差约在 1 0 %。这表明同一研究中应保持试验条件的相对一致以保证分析结果的可靠性和可比性     

Changes in penetration resistance of Ultisols from southern China as affected by shearing

Shear stresses and soil properties modified due to stress play an important role during formation of seals in a series of rainfall events and during tillage. The objectives of the study were to evaluate the effects of the penetrometer geometry on the penetration resistance as affected by shearing under different initial soil conditions and to use the information on soil strength to elucidate shearing process. Nine homogenous air-dried soils (<2 mm) were sprayed and stored so as to obtain equilibrium soil water contents. The moist soils were sheared by horizontal displacement of layers of soil particles/aggregates in between hands in one direction. The soil cores were prepared with comparable bulk density before the measurement of maximum penetration resistance (P_max) with a small flat tip and a cone tip penetrometers. At a wide range from 0.05 to 6.2 MPa, P_max was linearly correlated between the small flat tip and the cone tip penetrometers. The conversion ratio was higher under the saturation condition irrespective of the shearing effect. The penetrometer with the small flat tip was more sensitive for the weak soils. Shearing generally increased P_max in most cases, but it decreased P_max for some sandy soils under both saturated and unsaturated conditions and for a clayey soil under the saturated condition. The soil consisting of swelling clay exerted a decrease in P_max. Rearrangement and/or sliding of particles/aggregates and increase in soil suction during shearing were attributed to the increase in P_max. Increase in porosity due to the aggregation during shearing was ascribed to the decrease in P_max. In addition, it was shown that agricultural cultivation resulted in a reduction in soil strength.