Soil Technology最新文献

Rate of change of surface soil aggregation under different cropping and subsurface drainage regimes was studied on a badly degraded lowland soil in the Lower Fraser Valley, British Columbia, Canada. The soil was the silty clay loam Humic Luvic Gleysol. Two cropping practices — continued spring-sown barley underseeded with clover for winter cover cropping and a 3 year grass ley — were established in a subsurface drained site and a poorly drained (no subsurface drainage) site. Grass ley consistently improved surface aggregate stability of drained and undrained soils when compared to cash-winter cover cropping integration. Improved aggregate stability with grass was significantly correlated with increasing soil organic carbon content. Aggregate stability and its correlation with organic carbon varied with time of sampling, being lower in the early spring and higher in the fall. Seasonal variation in aggregate stability was attributed to soil water content at sampling.

A three year field trial assessing the suitability of mine waste rock as a surrogate subsoil with different depths of topsoil showed that pasture yield was significantly lower in the unmodified waste rock (UWR) treatments compared to waste rock modified with lime and potassic superphosphate (MWR) during the first two years but there was no difference in yield in the third year between the waste rock treatments. The reduced yield in UWR during the first two years was considered to be due to phytotoxic levels of aluminium (Al) in the UWR soil solution. Soil samples from the waste rock interface (A) and waste rock at depth ≥ 300 mm (B) collected at the end of the three year trial were analysed for different forms of soil Al, total soluble fluoride (F), dissolved organic carbon (DOC) and soil pH to determine whether organic matter and F leachate from the topsoil reduced Al toxicity at the waste rock interface (A) during soil development over 3 years. Results showed that after 3 years, 0.02 M CaCl₂ extractable Al (Al_Ca) and 1 M KCl extractable exchangeable + soluble Al (Al_K) were effectively reduced in the MWR interface (A) by lime and fertiliser applications but they remained at very high phytotoxic levels (Al_Ca = 17–21 μg g⁻¹, Al_K = 261–339 (μg g⁻¹) in the UWR interface (A) irrespective of topsoil depth treatment. The corresponding organic bound Al (Al_OM) ranged from 200 to 214 μg g⁻¹ and DOC was in the range 169–203 μg g⁻¹ in both UWR and MWR interfaces (A). These values were a significant two-fold higher than the values at depth ≥ 300 mm (B) which were considered to be the original levels of Al_OM and DOC in UWR. The increase in Al_OM and DOC by the third year is probably due to progressive leaching of organic ligands produced from the decomposition of organic matter in the topsoil subject to an annual rainfall of 2500 mm. This evidence for the reduction in Al toxicity by organic matter is further supported by significant dry root density (DRD) in the UWR interface (A). This indicated that organic matter may have complexed toxic Al in UWR and alleviated Al toxicity in the third year of the field trial. Total soluble F levels were similar between interface (A) and waste rock depth (B) of the UWR, suggesting that F levels have not changed during the three years of the trial and therefore there was no evidence of F complexing with phytotoxic Al in the soil solution in the presence of organic ligands.

The potential of compost as an anti wind erosion agent was studied in a wind tunnel on a sandy soil susceptible to wind erosion. Soil treated with a compost-water mixture, which forms a crust on the soil surface after drying, was exposed to a series of increasing wind speeds. Two composts were compared (28 or 34% (w/w) organic matter) at two roughnesses of the soil surface (flat or with a regular pattern of ridges). Wind erosion at the untreated soil started at wind speeds of 6 m s⁻¹, both for the flat and rough surface. After application of 5.6 ton ha⁻¹ (on dry matter basis) compost, the wind speed had to be increased to 12–14 m s⁻¹ before wind erosion started. The differences in wind erosion between the two composts were small. The roughness of the soil surface hardly affected wind erosion.

Erosion process information from aggregated tropical soils is under-represented in the literature. Thus, an Oxisol was used in laboratory rainfall simulation experiments to examine the importance of antecedent moisture content (AMC) and rainfall energy flux density (EFD) on splash. Ten splash experiments were conducted at EFD-values ranging from 0.064 to 0.53 W m⁻² for 1 h dry and 1 h wet runs. Results indicated that AMC had no significant influence on total splash flux or splash flux per aggregate size fraction. However, splash increased linearly with EFD. The Oxisol exhibited a very high resistance to splash detachment (whole-soil basis), and the 2000–4000 μm aggregate size fraction was the most resistant to splash detachment. There was no significant difference for total splash flux between dry AMC-low EFD and wet AMC-low EFD events; or between dry AMC-high EFD and wet AMC-high EFD events. However, time trends differed significantly, and these reflected the influence of variable water content on near-surface soil strength, panicle shielding and availability of material. Splash enrichment ratios (ER) for all AMC and EFD data indicated that the 425–2000 μm aggregates were preferentially transported (i.e., ER significantly > 1.0). Aggregates of 250–500 μm were splashed in similar proportion to their content in the original soil, and aggregates < 250 μm and > 2000 μm were significantly depleted in splashed material (i.e., ER < 1.0). The reasons for depletion include either increased cohesion with fine grained aggregates or the inability of simulated rainfall to transport the most massive aggregates. Our data show that splash is a time-dependent process influenced primarily by rainfall energy flux and to a lesser extent by interactions with antecedent soil moisture status. Data of this type are essential for incorporation into state-of-the-art erosion prediction models if they are to be truly universal.

Atrazine was applied on a sandy loam, Typic Fluvaquent and a silty loam, Typic Udifluvent at a 1.4 kg ha⁻¹ a.i. rate on March 28, 1989. One month later, soil samples were taken at a 60 cm depth for measurement of the atrazine concentration. Similar concentrations were measured in the two soils. The atrazine transport was also simulated by using a physically-based model (HYDRUS). Analyses showed that HYDRUS predicted the atrazine mobility. A sensitivity analysis of the model with respect to sorption, degradation and hydraulic parameters showed that the sorption one was the most relevant in the simulation process. By calibrating the model with the best-fitted Kd value, the model predictions were appreciably improved.

Iron and manganese transformations were studied in a suspension of rice soil at controlled redox potentials (E_h) of − 300, − 150, 0, + 150 and + 300 mV only or in combination with three pH values of 6, 7 and 8. These experiments were carried out with and without addition of 1% (W/W) ground raw wheat straw. The E_h of theE_h-pH combination was kept on a constant level for 5 days, after which the different fractions of iron and manganese were determined. The incubation was carried out at 25 °C. Under controlled redox potential conditions, lowering in E_h caused an increase in pH. The soil suspension was kept at − 300 mV contained approximately a double amount of water-soluble plus exchangeable iron as compared with the other controlled redox potentials. The obtained data also showed that the concentration of water-soluble manganese was slightly affected by the redox potential. Meanwhile, the exchangeable manganese was strongly influenced by the E_h value. The threshold E_h value for the total soil (water-soluble + exchangeable) of iron and manganese was about − 150 to 0 mV. The residual iron and manganese decreased when the easily reducible iron and manganese increased with decreasing soil redox potential value and vice versa. The inflection point for the two fractions is about 0 mV. The addition of 1% organic matter led to a slight decrease in pH at different controlled E_h values. Generally, it increases water-soluble iron and manganese, exchangeable manganese and easily reducible manganese, meanwhile, slightly decreasing the exchangeable and reducible iron. Under controlled E_h-pH conditions, the redox potential and pH values affected the concentrations of water-soluble and exchangeable iron and manganese. Substantial amounts of both fractions were found under relatively low pH low redox potential conditions. Threshold E_h value for total water-soluble and exchangeable iron was at about − 150 mV and pH 8 and 7 while it increased to + 200 mV at pH 6. However, E_h was + 150 mV at pH 7 and 8 for manganese. Addition of organic matter slightly increased the amount of water-soluble iron at both pH 8 and 7 but it sharply decreased the amount of water-soluble iron at pH 6. The addition also decreased the exchangeable iron fraction at pH 8, while it increased the same fraction at both pH 7 and 6. The amount of reducible iron generally decreased, but no difference was found in the inflection point at pH 7 and 6 between the control and the addition of organic matter. Addition of organic matter only slightly decreased the water-soluble manganese fraction at pH 8, the decrease was important at pH 7. However, there was a sharp increase at pH 6. The effect of the addition of organic matter on the exchangeable manganese showed the same trend as observed for the wate