Microbial biomass and mineralizable nitrogen distributions in no-tillage and plowed soils

Summary Distribution of soil microbial biomass and potentially mineralizable nitrogen (PMN) in long-term tillage comparisons at seven sites in the United States varied with tillage management and depth in soil. Microbial biomass and PMN levels of no-tillage soils averaged 54% and 37% higher, respectively, than those in the surface layer of plowed soil. Biomass and PMN levels were greatest in the surface 0 to 7.5-cm layer of no-tillage soil and decreased with depth in soil to 30 cm. Biomass and PMN levels of plowed soil, however, were generally greatest at the 7.5 –15 cm depth. Microbial biomass levels were closely associated with soil distributions of total C and N, water content, and water-soluble C as influenced by tillage management. Potentially mineralizable N levels in soil were primarily associated with distributions of microbial biomass and total N. Absolute levels of PMN and microbial biomass and the relative differences with tillage management were dependent on climatic, cropping, and soil conditions across locations. The additional N contained in soil biomass and PMN in the surface 0–7.5 cm of no-tillage compared with plowed soils ranged from 13 to 45 and 12 to 122 kg N/ha, respectively, for 6 of 7 locations. Fertilizer placement below the biologically rich surface soil layer and/or rotational tillage may improve short-term nitrogen use efficiency and crop growth on reduced-tillage soils.Contribution from USDA-ARS in cooperation with the Nebraska Agricultural Experimental Station, published as paper no. 8086, Journal Series, Nebraska Agricultural Experimental Station     

Thermal diffusivity of plowed leached meadow-chernozemic soils in the Adygeya Republic

Thermal diffusivity of the upper horizons of leached meadow-chernozemic soils varies in dependence on the soil water content within the following limits: 1.20–4.11 × 10⁻⁷ m²/s for the Ap horizon, 1.21–3.85 ×10⁻⁷ m²/s for the A1 horizon, and 1.35–3.73 × 10⁻⁷ m²/s for the A1B horizon. The relationships between the thermal diffusivity and the soil water content are described by S-shape curves with a long gently inclined segment within the range of water contents of <0.20 cm³/cm³, a distinct rise in thermal diffusivity within the water contents from 0.20 to 0.30–0.35 cm³/cm³, and a flattened or somewhat declining segment in the area with the high (>0.30–0.35 cm³/cm³) water contents. The thermal diffusivity of air-dried soil samples correlates with the physical clay (<0.01 mm) content. The Pearson correlation coefficient for these two variables equals −0.67 and is statistically significant at the significance level of 0.05. Regression equations allowing one to calculate the thermal diffusivity of the investigated soil horizons on the basis of data on the soil water content have been obtained.     

Evaluation of gas diffusivity models for no-tilled and tilled volcanic ash soils

Accurate quantification of soil gas diffusion is essential to understand the gas transport mechanism in soils, especially for soil greenhouse gas emissions. To date, the performance of soil gas diffusivity (D_p/D₀, where D_p is the soil gas diffusion coefficient and D₀ is the diffusion coefficient in free air) models has seldom been evaluated for no-tilled and tilled volcanic ash soils. In the present study, six commonly used models were evaluated for volcanic ash soils under two treatments by comparing the predicted and measured soil gas diffusivities at water potentials of pF 1.3–3. The Buckingham-Burdine-Campbell (BBC), soil-water-characteristic-dependent (SWC-dependent), and two-region extended Archie’s Law (2EAL) models showed better performance for both no-tilled and tilled volcanic ash soils, which is likely because porosity and pore size parameters of bimodal soils were taken into consideration in these models. Since the BBC model showed better accuracy than the SWC-dependent and 2EAL models and required fewer, more easily measurable parameters, this study recommends the BBC model for predicting soil gas diffusivity of volcanic ash soil under different tillage managements. In future studies, the BBC model should be further tested at water potentials of pF > 3, and may be improved by including the parameters of pore continuity and saturation.     

Modeling organic carbon dynamics under no-tillage and plowed systems in tropical soils of Brazil using CQESTR

CQESTR simulates the effect of management practices on soil organic carbon (SOC) stocks. The beta version of the model had been calibrated and validated for temperate regions. Our objective was to evaluate the CQESTR model performance for simulating carbon dynamics as affected by tillage practices in two tropical soils (Ultisol and Oxisol) in southeastern and northeastern Brazil. In the southeast (20.75 S 42.81 W), tillage systems consisted of no tillage (NT); reduced tillage (RT) (one disc plow and one harrow leveling [RT1] or one heavy disc harrow and one harrow leveling [RT2]); and conventional tillage (CT) (two heavy disc harrows followed by one disc plow and two harrow levelings). In the northeast (7.55 S 45.23 W), tillage systems consisted of NT, RT (one chisel plow and one harrow leveling), and CT (one disk plow, two heavy disk harrowings, and two harrow levelings). CQESTR underestimated SOC at both sites, especially under NT systems, indicating that adjustments (e.g., the inclusion of clay mineralogy factor) are necessary for more accurate simulation of SOC in the tropics. In spite of this, measured and simulated values of SOC in the 0–20 cm depth were well correlated (southeast, R² = 0.94, p < 0.01; northeast, R² = 0.88, p < 0.05). With respect to initial conditions (native forest), CQESTR estimated a decrease in SOC stocks in plowed and no-tillage systems. In 2006, in the southeast, SOC stocks were 28.8, 23.7, 23.2, and 22.0 Mg ha^?1 under NT, RT2, RT1, and CT, respectively; in the northeast, stocks were 36.0, 33.8, and 32.5 Mg ha^?1 under NT, RT, and CT, respectively. The model estimated carbon emissions varying from 0.36 (NT) to 1.05 Mg ha^?1 year^?1 (CT) in the southeast and from 0.30 (NT) to 0.82 (CT) Mg ha^?1 year^?1 in the northeast. CQESTR prediction of SOC dynamics illustrates acceptable performance for the two tropical soils of Brazil.     

长期施肥条件下潮土耕层有机磷含量与组分的变化研究

以15年肥料长期定位试验为基础,采用Bowman-Cole有机磷分组方法,研究长期施肥对潮土耕层有机磷组分及其变化的影响.结果表明:耕层有机磷含量相对较低,有机磷总量为22.35～66.95 mg·kg-1,占土壤全磷的4.47%～9.86%.各组分中以中度活性有机磷为主要部分,占有机磷58.93%～82.40%.长期施肥对土壤各组分有机磷含量产生明显影响,与对照CK相比,PK处理活性有机磷和中度活性有机磷增加,NP处理活性有机磷和中度活性有机磷减少,两处理间差异显著.施用有机肥显著增加耕层土壤中度稳定性有机磷含量.耕层土壤碱性磷酸酶与中稳定性有机磷呈显著正相关.     

Assessment of changes in the physical properties of plowed loamy soddy-podzolic soils in the nonchernozemic zone of European Russia under the impact of anthropogenic loads

The main physical characteristics of the plow layer of medium and heavy loamy soddy-podzolic soils were assessed. These soils were subdivided into the groups of degrading and improving soils. Permissible and critical values of the physical characteristics of the plow layer upon multiple anthropogenic impacts on it and the development of degradation processes were determined. A forecast of changes in the physical properties of the plow layer in soddy-podzolic soils upon their technogenic compaction was given.     

Soil fabrics of the plowed layer of flooded rice fields

For a long while Japanese agricultural workers have centered their efforts to an increase in rice production, confirming the extreme importance of appropriate water controlling for a good crop. Meanwhile, Japanese farmers have traditionally practiced to keep their fields in a dry state for several days in the mid-summer. They have been convinced of healthy plants with temporarily draining off water. Its season is generally in the dog-days from the end of July to the beginning of August, and the degree of drainage seems to be decided by farmer's private views or experience. For instance, the Japan's No. 1 prize winner in technical skill of rice competition in 1950 withdrew water until light marks remained when stepped in the field, while the 1952's winner drained his field until slight cracking on ground for the period August 11 to 13 (4). They were really successful in obtaining 7.71 and 9.27 tons of brown rice per hectare, respectively. However, it appears to be needed to bring out the scientific meanings of the practice more clearly in order to make it reasonably and universaly, provided the practice is indispensable for a good rice crop.     

Geostatistical analysis of sorptivity for a soil under tilled and no-tilled conditions

The properties of soils, even in short distances differ from point to point. These spatial variabilities may be described by geostatistics. This method determines the spatial structure of a specified variable. In this study, we measured the sorptivity of soil in field under tilled and no-tilled conditions with different sampling distances by using a simple method and performed the geostatistical analysis on the obtained data. The measurements were done on the corners of a regular network having dimensions of 5 m × 5 m in a tilled and no-tilled soil, and 0.5 m × 0.5 m in the same tilled soil. The results revealed that sorptivity had spatial structure in a tilled soil with 0.5 m × 0.5 m grid distances and no spatial structure occured in 5 m × 5 m distances, so it was believed that sorptivity is a structural variable only for short distance. The range of variogram was between 3.09 and 3.42 m for the sorptivity with 0.5 m × 0.5 m grids. The spherical model was the best-fitted theoretical variogram. In addition to the simple method for sorptivity measurement, we measured the sorptivity using double rings, which is known as Talsma method. Statistical tests showed a significant and non-significant difference between the two methods in 5 m × 5 m and 0.5 m × 0.5 m grids, respectively. In the simple method for sorptivity measurement, a ring with 10 cm height, 10 cm diameter, and about 2 cm depth of water was applied, but the rings used in the Talsma method were about three to four times larger. Therefore, it is concluded that for short distances, the sorptivity of simple method is in accordance with that obtained in Talsma method. The kriging method was used to estimate the presumed unknown values of sorptivity in some locations in the 0.5 m × 0.5 m grid distances. Results revealed that kriging method is capable enough to estimate the sorptivity if the variable has a spatial structure.     

Distribution characteristics of iron,carbon, nitrogen and phosphorus in the surface soils of different land use types near Xingkai Lake

Purpose

The purpose of this study was to research the differences in iron, phosphorus, nitrogen and organic matter contents at two soil depths in areas with different land use types in the Xingkai Lake National Nature Reserve and to determine the causes of those differences. Additionally, this study sought to analyse the correlations between the contents of different nutrients and to determine the reasons for those correlations.

Materials and methods

Five typical land use types, namely, lakeshore sandy land, grassland, forestland, dryland and wetland, were selected in the Xingkai Lake National Nature Reserve. The contents of amorphous iron (Fe_o), complexed iron (Fe_p), dithionite-extractable iron (Fe_d), total iron (TFe), total phosphorus (TP), total nitrogen (TN) and organic matter (OM) were measured in these soils at two depths: 0–5 cm (soil depth 1) and 5–10 cm (soil depth 2).

Results and discussion

For soil depth 1 and soil depth 2, the land use type had no significant effect on the element contents. For the entire soil depth range (0–10 cm), the land use type had the most significant impact on the TP content (p?<?0.01). Furthermore, soil depth had a significant effect on the contents of Fe_o (p?<?0.01), TP (p?<?0.01) and OM (p?<?0.05). Overall, the element content at soil depth 2 was higher than that at soil depth 1. The interaction between land use type and soil depth significantly influenced the contents of TN and OM (p?<?0.05). The contents of TN and OM in the lakeshore sandy land and dryland were high, and the contents of TN and OM were highly positively correlated (r?=?0.90652, p?<?0.01).

Conclusions

Different land use types caused different degrees of disturbance in the soil, resulting in differences in the element contents in the soils. The differences in the distribution of soil element contents in the topsoil were the result of important natural and human factors.

     

Specific surface area and surface charges of some argentinian soils

The specific surface areas of nine argentinian soils obtained by adsorption followed the order N₂ < ethylene glycol < H₂O, attributed to the presence of smectites (verified by XRD analysis) and some organic coating. The H₂O₂ treatment of these soils modified the former order of surface area determined by different absorbents. This order was modified because the mineral surface was evidenced and an increase of cation adsorption was produced by organic matter removal. This fact was supported by the decrease of PZC values of soils after H₂O₂ treatment. The specific surface area of initial soils obtained by water and ethylene glycol adsorptions showed a good correlation with carbon content and CEC of untreated soils and with the PZC of protonated soils.     

Physical properties of soils in Rostov agglomeration

Physical properties of natural and anthropogenically transformed soils of Rostov agglomeration were examined. The data obtained by conventional methods and new approaches to the study of soil physical properties (in particular, tomographic study of soil monoliths) were used for comparing the soils of different functional zones of the urban area. For urban territories in the steppe zone, a comparison of humus-accumulative horizons (А, Asod, Ap, and buried [A] horizons) made it possible to trace tendencies of changes in surface soils under different anthropogenic impacts and in the buried and sealed soils. The microtomographic study demonstrated differences in the bulk density and aggregation of urban soils from different functional zones. The A horizon in the forest-park zone is characterized by good aggregation and high porosity, whereas buried humus-accumulative horizons of anthropogenically transformed soils are characterized by poor aggregation and low porosity. The traditional parameters of soil structure and texture also proved to be informative for the identification of urban pedogenesis.     

Physical properties and spatial distribution of the plowpan in different arable soils

The morphology, water-physical properties, and spatial distribution of plowpans were studied. The presence of a plowpan in the root layer is most reliably detected from the macro- and micromorphometric indices and a reliable decrease in the interaggregate porosity and in the range of active moisture. As a rule, the plowpan does not have a continuous character; its appearance in the soil profile depends on the soil texture and wetting and is usually confined to the lower and wetter mesorelief elements. Loamy and clay loamy soils are more liable to form a plowpan. The current farming system favors the propagation of overcompaction deep into the soil profile. The areas with a plowpan within plowed fields vary in a wide range. The main reasons for the unfavorable physical properties of the subplow layer in a plowland are the natural extenuation of the soil-forming processes in this layer, which is manifested in a poorer aggregation, and the residual soil deformation under the long-term pressure of heavy machines. It is suggested that the plowpan can be destroyed via deep chiseling with the use of precision agriculture technologies.     

Physical properties and moisture retention characteristics of some nigerian soils

Measurements were made of physical characteristics of 119 samples from 23 profiles derived from two parent materials in Nigeria. The laboratory analyses included texture, plasticity and shrinkage characteristics, and a range of soil moisture constants including saturation point and moisture retention at various suctions. Simple and multiple correlation coefficients and regression analyses were conducted to investigate the possibilities of obtaining estimates of soil moisture retention from the textural analysis. Clay and sand contents are correlated with various soil moisture constants. The textural analysis may therefore be used to estimate moisture holding capacity at different suctions for these and similar soils with a predominantly uniform clay mineralogy, dominated by kaolinite and sesquioxides. Moisture retention curves indicate that the “field capacity” for most of these soils is better estimated at 60 or 100 cm of water suction rather than at 0.3 bar. A plot of the pF curves indicated only slight differences between moisture retention at 2 or 3 bar suction and at 15 bar suction.     

Physical properties of park soils of the objects of landscape architecture

Here the comparative characteristics of the physical properties of park soils, viz., anthropogenically transformed and engineered soils of the objects of landscape architecture, are given. The mechanical strength of aggregates, density, and aggregate physical properties to characterize the soil and agro-physical and environmental condition of soil objects of landscape architecture and establish the similarities or differences of engineered soil objects with zonal soils are described. We studied the physical properties of soils of different structural and functional elements of the landscape and the regular area of the Arkhangelskoe memorial estate. The structural state of the park soils is characterized as good. The engineered soils of the regular area of the park appear to have excessively high water resistance, while the postagrigenic sod-podzolic soils of the landscape area of the park are absolutely water resistant.     

Mobility of heavy metals in polluted soils near zinc smelters

The distribution and the availability of Cd, Zn, Cu, and Pb along the entire profile of two highly polluted soils located near Zn smelters have been related to the chemical and mineralogical composition of the soil. Lead and Cu deposits always remain in the surface layers and their availability measured by neutral ammonium acetate extraction was very weak. The behavior of Cd and Zn appears different in sandy acidic podzolic soils and in neutral loamy soils. These metals are associated with the organic matter migration in podzolic soils, while they remain in the upper layers in loamy soils provided that the pH is higher than 6. When the pH drops below 6, the mobility of Cd increases while that of Zn increases only below pH 5. The availability of heavy metals is lower in neutral loamy soils than in sandy acidic soils due to precipitation of carbonates and phosphates. With increasing depth, Cd and Zn are more available if the soil is acid; but, if the soil is neutral and loamy the availability is kept low by adsorption on clays and free oxides. The results of the complex trace metals interactions with the soil components show a higher accumulation capacity for loamy soils than for sandy soils notwithstanding the fact that their CEC is similar.     

Carbon dioxide emission from the surface of podzolic soils

The regularities of the seasonal dynamics of the CO₂ emission from the surface of a podzolic soil under a bilberry pine forest of the middle taiga were revealed. In mid-May, after the snow melt, the CO₂ emission was 0.10–0.20 g of CO₂/m² per h. Then, the intensity of the CO₂ emission increased, reached its maximum (1.0 to 1.5 g of CO₂/m² per h) in July–August, and decreased down to 0.04–0.10 g of CO₂ g/m² per h in mid-October. The correlation between the rate of the CO₂ emission and the temperature and moisture of the soil was positive and negative: r = 0.34 to 0.91 and ?0.44 to ?0.86, respectively. According to the empirical model, 2.26–2.69 t of C-CO₂/ha were emitted during the warm time of the year.     

Determination of surface charge density of soils

Abstract

A simple and precise method for determination of surface charge density of soils is described. It involves saturating the negative and positive exchange sites with NH⁺ ₄ and NO^‐ ₃ ions, respectively, removing the excess solution by centrifugation, and determining the ions on the exchange sites by a steam distillation method. Results showed that the concentration and type of saturating ions and the extractant used significantly affected the surface negative charge densities. The average value of surface negative charge densities of 10 surface soils from Iowa, Chile, and Costa Rica by the proposed method agreed closely with that obtained by the original method proposed by Schofield in 1949 (14.6 vs. 13.7 cmol(‐) kg^‐1 soil). The advantages of the proposed method are no need for the laborious extraction steps and simplicity of the steam distillation method for determination of NH⁺ ₄ and NO^‐ ₃ in soil samples.