PH—Postharvest Technology: Diffusive Drying Kinetics in Wheat,Part 2: applying the Simplified Analytical Solution to Experimental Data

Reanalysis of the drying background in wheat showed that analytical solutions may be employed in this grain to estimate diffusion coefficients by using the simplified equation for short times instead of the time-consuming series. Sixteen thin-layer drying curves of hard wheat were measured (airflow ≈ 0·3 kg m⁻²s⁻¹) covering four air temperatures (35–70°C) at each of four initial moisture content levels (0·189–0·269 decimal, d.b.). Experimental curves of the moisture ratio versus time grouped by initial moisture content showed the expected strong accelerating effect of temperature on drying rate. Besides, when the same curves were grouped by temperature, the moisture ratios corresponding to higher initial moisture contents fell, after some time, consistently faster, showing that the diffusion coefficient should increase somehow with water concentration. The short time simplified diffusive equation fitted each curve very well, with values of the coefficient of determination above 0·99. Values of the diffusion coefficient for the whole kernel ranged from 1·4×10⁻¹¹to 7·1×10⁻¹¹m⁻²s⁻¹, presenting the classical Arrhenius temperature dependency (activation energy ≈ 27·0 kJ mol⁻¹), but with a pre-exponential factor that depends linearly on initial moisture content. This diffusive kinetics is expected to be useful for fast and accurate dryer simulation.     

Erodibility in relation to water‐dispersible clay for some soils of eastern Nigeria

Water dispersible clay (WDC) can influence soil erosion by water. Therefore, in highly erodible soils such as the ones in eastern Nigeria, there is a need to monitor the clay dispersion characteristics to direct and modify soil conservation strategies. Twenty‐five soil samples (0–20 cm in depth) varying in texture, chemical properties and mineralogy were collected from various locations in central eastern Nigeria. The objective was to determine the WDC of the soils and relate this to selected soil physical and chemical attributes. The soils were analysed for their total clay (TC), water‐dispersible clay (WDC), clay dispersion ratio (CDR), dispersion ratio (DR), dithionite extractable iron (Fed), soil organic matter (SOM), exchangeable cations, exhangeable sodium percentage (ESP) and sodium adsorption ratio (SAR). Total clay contents of the soil varied from 80–560 g kg⁻¹. The USLE erodibility K ranges from 0·02 to 0·1 Mg h MJ⁻¹ mm and WEPP K fall between 1·2 × 10⁻⁶–1·7 × 10⁻⁶ kg s m⁻⁴. The RUSLE erodibility K correlated significantly with CDR and DR (r = 0·44; 0·39). Also, a positive significant correlation (r = 0·71) existed between WEPP K and RUSLE K. Soils with high clay dispersion ratio (CDR) are highly erodibile and positively correlates (p < 0·51) with Fed, CEC and SOM. Also, DR positively correlates with Mg²⁺ and SOM and negatively correlate with ESP and SAR. Principal component analysis showed that SAR, Na⁺ and percent base saturation play significant role in the clay dispersion of these soils. The implication of this result is that these elements may pose potential problem to these soils if not properly managed. Copyright © 2005 John Wiley & Sons, Ltd.     

Modelling Thermal Diffusivity of Differently Textured Soils

A series of models has been proposed for estimating thermal diffusivity of soils at different water contents. Models have been trained on 49 soil samples with the texture range from sands to silty clays. The bulk density of the studied soils varied from 0.86 to 1.82 g/cm³; the organic carbon was between 0.05 and 6.49%; the physical clay ranged from 1 to 76%. The thermal diffusivity of undisturbed soil cores measured by the unsteady-state method varied from 0.78×10^–7 m²/s for silty clay at the water content of 0.142 cm³/cm³ to 10.09 × 10^–7 m²/s for sand at the water content of 0.138 cm³/cm³. Each experimental curve was described by the four-parameter function proposed earlier. Pedotransfer functions were then developed to estimate the parameters of the thermal diffusivity vs. water content function from data on soil texture, bulk density, and organic carbon. Models were tested on 32 samples not included in the training set. The root mean square errors of the best-performing models were 17–38%. The models using texture data performed better than the model using only data on soil bulk density and organic carbon.     

Soil degradative effects of slope length and tillage methods on alfisols in western Nigeria. III.Soil physical properties

Effects of six slope lengths, 60 m to 10 m with 10-m increments, on soil physical properties were evaluated for plough-based conventional till and no-till seedbed preparation on field runoff plots for three consecutive years from 1984 to 1987. Soil physical properties measured included texture, bulk density, infiltration capacity, and soil moisture retention characteristics. Conventional till treatment caused a rapid increase in soil bulk density and penetration resistance, and decrease in available water capacity and equilibrium infiltration rate. Gravel content increased with cultivation duration. Soil bulk density of 0–5 cm depth was 1·20 Mg m⁻³ for 1984, 1·39 Mg m⁻³ for 1985 and 1·46 Mg m⁻³ for 1986 for conventional till; and 1·13 Mg m⁻³ for 1984, 1·33 Mg m⁻³ for 1985, and 1·27 Mg m⁻³ for 1986 for the no-till treatment. The penetration resistance of the no-till treatment was relatively low and increased with cultivation duration. Mean penetration resistance for 0–5 cm depth was 2·2 kg cm⁻² in 1984, 2·71 kg cm⁻² in 1985, and 3·79 kg cm⁻² in 1986. The available water capacity decreased in both tillage methods without any consistent trends with regard to slope length. The equilibrium infiltration rate declined drastically for long slopes and conventional till methods. The data support the conclusion that these soils should be managed with short slope lengths and a no-till method of seedbed preparation. © 1997 John Wiley & Sons, Ltd.     

Release Kinetics of Nonexchangeable Potassium by Different Extractants from Soils of Varying Mineralogy and Depth

Abstract

Nonexchangeable potassium (K) release kinetics of six major benchmark soil series of India as affected by mineralogy of clay and silt fractions, soil depth and extraction media was investigated. The cumulative release of nonexchangeable K was greater in smectitic soils (353 mg K kg^?1 at 0‐ to 15‐cm depth and 296 mg K kg^?1 at 15‐ to 30‐cm depth, averaged for 2 soils and 3 extractants) than in illitic (151 mg K kg^?1 at 0‐ to 15‐cm depth and 112 mg K kg^?1 at 15‐ to 30‐cm depth) and kaolinitic (194 mg K kg^?1 at 0‐ to 15‐cm depth and 167 mg K kg^?1 at 15‐ to 30‐cm depth) soils. Surface soils exhibited larger cumulative K release in smectitic and illitic soils, whereas subsurface soils had larger K release in kaolinitic soils. Among the extractants, 0.01 M citric acid extracted a larger amount of nonexchangeable K followed by 0.01 M CaCl₂ and 0.01 M HCl. The efficiency of citric acid extractant was greater in illitic soils than in smectitic and kaolinitic soils. Release kinetics of nonexchangeable K conformed fairly well to parabolic and first‐order kinetic models. The curve pattern of parabolic diffusion model suggested diffusion controlled kinetics in all the soils, with a characteristic initial fast rate up to 7 h followed by a slower rate. Greater nonexchangeable K release rates in smectitic soils, calculated from the first‐order equation (b=91.13×10^?4 h^?1), suggested that the layer edge and wedge zones and swelling nature of clay facilitated the easier exchange. In contrast to smectitic soils, higher release rate constants obtained from parabolic diffusion equation (b=39.23×10^?3 h^?1) in illitic soils revealed that the low amount of exchangeable K on clay surface and larger amount of interlayer K allowed greater diffusion gradients, thus justifying the better fit of first‐order kinetic equation in smectitic soils and parabolic diffusion equation in illitic soils.     

Diffusion coefficients of nitrate, chloride, sulphate and water in cracked and uncracked Chalk

The rates of diffusion of chloride, sulphate and water, labelled respectively with ³⁶Cl, ³⁵S and ³H, and unlabelled nitrate, were measured in small cylindrical Chalk monoliths. Using a simple mathematical model, diffusion coefficients were calculated to provide a basis for comparing the movement of these substances through Chalk rock in the absence of hydrostatic pressure gradients. The diffusion coefficients of chloride and nitrate were similar, with a range of values (0.52–3.23 × 10^?6 cm² s^?1) and (0.53–3.20 × 10^?6 cm² s^?1) respectively. These were slightly less than for tritiated water (0.60–3.51 × 10^?6 cm² s^?1), while the coefficient for sulphate was about half that of the others (0.28–1.47 × 10^?6 cm² s^?1). The coefficients indicate the absence of any interaction with the Chalk surfaces.     

Thermal properties of typical chernozems in Kursk Oblast

Thermal diffusivity and heat capacity of virgin and plowed heavy loamy typical chernozems of Kursk oblast were studied. Thermal diffusivity was determined in the course of step-by-step drying of the initially capillary-saturated samples to the air-dry state. Specific heat capacity was determined for absolutely dry samples. Volumetric heat capacity was calculated according to the de Vries equation. Thermal diffusivity varied within the ranges of (1.15–3.46) × 10^–7 m²/s in the Ap horizon, (1.14–3.35) × 10^–7 m²/s in the А1 horizon, (1.49–3.70) × 10^–7 m²/s in the АВ horizon, (1.49–3.91) × 10^–7 m²/s in the В1 horizon, and (1.60–3.80) × 10^–7 m²/s in the Вса horizon. The thermal diffusivity vs. water content dependencies had distinct maximums and were flattened in the range of low water contents. The maximums were most pronounced for the mineral B1 and Bca horizons; for the A1 and Ap horizons, the curves were rather S-shaped. Volumetric heat capacity of the air-dry soils varied from 0.96 J/(cm³ K) in the A1 horizon to 1.31 J/(cm³ K) in the Bca horizon; in the state of capillary saturation, it varied from 2.79 J/(cm³ K) in the А1 horizon to 3.28 J/(cm³ K) in the Вса horizon. Thermal properties of topsoil horizons were higher in the plowed chernozem compared with the virgin chernozem, which is explained by an increase in the bulk density and a decrease in the organic matter content in the plowed soil.     

SW—Soil and Water: Construction of an Artificial Perched Watertable,Part 1: Air Permeability of Soils and Aspects of Soil Failure

The annual precipitation in the Three-river Plain of the People's Republic of China is only 500–600 mm and, besides, the rainfall is uneven; 60–70% of the annual precipitation occurs in July and August and there is almost no rainfall in the winter and spring seasons. Experiments were conducted to form the artificial perched watertable where the runoff caused in summer could preferably be held, by injecting high-pressure air into the soil. A horizontal soil cavity is required, so this paper deals with the determination of the air permeability of soils and the difference in the soil failure mechanisms due to the different air permeabilities.The results show that the air permeability k of 10 m² s⁻¹ MPa⁻¹ defined the situation between the fluidization and the V-shaped soil failure. When the value of k was from 10 to 0·1 m² s⁻¹ MPa⁻¹, the V-shaped soil failure took place and when it was less than 0·1 m² s⁻¹ MPa⁻¹, the soil cavity production took place. In order to produce the soil cavity in the B horizon of the planosol or Cg1 horizon of the meadow soil by air injection, the value of k for these soils should be less than 0·1 m² s⁻¹ MPa⁻¹ and the soil water content of these soils should be more than 30% d.b.     

Soil‐gas diffusivity in large soil monoliths

The variability of gas diffusion in soil is not well known, but is important for assessing greenhouse gas emissions, soil decontamination, oxidation in soil and plant and root respiration. The goal of this study was to assess small‐scale variability of the relative soil‐gas diffusivity (D_s / D_o, m_{soil air}) using large intact soil monoliths and to compare D_s / D_o calculation methods. Neon (Ne) was maintained constant at the lower boundary of three monoliths of two soils (a sand and an organic soil). Ne concentration was measured at large spatial and temporal frequencies. Calculation methods included the use of average concentration, and average D_s / D_o per horizon, per section, or for the entire soil profile. Considering all sections of the monoliths, D_s / D_o varied from 3.5 × 10⁻³ to 1.2 × 10⁻¹ for the A_p horizon and from 4.8 × 10⁻³ to 8.3 × 10⁻¹ for the B_f horizon in the sand and from 1.0 × 10⁻³ to 7.9 × 10⁻³ for the O_hp horizon and from 2.4 × 10⁻⁴ to 7.7 × 10⁻² for the O_f horizon in the organic soil. For the entire soil profile, variations in D_s / D_o between monoliths reached 125% in the sand and 56% in the organic soil. The D_s / D_o calculation method influenced the apparent variability (CV) of D_s / D_o and, to a lesser extent, D_s / D_o values of the overall soil profile. Differences in D_s / D_o between monoliths could not be explained solely by the variability of total soil porosity and air‐filled porosity. Soil macroporosity (cracks and earthworm burrows) and layering greatly influenced variability of gas movement. Thus, the choice of sampling procedure, calculation method and modelling must be governed by the scale of the processes of interest and soil variability attributes.     

Molecular simulations to estimate thermodynamics for adsorption of polar organic solutes to montmorillonite

Ideally, one could use molecular mechanics or quantum mechanics to predict the magnitude of organic solute adsorption from water to soil minerals. Reproduction and/or prediction of mineral and interfacial structures remains challenging, but calculation of meaningful energy relations through computational chemistry techniques is even more difficult than structural calculations. This paper attempts to define the necessary and relevant components for an overall scheme that allows translation of computed interaction enthalpies to experimental adsorption enthalpies and vice versa. While the scheme could be applied to quantum calculations, we test it for the possibility of using empirical molecular mechanics to estimate relative energies for the adsorption of non‐ionic organic solutes in clay mineral‐water‐solute systems. We used molecular dynamics’ simulations to estimate relative clay–organic interaction enthalpies for a series of nitro‐aromatic solutes and hydrated, K‐saturated montmorillonite, for comparison with experimental adsorption isotherm data for the same clay‐nitroaromatic systems. The trend of computed interaction enthalpies (e.g. −234 ± 17 kJ mol⁻¹ for trinitrobenzene and −154 ± 16 kJ mol⁻¹ for p‐nitrobenzene) agreed modestly well with the trend of adsorption maxima from the experiments. Furthermore, we developed several variants on a thermodynamic cycle framework for comparing computed interaction energies with experimentally determined adsorption enthalpies. The algorithms, which include estimates for enthalpy changes both in bulk solution and in the clay interlayer, show promise: for p‐dinitrobenzene and for 1,3,5‐trinitrobenzene, the overall predicted adsorption enthalpies (e.g. −13 ± 22 and −67 ± 23 kJ mol⁻¹, respectively) were in modest agreement with experiments (−18 ± 1 and −28 ± 4 kJ mol⁻¹, respectively). We discuss shortcomings of the methods, in hopes of encouraging better estimates for the various energy terms, improvement of the algorithms, and more valid comparisons between quantum mechanical or molecular mechanical interaction energies and experimental enthalpies.     

Contribution of Specific Flour Components to Water Vapor Adsorption Properties of Wheat Flours

The dynamic water vapor adsorption properties were determined for two wheat flours (hard wheat flour and soft wheat flour) and compared with those of flour components (starch, damaged starch, gluten, water‐soluble pentosans, and water‐insoluble pentosans). Water vapor adsorption rates were determined from the changes in sample mass as a function of time during hydration after a step increase in relative humidity (rh). It was not possible to significantly discriminate the selected products by initial rates of adsorption (5.1 × 10^‐2 to 6.4 × 10^‐2 g/100 g of dry matter/min), except the water‐insoluble pentosans that were characterized by high values of adsorption rates (14 × 10^‐2 g/100 g of dry matter/min). Changes in initial relative humidity conditions and %rh step sizes induced significant changes in adsorption rates. Calculations of apparent water diffusion coefficients were done using a derived form of Fick's law for polydisperse spherical particles. Apparent water diffusion coefficients (at 25°C and 60% rh) were estimated between 2.19 × 10^‐15 and 3.72 × 10^‐15 m²/sec for the selected wheat flours. Water‐insoluble pentosans are characterized by the highest values of diffusion coefficients (1.53 × 10^‐13 m²/sec) when compared with the other wheat components. The calculated values of apparent water diffusion coefficient were discussed in regard to experimental conditions.     

Improved prediction of water-retention properties of clayey soils by pedological stratification

The water-retention properties of clayey soils have been studied at ?0.3 × 10⁵ and ?15 × 10⁵ Pa matric potentials using three sets of clayey horizons differing in their pedological origin. Measurements were made on small clods collected in winter when swelling is at a maximum. The results are discussed in relation to variations in the clay content and clay fabric. The bulk volume, which appears to be closely related to both clay content and clay fabric, allows the variations in water retained to be explained better than with clay content alone. With clayey horizons originating from a single soil family, differences in water retained can be explained by variations in clay content alone because clay fabric does not change greatly. These results demonstrate the significance of pedological stratification in estimating the water-retention properties when a single soil characteristic, such as clay content, is used.     

POTASSIUM RESERVES IN A 'HARWELL' SERIES SOIL

A sample of Harwell soil containing 36 percent fine clay (< 0.3 μm) and 14 per cent coarse clay plus fine silt (0.3–5μm) was separated into fractions, and the K-supplying power of soil and fractions measured by cropping with ryegrass, exchange with Ca resin and double-label isotopic exchange with ⁴²K and ⁴⁵Ca ions. Mineralogical examination of the fractions coupled with the cropping experiments showed that the K-supplying power of the soil to ryegrass can be explained by the presence of a zeolite, clinoptilolite-heulandite, in addition to the clay minerals, mica, and interstratified illitic smectite, commonly found in a glauconitic clay-rich soil. The 0.3–5 μm fraction, containing much zeolite, has an exchange diffusion coefficient for K ions to Ca resin of 1.8 × 10^?16 cm²sec^?1 compared with a value of 5.7 × 10^?20 for the < 0.3μm fractions in which interstratified illitic smectite is the dominant mineral. Isotopic exchange shows that all Ca ions in fractions < 50μm are isotopically exchangeable. In fractions coarser than 20μm, some of the K ions in felspar and mica were not exchangeable within the duration of the experiments.     

Deforestation and land-use effects on soil degradation and rehabilitation in western Nigeria. I. Soil physical and hydrological properties

Assessments of the effects of deforestation, post-clearance tillage methods and farming systems treatments on soil properties were made from 1978 through 1987 on agricultural watersheds near Ibadan, southwestern Nigeria. These experiments were conducted in two phases: Phase I from 1978 through 1981 and Phase II from 1983 to 1987, with 1 year (1982) as a transition phase when all plots were sown with mucuna (Mucuna utilis). There were six treatments in Phase I involving combinations of land clearing and tillage methods: (1) manual clearing with no-till (MC-NT); (2) manual clearing with plough-till (MC-PT); (3) shear-blade clearing with no-till (SB-NT); (4) tree-pusher/root rake clearing with no-till (TP-NT); (5) tree-pusher/root-rake clearing with plough-till (TP-PT); (6) traditional farming (TF). The six treatments were replicated twice in a completely randomized design. The traditional treatment of Phase I was discontinued during Phase II. The five farming systems studied during Phase II with a no-till system in all treatments were: (1) alley cropping with Leucaena leucocephala established on the contour at 4-m intervals; (2) and (3) fallowing with Mucuna utilis on severely degraded and moderately degraded watersheds, respectively, for 1 year followed by maize-cowpea rotation for another; (4) and (5) ley farming involving establishment of pasture in the first year on severely and moderately degraded plots, respectively, controlled grazing in the second year, and growing maize (Zea mays)-cowpea (Vigna unguiculata) in the third year. All treatments, imposed on watersheds of 2–4 ha each, were replicated twice. The soil properties analyzed were particle size distribution, total aggregation and mean weight diameter of aggregates, soil bulk density, penetrometer resistance, water retention characteristics, infiltration capacity and saturated hydraulic conductivity. These properties were measured under the forest cover in 1978, and once every year during the dry season thereafter during Phases I and II. Prior to deforestation, mean soil bulk density was 0·72 Mg m⁻³ and 1·30 Mg m⁻³, soil penetration resistance was 32·4 KPa and 90·7 KPa, and mean weight diameter of aggregates was 3·7 mm and 3·2 mm for 0–5 cm and 5–10 cm depths, respectively. The infiltration rate was excessive (54–334 cm hr⁻¹) and saturated hydraulic conductivity was rapid (166–499 cm hr⁻¹) under the forest cover. Furthermore, water transmission properties varied significantly even over short distances of about 1 m. Deforestation and cultivation increased soil bulk density and penetration resistance but decreased mean weight diameter of aggregates. One year after deforestation in 1980, mean soil bulk density was 1·41 Mg m⁻³ for 0–5 cm depth and 1·58 Mg m⁻³ for 5–10 cm depth. Soil bulk density and penetration resistance were generally higher for NT than for PT methods, and the penetration resistance was extremely high in all treatments by 1985. During Phase II, soil bulk density was high during the grazing cycle of the ley farming treatment. Sand content at 0–5 cm depth increased and clay content decreased with cultivation duration. Soon after deforestation, saturated hydraulic conductivity and equilibrium infiltration rate in cleared and cultivated land declined to only 20–30 per cent of that under forest. Mean saturated hydraulic conductivity following deforestation was 46·0 cm hr⁻¹ for 0–5 cm depth and 53·7 cm hr⁻¹ for 5–10 cm depth. Further, infiltration rate declined with deforestation and cultivation duration in all cropping systems treatments. During Phase I, mean infiltration rate was 115·8 cm hr⁻¹ under forest cover in 1978, 20·9 cm hr⁻¹ in 1979, 17·4 cm hr⁻¹ in 1980 and 20·9 cm hr⁻¹ in 1981. During Phase II, mean infiltration rate was 8·5 cm hr⁻¹ in 1982, 11·9 cm hr⁻¹ in 1983, 11·0 cm hr⁻¹ in 1984, 11·3 cm hr⁻¹ in 1985 and 5·3 cm hr⁻¹ in 1986. Infiltration rate was generally high in ley farming and mucuna fallowing treatments. Natural fallowing drastically improved the infiltration rate from 19·2 cm hr⁻¹ in 1982 to 193·2 cm hr⁻¹ in 1986, a ten-fold increase within 5 years of fallowing. High-energy soil water retention characteristics in Phase I were affected by those treatments that caused soil compaction by mechanized clearing and no-till systems. Soil water retention at 0·01 MPa potential in 1979 was 19·2 per cent (gravimetrics) for SB, 17·9 per cent for TP, 15·9 per cent for MC and 17·8 per cent for TF methods. With regards to tillage, soil water retention was 17·8 per cent for NT compared with 16·8 per cent for PT. During Phase II, water retention characteristics were not affected by the farming system treatments. Mean soil water retention (average of 4 years' data from 1982 to 1986) at 0·01 MPa for 0–5 cm depth was 16·6 per cent for alley cropping, 16·7 per cent for mucuna fallowing and 16·8 per cent for ley farming. Mean soil water retention for 1·5 MPa suction was 9·3 per cent for alley cropping, 8·7 per cent for mucuna fallowing, and 9·3 per cent for ley farming. Water retention at 1·5 MPa suction correlated with the clay and soil organic carbon content.     

AVAILABILITY OF POTASSIUM TO RYEGRASS FROM SCOTTISH SOILS II. UPTAKE OF INITIALLY NON-EXCHANGEABLE POTASSIUM

The stable desorption parts of soil Quantity/Intensity isotherms were used to determine the contributions of initially exchangeable and non-exchangeable potassium to plant uptake from ten soils. The activity ratio, AR^K= a_K/√^aC_a, Mg at which K was first taken up from non-exchangeable sources varied from 3 × 10^?3 to 8 × 10^?3 M^1/2 depending on the soil. Uptake rates of two categories of initially non-exchangeable K were linearly related to √times;. The first category appeared to be close to equilibrium with the initially exchangeable K, and gave effective diffusion coefficients of 10^?7 cm² s^?1 for four soils. The second category gave diffusion coefficients from 10^?20 to 10^?22 cm² s^?1, probably came from internal surfaces of micaceous clays, and began to be released at activity ratios below 3 × 10^?4 to 6 × 10^?4 M^1/2 depending on soil type. The soils fell into three groups, broadly consistent with soil series, on their ability to release the second category of potassium.     

Measuring the millimetre-scale oxygen diffusivity in soil using microelectrodes

The diffusivity of oxygen in soil was measured by periodically changing the gas above a soil core from nitrogen to air and vice versa. The concentration wave was measured as a function of depth with an oxygen electrode. For different Fourier components in the signal, phase shifts were calculated. The diffusivity follows from the increase of the phase shift with depth. Phase shifts are more suitable than signal amplitudes for the derivation of diffusivity. They are also easier to measure and do not require electrode calibration. For a clay soil with an air–filled porosity of about 0.05 m³ m^?3 a local diffusivity of 0.9 × 10^?9 m² s^?1 was measured. This is several orders of magnitude smaller than macroscopic values for entire core samples of the same soil type. This low value can be explained by the presence of locally water–saturated clay.     

Use of soil nonexchangeable potassium by paddy rice with clay structural changes under long-term fertilizer management

To prove the hypothesis that paddy rice utilizes soil nonexchangeable potassium (neK) and causes associated structural changes in clay minerals, K status and clay mineralogy of 22 surface soils from three paddy fields under long-term fertilizer management for 51–93 years were investigated. Soil neK content was determined as the difference between 1 mol L⁻¹ hot HNO₃ extractable K and 1 mol L⁻¹ ammonium acetate exchangeable K. Clay mineralogy was identified by X-ray diffraction (XRD). The radiocesium interception potential (RIP), an index of frayed edge sites in the interlayer sites of 2:1 type clay minerals, was also determined. The neK contents under the -K and NPK treatments were considerably lower than those under the unfertilized treatment in all the fields, indicating the exploitation of soil neK by rice. XRD analysis of the clay samples revealed 7% shift from the 1.0 peak to 1.4 nm one under the -K treatment compared with the unfertilized one, and the amounts of neK were negatively correlated with those of RIP (p < .01), suggesting the expansion of interlayer spaces of the 2:1 type phyllosilicates such as mica due to the release of neK. In addition, the neK content positively correlated with K balance of the long-term experiments (p < .05). The differences of neK between unfertilized K and -K treatments corresponded to 22–157 kg K ha⁻¹, or 0.42–1.68 kg K ha⁻¹ year⁻¹. In conclusion, utilization of considerable amount of soil neK under K depleted conditions should be considered to establish sustainable K management for paddy rice.     

黄河中游河道生态环境需水量研究

河流生态环境需水量作为维持河流生态系统功能的重要因素已成为当前研究的热点问题之一.本文在探讨河流系统生态环境需水量内涵的基础上,系统阐述了生态环境需水各分项的计算方法,并以黄河中游为例,针对该区的实际情况,采用蒙大拿法、最小月平均流量法、最大月平均含沙量法等计算研究区主要支流的生态环境需水量.计算结果表明,黄河中游生态环境需水量为47.356亿m3,输沙需水量为40.666亿m3,水面蒸发需水量为10.314亿m3.窟野河、无定河、汾河、泾河、北洛河、渭河、伊洛河和沁河的河道生态环境需水总量分别为2.071亿m3、3.393亿m3、10.143亿m3、8.699亿m3、3.575亿m3、34.601亿m3、6.481亿m3和2.505亿m3.由于黄河中游并非一个独立的河流系统,与上、下游有着密切的水利联系,难以确定黄河中游河道生态环境需水总量,有待进一步探讨和研究.     

Effects of Single and Mixed Ion Solutions on Hydraulic and Physical Properties of a Clay Soil

In this work, the influence of solute concentration of two types of electrolyte solutions single-ion (Na) and mixed-ion (Na–Ca) systems on hydraulic and some physical properties of a clay soil was investigated. Saturated hydraulic conductivity (HC) declined noticeably using lower solute concentration in single ion system. The highest reduction in HC was observed at 250 mole_c m^?3 solute concentration. Application of high solute concentration of single-ion system reduced meanweight diameter (MWD) to less than half of the control treatment (0.16 mm compared with 0.33 mm). Resistance to penetrometer increased with decreasing solute concentration. In mixed-ion system the MWD was increased whereas the resistance to penetrometer was decreased. HC values ranged from 6.5?×?10^?4 to 9.0?×?10^?4 mm s^?1 in mixed ion system compared with 7.2?×?10^?4 to 13.0?×?10^?4 mm s^?1 in single-ion system. The improvement of some physical properties in mixed-ion solution treatment is attributed to the presence of calcium ion that usually acts as amendment to sodium-affected soil. Soil HC showed lower values at low solute concentrations.     

Implication of Gypsum Rates to Optimize Hydraulic Conductivity for Variable‐Texture Saline–Sodic Soils Reclamation

Sodium (Na⁺) dominated soils reduce saturated hydraulic conductivity (K_s) by clay dispersion and plugging pores, while gypsum (CaSO₄•2H₂O) application counters these properties. However, variable retrieval of texturally different saline–sodic soils with gypsum at soil gypsum requirement (SGR) devised to define its quantity best suited to improve K_s, leach Na⁺ and salts. This study comprised loamy‐sand (LS), sandy loam (SL), and clay loam (CL) soils with electrical conductivity of saturation extract (EC_e) of ~8 dS m⁻¹, sodium adsorption ratio (SAR) of ~44 (mmol L⁻¹)^1/2 and exchangeable sodium of ~41%, receiving no gypsum (G₀), gypsum at 25% (G₂₅), 50% (G₅₀) and 75% (G₇₅) of SGR. Soils packed in lysimeters were leached with low‐carbonate water [EC at 0·39 dS m⁻¹, SAR at 0·56 (mmol L⁻¹)^1/2 and residual sodium carbonate at 0·15 mmol_c L⁻¹]. It proved that a rise in gypsum rate amplified K_s of LS ≫ SL > CL. However, K_s of LS soil at G₂₅ and others at G₇₅ remained efficient for salts and Na⁺ removal. Retention of calcium with magnesium (Ca²⁺ + Mg²⁺) by LS and SL soils increased by G₅₀ and decreased in G₇₅, while in CL, it also increased with G₇₅. The enhanced Na⁺ leaching efficiency in LS soil with G₂₅ was envisaged by water stay for sufficient time to dissolve gypsum and exchange and leach out Na⁺. Overall, the superiority of gypsum for LS at G₂₅, SL at G₅₀ and CL at G₇₅ predicted cost‐effective soil reclamation with a decrease in EC_e and SAR below 0·97 dS m⁻¹ and 5·92 (mmol L⁻¹)^1/2, respectively. Copyright © 2015 John Wiley & Sons, Ltd.