Characterizing the soil moisture regime of a Typic Haplohumod

The saturated hydraulic conductivities (K_sat) of 22 spodic horizons with and without a thin iron pan, were measured in situ with a new technique, using large, carved-out columns, encased in gypsum. Measured infiltration rates and pressure heads above and below the spodic horizons allowed calculation of K_sat, which averaged 8 cm d^?1. Flow rates averaged 32 cm d^?1, however, due to a hydraulic head gradient across the spodic horizon of 4 cm cm^?1. Occurrence of a thin iron pan in the spodic horizon did not affect its K_sat-value. The measured high flow rates exclude the occurrence of perched watertables. Lateral flow of water, forming surface ponds in local depressions, was due to surface runoff, rather than to lateral movement of perched water: surface ponding of water occurred also in soils in which the spodic horizon had been mixed by tillage.     

Drainability of some Dutch clay soils: A case study of soil survey interpretation

Riverine and marine non-calcareous Dutch clay soils have moderate limitations for use as grassland under existing conditions due to high ground-water levels in winter and early spring, which have traditionally been attributed to a very low K_sat of the clay. Physical research, which used soil morphology to define sample size and soil maps to locate test sites within defined mapping units, showed that permanent high ground-water levels were primarily due to low hydraulic gradients and not to a low K_sat. Well-maintained tile drainage, to be associated with low water levels in the ditches in winter, resulted in much lower ground-water levels in the soil, thereby effectively reducing use limitations imposed by existing conditions and improving soil suitability. The latter was specifically characterized in this study in terms of the assessment factor: “drainage status”. Tile drainage resulted in a significant increase of K_sat which was thought to be due to increased drying and cracking of the relatively young riverine soil. In the older marine soils, the increase of K_sat upon tile drainage was due to deep earthworm activity. Existing suitability can thus be improved by using appropriate technology, i.e., tile drainage associated with better water management. The detail by which the technology is defined in soil survey interpretation is critical. The detail should not exceed the generality-level dictated by the variability of regional field data.     

Effect of an anionic surfactant on hydraulic conductivities of sodium- and calcium-saturated soils

The effect of sodium dodecylbenzenesulfonate （SDBS）, an anionic surfactant used widely in household products and industrial processes, on saturated hydraulic conductivities （Ksat） of an Anthrosol saturated with sodium （Na-soil） or calcium （Ca-soil） was analyzed in a laboratory experiment using the constant head method, and adsorption and dispersion experiments were also conducted to infer the possible mechanisms of Ksat fluctuations. The results showed that SDBS was more intensely adsorbed in the Ca-soil than in the Na-soil. With an increase in the SDBS concentration, the stability of the Na-soil suspensions decreased when the SDBS concentration was less than 1.2 mmol L^-1 and then above this concentration, increased markedly, while the stability of the Ca-soil suspensions increased gradually at all SDBS concentrations studied. With an increase in the SDBS concentration, the Ksat of the Na-soil increased, which resulted mainly from the increase of water channels in the soil because of the coagulation of the soil particles, while the Ksat of Ca-soil decreased mainly on account of the clogging of partial water channels by precipitated Ca（DBS）2 and the fine soil particles generated.     

RZWQM simulation of long-term crop production, water and nitrogen balances in Northeast Iowa

Agricultural system models are tools to represent and understand major processes and their interactions in agricultural systems. We used the Root Zone Water Quality Model (RZWQM) with 26 years of data from a study near Nashua, IA to evaluate year to year crop yield, water, and N balances. The model was calibrated using data from one 0.4 ha plot and evaluated by comparing simulated values with data from 29 of the 36 plots at the same research site (six were excluded). The dataset contains measured tile flow that varied considerably from plot to plot so we calibrated total tile flow amount by adjusting a lateral hydraulic gradient term for subsurface lateral flow below tiles for each plot. Keeping all other soil and plant parameters constant, RZWQM correctly simulated year to year variations in tile flow (r² = 0.74) and N loading in tile flow (r² = 0.71). Yearly crop yield variation was simulated with less satisfaction (r² = 0.52 for corn and r² = 0.37 for soybean) although the average yields were reasonably simulated. Root mean square errors (RMSE) for simulated soil water storage, water table, and annual tile flow were 3.0, 22.1, and 5.6 cm, respectively. These values were close to the average RMSE for the measured data between replicates (3.0, 22.4, and 5.7 cm, respectively). RMSE values for simulated annual N loading and residual soil N were 16.8 and 47.0 kg N ha⁻¹, respectively, which were much higher than the average RMSE for measurements among replicates (7.8 and 38.8 kg N ha⁻¹, respectively). The high RMSE for N simulation might be caused by high simulation errors in plant N uptake. Simulated corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] yields had high RMSE (1386 and 674 kg ha⁻¹) with coefficient of variations (CV) of 0.19 and 0.25, respectively. Further improvements were needed for better simulating plant N uptake and yield, but overall, results for annual tile flow and annual N loading in tile flow were acceptable.     

Effects of Cow Dung Biochar Amendment on Adsorption and Leaching of Nutrient from an Acid Yellow Soil Irrigated with Biogas Slurry

Knowledge of the saturated hydraulic conductivity (K _sat) of porous filters used in water treatment technologies is important for optimizing the retention of nutrients and pollutants. This parameter determines the hydraulic capacity, which together with the chemical properties of the filter media, affects the treatment performance of the filter system. However, measuring K _sat is time consuming and expensive. This study developed a novel transfer function to predict K _sat of coarse porous media from easily measured parameters. The hydro-physical parameters determined were K _sat, grain size distribution, bulk density, uniformity coefficient, particle density, and porosity of 46 porous media fractions. The fractions ranged in grain size from 0.5 to 20 mm and were obtained from seven commercial available coarse filter materials. A backward stepwise regression analysis was performed between K _sat and 10 variables obtained from the grain size distribution and bulk density. The optimal model for predicting K _sat contained two parameters, D₂₀ and D₅₀, which describe respectively the particle diameters, where 20 and 50 % of all particles are finer by weight. The predicted K _sat values were in good agreement with the measured values (R ²?=?0.91). The transfer function can find potential usage in relation to dimensioning of permeable agricultural drainage filters or subsurface-flow constructed wetlands. The predicted values of K _sat can also be used as input to numerical models that simulate filter treatment performance.     

Calculation of hydraulic conductivities of horizons in some major soils in Wisconsin

Hydraulic conductivity between saturation and a tension of 100 cm water was calculated with moisture-retention data for nine soil horizons and compared with results from in situ measurements with the crust test. Agreement was good for sandy, apedal soil horizons with simple packing voids but only if matching factors were used. Results were unreliable in clayey, pedal soil horizons in which a few relatively large planar and tubular pores determine K in the measured tension range, whereas the greatest fraction of total porosity is composed of fine pores inside peds that hardly contribute to flow. Varying the number of pore classes (n) and the water-filled porosity at saturation made no significant difference in the calculations for the apedal soils, but drastically changed the shape of the calculated curves for the pedal soils. Matching factors based on K_sat measurement had to be used for all studied soil horizons, indicating that Marshall's pore-interaction model never predicted K_sat accurately.     

Anisotrope Variation der gesättigten Wasserleitfähigkeit einer unterschiedlich beweideten Salzmarsch im Deichvorland

Anisotropic variation of saturated hydraulic conductivity of a variously grazed salt marsh soil Undisturbed core samples were taken in horizontal and vertical direction from a variously grazed salt marsh soil for investigation of the anisotropic variation of saturated hydraulic conductity K_sat, bulk density, and pore size distribution. The results show that saturated hydraulic conductivity varies significantly anisotropically. The average Kv/Kh ratio is 0.38 for the soil profile and 0.44 for the surface soil. This anisotropy of K_sat is mainly attributed to the stratified structure of soil due to the sedimentation conditions in the salt marsh environment and decreases if soil structure development through pedological processes progresses. Furthermore. K_sat decreases significantly if the stocking rate of grazing is larger than 1.0 sheep unit/ha and the effect is more pronounced near the dike. However, both the Kv and Kh are affected by grazing in the same manner, so that the anisotropy of K_sat is independent from grazing. Bulk densitiy and macroporosity are affected by grazing but not by the direction of sampling. There are significant correlations between K_sat and > 50 μm as well as > 10 μm pore volume. The correlation between K_sat and total porosity is however not significant. The anisotropy of K_sat implicates the favouring of the lateral water flux and in the hydrological research and modelling of the salt marsh ecosystem the anisotropy of K_sat should be taken into account.     

Effect of Soil Sample Size on Saturated Soil Hydraulic Conductivity

Saturated hydraulic conductivity (K_sat) is regarded as a key soil physical variable to determine soil infiltration rate, percolation depth and other hydrological processes. The purpose of this study was to determine the best soil sampling’s ring size for measuring K_sat. For this purpose, 25 rings with five different diameters (2, 3, 4, 5 and 6 inch) and with the same depth of 20 cm (five replicates) were hammered in close vicinity to each other into the ground of undisturbed loess deposits of a small farm to measure K_sat and bulk density. Hydraulic conductivity was measured at three constant loads of 22, 27 and 32 cm. The results showed that the ring with the internal diameter of 6 inches had the minimum variation coefficient and maximum K_sat for all the three hydraulic heads. In addition, the bulk density of this ring size was less than the other rings.     

渝东北紫色土饱和导水率传递函数研究

为研究渝东北紫色土理化性质在垂直空间上的分布情况以及对饱和导水率的影响,进而建立饱和导水率与各理化性质间的关系函数,推求饱和导水率的传递函数,选择渝东北开州区、云阳县等7个区县内45个紫色土典型田块为研究区域,运用Excel 2013和Matlab 2015b软件统计分析后,利用多元非线性回归法推求并验证了渝东北紫色土饱和导水率传递函数模型和模型参数。研究表明:①研究区土壤饱和导水率变化范围在0.16～195.68 cm/d,变化范围广,空间变异系数大,变异性较强;同一采样点深度越大,饱和导水率越小;②土壤饱和导水率与有机质含量有显著的指数函数关系,与饱和含水量有较强的二次函数关系,与土壤容重和土壤颗粒的相关性不大;③本次试验建立的土壤饱和导水率传递函数模型及模型系数检验合格,预测值与实际测算值误差较小,精度良好,可用于渝东北紫色土饱和导水率的预测工作。     

Change of dry bulk density and Ksat after incubation of a soil in the presence of organic amendments

Abstract

Kamouraska Ap horizon samples were incubated in the presence of organic amendments, peat moss, straw, compost and green manure, applied at a rate equivalent to 7.5 t of carbon/ha. Water was added to reach 80% of field capacity. The soil‐amendement mixtures were incubated at 37°C for periods of 4, 8, 16, 32 or 64 weeks. Settling tests were performed using a jolting volumeter. Minimum dry bulk density (mDBD), saturated hydraulic conductivity (K_sat) and water content at field capacity were determined. For the unamended soil, mDBD corresponded to 1.1 g.cm^‐3 and K_{sat max} to 265 cm/h. After incubation, mDBD varied from 1.02 to 1.12 g.cm^‐3 and K_{sat max} values were generally below 150 cm/h. The results were discussed in relation to the decomposition of the organic amendments and the formation of stable aggregates.     

Earthworm burrowing activity of two non-Lumbricidae earthworm species incubated in soils with contrasting organic carbon content (Vertisol vs. Ultisol)

The aim of this study was to investigate the burrowing activity of two earthworm species: the endogeic Drawida sinica and one undescribed Amynthas species incubated in Vertisol and Ultisol presenting different soil organic C content. Because of their contrasting feeding behaviours, we hypothesised that soil type would have a bigger influence on the burrowing activity of the endogeic than the anecic species. Repacked soil columns inoculated with earthworms for 30 days were scanned using X-ray tomography and the compiled images used to characterise the burrow systems. After scanning, the saturated hydraulic conductivity (K _sat) was also measured. The Amynthas species burrows were less numerous (30 vs. 180), more vertically oriented (57 vs. 37°), more connected from the surface to the bottom of the columns (73 vs. 5 cm³) and had a higher global connectivity index (83 vs. 28%) than those of D. sinica. The K _sat was threefold faster in columns incubated with Amynthas and was linked to the volume of percolating burrows (R ² = 0.81). The soil type did not influence Amynthas burrow characteristics. In contrast, there were 30% more D. sinica burrows in the Vertisol than in the Ultisol while other burrow characteristics were not affected. This result suggests that these burrows were more refilled with casts leading to shorter and discontinuous burrows. The K _sat was negatively related to the number of burrows (R ² = 0.44) but was not statistically different between the Vertisol and the Ultisol, suggesting a constant impact of this species on the K _sat. We found that a decrease in the amount of soil organic C by 50% had only a small influence on earthworm burrowing activity and no effect on the K _sat.     

Linking fragipans,perched water tables,and catchment-scale hydrological processes

Soils with very slowly permeable fragipans and fragipan-like argillic horizons are extensive throughout the Palouse Region of northern Idaho and eastern Washington, USA. These soils develop seasonal perched water tables (PWTs) under the xeric moisture regime of the region. The objective of this study was to utilize a hydropedology approach to examine the linkages between fragipans, PWTs, and catchment-scale hydrological processes such as soil water storage, runoff, and lateral throughflow. A 1.7-ha catchment dominated by Fragixeralfs (Fragic Luvisols) was instrumented with 135 automated shallow wells to monitor PWTs. Soil water content was measured with water content reflectometry probes, and catchment outflow was measured with a flume. A 35 m × 18 m plot was isolated hydrologically from the surrounding hillslope using tile drains and plastic sheeting to measure perched water outflow. Results show that during the wet winter and spring months, the transition from unsaturated to saturated conditions is accompanied by changes in volumetric water storage of only 4–5%. PWT levels are at the surface of ∼ 26–45% of the catchment soils during periods of high rainfall and snowmelt, thereby generating saturation-excess surface runoff from hillslopes. Observed solute movement via subsurface flow is very rapid and ranges between 2.9 and 18.7 m d^− 1 when PWTs are maintained in more-permeable Ap and Bw horizons. Subsurface lateral flow accounts for as much as 90% of the incident precipitation and snowmelt during early spring. Data indicate that the relatively shallow depth to the fragipans and high K_sat in surface soil layers combine to create a very flashy hydrological system characterized by considerable temporal and spatial variation in patterns of saturation-excess runoff.     

Soil hydraulic and physico-chemical properties of Ultisols and Inceptisols in south-eastern Nigeria

Understanding soil water dynamics and storage is important to avoid crop failure on highly weathered, porous and leached soils. The aim of the study was to relate soil moisture characteristics to particle-size distributions and chemical properties. On average, Atterberg limits were below 25% in the A-horizon and not more than26.56% in the B-horizon, whereas soil bulk density was between 1.27 and 1.66Mgm^?3. The saturated hydraulic conductivity (K_sat) was generally between 0.20 and 5.43 cm h^?1 in the top soil and <1.31 cm h^?1 in the subsoil. The higher K_sat values for the A-horizons were attributed to the influence soil microorganisms operating more in that horizon. The amount of water retained at field capacity or at permanent wilting point was greater in the B-horizons than in the A-horizons, suggesting that clay accumulation in the B-horizon and evapotranspiration effects in the A-horizon may have influenced water retention in the soils. Soil moisture parameters were positively related to clay content, silt content, exchangeable Mg²⁺, Fe₂O₃ and Al₂O₃, and negatively related to sand content, SiO₂, sodium absorption ratio, exchangeable sodium percentage and bulk density. The low clay content may explain why drainage was so rapid in the soils.     

Development of QSAR's in soil ecotoxicology: Earthworm toxicity and soil sorption of chlorophenols,chlorobenzenes and chloroanilines

Soil adsorption and the toxicity of four chloroanilines for earthworms were investigated in two soil types. The toxicity tests were carried out with two earthworm species, Eisenia andrei and Lumbricus rubellus. LC₅₀ values in mg kg^?1 dry soil were recalculated towards molar concentrations in pore water using data from soil adsorption experiments. An attempt has been made to develop Quantitative Structure Activity Relationships (QSAR's) using these results and data on five chlorophenols and dichloroaniline in four soils and five chlorobenzenes in two soils published previously (Van Gestel and Ma, 1988, 1990; Van Gestel et al., 1991). Significant QSAR relationships were obtained between 1) adsorption coefficients (log K _om ) and the octanol/water partition coefficient (log k _ow ), and 2) LC₅₀ values (in itμmol L^?1 soil pore water) and log K _ow . It can be concluded that both earthworm species tested are equally sensitive to chlorobenzenes and chloroanilines, E. andrei is more sensitive than L. rubellus to chlorophenols.     

Effect of straw and plastic film management under contrasting tillage practices on the physical properties of an erodible loess soil

The current cropping system of excessive tillage and stubble removal in the northwestern Loess Plateau of China is clearly unsustainable. A better understanding of tillage and surface cover management on surface soil structure is vital for the development of effective soil conservation practices in the long term. Changes in surface soil structure and hydraulic properties were measured after 4 years of straw and plastic film management under contrasting tillage practices (no tillage vs. conventional tillage) in a silt loam soil (Los Orthic Entisol) which had been under conventional management for hundred of years in the northwestern Loess Plateau, China. Surface soil (0–10 cm) under no tillage with straw cover had the highest water stability of macro-aggregates (>250 μm) and the highest saturated hydraulic conductivity. Compared with straw cover, plastic film cover did not change macro-aggregate stability and the soil had the lowest saturated hydraulic conductivity (K_sat) but the highest % <50 μm soil particles. Significant correlation was found between water stable macro-aggregates and soil organic carbon content, indication the importance of the latter on soil structural development. No tillage on its own (without straw cover) was not sufficient to improve structural stability probably due to lack of organic carbon input. While use of plastic film cover might lead to short term yield increases, results indicated that it did little to improve soil physical fertility. On the other hand, no tillage with straw cover management should lead to long-term improvement of physical quality of this structurally fragile soil.     

Spatial and temporal variability of some soil physical properties following tillage of a Nigerian Paleustult

The objective of this study was to evaluate quantitatively the magnitude of the spatial and temporal variation for 7 soil physical properties on a conventionally-tilled Nigerian Paleustult. A 0.4-ha plot was disc-ploughed, disc-harrowed twice, subjected to tractor-wheel traffic at regular space intervals and then seeded to maize (Zea mays, L.). There were significant differences in the physical properties owing to tillage position (spatial variability) and date of sampling (temporal variability), more so in the 0–10-cm layer than in the 10–20-cm layer. In the surface layer, bulk density (Db) and penetrometer resistance (PR) were significantly higher (P ⩽ 0.01) along the tyre marks (maximum Db = 1.76 Mg m⁻³) than in the uncompacted crop row (maximum Db = 1.35 Mg m⁻³) and interrow positions (maximum Db = 1.46 Mg m⁻³). Saturated hydraulic conductivity (K_sat), total porosity (TP) and macroporosity (M) were significantly lower along the tyre mark than in the crop row and interrow positions. K_sat ranged from 0.6 to 42.8 cm h⁻¹, TP, from 0.34 to 0.50 cm³ cm⁻³ and M from 0.06 to 0.25 cm³ cm⁻³ along the tyre mark and crop row positions, respectively. Significant temporal changes were noticed only in K_sat, soil moisture content (MC) and PR. K_sat increased steadily with time along the tyre mark, but showed an irregular trend in the other two positions. PR did not change with time along the tyre marks but it increased significantly with time along the other two positions. MC changed according to the periodicity of rainfall. Only TP varied, owing to tillage position × date interaction. The 10–20-cm layer was spatially less variable but temporally more viarable than the surface layer. Only K_sat and PR showed significant changes owing to the tillage positions, but Db, K_sat, PR and moisture retained at 10 kPa suction (τv10) showed significant temporal changes. Only τv110 varied owing to position × date interaction in this layer.     

Effect of long‐term swine‐manure application on soil hydraulic properties and heavy metal behaviour

This study evaluated the effect of 13 years of swine‐manure application on the changes in soil hydraulic properties, and as associated physicochemical properties, with a focus on heavy metal mobility. Various soil hydraulic properties were measured, including soil water retention (SWR), saturated field hydraulic conductivity (K_fs) and unsaturated field hydraulic conductivity (K_funsat) using a disc infiltrometer. Heavy metal mobility was evaluated with a sequential extraction procedure. At 0–30 cm soil depth in the heavily manured plot (SMhigh plot), SWR at 0 to ?100 kPa was significantly larger than in plots amended with a standard amount of manure (SMstd plot) or with chemical fertilizer (CF plot). K_fs and K_funsat values in both manure‐amended plots were less than in the CF plot under dry soil conditions but greater than those of the CF plot under wet soil conditions. Furthermore, K_fs and K_funsat did not necessarily increase with manure application rates. On the other hand, high‐mobility metal fractions, such as the exchangeable fraction of Zn, and the CH₃CO₂Na‐extractable fraction of Zn and Mn, and the metal–organic complex fractions of Zn, Cu and Mn, increased with the greater manure application rate. In addition, low‐mobility metal fractions, the organically bound fractions of Zn, Cu and Mn in the high SM plot and the easily reducible metal oxide fraction of Mn in both manure‐amended plots were probably affected and released into high‐mobility fractions. This indicated that manure application changed the soil redox conditions by improving the soil structure, depending on the water content of soil pores. Despite the reduction of K_fs and K_funsat by heavy manure application, the transport of high‐mobility metal fractions with either surface water flow or infiltration water flow could be controlled by soil water content at the beginning of a rain or irrigation event.     

Surface soil hydraulic properties in four soil series under different land uses and their temporal changes

The concepts of “genoform” and “phenoform” distinguish the genetically-defined soil series and the variation of soil properties resulted from different land uses and management practices. With the repeated field measurements over time, we attempted to understand the difference of soil hydraulic properties among different land uses for a given soil series, and their temporal dynamics. Four soil series (Glenelg, Hagerstown, Joanna, and Morrison) in Pennsylvania with contrasting textures, structures, and parent materials were investigated. Within each soil series, four common land uses (woodland, cropland, pasture, and urban) were examined. At each site of soil series–land use combination, field-saturated and near-saturated hydraulic conductivities, K(ψ), were measured at the soil surface using standard tension infiltrometers at water supply potentials (ψ) of − 0.12, − .06, − 0.03, − 0.02, − 0.01, and 0 m. Surface infiltration measurements were repeated at each site in May and October from 2004 to 2006. The analysis of variance indicated that the measurement time (May or October) had the greatest impact on all measured hydraulic conductivities (p < 0.001), followed by the land use (p < 0.05 for K_ψ = 0 and K_{ψ = − 0.06}) and soil series (p < 0.06 for K_{ψ = − 0.01} to K_{ψ = − 0.03}). The interactions between the time and land use and between the soil series and land use were statistically significant for K_ψ = 0 and K_{ψ = − 0.01.} When separated by the measurement time, land use showed greater impacts in October than in May, while soil series had greater impacts in May than in October. Among the four land uses, woodland showed less obvious temporal change compared to the other three land uses because of less human-induced impacts and more consistent ground cover. Other three land uses generally showed a higher hydraulic conductivity in May than in October due to the drier initial soil moisture condition and related management practices in the spring that gave rise to more significant macropore flow. The results suggested that the initial soil moisture is an important variable that drives the temporal variation of the surface soil hydraulic properties.     

Applying a Lagrangian dispersion analysis to infer carbon dioxide and latent heat fluxes in a corn canopy

Warland and Thurtell (2000) proposed an analytical dispersion Lagrangian analysis (hereafter WT analysis) to relate the mean scalar concentration field to source profiles inside the canopy. The first objective of this study was to evaluate the performance of the WT analysis with existing turbulence statistics parameterizations in a corn canopy, by comparing its inferred net ecosystem CO₂ exchange (NEE) and latent heat flux (λE) with eddy covariance measurements. The second objective was to assess the performance of the WT analysis to infer the soil CO₂ flux. Four parameterizations of turbulence statistics were used to estimate Lagrangian time scale (T_L) and standard deviation of vertical wind velocity (σ_w) profiles. The estimated T_L and σ_w profiles were then corrected for atmospheric stability conditions. The field experiment was carried out in a corn field from August to October 2007 and 2008. Profiles of water vapour and CO₂ mixing ratios were measured using a multiport sampling system connected to an infrared gas analyzer. Wind velocity within and above the canopy and eddy covariance measurements over the canopy were taken. The soil respiration, estimated using the WT analysis, was compared to estimates obtained by an empirical model. WT analysis fluxes showed good correlation (R² = 0.77-0.88) with NEE and λE obtained by the eddy covariance technique, but overestimated net fluxes, especially when corrections for atmospheric stability were applied. The optimization of T_L and σ_w profiles using in-canopy turbulence measurements improved the agreement between measured and modeled NEE and λE. Inferred soil CO₂ fluxes were underestimated and were poorly correlated (R² = 0.02-0.01) with estimates obtained using an empirical model based on soil temperature. This poor performance in estimating the soil respiration is likely caused by the decoupling between inside and above canopy flows.     

Soil hydraulic properties influenced by corn stover removal from no-till corn in Ohio

Corn (Zea mays L.) stover removal for biofuel production and other uses may alter soil hydraulic properties, but site-specific information needed to determine the threshold levels of removal for the U.S. Corn Belt region is limited. This study quantified impacts of systematic removal of corn stover on soil hydraulic parameters after 1 year of stover management under no-till (NT) systems. These measurements were made on three soils in Ohio including Rayne silt loam (fine-loamy, mixed, active, mesic Typic Hapludult) at Coshocton, Hoytville clay loam (fine, illitic, mesic Mollic Epiaqualfs) at Hoytville, and Celina silt loam (fine, mixed, active, mesic Aquic Hapludalfs) at South Charleston. Interrelationships among soil properties and saturated hydraulic conductivity (K_sat) predictions were also assessed. Earthworm middens, K_sat, bulk density (ρ_b), soil water retention (SWR), pore-size distribution, and air permeability (k_a) were determined for six stover treatments. Stover treatments consisted of removing 0 (T100), 25 (T75), 50 (T50), 75 (T25), 100 (T0) and adding 100 (T200)% of corn stover corresponding to 0, 1.25, 2.50, 3.75, 5.00, and 10.00 Mg ha⁻¹ of stover, respectively. Stover removal reduced the number of middens, K_sat, SWR, and k_a, and increased ρ_b at all sites (P < 0.01). Compared to normal stover treatment (T100), complete stover removal (T0) reduced earthworm middens 6-fold at Coshocton and about 14-fold at Hoytville and Charleston. Geometric mean K_sat decreased from 3.1 to 0.1 mm h⁻¹ at Coshocton, 4.2 to 0.3 mm h⁻¹ at Hoytville, and 4.2 to 0.6 mm h⁻¹ at Charleston while soil ρ_b increased about 12% in the 0–10-cm depth at Coshocton and Hoytville from T100 to T0. The SWR for T0 was about 70% of that for T100 and 58% of that for T200 at 0 to −6 kPa suctions across sites. The log k_a for T200, T100, and T75 significantly exceeded that under T50, T25, and T0 at Coshocton and Charleston. Differences in the number of middens, ρ_b, SWR, K_sat, and k_a between T100 and T200 were not generally significant although the T200 retained slightly more water for the 0 to −100 kPa at Charleston and had higher k_a at Hoytville compared to T100. Measured parameters were strongly correlated, and k_a was a strong K_sat predictor. Stover harvesting induces rapid changes in soil hydraulic properties and earthworm activity, but further monitoring is needed to ascertain the threshold levels of stover removal for soil-specific conditions.