Measured Soil Physical Properties Research Articles

Irrigation scheduling needs to consider both plant‐available water and soil aeration requirements

AbstractGlobal food production relying on irrigated agriculture accounts for >70% of the global freshwater withdrawal. A thorough understanding of soil–water characteristics (SWCs) and critical soil–water values in the soil and subsoil is important for effective management of irrigated water. A critical soil–water “window” for plants is generally taken as the plant‐available water window without considering diffusion‐dominated soil aeration as a co‐requisite. This study examined SWC curves in vadose soil profiles (up to 1.5‐m depth) in eight pasture soils. The soil moisture measurements were made over matric potentials ranging from −1 to −1500 kPa using tension table and pressure plate apparatus. The van Genuchten model was used to parameterize the measured SWC curve, while the Millington‐Quirk model was used to derive soil–gas diffusivity from measured soil physical properties. We defined critical soil–water windows considering the threshold values for both plant‐available water and soil–gas diffusivity to ensure water and aeration corequisites for plant growth. The results clearly distinguished depth‐dependent regimes of gravitational, plant‐available, and unavailable water in selected profiles and their responses to soil structural changes across the depth. In some of the observed soil profiles, only 30%–60% of the plant‐available water window was able to be utilized by plants because the remainder existed under soil conditions where soil aeration was inadequate for plant growth, emphasizing the importance of considering both the plant's water and aeration requirements during irrigation scheduling. Further, the infiltration profiles in two selected soils under simulated irrigation highlighted the importance of a priori knowledge of the soil structure in deeper soil layers for scheduling irrigation.

New empirical-point pedotransfer functions for water retention data for a wide range of soil texture and climates

Knowing soil hydraulic properties is essential to support soil use and management practices; however, their measuring is commonly expensive and time-consuming. Thus, pedotransfer functions (PTFs) have been used to quantify physical properties such as the soil water retention curve (SWRC). SWRC relates the volumetric soil water content (θ) as a function of the matric potential (h) and plays a vital role in soil hydraulic modeling. Point-PTFs estimate key-points of the SWRC, often from measured texture, bulk density, and organic matter. This study aimed to formulate new point-PTFs to estimate θ(h) data ranging from θ(-0.1 m) to θ(-150 m) to be applied in subtropical, tropical and temperate soils. The PTF equations were derived from linear and non-linear regressions of measured soil physical properties against to the water retention data. The prediction performance of the new-formulated PTFs overcame the performance of already existing and widely-known PTFs recognized in the literature and can be, therefore, applied in soil water retention topics under a wider textural range.

Cover crop and biofuel crop effects on hydraulic properties for claypan soils

AbstractPerennial biofuel and cover crops systems are important for enhancing soil health and can provide numerous soil, agricultural, and environmental benefits. The study objective was to investigate the effects of cover crops and biofuel crops on soil hydraulic properties relative to traditional management for claypan soils. The study site included selected management practices: cover crop (CC) and no cover crop (NC) with corn/soybean rotation, switchgrass (SW), and miscanthus (MI). The CC mixture consisted of cereal rye, hairy vetch, and Austrian winter pea. The research site was located at Bradford Research Center in Missouri, USA, and was implemented on a Mexico silt loam. Intact soil cores (76‐mm diam. by 76‐mm long) were taken from the 0–10, 10–20, 20–30, and 30–40 cm depths with three plot replicates and two sub‐samples per plot replicate per depth. Soil hydraulic properties evaluated for each sample included: saturated hydraulic conductivity (Ksat), water retention, bulk density, and pore size distributions. Results showed with the test of Duncan's least significant differences that treatments of MI (1.18 Mg m−3) and SW (1.21 Mg m−3) had lower values of bulk density averaging across soil depth than CC (1.27 Mg m−3) and NC (1.31 Mg m−3). Management systems significantly increased Ksat with the biofuel treatments at 0–10 cm compared to NC system. The MI management showed a significant increase in macroporosity and fine mesoporosity as compared to other management systems. Slight changes have occurred in the measured soil physical properties for CC system compared to NC plots. Overall, increasing soil organic matter from more plant roots from long‐term biofuel cropping systems can improve soil water storage and crop productivity.

Representative Elementary Volume as a Function of Land Uses and Soil Processes Based on 3D Pore System Analysis

Representative elementary volume (REV) is required for representative measurements of soil physical properties. However, questions may arise whether REV depends on how the soil structure is modified or whether processes in the soil affect REV. Here, we explore REV dependence for contrasting land uses (conventional tillage, no-tillage, and minimum tillage) and applying wetting and drying (W-D) cycles. The effect of different subvolume selection schemes (cube and core) on REV was also investigated. For this study, high-resolution three-dimensional images obtained using the X-ray Computed Tomography (XCT) technique were analyzed. The micromorphological properties measured were porosity (P), fractal dimension (FD), degree of anisotropy (DA), and pore connectivity (C). The results show that REV depends mainly on the land uses for P and C (both selection schemes). The core method showed lower REV due to the larger volume analyzed than that in the cube method. It was not possible to define a REV for DA. The REV obtained using the cube method was more sensitive to changes in the scale of analysis, showing an increasing trend with applied W-D cycles for P and FD. Our results indicate that REV cannot be considered static since land uses and processes influence it.

Paddy Field Water Movement Through Soil Profiles Under Different Water Management Practices: A HYDRUS 1D Model Study

Physical measurement of hydrological processes through soil profile is very complicated and timeconsuming. Complex and coupled physical processes like water movement with soil matric potential in puddled paddy field can be simulated using physical process-based model HYDRUS 1D. The model simulation was setup for the multilayered (different soil materials at 0-15 and 15-30 cm depth) paddy fields having continuous flooded irrigation (CFI) practice and water saving Alternate Wetting and Drying (AWD) practice. Measured soil physical properties of three Bangladesh Rice Research Institute (BRRI) regional station farms (Kushtia, Sirajganj, and Rangpur) were used as model input, initial and boundary conditions configuration. The model was calibrated and validated using the water data of a dry season field experiment in Kushtia. The calibrated (RMSE of 0.54 cm, d of 0.94, NSE of 0.89) water level data validated successfully with observed water level data of AWD practiced paddy field (d of 0.95, NSE of 0.92). Soil water content reached the threshold/critical level in AWD practice (-101 cm of water soil matric potential at 15 cm soil depth) earlier in light textured soil (loam or sandy loam) compared to heavy textured soil (clay). The physical properties of the layered soils (i.e., soil particle size distribution and soil water release curve, SWRC) did not affect much on water movement in CFI practice, but it had substantial impact on field water movement under AWD practice. The change in soil water storage followed the general trend for respective soil water holding and releasing capacity, clay soil was heavier and released water slowly than that of loam or sandy loam soils. The positive water flux above 15 cm of soil profile mainly drove the water flow due to evapotranspiration and soil water and pressure distribution along the soil profile while the negative fluxes below 15 cm of soil depth due to infiltration or percolation contributed as a secondary force. A basic understanding of HYDRUS simulated results would lead to realize the total physiohydrological environment in the paddy field. Bangladesh Rice J. 25 (2) : 57-67, 2021

Increased nutrient availability speeds up permafrost development, while goose grazing slows it down in a Canadian High Arctic wetland

Abstract It is of prime importance to understand feedbacks due to the release of carbon (C) stored in permafrost soils (permafrost‐climate feedback) and direct impacts of climatic variations on permafrost dynamics therefore received considerable attention. However, indirect effects of global change, such as the variation in soil nutrient availability and grazing pressure, can alter soil and surface properties of the Arctic tundra, with the potential to modify soil heat transfers toward the permafrost and impact resilience of Arctic ecosystems. We determined the potential of nutrient availability and grazing to alter soil energy balance using a 16‐year split‐plot experiment crossing fertilization at different doses of nitrogen (N) and phosphorus (P) with protection from goose grazing. Moss biomass and some determinants of the surface energy budget (leaf area index (LAI), dead vascular plant biomass and albedo) were quantified and active layer thaw depth repeatedly measured during three growing seasons. We measured soil physical properties and thermal conductivity and used a physical model to link topsoil organic accumulation processes to heat transfer. Fertilization increased LAI and albedo, whereas grazing decreased dead vascular plant biomass and albedo. Fertilization increased organic accumulation at the top of the soil leading to drier and more porous topsoil, whereas grazing increased water content of topsoil. As a result, topsoil thermal conductivity was higher in grazed plots than in ungrazed ones. Including these properties into a simulation model, we showed that, after 16 years, nutrient addition tended to shallow the active layer whereas grazing deepened mean July active layer by 3.3 cm relative to ungrazed subplots. As a result of OM accumulation at the surface, fertilization increased permafrost vertical aggradation rate by almost an order of magnitude (up to 5 mm year−1 instead of 0.7 mm year−1), whereas grazing slowed down permafrost aggradation by reducing surface uprising and deepening thaw depth. Synthesis. We demonstrated that long‐term grazing and N and P addition, through their impact on vegetation and soil properties have the potential to impact permafrost dynamics to the same extent as contemporary temperature increase in High Arctic polygonal wetlands.

Visual soil structure quality and its correlation to quantitative soil physical properties of upland rice site in Falcataria moluccana agroforestry system

Abstract. Briliawan BD, Wijayanto N, Wasis B. 2022. Visual soil structure quality and its correlation to quantitative soil physical properties of upland rice site in Falcataria moluccana agroforestry system. Biodiversitas 23: 1894-1903. Sengon and upland rice are plants that have the potential to be combined in the agroforestry system. However, its development often results in poor quantitative soil physical properties. Measuring the soil’s physical properties is expensive and complicated to do by some people. This study aims to measure the visual soil structure quality from different land covers and calculate its correlation to the parameters of the soil’s physical properties. The research was conducted in the Cikabayan forest and used the purposive sampling method to take soil samples. The research was conducted by comparing nine land covers in the form of agroforestry and monoculture developed in organic and conventional agriculture with tropical rainforests as natural vegetation. Three samples were taken for each land cover type and analyzed with a completely randomized design. The research showed that the vegetation of tropical rainforest generated the best score on all visual soil structure quality measurement methods (VESS, GrassVESS Sq and GrassVESS Rm). The measurement of soil physical properties at natural vegetation of tropical rainforests generated the highest score on the porosity (57.303%). Meanwhile, monoculture-conventional land generated the highest bulk density (1.373 g.cm-3). The VESS method had the highest correlation with soil physical properties compared to other visual soil structure quality measurement methods. Thus, natural vegetation is the best type of land cover compared to all cultivated land and the VESS method is the most appropriate method for estimating soil physical properties.

Monitoring the behaviour of Australian Vertosols in response to the shrink–swell characteristic and cotton picker traffic

Vertosols are widely used for cotton production globally. One main advantage of this soil type is its capacity to improve its structure gradually due to natural processes over time. However, Vertosols are highly susceptible to compaction, especially under wet soil conditions. This study investigated the change in characteristics of Australian Vertosols due to the impact of rainfall, seasonal variability, and John Deere 7760 cotton picker traffic. Soil cores were collected between October 2016 and May 2017. Measurements of soil physical properties (soil water content, dry bulk density, and soil penetration resistance) were carried out in the 0–80 cm depth profile during the study period. Increasing soil water content due to rainfall caused the Vertosol to swell, providing some degree of natural compaction alleviation and decreasing the dry bulk density and soil penetration resistance. Increased temperatures from October 2016 to January 2017 resulted in increased moisture evapotranspiration. This led to shrinkage of the Vertosol and resulted in increased dry bulk density and soil penetration resistance, particularly in the top 0–30 cm of soil. Traffic from the JD7760 cotton picker induced significant compaction throughout the depth profile. These findings have important implications for farmers intending to grow crops in Vertosols and managing the issue of soil compaction.

Vegetation and soil recovery following Eucalyptus grandis removal in Limpopo Province, South Africa

South African terrestrial ecosystems are invaded by hundreds of alien plant species, and large‐scale clearing based on the passive restoration assumption that cleared areas will recover unaided is underway. This study assessed the recovery of vegetation and soil properties, three years following Eucalyptus grandis clearing using fell‐and‐removal and fell‐and‐stackburn methods at Zvakanaka Farm in Limpopo Province, South Africa. The main aim was to ascertain the extent of vegetation and soil recovery, as well as determining which clearing methods facilitate passive vegetation and soil restoration. Results indicate significantly (p < 0.001) lower native species diversity, cover and composition in cleared than in uninvaded sites. However, the recorded low species diversity and composition in cleared sites were more pronounced in the fell‐and‐stackburn than in the fell‐and‐removal sites. Measured soil physical properties varied, with compaction being higher in fell‐and‐removal, whereas soils were more repellent in fell‐and‐stackburn sites. The study concludes that vegetation and soil recovery, following E. grandis clearing, is complex and involves several interacting factors, which are linked to invasion history and intensity. Therefore, for vegetation and soil properties to recover, following E. grandis removal, the clearing programme should consider active restoration techniques, for example soil manipulation and native plant seeding.

Can complementary preferential flow and non-preferential flow domains contribute to soil water supply for rubber plantation?

Preferential flow has always been hotspot of research regarding soil water flow, biological activity, and carbon and nitrogen dynamics. However, the mechanism of water flow exchange between two adjacent zones (with and without root system) and the pattern of soil water supply for rubber are still unclear. In the present study, we considered two plots experiencing similar farming history: in the first plot we measured soil physical properties and soil volumetric water content (VWC) during rainfall, and the second plot was used to visualise water flow path and to measure root biomass. Besides, a model was developed on preferential flow domain (PFD, matching the root zone) and on non-preferential flow domain (NPFD, matching the remote root zone) to compute differences in soil properties between the PFD and NPFD. The results revealed that the dominant flow type in the PFD was preferential flow and the one in the NPFD was capillary flow. Dye stained area and wetting front rate negatively correlated with bulk density, while they positively correlated to non-capillary porosity and root biomass. Accordingly, PFD showed a quick response to rainfall. Indeed, during the rain, a lateral flow (driven by water gravity and pressure head gradient) predominantly carried water (0.95, 0.27, and 0.44 cm3 cm−3 for various rainfall events 1, 2, and 3, respectively) from PFD to NPFD. During the soil drainage stage, the lateral flow direction changed, and water (about 0.63, 0.30, and 0.39 cm3 cm−3 for rainfall events 1, 2, and 3, respectively) flowed from NPFD to PFD. As a result, PFD presented low storage and high flow characteristics compared with NPFD, suggesting this complementary relationship for water interaction between the two domains could be beneficial for rubber plants growth and development.

Spatial variability of soil thermal properties and their relationships with physical properties at field scale

Characterizing the spatial variability of soil thermal properties and quantifying their relationships with commonly measured soil physical properties is important for successful implementation of precision agriculture practices. However, such information at field scale is scarce. This study aimed to characterize the spatial variability of soil thermal properties and to quantify their spatial relationships with soil physical properties at a field scale. Measurements of soil water content (SWC) and thermal properties were carried out at 80 locations using a time domain reflectometry (TDR) probe and a heat pulse probe (Decagon KD2 Pro), respectively in a cultivated cornfield in southwestern QC, Canada. Soil texture and total organic carbon (TOC) at those locations were also determined in the laboratory. Both coefficient of variation (CV%) and variogram range showed a weak to moderate variability and spatial dependency for the soil properties which was attributed to the homogeneity of the soil, crop, and land management practices. Results of principle component analysis (PCA) indicated that the soil thermal properties and soil water content (SWC) had strong correlations with principle component 2 (PC2). The variogram ranges indicated that the soil thermal properties varied on a similar spatial scale as the SWC in the field. Cross variograms indicated strong spatial correlations between SWC and thermal properties, particularly thermal conductivity (k) and thermal diffusivity (D). Overall, results of this study showed that the SWC had a stronger influence on the spatial variability of soil thermal properties than the other properties such as TOC and soil texture at the field scale. Therefore, the results of this study could be useful for accurate modeling of the soil thermal regimes and mass-energy exchange processes at the field scale as well as developing successful agricultural management strategies such as precision irrigation. Future studies should explore the relationships between the thermal properties and other soil properties such as bulk density under various cropping systems.

Soil moisture dynamics alone does not explain differences in growth associated to organic amendment in a reforestation of a semiarid ecosystem

The success of reforestation of degraded areas in semiarid environments is constrained by low soil water content and fertility. In order to overcome these limitations, several site preparation techniques previous to plantation have been developed. Organic amendments have been used to improve physical soil properties in order to increase water availability for plants. However, the role of improvement in nutrient availability produced by organic amendment could have been neglected in semiarid vegetation restoration. In this paper, we analyze the effect of two site preparation treatments on soil moisture dynamics of an experimental reforestation with Pinus halepensis Mill. in a semiarid Mediterranean ecosystem. In one treatment (S) only lineal subsoiling (60–80 cm deep) was applied, in the other (SFF) a fresh urban refuse was added at a dose of 10 kg m−1 into the subsoiled furrow. During the first 5 years the growth of pines was significantly higher in SFF. At this time, we studied soil moisture dynamics at 0–20 cm in transects (for 8 months) and in soil profiles at 5, 15, 25 and 45–55 cm depth (for 23 months). Measurements made in two adjacent off-lines unaffected by site preparation were used as covariates. We also measured soil physical properties, macronutrients (N,P,K) and total organic carbon (TOC) content. No significant differences in soil physical properties were found between the amended versus not amended treatment except for hydraulic conductivity and sand fraction content. SFF treatment showed higher hydraulic conductivity, especially in top soil layers (0–10 cm), and lower content of sand fraction. Phosphorus availability was significantly higher in soil amended with organic refuse while no effect was detected in the content of the rest of macronutrients measured. In the transects, a reduction of 30% of the mean soil water content was observed in planting lines (0.14 cm 3 cm−3) in contrast with adjacent off-lines (0.20 cm 3 cm−3); no statistically significant differences between site preparation techniques were found. Soil profiles observations revealed that soil water content was significantly higher in S than in SFF treatment. This suggests that improvement in soil moisture associated to improvement in the physical structure of the soil cannot explain differences in growth. We argue instead this is mostly attributable to improved nutrient availability and microbiological activity associated with the organic amendment. These results stress the importance of a better understanding of the role of nutrients in the restoration of water-stressed ecosystems.

Analysis of soil hydraulic and thermal properties for land surface modeling over the Tibetan Plateau

Abstract. Soil information (e.g., soil texture and porosity) from existing soil datasets over the Tibetan Plateau (TP) is claimed to be inadequate and even inaccurate for determining soil hydraulic properties (SHP) and soil thermal properties (STP), hampering the understanding of the land surface process over TP. As the soil varies across three dominant climate zones (i.e., arid, semi-arid and subhumid) over the TP, the associated SHP and STP are expected to vary correspondingly. To obtain an explicit insight into the soil hydrothermal properties over the TP, in situ and laboratory measurements of over 30 soil property profiles were obtained across the climate zones. Results show that porosity and SHP and STP differ across the climate zones and strongly depend on soil texture. In particular, it is proposed that gravel impact on porosity and SHP and STP are both considered in the arid zone and in deep layers of the semi-arid zone. Parameterization schemes for porosity, SHP and STP are investigated and compared with measurements taken. To determine the SHP, including soil water retention curves (SWRCs) and hydraulic conductivities, the pedotransfer functions (PTFs) developed by Cosby et al. (1984) (for the Clapp–Hornberger model) and the continuous PTFs given by Wösten et al. (1999) (for the Van Genuchten–Mualem model) are recommended. The STP parameterization scheme proposed by Farouki (1981) based on the model of De Vries (1963) performed better across the TP than other schemes. Using the parameterization schemes mentioned above, the uncertainties of five existing regional and global soil datasets and their derived SHP and STP over the TP are quantified through comparison with in situ and laboratory measurements. The measured soil physical properties dataset is available at https://data.4tu.nl/repository/uuid:c712717c-6ac0-47ff-9d58-97f88082ddc0.

EFFECT OF FARM MACHINERY ON SOME SOIL PHYSICAL PROPERTIES USING HYPERSPECTRAL DATA

Traditional soil analyses are expensive, time-consuming, and may also result in environmental pollutants. The objective of this study was to develop a methodology to predict soil physical properties specifically the soil bulk density using spectral reflectance (SR) as an alternative to traditional methods. Additionally to critically examine the suitability of Visible and Near-infrared (Vis- NIR) (350–2500 nm) measurements for calibration procedures and methods to predict the value of soil bulk density. Five different seedbed preparation systems were applied. Spectroradiometer ASD was used to measure the soil spectral reflectance of each system. Stepwise multiple linear regression (SMLR) was used to construct calibration models subjected to the independent validation. The obtained regression models were of good quality (R2 = 0.959, 0.868, 0.811, 0.751 and 0.677 for system 5, system 1, system 3, system 4 and system 2, respectively). Thus, Visible and Near-infrared (Vis-NIR) reflection spectroscopy is cost- and time-effective procedure that can be used as an alternative to the traditional methods of measuring soil physical properties.

Vegetation as a driver of temporal variations in slope stability: The impact of hydrological processes

AbstractAlthough vegetation is increasingly used to mitigate landslide risks, how vegetation affects the temporal variability of slope stability is poorly understood, especially in earthquake‐prone regions. We combined 3‐year long soil moisture monitoring, measurements of soil physical properties and plant functional traits, and numerical modeling to compare slope stability under paired land uses with and without trees in tropical, subtropical, and temperate landslide‐ and earthquake‐prone regions. Trees improved stability for 5–12 months per year from drawdown of soil moisture and resulted in less interannual variability in the duration of high‐stability periods compared to slopes without trees. Our meta‐analysis of published data also showed that slopes with woody vegetation were more stable and less sensitive to climate and soil factors than slopes with herbaceous vegetation. However, estimates of earthquake magnitude necessary to destabilize slopes at our sites suggest that large additional stabilization from trees is necessary for meaningful protection against external triggers.

Soil health – What should the doctor order?

AbstractThe concept of soil health has been extensively reviewed in the scientific literature, but there is only patchy and inconsistent information available to farmers and growers who are concerned about the declining condition of their soils and are looking for appropriate test methods and management interventions to help reverse it. Although there are well‐established laboratory methods for soil chemical analysis, and a range of laboratory and field methods for measuring soil physical properties, only now are methods starting to emerge for soil biological analysis. This study provides an overview of the methods that are currently available commercially (or are close to commercialization) for farmers and growers in the UK. We examine the science underpinning the methods, the value of the information provided and how farmers and advisors can use results from such assessments for informed decision‐making in relation to soil management.

Land use effects on subtropical, sandy soil under sandyzation/desertification processes

Very fragile sandy soils have high erosion susceptibility, low water retention, and low nutrient and carbon storage. In southern Brazil, substitution of native grassland by grain production in conventional tillage has caused severe degradation, even reaching an extreme state of “sandyzation” or non-vegetated sand. We measured indicators to assess soil quality in a Quartzipsamment (“Neossolo Quartzarênico”) under different uses and also in extreme state of “sandyzation” or non-vegetated sand, where annual average rainfall is 1511mm with regular distribution throughout the year. Four land uses/conditions were evaluated: (i) native grassland (NG) (4% clay); (ii) nine years-old eucalyptus forest (EF) (4% clay); (iii) corn production in conventional tillage (CT) (3% clay); and (iv) extreme state of “sandyzation” or non-vegetated sand (NVS) (2% clay). Measured soil chemical properties were soil organic carbon (SOC) in 0–2.5, 2.5–5, 5–7.5, 7.5–10 and 10–20cm soil layers, Ca, Mg, K, Al saturation, and effective cation exchange capacity (CEC) in 0–2.5cm layer. Measured soil physical properties were soil bulk density (BD), total porosity (TP), macroporosity (Macro), microporosity (Micro), water retention, and saturated hydraulic conductivity (Ks) in 0–3, 5–8, and 10–13cm soil layers, whereas aggregate stability in water was measured in 0–5cm soil layer. Soil chemical and physical properties indicate an extreme state of degradation of NVS, which had significantly lowest SOC and thus low CEC, associated to leaching of exchangeable bases and high aluminum saturation. CT also provided a significant decrease in SOC in all soil layers, and other in chemical properties in the 0–2.5cm layer, whilst EF was the most efficient system to build up SOC compared to NG in surface layers (0–2.5 and 2.5–5cm) and presented better chemical conditions. In general, soil physical quality was degraded in NVS and improved in EF, whilst there were no significant differences in CT compared to NG for most soil physical properties. Soil physical properties were closely related to surface SOC of the different land uses. NVS provided a significant decrease in Micro, whilst EF provided a significant increase in TP and Macro in 0–3 and 5–8cm soil layers. High TP and Macro, low Micro, and very high Ks were observed in NVS. The CT provided significant decrease in water aggregate stability compared to NG and the water aggregate stability rank was EF>NG>CT, whereas NVS soil was completely devoid of aggregation. NVS restricts plant growth, root development, plant nutrient uptake and soil cover, thus creating an environment prone to wind erosion and soil degradation. Management practices that include permanent soil cover, restore SOC, improve soil aggregation and create pores for water retention and availability, increase base saturation and promote nutrient cycling are necessary to preserve these fragile lands.

Assessing soil structural quality under Brazilian sugarcane expansion areas using Visual Evaluation of Soil Structure (VESS)

Increasing global demand for biofuel has accelerated land-use change (LUC) in Brazil, primarily through the planting of sugarcane (Saccharum officinarum) to replace degraded pastures. The intensive mechanization associated with this LUC has increased concerns regarding structural quality of Brazilian tropical soils. Through decades of research focusing on identifying sensitive indicators of soil degradation due to land use and management, the Visual Evaluation of Soil Structure (VESS) method has emerged as a simple, fast, reliable and accurate semi-quantitative approach for assessing soil structure changes. VESS integrates soil properties related to size, strength and porosity of aggregates, and root characteristics into a single score (Sq – structural quality) that ranges from 1 (good structural quality) to 5 (poor structural quality). Although the VESS method was developed for temperate soils, it has been used successfully as an indicator of soil and crop management practice effects on structural quality of tropical and subtropical soils. Our objectives were to evaluate soil structural quality changes associated with a LUC sequence (i.e., native vegetation to pasture to sugarcane) at three sites under Oxisols, Alfisols and Ultisols across central-southern Brazil using the VESS; and to correlate VESS scores with quantitative measurements of soil physical properties. Average VESS scores were 2.0, 2.7, and 3.1 for native vegetation, pasture, and sugarcane, respectively. Overall the VESS method was able to detect soil structural quality changes under LUC for sugarcane cultivation, indicating a decrease in soil quality from native vegetation through pasture to sugarcane. The VESS scores were significantly correlated with quantitative soil physical property measurements, suggesting VESS is a reliable indicator of soil structural quality in tropical soils. A VESS score Sq=3.0 seems to be suitable as a guide for management decisions. We conclude that VESS scores provide an efficient method to identify impacts of sugarcane expansion on soil structural quality, and recommend that VESS assessment be incorporated into monitoring protocols for evaluating not only sugarcane expansion areas, but also overall soil quality/health in Brazil.

Long-term effects of wet and dry site harvesting on soil physical properties mitigated by mechanical site preparation in coastal plain loblolly pine (Pinus taeda) plantations

Wet site forest harvesting may damage soil physical properties, altering long-term site productivity. In 1993, a study was installed to evaluate effects of machine trafficking with site preparation during wet and dry harvest conditions on a poorly drained, wet pine flat in the Coastal Plain of South Carolina, USA. Five soil disturbance classes (Minimum Traffic, Compacted, Shallow Ruts, Ruts, and Churned) were documented following harvest (prior to site preparation). Three site preparation treatments and two harvest conditions (Wet Mole-Plowed, Wet-Flat, Wet-Bedded, Dry-Flat, and Dry-Bedded) were operationally replicated three times. Soil physical properties and carbon were measured 17years after stand re-establishment to document long-term changes associated with traffic disturbance and site preparation. Results show that all measured soil physical properties at surface and subsurface horizons (except macroporosity in surface horizons) were similar among site preparation treatments and soil disturbance classes. Previous research showed that Mole-Plowed treatment proved beneficial for tree growth parameters at stand age 16years, which corresponded to macroporosity levels within soil surface horizons at stand age 17years. Statistical analyses indicated greater (p=0.04) macroporosity of surface horizons in the intensive Mole-Plowed treatment (14.7%, ±1.6%). Wet-Flat (9.1%, ±0.9%), Wet-Bedded (9.1%, ±0.8%), Dry-Bedded (9.5%, ±1.0%), and Dry-Flat (9.8%, ±1.0%) had significantly less macroporosity, but were not significantly different from each other. Macroporosity of surface horizons was also significantly different among soil disturbance classes (p=0.08). However, macroporosity had not recovered to pre-harvest levels for any site preparation treatments except Mole-Plowed. Bulk density and total porosity recovered to near pre-harvest levels for all treatment combinations, but saturated hydraulic conductivity rates remained lower than pre-harvest values. Mole plowing with bedding improved microsite drainage, which likely reduced areas of locally high water tables and somewhat reduced areas with root restriction due to poor aeration. Based on tree productivity, treatment drainage appeared to be the most limiting growth factor for this site. Recovery of soil properties on non-bedded treatments indicate site amelioration through natural mechanisms which may include shrinking and swelling of clays, activities of soil macrobiota, and root dynamics. On these sites, natural processes ameliorated almost all post harvesting soil differences by age 17 (before the end of the rotation). The benefits of both minimizing soil disturbance and/or employing ameliorative site preparation treatments were largely restricted to early in the rotation where they could contribute to initial survival and early growth increases. As the cost of ameliorative site preparation is high, minimizing soil disturbance is recommended.

Predicting the mobile water content of vineyard soils in New South Wales, Australia

Better understanding of the relationship between soil properties and soil function is required to minimise nutrient losses from agriculture and protect the environment. There is a need to predict the solute movement through horticultural soils because of the intensive management practices. Thus, the mobile water content (θm), the active fraction of soil water content engaged in solute transport, is a suitable soil property to investigate further. Accurate measurement of such solute transport properties in the field are costly, labour intensive and time consuming but there are opportunities to establish predictive relationships. θm was measured together with other basic soil properties to test established predictive relationships (known as pedotransfer functions, PTFs) and to develop new PTFs. The field measurements were taken on a diverse range of vineyard soils across New South Wales (NSW), Australia. Poor predictions were found with available PTFs for θm and the mobile water fraction f (=θm/θfm; where θfm=volumetric water content at which θm was measured). Backward stepwise multiple regression analysis produced better PTF model predictions than the multiple linear regression analysis for new PTFs that were calculated. Differences in the analysis methods showed a trade-off between the prediction capacity and the number of predictor variables in each PTF model. A prediction accuracy of between 80 to 90% was found with 3 predictor variables in the PTFs for θm and f. Both the PTFs developed were in strong agreement with the measured properties (minimum R2=0.82). For the θm PTF, the % clay content (varied from 11 to 59) was the strongest predictor variable while bulk density (ranged from 1.2 to 1.51gcm−3) contributed the smallest. The PTF for f was similar to θm except it was the % soil organic carbon which had the smallest contribution. These relationships are useful to predict θm and f from easily measured soil physical properties of vineyard soils in NSW, but further testing on a wider range of soils is required.