Vertic Soils Research Articles

Application of a simplified Green-Ampt model to the Maga earthfill dam under rainfall conditions: A sensitivity analysis case of an infiltration model

The present paper applies a simplified Green-Ampt (GA) infiltration model for the numerical modelling of seepage processes within the body of the Maga earth dam, located in the Far-North Cameroon, under rainfall conditions. The parametrization approach makes possible the predictions of infiltrations parameters for various textures that constitute the body of earth dam and its vicinities. The effects of soil texture, permeability coefficient, rain intensity and initial moisture on infiltration rate and cumulative depth are investigated using numerical simulations carried out by running an Excel VBA code. A proposed optimization procedure of the literature is then used to improve the GA model parameters and accuracy of predictions. A case sensitivity analysis of the infiltration model parameters has also been made. Initial and saturated water contents, rain intensity and permeability coefficient at saturation have been identified as the most influents parameters for the model predictions, with obvious interactions between inputs. The contribution of main effects and interactions of above inputs ranges between 68.8 % and 90.03 % of the total variance. Comparisons of numerical results with the experimental ones obtained from the literature on real cases of simulated rainfall on main sub-Saharan soils have been done. The results show that numerical simulations underestimated 60 % and 56.25 % of the hydrodynamics parameters respectively for one and four simulated rain-sequence with relative errors (RE) ranging between −76.22 % and 300.25 %. The most representative results were obtained for 53.13 % of the predicted hydrodynamics parameters with RE value ranging between −23.90 % and 12.75 %. The obtained results proved that, the simplified GA model exhibited an acceptable accuracy in predicting seepage processes for ferruginous and degraded vertic soils. Therefore, the present study contributes to understand the role of numerical simulations tools in modelling and predicting subsurface phenomenon as seepage, for areas with high floods risks in a context of significant climate changes.

Effect of land configuration and fertilizer dosage on growth and yield of African marigold under vertic ustochrept soil regimes

Adopting proper land management systems and nutrient levels could improve growth, yield and quality by rendering better soil physical structure and mineral nutrition under heavy rainfall areas. An experiment was conducted to identify appropriate land configuration and fertilizer dose for African marigold var. Punjab Gainda-1, in split plot design with three land configuration methods viz., flat bed, raised bed and ridge & furrow system as main plots, and three fertilizer doses (RDF/ha) viz., 100%, 80% and 60% as subplots with recommended dose of fertilizer (RDF) being 10 t FYM + 150:100:100 kg/ha NPK. Results showed that adopting raised bed method of land configuration with the application of 8 t FYM + 120:80:80 kg/ha NPK exhibited enhanced vegetative growth and flower yield (16.26 t/ha) with greater benefit cost ratio (2.88) and, hence, found economically best for commercial production of African marigold.

Removal of pruned vine biomass (PVB) from vineyards – Examining the impact of not incorporating PVB into vineyard soils

The wine industry worldwide faces increasing challenges to achieve sustainable levels of carbon emission mitigation. This study seeks to establish the feasibility of harvesting winter pruned vineyard biomass (PVB) for potential use in carbon footprint reduction as a renewable biofuel for energy production. Of particular interest is the role PVB plays as a carbon source in vineyard soils and what effect annual removal might have on soil carbon. An investigation was carried out in the Coombe vineyard, Waite Campus (University of Adelaide), Australia. Vines are grown in a Vertic clay loam soil with well-managed mid-row swards in a temperate zone. A comparison was undertaken of two mid-row treatments after 13 years of consistent management: 1) the deliberate exclusion of PVB from every third row, and 2) in the remaining rows PVB was incorporated at an average of 3.4 and 5.5 t/ha in two 0.25 ha blocks containing Shiraz and Semillon respectively. In both 0-10 cm and 10-30 cm soil core sample depths, combined soil carbon % values in the desired range of 1.80 to 3.50 were not significantly different between treatments or cultivars and yielded an estimated 42 t/ha of soil carbon. Other key physical and chemical values were likewise not significantly different between treatments. Results suggest that in a temperate zone vineyard, managed such as the one used in this study, there is no long-term negative impact on soil carbon sequestration through removing PVB. This implies that growers could confidently harvest PVB for use in biofuel production.

Soil–Water–Atmosphere Effects on Soil Crack Characteristics under Field Conditions in a Semiarid Climate

Soil’s physical and hydrological properties influence the proper modeling, planning, and management of water resources and soil conservation. In areas of vertic soils subjected to wetting and drying cycles, the soil–water–atmosphere interaction is complex and understudied at the field scale, especially in dry tropical regions. This work quantifies and analyzes crack development under field conditions in an expansive soil in a semiarid region for both the dry and rainy seasons. Six 1 m2 plots in an experimental 2.8 ha watershed were photographed and direct measurements were taken of the soil moisture and crack area, depth and volume once a week and after a rainfall event from July 2019 to June 2020. The rainfall was monitored for the entire period and showed a unimodal distribution from December to May after five months without precipitation. The cracks were first sealed in the plots with a predominance of sand and when the soil moisture was above 23% and had an accumulated precipitation of 102 mm. The other plots sealed their cracks when the soil moisture was above 32% and with an accumulated precipitation in the rainy season above 222 mm. The cracks redeveloped after sealing upon a reduction of 4% in the soil moisture. The depth of the cracks showed a better response to climatic variations (total precipitation, soil moisture and continuous dry and wet days). The higher clay content and the higher plasticity index plots developed more cracks with greater depth and volume.

Spatial variability of soil organic carbon stock in an olive orchard at catchment scale in Southern Spain

Orchards have a high potential for carbon sequestration. However, little research is available on the spatial variability at catchment scale and on the difference between the tree area and the lanes. We analyzed theik spatial variability of soil organic carbon stock, SOCstock at 90 cm depth in an 8-ha catchment in Southern Spain with olives on a vertic soil. Results showed higher soil organic carbon concentration, SOC, in the tree area as compared to the lane up to 60 cm depth, but its impact on SOCstock was negligible since it was compensated by the higher soil bulk density in the lane. SOC at different depths was correlated with that in the top 0–5 cm. The overall SOCstock of the orchard was 4.14 kg m−2, ranging between 1.8 and 6.0 kg m−2. This SOCstock is in the mid-lower range of values reported for olive orchards, measured at smaller scale, and similar to those other intensive field crops and agroforestry under comparable rainfall conditions. The spatial variability in SOCstock was correlated to several geomorphological variables: elevation, cumulative upstream area, topographic wetness index, sediment transport index, and tillage erosion. Differences in SOC and SOCstock are driven by the sediment redistribution downslope, mainly by tillage erosion, and higher soil water availability in lower areas allowing higher biomass production. These topographic indexes and the correlation between SOC in the topsoil and SOCstock up to 90 cm should be further explored in other typology of olive orchards for facilitating the mapping of SOCstock.

RESPON BEBERAPA SIFAT FISIKA TANAH ALUVIAL PADA KOMBINASI KOMPOS SAMPAH KOTA DAN PUPUK KANDANG SAPI SETELAH DITANAMI PAKCOY

Alluvial soil in this study is a vertic endoaquepts paddy soil type, which is an alluvial paddy soil with a wide distribution in the Pantura area, West Java, originating from a long river deposition system with various types of erosion materials. This soil has a high mineral content of easily weathered sand, especially feldspars. The presence of quartz, orthoclase and sanidine minerals indicates the presence of acidic materials. This also causes the content of chemical elements in this alluvial deposit to be low, so it is necessary to add organic materials such as municipal waste compost and cow manure which can improve the physical, chemical and biological properties of the soil. The aim of the study was to determine the response of several physical properties of alluvial soil to a combination of municipal waste compost and cow manure after being planted with pakcoy in Alluvial, Indramayu. The objective of this research was to find out relationship between water content and soil bulk density to the harvest of pakcoy after combined with municipal waste compost and cow manure in Alluvial, Indramayu. This study used a randomized block design factorial with two factors. The first factor is municipal waste compost and the second factor is cow manure. Each of them consisted of 4 levels : 0%, 3.0%, 6.0%, and 9.0% with two replication. The results showed that there was no interaction between municipal waste compost with cow manure and municipal waste compost with cow manure had no significant effect on soil water content of pakcoy plants after harvest. Meanwhile, cow manure has an independent effect on soil bulk density in pakcoy plants after harvest. The largest decrease in soil density occurred at a dose of 9.0% (k4), but the addition of cow manure at a dose of 3.0% (k2) was able to reduce the soil bulk density. This K2 treatment was not significantly different from the other treatments. A decrease in soil density to 1.15 g cm-3 (k2) is considered ideal for mineral soils, because in general the bulk density of mineral soils is between 1.1 – 1.6 g cm-3.

Onion-forage cropping systems on a Vertic Argiudoll in Uruguay: Onion yield and soil organic matter, aggregation, porosity and permeability

Hostipastoral systems in small farming units that integrate horticulture crops, as main cash crop, with sheep/cattle raising on cultivated forage, in Uruguay, present physical restrains to crops because of high consistency and compaction of the vertic soils and unique tillage requirements. The objective of this study was to evaluate the effect of different hortipastoral systems on soil organic matter, aggregation, porosity, permeability and onion yield during a cropping year in onion-forage hortipastoral systems. A long-term experiment was installed in 1995 in the National Institute for Agricultural Research (INIA-Las Brujas) in Uruguay, on fine (mixed) smectitic thermic superactive Vertic Argiudolls. The soil was previously under native grasslands, and treatments consisted of cropping systems for onion (Allium cepa L.) production, maintained for three years and then rotated. Onion yield was evaluated during the period 1998–2006, and in the cropping year 2006–2007, corresponding to the end of a 3-year cropping cycle, we evaluated soil organic matter and physical properties and functioning in the cropping systems: alfalfa, fescue, forage consortium (birdfoot trefoil, alfalfa and white clover), onion after alfalfa, onion after fescue, and onion after consortium. At four times during the cropping year, aggregate stability and organic matter were determined for the 0–0.05 m soil layer, whereas soil bulk density, porosity, and hydraulic conductivity were determined in 0–0.10 and 0.10–0.20 m layers. The results showed high variability in onion yields from 1998 to 2006 (10.8–36.4Mgha−1), mainly related to high rainfall (higher than 150 mm) that affected crop planting, and the low rainfall (lower than 30 mm) that affected growth and development. In two out of eight years, there were significant differences in onion yield among treatments, where alfalfa (1999) and fescue (2006) crops are more beneficial to onion yield than pasture consortium. To establish the onion crop in the vertic soil tillage is needed, but tilling the soil under forage crops reduces macro and increases microaggregation (reduces GMDw from 1.8 to 0.8 mm), increases macroporosity (close 0.07 to 0.25 m3 m−3) and functioning in terms of water and air permeability (Ka increase above 3 µm2 after tillage) and decreases the degree of compaction (under forages decreased DC from 69-84% to 58–60% in surface layer). In conclusion, there is a significant potential of hortipastoral systems and proper management of soil organic matter to minimize adverse effects of climate, and improve productivity stability of intensive production systems. Single forage crops, either legume or grass, are more beneficial to onion yield than consortium of grass plus legumes.

Black clayey soil (Vertisol) in the Lerma valley, Michoacán, North‐Central Mexico: A hint of the environmental and cultural changes during the Late Classic period?

AbstractCatastrophic events (climatic, tectonic, volcanic, etc.) frequently cause geomorphological instability, which interrupts normal pedogenesis and switches the processes of surface erosion and/or sedimentation. These processes have an effect on the distribution of ancient settlements and can be the cause of the abandonment of cities. In the Lerma Valley, particularly in the Tres Mezquites area, surveys and extensive excavations have been conducted to estimate the nature and density of pre‐Hispanic settlements on the alluvial plain and in the piedmonts. Most of the archaeological structures are covered by dark clayey soils (Vertisols). This includes the PA3_El Pitayo site, where an accumulation of black earth has been detected on the floors and walls of a collapsed building. We have studied in detail the Vertisols and the black earth around the site to establish to what extent this dark earth is an in situ product of the soil‐forming factors, or if its accumulation is due to erosion/sedimentation processes, which could affect the occupation of the site, or the result of anthropic activity for leveling. The Vertisols and the dark earth are characterized by different means (physical, chemical, micromorphology, clay mineralogy, and radiocarbon dating). The results show that both the Vertisols and the black earth are very clayey, with angular blocky structures and slickensides (properties that are typical of vertic soils), and smectite as the main clay mineral. Besides smectite, under the microscope, a high amount of fresh volcanic glass is identified, suggesting that volcanism could be responsible for the abandonment of the study site. However, there are no known volcanic events related to the age of abandonment. As a consequence, we consider that landslides triggered by seismic activity/climatic events impacted the settlement.

Flood‐Induced Recharge of Matrix Water in a Vertic Forest Soil

AbstractVertisols shrink and swell with changes in soil moisture, influencing hydraulic properties. Vertisols are often in floodplains, yet the importance of flooding as a source of soil moisture remains poorly understood. We used blue dye and deuterated water as tracers to determine the role of the macropore network in matrix recharge under artificial flood durations of 3 and 31 days in large soil monoliths extracted from a forested soil. Gravimetric soil moisture content increased by 47% in the first three days, then increased only 3.5% from day 3–31. Post‐flood moisture content was greatest in the organic‐rich, top 10 cm and was lower at 10–75 cm where organic matter was less. Deuterium concentration revealed that soil moisture in the top 10 cm was quickly dominated by artificial flood water, but at depth remained <80% floodwater even after 31 days. Pervasive dye staining of ped surfaces in the top 4 cm indicated connectivity to flood waters but staining at depth was less and highly variable. The isotopic composition of soil water at depth continued to shift toward flood water despite no differences in dye staining between days 3 and 31. Results indicate flooding initially but incompletely recharges matrix water via macropores and suggest the importance of flooding as a source of matrix recharge in vertic floodplain soils may depend more on flood frequency than duration. Isotopic composition of matrix water in vertic soils depends on both advective and diffusional processes, with diffusion becoming more dominant as porosity decreases.

Study of Digital Surface Data for Soils and Flood Risk Areas Mapping in Sudano-Sahelian Zone (Mayo-Danay Division, Far North Cameroon)

In general, living close to a river is advantage, but there is always of flooding risk, that recurrence in recent decades provokes serious material damage and loss of life. Thus, in order to protect environmental health, economic viability and human activity zones of Mayo-Danay, a careful study of components of natural environment, mainly soil, has proved essential. Clearly, use of GIS in management of natural disasters is most relevant method, designed on integration, Multicriteria Analysis (MCA) and spatial data. Thus, Digital Elevation Model is obtained by manual digitization of contour lines, in order to define the large pedological sets on which wells have been opened, profiles described, soil samples taken and analyzed in laboratory. Main results reveal that soils are sandy to clayey, with neutral and basic pH (7 to 8), high CEC and low organic matter. While, quartz is predominant, associated with smectites, illites, feldspars and iron oxyhydroxides. Updated soil map shows five soil units (1) vertisols with hydromorphic characters (26%), (2) tropical ferruginous soils (32%), (3) less evolved hydromorphic soils (15%), (4) halomorphic vertic soils (9%), and (5) hydromorphic vertic soils (18%). It is an excellent tool for work and research, that responds to agronomic and development problems. It is therefore an excellent tool for work and research, which responds to agronomic and development problems. The multi-criteria spatial analysis establishes hazard and vulnerability, crossing of which gives of flood risk areas map, according to hazard level, very high (12%), high (16%), moderate (14%), low (30%) and very low (28%) risks. For this purpose, it emerges that rainfall is relatively low (700 mm/year), but falls very abruptly during short periods, at high intensity with flows exceeding the infiltration capacities. Morphology of low-slope "yayrés" (280 m) (2‰) is bordered by high landscape (500 to 1400 m) that prevent flow of many rivers that converge into plain. Sandy soils dominated by quartz favor fast rising in water table, while very clayey soils governed by 2/1 clayey (smectites) whose behavior induce waterproofing and intense surface runoff that generate flooding. Evidently, land use change leads to transformation of natural spaces into agricultural and urban environments, which makes soils more compact and impermeable, favorable to flooding. Keywords Soil; Flood risks; Mapping; Mayo-Danay Division; Spatial data DOI: https://doi.org/10.23953/cloud.ijarsg.501

Growth performance and fruiting of breadfruit (Artocarpus altilis) clonal plantation at vertic soil area in Gunungkidul, Yogyakarta for conservation strategy

Breadfruit is one of the tree species with a wide distribution in the Indonesian archipelago and shows variations in growth morphology, leave, and fruits. Therefore, the breadfruit clonal test plantation was carried out from several origin distributions at vertisol land in Gunungkidul, Yogyakarta, with a spacing of 5 x 5 m. This study aimed to identify the variation in growth and fruit production of 12 breadfruit cultivars at 10 years old. They were collected from Gunungkidul, Kediri, Banyuwangi, Sukabumi, Banten, Bali, Mataram, Lampung, Bone, Malino, Sorong, and Manokwari. The study was conducted by selecting 4 trees from each cultivar that have average growth and replicated five times. The growth characters of breadfruit trees were observed, namely height, stem diameter at breast height, canopy width, and a number of fruits. The observation results showed that there is a significant influence of origin distribution of breadfruit on growth and fruiting performance. The average tree height was 6.1-9.7 m, stem diameter 14.2-22.0 cm, canopy width 3.2-6.1 m, and the number of ripe fruit 3-21 fruit/tree. Breadfruit clones from South Sulawesi (Bone, Malino) and Papua (Sorong, Manokwari) were relatively stable, showing the best performance in all the characters observed. It is indicated that cultivars from South Sulawesi and Papua were adaptable in vertic soil.

A Study of Soil Organic Matter Stability Using Derivatography and Long-Term Incubation Methods

Soil organic matter (SOM) includes many classes of labile compounds available for microbial decomposition or, conversely, stable compounds protected from biodegradation by biological, chemical, and physical stabilization. It is believed that the more thermal energy is spent on the destruction of soil organic matter, the more stable and more resistant for biodegradation it is. We compared the thermal and biological stabilities of organic matter in eleven soil types from deciduous forest, forest-steppe, steppe, and semidesert bioclimatic areas of the European Russia. According to the activation energy (Ea), the highest SOM thermal stability was typical of the ordinary chernozem and meadow vertic soil. The lowest SOM thermal stability was found for gray forest soil; other soil types were characterized by an intermediate resistance towards thermal oxidation. The thermally labile pool (<390–400°C) of organic matter in soils was on the average 41% (32–60%) of the total SOM, while the thermally stable pool (>390–400°C) was on the average 59% (40–68%). The SOM biological stability estimated by the ratio of potentially mineralizable organic matter to that resistant to mineralization (biological stability index) decreased in the following order: ordinary chernozem (Haplic Chernozem (Loamic, Pachic)) > meadow vertic soil (Pellic Vertisol (Gleyic, Humic)) > gray forest soil (Luvic Greyzemic Phaeozem (Loamic)) = meadow chestnut soil (Gleyic Kastanozem (Chromic)) > meadow solonetz (Endosalic Gleyic Solonetz (Loamic, Cutanic)) > alluvial meadow soil (Eutric Fluvisol (Humic, Oxyaquic)). The potentially mineralizable SOM pool in the studied soils was 6–27-fold lower as compared with the pool of thermally labile SOM, and the parameters that characterize SOM thermal stability did not correlate with the biological stability index. Thus, SOM thermal lability is not identical to its biodegradability.

Review of Novel and Emerging Proximal Soil Moisture Sensors for Use in Agriculture.

The measurement of soil moisture in agriculture is currently dominated by a small number of sensors, the use of which is greatly limited by their small sampling volume, high cost, need for close soil–sensor contact, and poor performance in saline, vertic and stony soils. This review was undertaken to explore the plethora of novel and emerging soil moisture sensors, and evaluate their potential use in agriculture. The review found that improvements to existing techniques over the last two decades are limited, and largely restricted to frequency domain reflectometry approaches. However, a broad range of new, novel and emerging means of measuring soil moisture were identified including, actively heated fiber optics (AHFO), high capacity tensiometers, paired acoustic / radio / seismic transceiver approaches, microwave-based approaches, radio frequency identification (RFID), hydrogels and seismoelectric approaches. Excitement over this range of potential new technologies is however tempered by the observation that most of these technologies are at early stages of development, and that few of these techniques have been adequately evaluated in situ agricultural soils.

Physical Indicators and Mechanism of Vertisolization: A Case Study of the Cis-Caucasian Vertic Chernozem

Vertisolization —the development of vertic properties and vertic horizons—is a widespread process leading to adverse physical and technological properties of chernozems.. There is still no generally accepted theory of the genesis of this phenomenon, although it is a priori clear that the physicochemical mechanisms of the interaction between fine particles and soil water in swell–shrink cycles are the underlying factors. Patterns of the dynamics of the main categories of soil porosity in dependence on the soil water content have been studied at a quantitative level in the genetic horizons of a Cis-Caucasian vertic leached chernozem (Luvic Chernozem (Epiloamic, Katoclayic, Aric, Novic, Bathyvertic)) in comparison with a chernozem without vertic properties. The physical state of vertic soils is represented by structural diagrams of porosity as a function of the specific volumes of various pore categories depending on the volumetric water content. The diagrams are constructed using the experimental data on the textural porosity of aggregates obtained by saturating individual aggregates with a nonpolar liquid (toluene) and humidification with hot water vapor and a fundamental ionic electrostatic model of the disjoining pressure. Vertisolization is characterized by a significant reduction in the textural porosity and a predominance of specific volumes of the external pore space (cracks and interaggregate voids) in the overall structure of the porous dispersed system. The most likely cause of vertisolization is a sharp (twofold) decrease in the effective width of the electrical double layer in the dispersed system with an increase in the particle interaction through stable layers of liquid phase (compaction effect). In turn, this brings about adverse technological properties of the vertic chernozems and lumpy fragmentation upon drying with the formation of large cracks, which complicates their tillage and agricultural activities in general.

Tillage and no-tillage effects on physical and chemical properties of an Argiaquoll soil under long-term crop rotation in Buenos Aires, Argentina

No-tillage systems are able to reduce the negative effects of agricultural intensification on soil properties. However, knowledge of long-term impacts of no-tillage systems on soil properties is insufficient. It is essential to know which soil quality indicators are the most sensitive to management practices in each particular environment. Therefore, the objective of this work is to determine which soil quality properties are more sensitive to the impact of two tillage systems in a vertic Argiaquoll soil from Buenos Aires, Argentina. This work started in 2006 and included crop rotation and tillage systems, including both tillage and no-tillage. Physical and chemical properties were measured in three consecutive years (2013–2015) at two depths (0–10 cm and 10–20 cm). The tillage system modified soil physical and chemical properties, mainly in the surface layer. No-tillage showed significantly higher bulk density (2013–2015 p < 0.05), gravimetric moisture (2013; 2014 p < 0.05), organic carbon (2013–2015 p < 0.05), and aggregates stability in the face of a heavy rain (2013; 2015 p < 0.05), than soil under tillage. Soil saturation (or total porosity) was significantly greater under tillage. The tillage system did not affect hydraulic conductivity, total nitrogen and extractable phosphorus from the surface, nor physical and chemical properties from the second depth. No-tillage alleviates, but is not enough to mitigate, the loss of soil organic carbon and aggregate stability caused by continuous cropping in this vertic Argiaquall. Bulk density, organic carbon, aggregates stability and saturation are indicators for future studies performed in environments with similar soil and climate conditions.

Agriculture Management Impacts on Soil Properties and Hydrological Response in Istria (Croatia)

The objective of this work is to study the effects of traditional land uses (vineyard, cropland, and olive orchard) on soil properties, overland flow, and sediment loss in the Istria region (Croatia), by using simulated rainfall. The results showed that soil bulk density (BD) was significantly higher in cropland plots compared to the vineyard and olive orchard. No differences were observed in soil water content (SWC) and mean weight diameter (MWD). Water stable aggregates (WSA), soil organic matter (SOM), and total nitrogen (TN) were significantly higher in the olive orchard compared to the other land uses. In cropland, during the experiment, we did not identify runoff or soil losses. Runoff (Run) and sediment loss (SL) were significantly higher in the olive orchard compared to the other plots. This was very likely a consequence of tillage practices in vertic soils, the use of herbicides, low vegetation cover, as well as the incorporation of hydrophobic organic matter in the soil matrix. The principal component analysis results showed that factor 1 explained the majority of the runoff and erosion variables. Erosion rates and nutrient losses were substantially different between olive orchard plots, and vineyard and cropland. Factor 2 showed that WSA was inversely related to the available phosphorus, water holding capacity, and sediment concentration. Management practices in the studied area should use minimum tilling frequency to have plant cover and avoid erosion.

Hydrological behaviour of vertisols in the Brazilian semi-arid region: the importance of rainfall of less than 30 mm

The greater probability of small rainfall events occurring in semi-arid regions, and the little understanding of their role in hydrological processes, has led to this investigation of surface runoff generated during these events in two adjacent micro basins in the Brazilian semi-arid region. The types of plant cover to be investigated were the Phytogeographical Caatinga Domain under regeneration for 35 years (CPDReg) and thinned CPD (CPDThin), which consisted of the elimination of trees with a diameter of <10 cm. Two historical series were considered, one of 40 years (1974-2013) with 2,259 events and the other consisting of 247 rainfall events of <30 mm from 2009 to 2013. The cumulative frequency distribution showed that the series of 247 24-hour events proved to be statistically representative in investigating hydrological processes in the Brazilian semi-arid region, compared to the long series of 2,259 events. Irrespective of the pattern, rainfall with an intensity of less than 17 mm h-1 generated effective precipitation with small depths (<2 mm). Regardless of the rainfall pattern, the lowest effective precipitation was registered for the plant cover of thinned CPD, both on an annual scale and per event. The occurrence of 3 or 4 consecutive dry days is enough for events of <30 mm to generate no runoff, due to the appearance of micro-cracks formed in vertisols during the drying process. It is believed, therefore, that the expansion and contraction of vertic soils is the main determinant for the start of Pe in areas with a water source (micro basins of <2 ha) in the CPD.

Soil organic carbon stocks under recommended management practices in different soils of semiarid vineyards

AbstractThe Intergovernmental Panel on Climate Change (IPCC) approach is widely used to estimate the C account through the use of standardized coefficients that are not site specific. For these reasons, the aim of the work was to define specific IPCC coefficient taking into account differences in pedological characteristics that affect soil C steady state.In a vineyard area of Sicily, the effectiveness of 5 years of recommended management practice (RMP) adoption on soil organic carbon (SOC) stock increases was evaluated by considering 100 paired sites distributed over four functional soil groups. Each site consisted of two neighbouring plots. The soil of one plot was managed with cover crops according to RMP, and the other plot was managed with conventional tillage practices. IPCC coefficients were also derived and specifically adjusted for semiarid environments.SOC changes following RMP adoption and SOC steady‐state levels were correlated with functional soil groupings. SOC increased from 24.8 to 28.3 t ha−1 in conventional and RMP vineyards, respectively, with the highest increases being observed in vertic and the lowest in calcic soils. The management factor (Fmg) ranged from 1.11 for calcaric to 1.44 for vertic functional soil groups. C maintenance requirement (C input) should be estimated in relation to soil functional groups.Findings of this study highlighted how the fine tuning of C steady state in relation to specific environmental characteristics is necessary to avoid overestimation of soil C sequestration. Awareness of correct soil C sequestration potential is useful for policymakers and stakeholders for future C account and land degradation control planning.

Past and current geochemical conditions influence silicon isotope signatures of pedogenic clay minerals at the soil profile scale, Ethiopia

Soil processes strongly govern silicon (Si) mobility in terrestrial environments and its relation to other global biogeochemical cycles. The nature of inherited soil clay minerals can be highly diverse given the variability of their weathering environment. The influence of Si isotope fractionation factor in the initial geochemical conditions of clay precipitation can therefore be still expressed in inherited clay minerals in their new environment. We studied top- and subsoil of an Ethiopian Vertic Planosol derived from parent materials of similar sources of volcanism. The selected Planosol has an abrupt textural change at a depth of ~40 cm separating a bleached, silty (25 ± 1.8% clay) ash-derived soil horizon with a crumby structure from a heavy clayey (68 ± 3.4% clay) lacustrine-derived vertic soil horizon. The mineralogical assemblage of the clay fraction in top- and subsoil is characterized by similar proportions of 1:1 (kaolinite) and 2:1 (illite and smectite) layer-type clay minerals. This specific soil profile provides a unique opportunity to elucidate the influence of clay formation processes (inheritance versus neoformation) on the Si isotope signature of pedogenic clay minerals. Minerals of the clay fraction in the clayey vertic horizon are significantly enriched in light Si isotope (δ30Si = −1.41 ± 0.02‰) compared to the bleached, silty horizon (δ30Si = −0.69 ± 0.03‰). These results are corroborated by the preferential enrichment in Ge, relative to Si, in the clay fraction of the clayey subsoil compared to the silty topsoil (Ge/Si = 6.3 ± 0.14 and 4.0 ± 0.10 μmol mol−1, respectively). Our results demonstrate that geochemical conditions in lacustrine environment favor kinetically-driven Si isotope fractionation factor leading to lower Si isotope ratios in 2:1 clay minerals inherited in the new soil profile environment. The inherited soil textural conditions in the soil profile also contribute to on-going processes that result in larger Si isotope differences between the soil solution (CaCl2 extractable) and clay minerals. This implies that Si isotope signatures of clay minerals in the studied soil profile are influenced by a combination of inheritance processes in lacustrine environment and on-going neoformation processes in the soil profile. This finding has important implications for environmental studies using geochemical and Si stable isotope tracers to better understand current soil processes, to model elemental cycling in soil-plant systems and to quantify land-ocean element mass-balances.

Effects of irrigation regime and soil clay content and their interaction on the biological yield, nitrogen uptake and nitrogen-use efficiency of rice grown in southern China

Rice is commonly grown in clay soils under flooding or water-saving irrigation. The combination of irrigation regime and soil texture tend to create the distinguished growing environment of crops. However, plant response to this combination environment is seldom studied in rice grown in southern China. To investigate the effects of irrigation regime, soil texture type and their interaction on the biomass production, nitrogen uptake and nitrogen-use efficiency of rice, a shelter experiment was conducted using a randomized complete block design with a factorial arrangement of treatments with four replications. The main treatment was irrigation regime, set in three levels as R (30mm-100%), (100% saturation, 30 mm flooded), R (30mm-90%), (90% saturation, 30 mm flooded) and R (30mm-70%), (70% saturation, 30 mm flooded). The subtreatment was the soil texture type, set in three levels as 40%, 50% and 60% clay content, respectively. The irrigation regime, soil texture, and their combined interaction had significant effects on the biomass yield and nitrogen-use efficiency of rice. Compared to that of anaerobic-flooded water regime, biomass yield, nitrogen uptake and nitrogen utilization efficiency of the aerobic-flooded water regime were markedly reduced in both seasons of 2016 and 2017. Higher soil expanding clay content improved the biomass production and nitrogen utilization of rice in the both seasons. Maintaining soil water content at saturation and then reflooding was the optimal water management practice for rice cultivation in the soil, with 60% swelling clay content. The optimal combination R (30mm-100%) S (60%) presented the greatest nitrogen-use efficiency, which was 34.7% in 2016 and 46.6% in 2017. Soil swelling was dominant in the combination R (30mm-100%) S (60%), as it increased the biomass yield, absorption and nitrogen utilization of the rice plant by 64.0%, 81.5% and 76.2% in 2016, and 67.2%, 82.9% and 77.9 in 2017, compared to the combination R (30mm-70%) S (40%). Allowing the expansive soil to dry to 30% below the saturation point and then reflooding resulted in a sharp reduction in the nitrogen-use efficiency of rice of 8.2% in 2016 and 10.3% in 2017 due to cracks in the soil that preferentially became the major routes of water and nutrient losses. Soil cracking is dependent on the irrigation regime and soil texture, and cracks must be avoided when yielding rice in vertic clay soil under water saving irrigation. Our results are valuable in deciding what water management option to practice when yielding rice in swell-shrink clay soil. The results are also an important contribution to knowledge of soil, water and rice relationships.