Subsurface Soil Research Articles

Mapping the environmental impacts from land subsidence hazard in Pekalongan City and its correlation with the subsurface condition

Land subsidence in Pekalongan city has affected almost the entire municipality for at least ten years. Land subsidence has occurred in almost all Pekalongan city areas at 2-12 cm/year rates. The direct and indirect environmental impacts of land subsidence are enormous. We aim to map the environmental impacts of land subsidence in Pekalongan city and evaluate the severity of the impacts with the subsurface condition of the affected area. We employed site investigation using resistivity and CPTu soundings at representative sites to reveal the subsurface soils and site survey to map the environmental impacts. Resistivity measurements using a Schlumberger array were carried out at 24 sites, along with 12 CPTu measurements up to 30 m deep. Results show that the subsurface condition up to the depth of 30 m consists of alluvial sediment of clay, silt, and organic soils intercalated with lenses of sand. The alluvial sediment in the southern part is dominated by sandy soils and has a higher stiffness with cone resistance of 1-2 MPa and a friction ratio of 50-200 kPa. The subsurface soils in the northern part are dominated by clay, silt, and organic soils with low cone tip resistance of <0.5- 1 MPa, and friction ratio of <0.25-100 kPa. These values indicate that the sandy soils in the southern part are more compact and have higher bearing capacity than the soft, fine-grained soils in the northern area. The visible impacts of land subsidence include flood and inundation, settlement of buildings and roads, and cracks in houses and infrastructure. The severity of impacts worsens from South to North of the city. This condition is related to the subsurface stratification and engineering properties, where lower bearing capacity occurs in the north.

Analysis of Subsurface Soil Radon with the Environmental Parameters and Its Relation with Seismic Events

Abstract This study reports continuous measurements of subsurface soil radon as well as environmental parameters for a period of three years. The survey was carried out along the active fault area in the Indo-Myanmar subduction zone in the north-eastern part which lies in the highest seismic zone of India. The wavelet-based decomposition of the environmental parameters was done using discrete wavelet transformation technique. The denoised environmental parameters by discrete wavelet transformation technique was fed as the inputs to the MLR (multiple linear regression) and MLP (multilayer perceptron) models. Residual radon was calculated and correlated with nearby seismic events. Many events of magnitude greater than or equal to 5 have occurred in the investigation area. It was possible to successfully correlate one event with the anomalous variation in soil radon. The correlated event was the only one with the shallow epicentral depth indicating that the investigated area has undergone a shallow rock fracturing due to the stress generated before the occurrence of the seismic event.

Estimation of Groundwater Potential at Khalid Bin Walid Boarding School Using the Schlumberger Configuration Geoelectric Method

Khalid Bin Walid Islamic Boarding School is one of the Islamic boarding schools in Rokan Hulu Regency. This school is located in a water crisis area with complex groundwater sources. This study aims to determine the potential of groundwater as a reference for drilling wells and to determine the structure of the subsurface layer by using the geoelectrical method. The geoelectrical method is a method that is widely used, and the results are promising, namely, to obtain an overview of the subsurface soil layers and the possibility of groundwater presence. The configuration used in this study is the Schlumberger configuration using the basic principle of current propagating in the earth when injected in all directions and the assumption that the potential of the subsurface rock layer is the same. Data will be collected on four tracks, with a track length of 100-200 m. From the data processing results, it was found that potential sources of groundwater on track 3 with a depth of 13.7–30.3 m with alluvium rocks were suspected. Groundwater on this track can be used as a source of clean water using drilling.

Coccidioides undetected in soils from agricultural land and uncorrelated with time or the greater soil fungal community on undeveloped land.

Coccidioidomycosis is a typically respiratory fungal disease that, in the United States, occurs primarily in Arizona and California. In California, most coccidioidomycosis cases occur in the San Joaquin Valley, a primarily agricultural region where the disease poses a risk for outdoor workers. We collected 710 soil samples and 265 settled dust samples from nine sites in the San Joaquin Valley and examined how Coccidioides detection varied by month, site, and the presence and abundance of other fungal species. We detected Coccidioides in 89 of 238 (37.4%) rodent burrow soil samples at five undeveloped sites and were unable to detect Coccidioides in any of 472 surface and subsurface soil samples at four agricultural sites. In what is the largest sampling effort undertaken on agricultural land, our results provide no evidence that agricultural soils in the San Joaquin Valley harbor Coccidioides. We found no clear association between Coccidioides and the greater soil fungal community, but we identified 19 fungal indicator species that were significantly associated with Coccidioides detection in burrows. We also did not find a seasonal pattern in Coccidioides detection in the rodent burrow soils we sampled. These findings suggest both the presence of a spore bank and that coccidioidomycosis incidence may be more strongly associated with Coccidioides dispersal than Coccidioides growth. Finally, we were able to detect Coccidioides in only five of our 265 near-surface settled dust samples, one from agricultural land, where Coccidioides was undetected in soils, and four from undeveloped land, where Coccidioides was common in the rodent burrow soils we sampled. Our ability to detect Coccidioides in few settled dust samples indicates that improved methods are likely needed moving forward, though raises questions regarding aerial dispersal in Coccidioides, whose key transmission event likely occurs over short distances in rodent burrows from soil to naïve rodent lungs.

Insights into the driving factors of vertical distribution of antibiotic resistance genes in long-term fertilized soils

The prevalence of antibiotic resistance genes (ARGs) in soils has aroused wide attention. However, the influence of long-term fertilization on the distribution of ARGs in different soil layers and its dominant drivers remain largely unknown. In this study, a total of 203 ARGs were analyzed in greenhouse vegetable soils (0–100 cm from a 13-year field experiment applied with different fertilizers (control, chemical fertilizer, organic manure, and mixed fertilizer). Compared with unfertilized and chemically fertilized soils, manure application significantly increased the abundance and alpha diversity of soil ARGs, where the assembly of ARG communities was strongly driven by stochastic processes. The distribution of ARGs was significantly driven by manure application within 60 cm, while it was insignificantly changed in soil below 60 cm under different fertilization regimes. The inter-correlations of ARGs with mobile genetic elements (MGEs) and microbiota were strengthened in manured soil, indicating manure application posed a higher risk for ARGs diffusion in subsurface soil. Bacteria abundance and MGEs directly influenced ARG abundance and composition, whereas soil depth and manure application indirectly influenced ARG abundance and composition by affecting antibiotics. These results strengthen our understanding of the long-term anthropogenic influence on the vertical distribution of soil ARGs and highlight the ecological risk of ARGs in subsurface soil induced by long-term manure application.

Strategic tillage is a promising alternative to conventional and no-tillage: Evidence from a 12-year field trial in a double-cropped rice system

No-tillage (NT) has obvious advantages in reducing input and labour costs. However, some farmers have raised concerns about adapting continuous NT to manage farmland due to problems such as soil stratification and less yield. Therefore, occasionally targeted tillage (known as strategic tillage, ST) has been proposed as a flexible management measure. To evaluate the potential impact of a typical ST pattern on soil properties and yield, a 12-year positioning field trial was conducted with three tillage practices, including long-term no-tillage (NT), ploughing tillage (CT), and ST (3-year NT and 1-year CT), in an intensive double-cropped rice system in southern China. ST could alter soil physicochemical properties by reducing soil stratification and potentially increasing nutrient availability. ST alleviated the bulk density (BD) stratification caused by the continuous decrease in 0–5 cm BD and the continuous increase in 5–10 cm BD under NT, due to the periodic use of CT. Compared with NT and CT, ST increased the soil available K (AK) and available P (AP) concentrations without affecting the SOC or TN storage throughout the profile. However, ST lowered the soil acidification at the soil surface (0–5 cm) while increasing the risk of soil subsurface acidification. Relative to ST, yields with NT trended lower over time, and the yield gap between NT and ST increased as the experiment progressed. The multiyear average yield of ST was 0.31 t ha−1 higher than that of NT but lower than that of CT. ST had the potential to improve the low yield under NT. It may be related to the fact that the seed setting rate (the proportion of filled to total seeds) of ST was significantly higher than that of NT (p < 0.05). In conclusion, strategic tillage is a more sustainable tillage method than continuous no-tillage and ploughing tillage in double-cropped rice systems in southern China.

Reforesting degraded hillslopes with exotic pines in Trinidad and Tobago: Infiltration, repellency and implications for runoff and recharge

In the Caribbean, planting resilient, fast growing exotic pine trees have commonly been used to reforest degraded landscapes. However, little is currently understood about how these practices alter soil water movement and subsequently runoff and recharge. We monitored the surface soil water repellency, hydraulic conductivity, and subsurface soil moisture response to individual storm events in an exotic pine plantation and native forest in the dry and wet seasons. During the wet season, neither forest had a repellent soil surface, and the hydraulic conductivity in the exotic pines (48 mm h−1) were not significantly higher than the native forest (36 mm h−1). The speed and magnitude of the soil moisture response did not differ substantially between both forests in the wet season. However, during the mid dry season, a threshold soil moisture level was reached in the pines which triggered the development of repellent/hydrophobic conditions across all locations. Repellency reduced the surface hydraulic conductivity to 1.6 mm h−1, which in turn severely reduced the soil moisture response to rainfall. Our findings illustrate that throughout most of the year, the exotic pine plantation does not have a substantial negative impact on runoff or recharge. Only under the driest conditions do they negatively affect these processes. Our work also highlights the importance of characterising soil water repellency, hydraulic conductivity, and subsurface soil water responses over longer time periods to account for temporal variability.

Preferential association of polycyclic aromatic hydrocarbons (PAHs) with soil colloids at an e-waste recycling site: Implications for risk of PAH migration to subsurface environment

Polycyclic aromatic hydrocarbon (PAH) contamination at e-waste recycling sites poses high ecological and human-health risks. Of note, PAHs in surface soils can be mobilized through colloid-facilitated transport, and may migrate into the subsurface and pollute groundwater. Here, we show that the colloids released from the soil samples at an e-waste recycling site in Tianjin, China contain high concentrations of PAHs, with total concentrations of 16 PAHs as high as 1520 ng/g dw. Preferential association of the PAHs with the colloids is observed, with the distribution coefficients of PAHs between colloids and bulk soil often above 10. Source diagnostic ratios show that soot-like particles are the main source of PAHs at the site, due to the incomplete combustion of fossil fuels, biomass, and electronic wastes during the e-waste dismantling practices. Due to their small sizes, a large fraction of these soot-like particles can be remobilized as colloids, and this explains the preferential association of PAHs with colloids. Moreover, the colloids-soil distribution coefficients are higher for the low-molecular-weight PAHs than for the high-molecular-weight ones, possibly attributable to the different binding routes/modes of these two groups of PAHs to the particles during combustion. Notably, the preferential association of PAHs with colloids is even more pronounced for the subsurface soils, corroborating that the presence of PAHs in the deeper soils is primarily the results of downward migration of PAH-bearing colloids. The findings highlight the important role of colloids as a vector for the subsurface transport of PAHs at e-waste recycling sites, and call for further understanding of colloid-facilitated transport of PAHs at e-waste recycling sites.

APPLICATION OF SEMI-VARIOGRAM ANALYSIS IN MEASURING SPATIAL VARIABILITY AND DISTRIBUTION OF SELECTED SOIL PROPERTIES IN NORTHEAST AKWA IBOM STATE, NIGERIA

Application of semi-variogram analysis in measuring spatial variability and distribution of selected soil properties in Northeast Akwa Ibom State, was carried out.The aim was to assess spatial variability and distribution of selected soil properties in the study area for effective site-specific soil management and precision agriculture using semi-variogram analysis. A digital elevation model (DEM) of the study area was acquired from United State Geological Survey (USGS) at 30m resolution. Slope gradient map that is capable of capturing the short-scale spatial variability of soil properties in the study area was generated from the DEM to guide field sampling. Modified conditioned Latin hypercube sampling technique was used in selecting observation points. Soil samples were collected from each observation point at 0-30 cm and 30-60 cm depths using soil auger. A total of 152 soil samples were collected for laboratory analysis. Analysed data of depth interval of 0-30cm and 30-60 cm were integrated to form depth interval of 0-60 cm. The data were subjected to normality test to ascertain the normal distribution of the data. Selected soil properties were subjected to semi-variogram analysis. The study revealed that slope gradient was able to captured short scale spatial variation in some soil properties understudy. Soil texture of the flat/nearly flat was sand in both surface and subsurface soil and sand in the surface soil and loamy sand in the subsurface soil in gently sloping and sloping. Soil pH was slightly acid in in flat/nearly flat and gently sloping and strongly acid in the sloping area in both surface and subsurface soil. Organic carbon was very high in the flat/nearly flat and gently sloping and high in sloping topography in both surface and subsurface soil. Total N was low in the sloping area and moderately low in gently sloping and nearly flat /flat. Base saturation was very high in the sloping topography and high in the gently sloping and nearly flat /flat. The results of semi-variogram analysis showed that all the selected soil properties exhibited spatial dependence within some distances. The range was 136.2 m for sand, 76.4m for silt, 1.6 m for clay, 1.7m for soil pH, 9.4m for organic carbon, 7.1m for total N, 9.2m for available P and 7.8 m for exchangeable K in the study area. Beyond this range, there is no longer relationship between sample points and sample values are not related to one another. The strength of the spatial dependence of sand, silt, soil pH, organic carbon, total N and available P was moderate; exchangeable K was strong while clay was weak. The semi- variance (sill) was 57.4 for sand, 23.8 for silt, 7.15 for clay, 0.21 for soil pH, 1.18 for organic carbon, 0.002 for total N, 85.1 for available P, and 0.03 for exchangeable K. The nugget variance or nugget effect was 25.9 for sand, 10.2 for silt, 5.9 for clay, 0.06 for soil pH, 0.60 for organic carbon, 0.001 for total N, 33.4 for available P and 0.003 for exchangeable K. The best fitted models were Exponential for sand and silt; Gaussian for available P and Spherical for clay, pH, organic carbon, total N and exchangeable K.

Soil carbon stabilization and potential stabilizing mechanisms along elevational gradients in alpine forest and grassland ecosystems of Southwest China

Alpine ecosystems potentially store a large amount of soil organic carbon (SOC), but they are highly sensitive to climate change. The assessment of SOC stabilization mechanisms in these ecosystems is therefore vital to understanding the C dynamics in terrestrial ecosystems. Here, we investigated the soil aggregate distribution, aggregate stability, and associated SOC contents within alpine forest and grassland soils along an elevation gradient (2600–3900 m a.s.l) in the Yulong Mountains of Southwest China. Our results showed that the SOC contents in bulk soils and aggregates were higher within grassland soils than in forestland soils, with higher levels in the topsoil (0–10 cm) than in the subsurface soil (10–20 cm) layers at each elevation. The large macroaggregates (>2000 µm) accounted for the largest proportions of aggregate fractions (50.54% and 49.11%) and contributed the greatest proportions of C (55.44% and 52.12%) to the whole soil C within forest and grassland soils, respectively. Generally, the proportions of large macroaggregates, microaggregates (53–250 µm), mean weight diameter, and geometric mean diameter increased significantly with increasing elevation across different soil depths and land types, suggesting that soil C stability was improved with increasing elevation. The SOC contents in bulk soils and aggregates also showed an increasing trend with increasing elevation, with the highest level observed at 3900 m within forestland and 3200 and 3900 m within grassland soils at both soil depths. Climate factors, soil factors, Al/Fe oxides, and aggregate stability indices interactively explained 86% and 52% of the variation in soil C within forest and grassland soils, respectively. Among them, the incorporation of the Al/Fe oxides increased the total explained SOC variations by approximately 10%, exceeding the SOC variations explained by climate or soil factors. Overall, our results provide useful insights into the patterns and mechanisms of soil C stabilization along elevation gradients in alpine ecosystems.

A Convolutional Neural Network Model for Soil Temperature Prediction under Ordinary and Hot Weather Conditions: Comparison with a Multilayer Perceptron Model

Soil temperature is a critical parameter in soil science, agriculture, meteorology, hydrology, and water resources engineering, and its accurate and cost-effective determination and prediction are very important. Machine learning models are widely employed for surface, near-surface, and subsurface soil temperature predictions. The present study employed a properly designed one-dimensional convolutional neural network model to predict the hourly soil temperature at a subsurface depth of 0–7 cm. The annual input dataset for this model included eight hourly climatic features. The performance of this model was assessed using a wide range of evaluation metrics and compared to that of a multilayer perceptron model. A detailed sensitivity analysis was conducted on each feature to determine its importance in predicting the soil temperature. This analysis showed that air temperature had the greatest impact and surface thermal radiation had the least impact on soil temperature prediction. It was concluded that the one-dimensional convolutional model performed better than the multilayer perceptron model in predicting the soil temperature under both normal and hot weather conditions. The findings of this study demonstrated the capability of the model to predict the daily maximum soil temperature.

THE COMBINED EFFECT OF THE TILLAGE DEPTH AND COMPOST APPLICATION ON CALCAREOUS SOIL AGGREGATES AND THE YIELD OF INTERCROPPED FABA BEAN WITH WHEAT

Calcareous soils crusting and low organic matter (OM) content are key problems restrict their management and productivity. The aim of this study is to assess the role of tillage at different depths along with the compost application for improving some characteristics of the calcareous soil as well as the yield, and its components of the intercropped faba bean with wheat (1:1 ratio). A field experiment was carried out at the Nubaryia Agricultural Experimental Station through the two successive winter seasons (2019/2020) and (2020/2021) in a split-plot design with three replicates. The main factor (F1) was the plough depth treatments: Chisel plough (20 cm depth) and subsoiler (40 cm depth) one time and twice. The sub-factor (F2) was the applied compost (C1= 5.95 and C2= 11.9 tons ha-1). A control without additions was involved. The wheat and fababean were sown in a 1:1 intercropping ratio mixed with the surface layers by hatchat under a surface irrigation system and the recommended agronomic practices were followed. The tillage treatments combined with increasing the rate of the applied compost have increased the total stable aggregates (TSA), the aggregation index and aggregation degree in the surface and subsurface soil layers (0 – 20 cm, 20 – 40 cm) as well as the saturated hydraulic conductivity (Ks) for both seasons. The water stable aggregates (WSA) distribution revealed that the 8-2 cm aggregates are the abundant size especially in the surface soil layers. The 40 cm depth subsoiler twice treatment combined with the compost rate C2 resulted in the maximum OM for both seasons. The relative maximum OM increase (%) compared to the corresponding control was by 32.3 and 26.7% in the 0 – 20 cm soil layer and by 64.9 snd 60.0% in the 20 – 40 cm soil layer. For the compost rate C2, the most significant relative increase in the wheat grains yield (kg ha-1) was by 74.8% with the plowing two times at 40 cm depth, while for the faba bean seeds yield (kg ha-1) it increased by 145.5% with the 20 cm depth plowing. The studied treatments were effective for improving the calcareous soil properties and productivity.

Geotechnical investigation of the sub-soils condition around Yelwa North central part of Nigeria For the construction of infrastructures

Investigation of the geotechnical conditions of the Sub-soils around Yelwa North Central part of Nigeria was carried out in order to know the possible causes of the infrastructural failures in the area. The investigation involves in-situ collection of the disturbed and undisturbed soil samples and were analysed in the laboratory based on British Standard (BS) method for soil testing for civil engineers. Results of the study reveals that; The Atterberg limit (Liquid limit ranged from 33.0% to 43.0%, Plastic limits from 16.23% to 26.37%, Linear shrinkage from 7.86% to 15.71%, Plasticity index from 7.63% to 24.77%). The Sieve analysis shows that; the percentage passing of the soil samples ranges from 31.62% to 67.60% which indicates poor materials. The Direct shear test revealed that the cohesive strength (c) ranges from 13 kN/m2 to 24 kN/m2 , angle of internal friction (ø)° from 12° to 16° and unit weight (ϒ) from 18.17 kN/m3 to 20.87 kN/m3 . From the Consolidation test; the Total settlement (Pc) ranges from 0.0008 m to 0.013 m, Coefficient of Consolidation (Cv) from 87.657 m2 /yr to 109.325 m2 /yr and Volume Compressibility (Mv) from 0.0048 kN/m2 to 0.0205 kN/m2 . The Soil pH ranges from 6.4 to 7.4, Specific gravity (SG) from 2.57 to 2.73, and Natural Moisture Content (NMC) from 8.48% to 25.77%. The Compaction test revealed that; the Optimum Moisture Content (OMC) ranged from 13.22% to 20.60%, Maximum Dry Density (MDD) from 1.59 g/cm3 to 1.88 g/cm3 which shows that the soil are mostly of silty-clay material and Un-soaked value of California Bearing Ratio (CBR) ranges from 50.88% to 96.51%. The findings have revealed that, the sub-soil is characteristically fair to poor, and this required a form of geotechnics. Information acquired from the findings are expected to serve as guide in the choice of design and construction and as a baseline subsurface soil compendium for the construction of infrastructure in the study area and for further studies.

Dehydrating subsurface clayey soils using plastic electrodes: a simple, fast, and yet reliable technique

The electrokinetic process seems to be interesting to the earthwork portion on the construction of buildings, and transportation projects since this simple, fast, yet reliable technique could expedite dehydrating of soil and reduce delays in the construction schedule. This paper examined the technical feasibility and a brief cost analysis of using plastic electrodes for electrokinetically dehydrating clayey soils with high moisture content were also carried out. The results from the experimental program carried out on a marine clayey soil with copper and plastic electrodes showed a great deal of soil improvement since positive changes in undrained shear strength occur due to the free water dehydration process induced by electroosmosis and to the adsorbed water dehydration process induced by electromigration. It was also observed that values of the undrained shear strength remained stable at the final stages of the electrokinetic process indicating a permanent soil improvement. Finally, it was noticed that dehydrating could be achieved at lower costs by employing plastic electrodes.

Spatial variability of soil micronutrients under paddy (Oryza sativa)-wheat (Triticum aestivum) cropping system in irrigated plains

Soil properties vary spatially over short distances and sometimes prove detrimental to crop productivity in farmlands even after uniform application of balanced nutrients. In the present study, spatial variability of micronutrients was studied in Chakroi farm of Sher-e-Kashmir University of Agricultural Sciences and Technology of Jammu (SKUASTJammu) during 2016 and 2017. Results indicated that mean concentrations of micronutrients were in the order of Fe &gt; Mn &gt; Cu &gt; Zn both in surface and sub-surface layers. Exponential model was the best fit for all micronutrients in surface soil layer. Linear model was best fit for Cu and Gaussian model for Mn in the sub-surface layer. Whereas for Zn and Fe, the best fit was defined by exponential model. All the four micronutrients showed strong spatial dependence in surface layer, whereas in sub-surface layer Mn and Zn showed strong spatial dependence as compared to Cu. More than 60% of the area in the surface layer had Cu in the range of 2.0–2.8 mg/kg of soil. A very small area was under high range on the eastern side of the farm while in the sub-surface layer, Cu was unevenly distributed. The soil maps of Zn showed that it is above the critical value in surface layer while in sub-surface layer nearly 40% of the area had Zn in the deficient range. Fe was unevenly distributed and in the sub-surface layer it was higher in the southern and north-western parts of the farm. Mn was above the critical limit in both surface and sub-surface soils of the farm.

Long coleoptile genotype and soil texture interactions determine establishment success and early growth parameters of wheat sown at depth

Long coleoptile (LC) - wheat genotypes sown deeper (> 10 cm) than current practice (< 5 cm) enables earlier deep sowing into subsurface soil moisture. The LC genotype shows promise to broaden sowing windows and remove reliance on the shifting seasonal break for crop establishment. The suitability of this sowing strategy to the highly variable soils of the southern Australian wheatbelt warrants investigation to identify suitable environments for potential establishment benefits. We conducted controlled environment room (CER) and field experiments using pairs of near-isogenic-lines (NILs) that differed genetically only for coleoptile length. The experiments investigated the suitability of deep sown (12 cm) LC wheats in soils with different texture (sand versus loam). The CER experiment identified that LC genotypes exhibited greater emergence and early seedling growth, producing greater shoot and root biomass, when deep sown (12 cm) in loam. While LC and short coleoptile (SC) genotypes produced similar shoot growth when sown at depth in sand, LC produced greater root biomass reflected in more seminal roots. In the field on sand, LC and SC had similar emergence and early shoot growth characteristics at all sowing depths (5, 8 and 10 cm). However, the heavy-textured, loam soil reduced seedling emergence and restricted leaf growth with deep sowing (12 cm) in the SC. Our results indicate that the LC trait was more critical for plant emergence and early growth parameters (shoot and root biomass) from depth in a heavier textured loam compared with a sand. By identifying environments that will likely benefit most from deep sown LC, we are one step closer to adapting crop production to shifting rainfall patterns in southern Australia.

Active plant biomass inputs influence pore system functioning in no-till soils

Available knowledge about the exact impact of plant growth on the properties and functioning of no-till soils is somewhat limited, especially in tropical and subtropical regions. The starting hypothesis for this work was that long-term active plant biomass Input-APBI (aboveground plant shoot biomass) would improve pore system functioning in surface and subsurface soil layers by playing different, complementary roles in a previously degraded subtropical Acrisol. The hypothesis was checked by examining the results of a 34-yr field experiment involving five different cropping systems, namely: bare soil (BS), perennial pasture (PAST), oat/maize (O/M), oat + vetch/maize (O + V/M) and oat + vetch/ maize + cowpea (O + V/M + C). The soil was supplied with APBIs varying from 0.13 to 1.48 kg dry matter ha−1 yr−1. The APBIs for each cropping system were very low (BS), low (O/M), medium (O + V/M), high (O + V/M + C), and very high (PAST). The surface (0–5 cm) and subsurface (5–15 cm) soil layer were analyzed for static and dynamic properties of the pore system including bulk density; total, macro, and microporosity; the ability of the system to conduct air and water; continuity in soil pores; and plant-available water capacity. Micromorphological images of the soil revealed a complex pore network whose structure and functioning were both improved by the action of plants. In the surface soil layer, very high APBIs from pasture and high inputs from O + V/M + C increased total porosity by 11 and 14 %, respectively; pore continuity (Ncont) by 11 and 40 %, respectively; and microporosity by 31 and 23 %, respectively —all relative to bare soil. In the subsurface soil layer, pasture, and O + V/M + C decreased Ncont by 44 and 40 %, respectively, but increased water permeability (kw) by a factor of 6.5 and 7, respectively. In addition, very high APBIs increased continuity and permeability to air in macropores relative to BS. Organized large macropores in the subsurface soil layer efficiently conducted water and air from the soil surface and acted as bridges between the surface and subsurface soil layer. Overall, our findings suggest that APBIs helped develop a pore system with differential properties and complementary functions that influenced water infiltration and air fluxes in the surface soil layer, and water availability to crops in the subsurface soil layer, through long-term self-organization in the system. Future research with a view to understanding the influence of species richness and roots on physical quality in no-till soils is recommended.

Evaluating the Soil Quality of Forest, Broom Grass and Cultivated Land Uses in Hilly Agro-ecosystem, Meghalaya Plateau, North East India

Soil quality can be inferred from selected chemical soil indicators and it may be altered under the impact of changes in land uses (LUS). For achieving sustainable management practices the soil quality indicators (SQI) should be measured. The objective of this study was to compare the soil quality index in forest, Broom and cultivated land use systems in some areas of Meghalaya, using a completely randomized design at nine different land uses containing Mixed-Forest, Pine-Forest, Broom-Grass, Rice-Potato, Rice-Cabbage, Upland Rice-Monocrop, Lowland Rice-Monocrop, upland pineapple crop and slash-burn cropping system with three replications and two depths. 54 soil samples were collected from the surface and subsurface soil depth of diverse LUS and 9 soil chemical attributes was selected for SQI. Values of SQI deduced using the average factorial deviation from the values of soil quality indicators of diverse LUS site relative to their value of the mixed forest as a (reference) scaled to 100 per cent. The results showed that the pine forest land use had the premier value of SQI (98.99) and poorest in the rice-potato (70.00) land use system in both the depth compared to mixed forest land. It can be concluded that cultivated land use decreases soil quality index such as rice-potato system.

DETERMINATION OF HEAVY METALS AND ENVIRONMENTAL HEALTH STATUS OF AGRO SOILS IN IKOT ABASI, NIGER DELTA, NIGERIA

Heavy metal pollution of soils is a worldwide concern due to the security of the agricultural products derivable from the heavy metal contaminated soils. The toxic metals enter the soil-agro ecosystem through natural processes derived from anthropogenic activities and geological weathered materials. This study is aimed at investigating the contamination status of soils from Ikot Abasi, Akwa Ibom State, being an area of intense agricultural and industrial activities. Twelve locations were demarcated for soil sampling, whereby top (0- 15 cm ) and sub-surface ( 15 – 30cm ) soil samples were obtained. The soil samples were air-dried and subjected to heavy metal determination (iron, Fe; cadmium, Cd; lead, Pb; zinc, Zn; copper, Cu; vanadium, V; nickel , Ni; chromium, Cr ; mercury, Hg ) by inductively coupled plasma– optical emission spectrometer (AGILENT 720 ICP-OES). The mean concentrations of heavy metals during the dry and wet seasons followed the order: Fe &gt; Zn &gt; Cu &gt; Cr &gt; Ni &gt; Pb &gt; V &gt; Cd &gt; Hg. The geo-accumulation index (Igeo) determined for all the metals studied were less than one , which falls in the Class zero , implying that the soils of the study area is practically unpolluted ; the potential ecological risk ( RI) were less than one , which was in the class of no potential ecological risk : modified degree of contamination ( mCd) calculated for both seasons falls in the category of less than 1.5 , which is nil to very low degree of contamination of the soils of the study area; pollution load index ( PLI), falls in the category of PLI of zero, which is excellence with no metal pollutant contamination. The public concern in respect of the security of the agricultural products derivable from the heavy metal contaminated soil, seem not to be applicable in the soils of Ikot Abasi, however, regular monitoring, is recommended to check possible future contamination.

Thirteen‐year stover harvest and tillage effects on soil compaction in Iowa

AbstractCorn (Zea mays L.) stover is an abundant biomass source with multiple end‐uses including cellulosic biofuel production. However, stover removal may increase soil compaction by reducing organic matter inputs and increasing vehicle loads during harvest. While numerous studies have reported stover removal impacts on soil physical quality, few have assessed the role played by traffic compaction. Our objective was to quantify subsurface soil compaction after 13 years of chisel plow versus no‐till management and no, moderate (3.5 ± 1.1 Mg ha−1 year−1), or high (5.0 ± 1.7 Mg ha−1 year−1) stover harvest rates. Penetration resistance was measured in most‐ and least‐trafficked interrow spaces. Chisel plowed plots with moderate and high levels of stover removal had higher penetration resistance in trafficked areas relative to least‐trafficked areas, whereas there was no evidence of traffic compaction when stover was retained. Traffic compaction did not negatively impact yields, which were greater with high levels of stover removal compared to no removal. The no‐till practice led to very small increases in penetration resistance with wheel traffic and had no evidence of increased compaction with residue removal. This lack of traffic compaction indicated soils under no‐till practice have a higher load‐bearing capacity than soils under chisel plow practice. Overall, there were no yield‐limiting effects of tillage practice or stover removal, and no evidence of soil compaction below the plow layer, suggesting stover removal with both tillage practices can be effectively employed without detrimental effects on plant or soil health.