Deep Subsoil Research Articles

Transformation of clay-sized minerals in soils exposed to prolonged regular alternation of redox conditions

The direction of the transformation of Fe-bearing minerals under harshly changing redox conditions is still under debate. Some studies suggest preferential accumulation of weakly crystalline Fe oxides while other studies showed that repeated redox cycles favour the presence of crystalline phases. Since characterized by distinct redox cycles, paddy soils are ideal for studying redox-related transformations of Fe oxides and Fe-bearing clay minerals. We analysed changes in the Fe mineral assemblage upon long-term reduction–oxidation cycles along a chronosequence of 100, 700, and 2000-year-old paddy soils developed on comparable parent material relative to two non-irrigated counterparts.The clay mineral assemblage, as indicated by X-ray diffraction, showed no significant differences between paddy and non-paddy soils as well as no changes with time under paddy management.Speciation of Fe mineral phases in top- and subsoil was accomplished by Mössbauer spectroscopy at room temperature and 4.2K, in combination with X-ray diffraction and selective chemical extractions (dithionite–citrate–bicarbonate, NH4 oxalate). We found ferrous and ferric Fe in silicates, nano- to micro-crystalline goethite and haematite, as well as a ferrihydrite-type phase. In topsoils, prolonged paddy cultivation resulted in general loss of silicate- and oxide-bound Fe in the topsoils and the remaining Fe oxide assemblage became more and more dominated by organic-rich weakly crystalline phases. Total contents of Fe oxides in subsoils increased due precipitation of Fe leached from the topsoils. Micro-crystalline goethite was the predominating Fe oxide phase in the upper subsoil, likely due to Fe2+-catalysed solid-state transformation of freshly precipitated hydrous Fe oxide phases. Lepidocrocite formed in the deeper subsoil, probably promoted by less CO2 in the soil water. Thus, paddy cultivation causes different Fe mineral weathering, forming, and transforming environments, with the depth differentiation of these environments becoming increasingly distinct with time under paddy management, i.e., the number of redox cycles the soils underwent.

Influences of micro-irrigation and subsoiling before planting on enzyme activity in soil rhizosphere and summer maize yield.

In order to explore the influences of micro-irrigation and subsoiling before planting on enzyme activity in soil rhizosphere and summer maize yield, an orthogonal experiment was carried out with three factors of micro-irrigation method, irrigation depth, and subsoiling depth. The factor of irrigation method included surface drip irrigation, subsurface drip irrigation, and moistube-irrigation; three levels of irrigation depth were obtained by controlling the lower limit of soil water content to 50%, 65%, and 80% of field holding capacity, respectively; and three depths of deep subsoiling were 20, 40, and 60 cm. The results showed that the activities of catalase and urease increased first and then decreased, while the activity of phosphatase followed an opposite trend in the growth season of summer maize. Compared with surface drip irrigation and moistube-irrigation, subsurface drip irrigation increased the average soil moisture of 0-80 cm layer by 6.3% and 1.8% in the growth season, respectively. Subsurface drip irrigation could significantly increase soil urease activity, roots volume, and yield of summer maize. With the increase of irrigation level, soil phosphatase activity decreased first and then increased, while urease activity and yield increased first and then decreased. The average soil moisture and root volume all increased in the growth season of summer maize. The increments of yield and root volume from subsoiling of 40 to 20 cm were greater than those from 60 to 40 cm. The highest enzyme activity was obtained with the treatment of subsoiling of 40 cm. In terms of improving water resource use efficiency, nitrogen use efficiency, and crop yield, the best management strategy of summer maize was the combination of subsurface drip irrigation, controlling the lower limit of soil water content to 65% of field holding capacity, and 40 cm subsoiling before planting.

Characterisation of agricultural drainage ditch sediments along the phosphorus transfer continuum in two contrasting headwater catchments

This study investigated the phosphorus (P) source, mobilisation and transport potential of ditch bed sediments as well as surrounding field and bank soils in two agricultural headwater catchments with contrasting soil drainage capacities. This information is important for discerning the potential for ditches to attenuate or augment transfers of P from upstream sources and thus for developing appropriate management strategies for these features. Phosphorus sources were characterised using the Mehlich3-P, water-soluble P and total P tests. Phosphorus mobilisation potential was characterised using the Mehlich3-AL/P, Mehlich3-Ca/P and DESPRAL P tests. Phosphorus transport potential was characterised using data collected on the presence/absence of surface water in ditches during field surveys and downstream turbidity data. Ditch sediments had similar P source contents (Mehlich3-P, water-soluble P and total P) to the surrounding field soils and higher P contents than bank soils. However, calcium contents of sediments in the poorly drained catchment reflected the deep sub-soils rather than the surrounding field and bank soils. Mehlich3-Al/P and Mehlich3-Ca/P contents of ditch sediments in the well (non-calcareous) and poorly (calcareous) drained catchments respectively indicated potential for P retention (above thresholds of 11.7 and 74, respectively). However, sediments were less aggregated than field soils and may mobilise more particulate P (PP) during rain events. Nevertheless, the majority of surveyed ditches dried out from March to September 2011; thus, their potential to mobilise PP may be less important than their capacity to attenuate soluble and PP during this time. In these and similar catchments, soluble P attenuation and particulate P mobilisation should be maximised and minimised, respectively, for example, by cleaning out the sediments before they become saturated with P and encouraging vegetation growth on ditch beds. This study also highlighted the influence of deep sub-soils on soluble P retention in ditches and thus the utility of characterising soils below depths normally included in soil classifications.

The δ18O signatures of HCl‐extractable soil phosphates: methodological challenges and evidence of the cycling of biological P in arable soil

SummarySoil phosphates exchange oxygen atoms rapidly with soil water once recycled by intracellular enzymes, thereby approaching an equilibrium δ18OP signature that depends on ambient temperature and the δ18OW signature of soil water. We hypothesized that in the topsoil, phosphates reach this equilibrium δ18OP signature even if amended by different fertilizers. In the subsoil, however, there might be phosphates with a smaller δ18OP value than that represented by the isotopic equilibrium value, a condition that could exist in the case of limited biological P cycling only. We tested these hypotheses for the HCl‐extractable P pool of the Hedley fractionation scheme of arable soil in Germany, which integrates over extended time‐scales of the soil P cycle. We sampled several types of fertilizer, the surface soil that received these fertilizer types and composites from a Haplic Luvisol depth profile under long‐term agricultural practice. Organic fertilizers had significantly smaller δ18OP values than mineral fertilizers. Intriguingly, the fields fertilized organically also tended to have smaller δ18OP signatures than other types of surface soil, which calls into question full isotopic equilibrium at all sites. At depths below 50 cm, the soil δ18OP values were even depleted relative to the values calculated for isotopic equilibrium. This implies that HCl‐extractable phosphates in different soil horizons are of different origins. In addition, it supports the assumption that biological cycling of P by intracellular microbial enzymes might have been relatively inefficient in the deeper subsoil. At depths of 50–80 cm, there was a transition zone of declining δ18OP values, which might be regarded as the first evidence that the degree of biological P cycling changed at this depth interval.

Fine root production and mortality in irrigated cotton, maize and sorghum sown in vertisols of northern New South Wales, Australia

Fine root (<2mm diameter) turnover (production and mortality) drives soil processes such as nutrient fluxes, carbon cycling and sequestration, activity of soil biota and structural stabilisation. Research on fine root dynamics has been focussed primarily on rainfed perennial and annual ecosystems in coarse and medium-textured soils with few studies conducted in irrigated fine-textured soils such as the vertisols. The objective of this study was to quantify the effects of tillage methods and the summer crops of cotton (Gossypium hirsutum L.), maize (Zea mays L.) and sorghum (Sorghum bicolor (L.) Moench.) on fine root number density in the non-sodic sub-surface (0.1–0.5m) and sodic subsoil (0.6–0.9m) of irrigated vertisols (average clay concentration 65g 100g−1 in the surface 1m) in northern New South Wales. It was hypothesised that fine root number density of cotton would be lower than that of maize and sorghum in the subsoil due to cotton's poor tolerance of anaerobic conditions. Fine root production, mortality and root number density of cotton, maize and sorghum, measured with a minirhizotron and a Bartz ICAP® image capture system, were evaluated for the 0.1–0.5m and 0.6–0.9m depth intervals in several irrigated experiments near Narrabri, NSW, Australia. Fine root density of cotton was low, with most occurring in the surface 0.5m. Subsoil (0.6–0.9m) root number densities of cotton were very low in continuous cotton under conventional tillage and on permanent raised beds (PRBs) but were greater with a cotton-wheat (Triticum aestivum L.) rotation sown on PRBs. Averaged over the two seasons, 2004–2005 and 2006–2007, and depth intervals, there were 3.4 roots×100mm−2 in continuous cotton sown after conventional tillage, 1.2 roots×100mm−2 in continuous cotton sown on PRBs and 6.0 roots×100mm−2 in cotton–wheat sown on PRBs. Between cotton genotypes, root number density during boll production and filling of a Bollgard®-Roundup-Ready® cotton variety was less than that of its corresponding non-Bollgard variant. Maize live root numbers did not differ significantly between continuous maize and a cotton-maize rotation but differed between depth intervals. Averaged over years and rotations, during tasselling maize had 21.5 roots×100mm−2 in the 0.1–0.5m depth interval and 5.3 roots×100mm−2 in the 0.6–0.9m depth interval. Root number density of sorghum was greater with no-tillage than with tillage in wetter seasons but generally similar or lower during a drier season. Average root numbers in the 0.1–0.5m depth interval during the “wet” seasons of 2010–2011 and 2011–2012 were 4.4 roots.100mm−2 with tillage and 9.3 roots×100mm−2 with no-tillage, and in the 0.6–0.9m depth interval were 4.5 roots×100mm−2 with tillage and 10.5 roots×100mm−2 with no-tillage. During the “dry” season of 2012–2013, however, root numbers in the 0.1–0.5m depth interval were 16.6 roots×100mm−2 with tillage and 11.8 roots×100mm−2 with no-tillage, and in the 0.6–0.9m depth interval were 13.8 roots×100mm−2 with tillage and 9.0 roots×100mm−2 with no-tillage. Fine root density of cotton was low, whereas those of sorghum and maize were high with relatively large values occurring in the deeper subsoil. Maize and sorghum were able to tolerate the waterlogged conditions in the sodic subsoils of these vertisols and may, therefore, be more suitable rotation crops for irrigated cotton farming systems than the more commonly sown wheat. These results, while relevant to other fine-textured soils that are irrigated or are periodically inundated, should not be extrapolated to medium and coarse-textured soils.

Water use sources of desert riparian Populus euphratica forests.

Desert riparian forests are the main body of natural oases in the lower reaches of inland rivers; its growth and distribution are closely related to water use sources. However, how does the desert riparian forest obtains a stable water source and which water sources it uses to effectively avoid or overcome water stress to survive? This paper describes an analysis of the water sources, using the stable oxygen isotope technique and the linear mixed model of the isotopic values and of desert riparian Populus euphratica forests growing at sites with different groundwater depths and conditions. The results showed that the main water source of Populus euphratica changes from water in a single soil layer or groundwater to deep subsoil water and groundwater as the depth of groundwater increases. This appears to be an adaptive selection to arid and water-deficient conditions and is a primary reason for the long-term survival of P. euphratica in the desert riparian forest of an extremely arid region. Water contributions from the various soil layers and from groundwater differed and the desert riparian P. euphratica forests in different habitats had dissimilar water use strategies.

Impact of energy saving cultivations on soil parameters in northern Kazakhstan

Recently the cost of soil processing for agricultural production has been rapidly increasing because of expensiveness of agricultural machinery, energy, and agricultural chemicals. Intensive soil cultivation is costly and adversely affects soil fertility due to accelerated mineralization of soil organic matter. By minimizing mechanical disturbance to the soil, costs can be reduced and the environment enhanced. About half of the global CO2 emissions from the soil come from decomposition of the annual plant litter including agricultural crops. We studied methods of soil tillage that would help stabilize the yield of crops while maintaining soil fertility and saving energy and labour at the same time. Three types of crop cultivation experiments were studied: 1) cultivation intensity (simplified ST, common CT, and intensive IT); 2) tillage depth (shallow S, and deep D subsoil till), and 3) minimum MT, and zero till ZT. The results showed that under ST the soil biological parameters were more favourable than under CT and IT. Shallow subsoil till maintained higher levels of soil nutrients, and reduced CO2 emission compared with the deep subsoil till. The minimum and zero tills positively influenced soil physical and biological properties through improvement in soil aggregate stability and soil enzymatic activity.

Characterization of alkali-soluble polysaccharides in deep subsoil layers

Plant cell wall polysaccharides undergo a slower degradation process in deep subsoil layers than in topsoil. Through the identification of organic compounds in subsoil, we may gain an understanding of this degradation process. In the present study, we extracted alkali-soluble polysaccharides from subsoil bore samples at depths of 5, 18, 29, 35 and 40–43 m, and performed sugar composition and sugar linkage analyses. Based on the results, we suggest that cellulose, arabinoxylan, mannan and pectic polysaccharides derived from plant cell walls and β-1,3-glucan and/or β-1,3:1,6-glucan from fungal cell walls exist in deep subsoil layers.

Biopores and root features as new tools for improving paleoecological understanding of terrestrial sediment-paleosol sequences

The important role of roots and rhizosphere processes is accepted for the top soil, but still under debate for the deep subsoil including soil parent material. Especially for terrestrial sediments like loess and dune sands, roots and root traces are mostly recognized in profile descriptions, but not interpreted in the paleoenvironmental context. Further, synchrony of sediment deposition and root trace formation is commonly assumed. This is challenged by partially large maximum rooting depths of plants, exceeding the soil depth, and by frequent occurrence of secondary carbonates and biopores of potential root origin below recent soil and paleosols. To improve understanding of paleoenvironmental records in terrestrial sediment-paleosol sequences, recent roots and root traces, including calcified roots and root-derived biopores, were investigated in six soil, loess and dune sand profiles across Central and SE Europe. Visualization of small carbonate accumulations (diameter≤1mm), frequently called ‘pseudomycelia’, by X-ray microtomographic scanning, and morphologic comparison with rhizoliths (calcified roots; diameter mostly 3–20mm, up to 100mm possible) indicate root origin of the former, therefore requiring renaming to microrhizoliths. Quantification of roots, biopores, rhizoliths and microrhizoliths on horizontal levels yielded maximum frequencies of 2100m−2, 4100m−2, 196m−2 and 12,800m−2, respectively. Considering the pore volume remaining from former root growth this indicates their significant contribution to structural properties of the sediments and paleosols. Depth distribution of roots and root traces was frequently related to soil and paleosols, respectively, and mostly showed maximum frequencies within or immediately below these units. Root traces are therefore not necessarily of similar age like the surrounding sediment, but are typically of younger age. The time lag between root traces and the surrounding stratigraphic unit can vary between small time periods (likely decades to centuries) in case of microrhizoliths and several millenia in case of larger rhizoliths penetrating several stratigraphic units. With assumed radii of former rhizosphere extension of 5mm for microrhizoliths, a frequency of 12,500m−2 corresponded to 100% rhizosphere area in the respective depth interval. These findings emphasize the meaning of root traces in sediment–paleosol sequences. Potential temporal and spatial inhomogeneity of root growth on the one hand, especially for shrub and tree vegetation, and occurrence of root remains of different age and origin in identical depth intervals on the other hand, hamper the assessment of the chronologic context of these with the surrounding sediment or paleosol. Nevertheless, root traces in terrestrial archives provide valuable information with respect to paleovegetation and paleoenvironmental conditions, if their chronological context is known.

Deep subsoiling of a subsurface-compacted typical hapludult under citrus orchard

Soil management practices which increase the root depth penetration of citrus are important to the longevity and yield maintenance of this plant, especially in regions where long periods of drought are common, even in soil conventionally subsoiled to a depth of 30-40 cm, when the orchard was first established. The objective of this study was to evaluate the efficiency of subsoiling on the physical and hydric properties of a Typical Hapludult and fruit yield in a 14-year-old citrus orchard located in Piracicaba, SP. The treatments consisted of: no-subsoiling (with no tilling of the soil after the orchard was planted); subsoiling on one side of the plant lines (SUB. 1); and subsoiling on both sides of the plant lines (SUB. 2). The subsoiling treatments were carried out 1.5 m from the plant lines and to a depth of 0.8 m. Soil samples were taken 120 days after this operation, at four depths, in order to determine physical and hydric properties. Fruit yield was evaluated 150 days after subsoiling. Subsoiling between the plant lines of an old established citrus orchard alters the physical and hydric properties of the soil, which is reflected in increased soil macroporosity and unsaturated hydraulic conductivity, and reduced soil bulk density, critical degree-of-compactness and penetration resistance. The improvements in the physical and hydric properties of the soil were related to an increase in fruit number and orchard yield.

Using Semivariogram and Moran's I Techniques to Evaluate Spatial Distribution of Soil Micronutrients

Spatial distributions of micronutrients in soils of Shouguang were evaluated using semivariogram and Moran's index (Moran‘s I) techniques to compare difference and veracity of these two spatial analysis methods. A total of 601 topsoil (0–20 cm) and 155 deep subsoil (150–200 cm) samples were collected on a symmetrical grid in the regional geochemical survey of soils in Shandong Province, and copper (Cu), iron (Fe), manganese (Mn), and zinc (Zn) concentrations were analyzed and compared. The results showed significant spatial correlations of micronutrients in Shouguang soils, and the spatial correlation degree was greater in topsoil than in deep subsoil. In topsoil and deep subsoil, the spatial correlation distance for each element obtained using the semivariogram technique was 20–60 km, whereas with Moran's I technique, the positive autocorrelation distance was 20–25 km and the negative autocorrelation distance was 25–55 km. The spatial autocorrelation degree was significant (P ≤ 0.05) for every micronutrient except deep subsoil Zn. Moran's I technique was able to distinguish between positive and negative autocorrelations and the results of semivariogram analysis gave the sum of the positive and negative autocorrelations. This study shows that Moran's I is more accurate and meaningful than semivariogram analysis for spatial autocorrelation of some soil attributes. These results provide the theoretical foundation for the application of spatial analysis methods, and Moran's I in particular, in environmental research.

Carbon stocks in primary and secondary tropical forests in Singapore

Tropical forests contain large reserves of carbon that are vulnerable to perturbation linked to human activities, including deforestation and climate change. Accurate estimates of forest carbon are therefore required urgently to support efforts to conserve tropical forests. We quantified carbon stocks in primary and 60-year-old secondary forest plots located on infertile Ultisols in Bukit Timah Nature Reserve, one of the few remaining areas of forest in Singapore. We used tree census data for 24.2ha of primary forest and 23ha of secondary forest, together with allometric equations, to estimate aboveground and coarse root biomass. Coarse woody debris stocks were censused along 2.44km and 2.12km of transects in primary and secondary forest, respectively. Soil carbon and fine root carbon stocks were assessed from soil samples taken to 3m depth in a 2-ha secondary forest plot and a 2-ha primary forest plot, combined with bulk density measured in a nearby soil profile pit. Total estimated carbon stock in the primary forest, which was located on the hilltop and upper slopes (80–115m elevation), was 337MgCha−1, of which 50% was aboveground biomass, 33% in soil, 12% in coarse roots, 4.6% in coarse woody debris, and 0.8% in fine roots. In the secondary forest, located on lower slopes and valley (50–85m elevation), the total carbon stock was 274MgCha−1 and the relative importance of aboveground biomass and soil were reversed, with 38% in aboveground biomass, 52% in soil, 6.9% in coarse roots, 1.5% in coarse woody debris, and 1.3% in fine roots. Including carbon in deep subsoil (i.e. to 3m) increased soil carbon stocks by ∼40% compared to 1m depth. Overall, the 60-year-old secondary forest contained 60% as much biomass as the primary forest, while the primary forest had lower carbon stocks than other primary forests in the region.

Selected soil properties as indicators of soil water regime in the Cathedral Peak VI catchment of KwaZulu-Natal, South Africa

The morphological features and physicochemical properties of 14 soil profiles, representing the major soil types, were studied in the Cathedral Peak VI catchment of KwaZulu-Natal, South Africa. The soils are characterised by a high organic carbon content in the topsoil, red and yellow freely drained subsoils, and some signs of water saturation in the deep subsoil and saprolite. The lack of variability in the morphology of the soils is probably a result of deep weathering of the chemically homogeneous basaltic parent material. Shelving controls the development of return flow on the slopes, feeding into the two prominent wetlands. The freely drained nature of the subsoil horizons are reflected in the red colour and low pH values of these horizons. The iron and manganese redoximorphic features, occurring in the lower horizons, are indicative of periodic short periods of water saturation.

Soft soil foundation improved by vacuum and surcharge loading

The Pacific Highway has been upgraded to support the high transportation demand between Sydney and Brisbane, along the north-east coast of Australia. To avoid the traffic through the busy town of Ballina, a bypass route was designed to traverse on a floodplain consisting of very soft, highly compressible, saturated marine clays up to 30 m deep in certain locations. A vacuum-assisted surcharge load scheme in conjunction with prefabricated vertical drains was selected to reduce the required time to consolidate the deep subsoil layers. The design of the combined vacuum and surcharge fill system and the construction of the embankment are described, and a comparison of the performance between the combined vacuum and surcharge loading system with the conventional surcharge only system is highlighted. Field data are presented and interpreted to demonstrate how the embankments performed during construction in both vacuum and non-vacuum areas. Suitable design charts for vertical drains are presented and discussed with a worked example, considering both vertical and radial drainage.

Effect of subsoiling and injection of pelletized organic matter on soil quality and productivity

Leskiw, L. A., Welsh, C. M. and Zeleke, T. B. 2012. Effect of subsoiling and injection of pelletized organic matter on soil quality and productivity. Can. J. Soil Sci. 92: 269–276. Subsoil compaction is a widespread problem in most reclamation and other industrial operations. The objective of our research was to evaluate effectiveness of coupling deep subsoiling with injection of 20 Mg ha−1 organic matter pellets. Research was conducted at seven sites on a pipeline right-of-way in central Alberta. Treatments were subsoiling, subsoiling with pellets and a compacted right-of-way (control), established in spring and fall 2009. Treatment effects on soil physical properties and nutrient status were assessed in fall 2009 for spring-established sites and on all sites in fall 2010. Density and height of canola plants were determined in late summer 2010. Relative to the control, subsoiling with pellet treatments had lower bulk density in the 20- to 40-cm depth interval (up to 40%) in 2010, particularly in clay-loam soils. This treatment often had higher available phosphorus and total organic carbon in 2010, and total nitrogen in spring treated sites in 2009. Relative to the control, subsoiling with pellets had 46% higher canola plant density in clay loam soils of fall-treated sites. Subsoiling with pellets is recommended on heavy-textured, compacted soils to alleviate compaction and increase plant productivity.

Simple physics-based models of compensatory plant water uptake: concepts and eco-hydrological consequences

Abstract. Many land surface schemes and simulation models of plant growth designed for practical use employ simple empirical sub-models of root water uptake that cannot adequately reflect the critical role water uptake from sparsely rooted deep subsoil plays in meeting atmospheric transpiration demand in water-limited environments, especially in the presence of shallow groundwater. A failure to account for this so-called "compensatory" water uptake may have serious consequences for both local and global modeling of water and energy fluxes, carbon balances and climate. Some purely empirical compensatory root water uptake models have been proposed, but they are of limited use in global modeling exercises since their parameters cannot be related to measurable soil and vegetation properties. A parsimonious physics-based model of uptake compensation has been developed that requires no more parameters than empirical approaches. This model is described and some aspects of its behavior are illustrated with the help of example simulations. These analyses demonstrate that hydraulic lift can be considered as an extreme form of compensation and that the degree of compensation is principally a function of soil capillarity and the ratio of total effective root length to potential transpiration. Thus, uptake compensation increases as root to leaf area ratios increase, since potential transpiration depends on leaf area. Results of "scenario" simulations for two case studies, one at the local scale (riparian vegetation growing above shallow water tables in seasonally dry or arid climates) and one at a global scale (water balances across an aridity gradient in the continental USA), are presented to illustrate biases in model predictions that arise when water uptake compensation is neglected. In the first case, it is shown that only a compensated model can match the strong relationships between water table depth and leaf area and transpiration observed in riparian forest ecosystems, where sparse roots in the capillary fringe contribute a significant proportion of the water uptake during extended dry periods. The results of the second case study suggest that uncompensated models may give biased estimates of long-term evapotranspiration at the continental scale. In the example presented here, the uncompensated model underestimated total evapotranspiration by 5–7% in climates of intermediate aridity, while the ratio of transpiration to evaporation was also smaller than for the compensated model, especially in arid climates. It is concluded that the parsimonious physics-based model concepts described here may be useful in the context of eco-hydrological modeling at local, regional and global scales.

Control of Soybean Nodule Formation by a Crack Fertilization Technique

Enhancement of nitrogen fixation activities by a cultivation technique is one of the potential targets to improve soybean yield in Japan. A cultivation technique named “crack fertilization” is described and the nodulation control by this technique is analyzed by experiments in two fields with different soil and environmental conditions, and a root box experiment. Crack fertilization is a technique that utilizes the irregularly shaped soil cracks formed by subsoiling just before the flowering stage of soybean, and introduces root nodule bacteria, fertilizers, and so on to the deep subsoil layer. Production of ureide-form nitrogen at six weeks after the crack fertilization (only nodule bacteria application to the subsoil layer) was 1.4 times higher than the control in the Hikone field. Acetylene reduction activity at four or eight weeks after the crack fertilization (application of both nodule bacteria and low level of fertilizer to the subsoil layer) tended to be higher than in the control in both fields. In the root box experiment, nodule number was four times higher than that in the control at the lower portion of the root system, where modified crack fertilization treatment was conducted, and the acetylene reduction activity was increased significantly by the treatment. These results indicated that the soybean nodulation control, i.e., timing and position of nodulation, as well as the enhancement of nitrogen fixation activity could be achieved by this crack fertilization technique.

The Spring Rigidity Values Analysis in Incremental Method of Deep Excavation with Considering Interaction among Soil Springs

Based on the theory of interaction between deep excavation support structure and subsoil, the influencing coefficient is presented in this paper in the condition of different foundation model. The calculation result shows that the foundation deformation considering interaction among soil springs is large than those not considering the interaction, and also larger than engineering practical condition. Theoretical analysis indicates the stiffness change of soil spring is related to spring rigidity in both active region and passive region when it is calculated by incremental method. The example proves that the method presented in this paper has good preciseness comparing with the results of engineering practical condition. So the theory of incremental method of deep excavation considering interaction is consummated.

Transmission of vertical stress in a real soil profile. Part II: Effect of tyre size, inflation pressure and wheel load

We urgently need increased quantitative knowledge about stress transmission in real soils that suffer heavy loads of agricultural machinery. 3D measurements of vertical stresses under tracked wheels were performed in situ in an annually ploughed Stagnic Luvisol continuously cropped with small grain cereals. The tests took place in the spring at field capacity when the topsoil had not been tilled for 1 1/2 years. Two Nokian ELS Radial-ply tyres (800/50R34 and 560/45R22.5) were loaded with two specific loads (30 kN and 60 kN), leading to four treatments labelled 800-30, 800-60, 560-30 and 560-60. We used rated tyre inflation pressures for traffic in the field (≤10 km h −1 driving speed). Seven load cells were inserted horizontally from a pit with minimal disturbance of soil at each of three depths (0.3, 0.6 and 0.9 m), covering the width of the wheeled area. The position of the wheel relative to the transducers was recorded using a laser sensor. Finally, the vertical stresses near the tyre–soil interface were measured in separate tests by 17 stress transducers across the width of the tyres. The level of maximum stress at 0.3 m depth was related to the surface-related stress expressions like the mean ground pressure and the tyre inflation pressure. The maximum stresses measured at 0.9 m depth were correlated with the wheel load (57 and 60 kPa at 60 kN load; 27 and 25 kPa at 30 kN load) and did not reflect the surface-related stress expressions. Our results show that the use of wide, low pressure tyres (within the technical opportunities available today) has no real effect on the stresses reaching deep subsoil layers. Our results further support the principle behind the elasticity theory. However, if fitting the Söhne model to stress measurements at all three depths, the stresses were underestimated at 0.3 and 0.6 m depth, and overestimated at 0.9 m depth. A fit of the model based on data only at 0.3 m depth indicates that stresses were transmitted nearly without attenuation through the 0–0.3 m soil layer, which cannot be described by the model of Söhne. We thus interpret the poor fit for the total profile as being due to differences in strength for the frequently tilled topsoil and the subsoil. Our results thus qualitatively confirm the principle of elasticity, but highlight the need to model arable soil as a two-layer system.

Impact of subsoil physicochemical constraints on crops grown in the Wimmera and Mallee is reduced during dry seasonal conditions

Subsoil physicochemical constraints can limit crop production on alkaline soils of south-eastern Australia. Fifteen farmer paddocks sown to a range of crops including canola, lentil, wheat, and barley in the Wimmera and Mallee of Victoria and the mid-north and Eyre Peninsula of South Australia were monitored from 2003 to 2006 to define the relationship between key abiotic/edaphic factors and crop growth. The soils were a combination of Calcarosol and Vertosol profiles, most of which had saline and sodic subsoils. There were significant correlations between ECe and Cl– (r = 0.90), ESP and B (r = 0.82), ESP and ECe (r = 0.79), and ESP and Cl– (r = 0.73). The seasons monitored had dry pre-cropping conditions and large variations in spring rainfall in the period around flowering. At sowing, the available soil water to a depth of 1.2 m (θa) averaged 3 mm for paddocks sown to lentils, 28 mm for barley, 44 mm for wheat, and 92 mm for canola. Subsoil constraints affected canola and lentil crops but not wheat or barley. For lentil crops, yield variation was largely explained by growing season rainfall (GSR) and θa in the shallow subsoil (0.10–0.60 m). Salinity in this soil layer affected lentil crops through reduced water extraction and decreased yields where ECe exceeded 2.2 dS/m. For canola crops, GSR and θa in the shallow (0.10–0.60 m) and deep (0.60–1.20 m) layers were important factors explaining yield variation. Sodicity (measured as ESP) in the deep subsoil (0.80–1.00 m) reduced canola growth where ESP exceeded 16%, corresponding to a 500 kg/ha yield penalty. For cereal crops, rainfall in the month around anthesis was the most important factor explaining grain yield, due to the large variation in rainfall during October combined with the determinant nature of these crops. For wheat, θa in the shallow subsoil (0.10–0.60 m) at sowing was also an important factor explaining yield variation. Subsoil constraints had no impact on cereal yield in this study, which is attributed to the lack of available soil water at depth, and the crops’ tolerance of the physicochemical conditions encountered in the shallow subsoil, where plant-available water was more likely to occur. Continuing dry seasonal conditions may mean that the opportunity to recharge soil water in the deeper subsoil, under continuous cropping systems, is increasingly remote. Constraints in the deep subsoil are therefore likely to have reduced impact on cereals under these conditions, and it is the management of water supply, from GSR and accrued soil water, in the shallow subsoil that will be increasingly critical in determining crop yields in the future.