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Hydrophobised soils are a new geomaterial to be used in hydraulic barriers. Insufficient knowledge of their potential harm and environmental risks is a primary hindrance in their application as a fill material. To address this environmental concern, leachate tests and seed germination tests were conducted on two soils (Fujian sand and completely decomposed granite) induced by two hydrophobising compounds (tung oil and dimethyldichlorosilane). Biological indicators – that is, soil respiration, enzyme assays and biosensor assays – were conducted on the hydrophobising agent, tung oil. The total concentrations of heavy metals measured by leachate tests remained below guideline values, indicating that leaching hazard will be negligible during their service life. Biological assays revealed minimal impact on soil microorganisms by tung oil. The results demonstrate negligible environmental impact of hydrophobised soils as fill materials.

Rice is often grown as multiple crops in one year, with reduced tillage upland cropping following flooded cropping gaining prominence due to water use, soil degradation and labour demands. This study explored whether a deep rather than shallow rooting rice cultivar grown in a flooded cropping cycle, benefited deeper root growth of follow-on rice in an upland, reduced tillage cropping cycle. In a greenhouse study, a simulated flooded paddy was planted with deep (Black Gora) and shallow (IR64) root cultivars and a plant-free control. Artificial plough pans were made in between the topsoil and subsoil to form different treatments with no plough pan (0.35 MPa), soft plough pan (1.03 MPa) and hard plough pan (1.70 MPa). After harvest of this ‘first season’ rice, the soil was drained and undisturbed to simulate zero-tillage upland, with a photoperiod insensitive variety (BRRI Dhan 28) planted. Root length, root surface area, root volume, root diameter, number of root tips and branches were measured. The number of roots penetrating the plough pan was measured from camera images and X-ray CT. The overall root length density (RLD), root surface area, number of root tips and branching of BRRI Dhan 28 did not vary between plough pan and no plough pan treatments. Compared to the shallow rooting rice genotype, the deep rooting rice genotype as a ‘first season’ crop promoted 19 % greater RLD, 34 % greater surface area and 29 % more branching of BRRI Dhan 28 in the subsoil. In the topsoil, however, BRRI Dhan 28 had 28 % greater RLD, 35 % greater surface area and 43 % more branching for the shallow rather deep rooting genotype planted in the ‘first season’. The results suggest that rice cultivar selection for a paddy cycle affects root growth of a follow-on rice crop grown under no-till, with benefits to subsoil access from deep rooting cultivars and topsoil proliferation for shallow rooting cultivars.

The resilience of microbial functions like carbon (C) and nitrogen (N) cycling to stress is likely heavily dependent on pH. Past research, however, has been limited to laboratory manipulations or a pH gradient resulting from differences in soil mineralogy. In this study, soils were collected from a >50-year field trial where plots have been maintained at pH 4.9, 6 and 7.1. We selected copper (Cu) and heat to represent persistent and transient stresses, respectively. Changes in C mineralization, ammonia oxidation, denitrification, and gene (16S rRNA, nirK, nirS and amoA) abundance were immediately measured after heat- (40 °C for 16 hours) and Cu- (500 µg Cu soil g-1 or 1 mg Cu soil g-1) induced stresses, during subsequent recovery over 56 days, and compared to an unstressed control. Higher soil pH significantly increased C mineralization (by 217%), ammonia oxidation (by 617%), and the gene abundances of 16S rRNA (by 77%), nirK (by 976%) and nirS (by 997%). Soil pH had a significant (P < 0.001) selection effect on the phylotypes of bacterial communities and ammonium oxidising bacteria (AOB). Ammonia oxidation was significantly (P < 0.05) more resistant and resilient to both Cu stresses in the pH 7.1 soil. C mineralization in the soil at pH 7.1 was significantly (P < 0.05) more resilient to low Cu than the soil at pH 4.9. Correspondingly, significantly (P < 0.001) distinct bacterial communities were present in these soils, indicating that bacterial composition triggered by the adaptation and tolerance to stress is a central factor governing functional resilience. Denitrification in the pH 7.1 soil was significantly (P < 0.05) more resilient to low and high Cu, compared to the soil at pH 4.9. Similarly, the abundances of nirS and nirK genes were greater in the higher pH soil. Although soil pH directly affects Cu but not heat stress, our results indicated that neutral soils harboured greater resilience of C and N cycling to both Cu (persistent) and heat (transient) stresses.

Aims Cracks and biopores in compacted soil such as plough pans could aid deep rooting, mitigating constraints to seasonal upland use of paddy fields for rice production. This research investigated how soil macropores through a simulated plough pan affects root growth of contrasting deep and shallow rooting rice genotypes. Methods Deep rooting Black Gora and shallow rooting IR64 rice varieties were grown in packed cores of unsaturated soil in a controlled greenhouse. Simulated biopores and cracks (macropores) were inserted through the plough pan to form treatments with no macropores, biopores, cracks, and combined cracks and biopores. Different root parameters such as root length density (RLD), root volume, root diameter, number of root tips and branches were measured. The number of roots was calculated manually, including the number of roots growing through macropores in the plough pan layer. Results Plough pans with macropores had 25–32% more roots than with no macropores. RLD was 55% greater in the plough pan layer if cracks were present compared to biopores. Conversely, RLD was 26% less in subsoil if the plough pan had cracks compared to biopores. Different root parameters were greatly influenced by the presence of macropores in the plough pan, and deep-rooted Black Gora produced 81% greater RLD, 30% more root numbers and 103% more branching than the shallow rooted rice genotype IR64 within the plough pan layer. Conclusions Macropores greatly improve rice root growth through plough pans for a deep rooting but not a shallow rooting rice variety. Whereas cracks produce a greater number of roots in the plough pan, biopores result in greater root branching and root numbers deeper in subsoil.

Applying wastewater in subsurface drip irrigation helps address water shortage in arid and semi-arid environments. Microbial contamination may result, but soil amendments such as biochar could help protect soil and water resources. To improve understanding, this study investigated spatio-temporal dynamics of fecal coliform retention in a biochar-treated soil under subsurface drip irrigation. Two dripper discharges rates of 2 and 4 l hr

Reduced tillage has been advocated as a practical measure to increase soil carbon in long-term cropping soils. We examine three medium-term experiments in sites with contrasting soil and climatic characteristics in the UK. The objectives were to determine the effects of different reduced and zero tillage practices on bulk density and soil carbon storage and depth distribution and to quantify the effect of stones in their calculation. The treatments were zero tillage, minimum tillage, conventional plough, deep non-inversion tillage and plough compaction. Soil samples were collected from three sites at five depth intervals to approximately 60 cm. Deep non-inversion and minimum tillage led to 6.5 and 1.6 Mg ha−1 greater SOC than conventional plough in sites under rotation systems. In a monoculture system in Scotland, conventional plough had 25.3, 21.6 and 17.7 Mg ha−1 greater SOC than plough compaction, minimum tillage and zero tillage, respectively. After harvest, bulk density was greater in the soil surface of conventional plough compared with minimum tillage. Our results suggest variable impacts of reduced tillage on SOC storage. Overall there is limited benefit in using shallow minimum tillage and zero tillage practices in the UK to increase soil carbon storage when a soil profile of 60 cm is considered but other benefits associated to these systems, such as speed of working and timeliness of operations, should be considered.

Structural disturbance of soil such as that caused by tillage or translocation for infrastructure projects can induce changes in soil microbial functions eliciting large fluxes of CO2. Soil pH, often referred to as a master variable in the context of soil biology, exerts a strong influence on both the structure and function of microbial communities as well as the physical structure of the soil. In order to better understand the interaction of soil pH and large-scale physical disturbances in controlling these fluxes, we took the opportunity presented when moving an entire experimental field to a new location to look at how changing soil structural conditions influenced the activity of the microbial community. Soils under long-term (60 years) pH manipulation were dug from the original experimental site (Woodlands Field, SRUC, Aberdeen) and transported to a new experimental site less than 1 mile away (Aberdeen Cropping Experiment (ACE), Aberdeen), excavated soils were thoroughly mixed before reinstatement. This produced a significant decrease in bulk density and concomitant increase in macroporosity as expected (p = 0.027 and p = 0.021 respectively), with more pronounced changes at lower pH. There were consistent increases in the fraction of water-stable aggregates from the soil translocation, where the field averages of Woodlands and ACE were 91% and 95% respectively (p < 0.001). However, there were no discernible differences across the pH range (p = 0.641), despite greater changes occurring at lower pH treatments. We also observed changes in respiration rates of soils after translocation, rates were slightly increased at low pH, reduced at mid-range pH, and stable at high pH, although none of these were significant changes (p = 0.081). Soil pH was a dominant factor in controlling some aspects of the soil physical properties. Soil pH had variable magnitudes of influence, in particular, more acidic soils were more vulnerable to changes in the physical structure, where the volume of large pore spaces increased dramatically. This could explain the increased CO2 efflux in acidic soils, however, microbial communities in mid-range pH treatments demonstrated the greatest vulnerability to large-scale physical disturbance, which is likely due to the threshold pH determining their respiration pathway. This research demonstrates that soil management in large-scale disturbance should have altered management, guided by the soil pH.

Efficient water use is a must for sustainable agriculture, driving the need for affordable soil moisture sensors to guide irrigation timing. Sensors are limited by cost, maintenance and the need for wires for data capture and charging. We are developing low-cost, long-life, wireless in-situ soil sensing networks, which can potentially enable a much higher sensor density for large farmland or intense research plot monitoring. This custom soil sensor is made from off-the-shelf electronics and consumes approximately 10x less energy per measurement, compared to commercially available sensors. Here we present our new sensor technology, while also investigating its repeatability and accuracy in controlled conditions and comparing it to that of commercially available soil moisture sensors. The final application of the custom soil moisture sensor is an underground in-situ sensing network, which will be enabled through wireless powering and telemetry systems implemented on autonomous vehicles, both ground and aerial.

Great potential exists to harness plant traits at the root-soil interface, mainly rhizodeposition and root hairs, to 'build' soils with better structure that can trap more carbon and resources, resist climate stresses, and promote a healthy microbiome. These traits appear to have been preserved in modern crop varieties, but scope exists to improve them further because they vary considerably between genotypes and respond to environmental conditions. From emerging evidence, rhizodeposition can act as a disperser, aggregator, and/or hydrogel in soil, and root hairs expand rhizosheath size. Future research should explore impacts of selecting these traits on plants and soils concurrently, expanding from model plants to commercial genotypes, and observing whether impacts currently limited to glasshouse studies occur in the field.

The dynamics of soil structure is caused by biotic and abiotic processes, with the onset and magnitude of deformation controlled by soil rheological and mechanical properties. Quantification of such properties is challenging because soil behaviour changes with soil moisture, but common rheological tests are not applicable over all consistency ranges. Here, we combine oscillation shear rheometry with spherical indentation mechanical measurements of soil to obtain greater characterization over a broader range of water contents. The elastic modulus could be measured with either approach, with good agreement found for measured silt and clay textured remoulded agricultural soils. For shear rheometry, plastic viscosity, complex modulus and shear yield stress were also obtained. The spherical indentation provided measurements of hardness and yield stress. Although yield stress was correlated between approaches, the values were orders of magnitude greater for the indenter (0.54 +/- 0.33 kPa vs. 34.4 +/- 31.2 kPa), presumably because of different loading and failure conditions. At drier water contents, yield stress varied more between the two tests on the clay soil, which corresponded with brittle fracture creating artefacts in shear rheometry measurements. Spherical indentation has not been widely applied to the testing of soils, but the good agreement over a wide water content range between elastic modulus obtained from spherical indentation measurements (0.66 +/- 0.27 MPa in wetter zone to 4.45 +/- 2.53 MPa in drier zone) and shear rheometry (0.47 +/- 0.11 MPa in wetter zone to 2.02 +/- 0.98 MPa in drier zone) is promising. Moreover, spherical indentation can be applied to materials varying from brittle to viscous and allows testing on structurally intact soil aggregates. The geometry of a spherical indenter may more closely mimic contacting soil aggregates, so scope exists to extend the approach to explore the slumping of aggregated seedbeds produced by tillage.

The area of karst terrain in China covers 3.63×106 km2, with more than 40% in the southwestern region over the Guizhou Plateau. Karst comprises exposed carbonate bedrock over approximately 1.30×106 km2 of this area, which suffers from soil degradation and poor crop yield. This paper aims to gain a better understanding of the environmental controls on crop yield in order to enable more sustainable use of natural resources for food production and development. More precisely, four kinds of artificial neural network were used to analyse and simulate the spatial patterns of crop yield for seven crop species grown in Guizhou Province, exploring the relationships with meteorological, soil, irrigation and fertilization factors. The results of spatial classification showed that most regions of high-level crop yield per area and total crop yield are located in the central-north area of Guizhou. Moreover, the three artificial neural networks used to simulate the spatial patterns of crop yield all demonstrated a good correlation coefficient between simulated and true yield. However, the Back Propagation network had the best performance based on both accuracy and runtime. Among the 13 influencing factors investigated, temperature (16.4%), radiation (15.3%), soil moisture (13.5%), fertilization of N (13.5%) and P (12.4%) had the largest contribution to crop yield spatial distribution. These results suggest that neural networks have potential application in identifying environmental controls on crop yield and in modelling spatial patterns of crop yield, which could enable local stakeholders to realize sustainable development and crop production goals.

Crop genotypes may respond differently to various physical soil conditions. The objective of this study was to investigate the responses of the root architectures of two maize cultivars (Zhengdan958 and Denghai605) to various soil compaction and moisture conditions. Two compaction levels (1.3 g cm− 3 and 1.6 g cm− 3) and two moisture conditions (60% and 80% field capacity) were investigated to determine their impact on root growth. The root architectures of maize seedlings were assessed via X-ray computed tomography (CT). Soil penetration resistance, above-ground biomass and root biomass values were also determined. Soil moisture had significant effects on root biomass, above-ground biomass, the ratio of root biomass to above-ground biomass, and all root traits except for root volume. Soil compaction reduced root surface area and total root length of Zhengdan958 at 80% field capacity but not at 60% field capacity. However, soil compaction had little impact on root traits of Denghai605 at both moisture levels. Zhengdan958 had larger root volume, total root length, root diameter, root biomass and above-ground biomass than Denghai605 under noncompacted conditions. The ratio of root biomass to above-ground biomass was greater for Zhengdan958 than Denghai605 at the noncompacted and 60% field capacity conditions. High moisture content has negative effects on root traits in compacted soil. The response of root architectures to soil compaction was more sensitive in Zhengdan958 than Denghai605. Zhengdan958 showed greater growth performance than Denghai605 under noncompacted conditions, and the drought tolerance of Zhengdan958 was greater than that of Denghai605.

Biological exudates, such as plant mucilage, can greatly stabilise soils but as the mechanical and hydrological drivers depend much on soil particle size composition, eroding and depositional areas of a slope may respond differently. Soils from an eroded midslope and a depositional footslope in an arable farm were amended with chia (Salvia hispanica) seed mucilage at concentrations of 0 g C kg−1, 0.46 g C kg−1 and 2.3 g C kg−1 mucilage, formed into cores, and then imparted with wetting and drying (WD) cycles. Mucilage increased the stability of these inherently stable soils from 80% to >98% water stable macroaggregates at 0WD cycles regardless of slope position. Aggregate stability was maintained after 5WD cycles by mucilage, whereas the stability of unamended soil dropped by 66.7% in the footslope and 30.1% in the midslope compared with 0 WD. Underlying physical stability properties were measured by tensile strength and penetration resistance for mechanical, water sorptivity and repellency for hydrological, and micro‐, meso‐, macro‐ and total porosity for structural properties. Almost every soil physical property measured changed less with WD cycles if mucilage was present. Compared to unamended soil, 2.3 g C kg−1 mucilage amendment decreased water sorptivity from 0.289 mm s‐1/2 to 0.122 mm s‐1/2 in the midslope and 0.230 mm s‐1/2 to 0.182 mm s‐1/2 in the footslope after 5 WD cycles. Aggregate stability, total porosity and water sorptivity were correlated. In the midslope, hydrology and penetration resistance were affected most, likely driven by mucilage deposition in the macropores of this more coarsely textured soil. In the footslope, the greater impact of mucilage on tensile strength was likely driven by buffering of macroporosity formation by WD cycles in this finer textured soil.

Tropical soils tend to harden during drying due to the generally low content of free-iron and organic carbon, combined with high fine sand and silt proportions. It was hypothesized that the change in soil physical condition induced by the addition of a leguminous mulch in cohesive tropical soil enriched with calcium may mitigate soil hardening through wetting and drying cycles by rain or irrigation, thereby improving the soil rootability. A leguminous mulch was added in different concentrations to a structurally fragile tropical soil enriched with calcium, which then had different irrigation intervals. The treatments were with or without mulch (10 t/ha), with or without added nitrogen (100 kg/ha at 2 intervals) and two irrigation intervals. In 2015 the irrigation intervals were either 4 or 8 days, and in 2016 they were either 6 or 9 days. Two years were used in the attempt to achieve greater differences, as for tested variables, between treatments. Maize planted in these soil treatments was measured for physiological performance, water use efficiency and yield. Mulch used on structurally fragile tropical soil enriched with calcium was found to delay increased penetration resistance from hardening by wet/dry cycles. In this context, an improved soil rootability led to an enlargement of the leaf area index, greater nitrogen uptake and increased CO2 assimilation. This had important physiological consequences due to the positive effect on increased dry matter production and maize yield. In addition, these results suggested that mulch, used with urea, can delay the water supply for 3 or 4 days due to improvements in soil rootability caused by calcium and organic matter interactions. This may be crucial to a region where small intervals without rain are increasingly common due to global climate change. Therefore, due to a greater water use efficiency, this strategy may be a profitable way to increase crop productivity in tropical conditions rather than increasing water and nutrient application alone.

Surface tension was measured for aqueous solutions of dl-malic acid, l-glutamine, l-serine, l-proline, l-methionine, l-valine, and l-lactic acid as a function of concentration using a Du Nouy ring ...

Recent discoveries of polyhalite (K₂SO₄.MgSO₄.2CaSO₄.2H₂O) in the UK provide an alternative to conventional fertilizer sources. This work investigated the interaction of polyhalite, commercially known as POLY4, with soil using leaching columns. Different physical forms of polyhalite (powder, crushed rock and granules) were compared to potassium chloride (KCl) for the movement of potassium, calcium, magnesium and sulphur (as sulphate) through the soil profile using 19.7 L of water, equivalent to 4,500 mm rainfall. The nutrients from polyhalite were found to be available at 30 cm depth, with calcium showing signs of interacting with the soil clay particles to release cationic nutrients. Polyhalite granules showed the greatest release of sulphate, magnesium and calcium as a proportion of the additional nutrient with 127%, 71% and 102%, respectively leached. For potassium, all forms of polyhalite had greater release than KCl (powder = 58%; granules = 86%; crushed rock = 57% and KCl 16%). Nutrients from polyhalite and those mobilized from soil interactions are present in soil solution indicating availability for plant growth.

Puddling of rice paddies is undertaken to create a soft soil bed for easy transplanting of rice seedlings, to control weeds and reduce water and nutrient leaching. There is a drive for less intense puddling because of its physical disturbance of soil, energy inputs and labour requirements, which may produce different soil physical conditions for root growth. The objective of this study was to investigate the influence of puddling intensity on soil structure and the subsequent impact on the growth of rice seedling roots. Three treatments with different puddling intensities were established: (1) No puddling; (2) Low and (3) High intensity puddling. The rice genotype, Nipponbare was grown in soil columns for 18 days. Soil bulk density, aggregate size distribution and three-dimensional (3D) macropore structure were measured. Two-dimensional root traits were determined by WinRhizo and 3D root traits were determined by X-ray Computed Tomography (CT). Our results show the percentage of large macroaggregates (> 2 mm) decreased by 69.6% (P 0.03 mm) of no puddling was 2.3 times greater than low intensity puddling and 3.5 times greater than high intensity puddling. The total root lengths of no and low intensity puddling were 1.56–1.86 times greater than that of high intensity puddling. Large roots, including radicle and crown roots, were the same length regardless of puddling intensity. Our study demonstrates that intensive puddling can degrade soil structure, which consequently limits rice root growth.

Rare earth oxides (REOs) as tracers for determining complex processes of soil aggregate formation, stabilization and breakdown could be limited by recovery rate. In this study, the impacts of soil properties, labelling methods and pre-existing aggregate structure on the recovery rate of REOs were analyzed. Our objectives were (i) to optimize the method of REOs as tracers for labelling aggregates; (ii) to investigate the effects of soil properties on the recovery rate of REOs; and (iii) to verify the feasibility of REOs as tracers for studying aggregate turnover. Natural and artificial soil aggregates with a difference in pore structure were labelled with REOs by either a wet or a dry labelling method. After incubating the labelled and repacked soil, the soil samples were separated into four aggregate size fractions (

International audience; Density and Speed of sound have been measured for pure components such furan, (DMF) 2-5-dimethylfuran, MDEA (n-methyldiethanolamine), DEG (diethylene glycol), TEG (triethylene glycol), and DMA (dimethylacetamide) using Anton Paar (DSA-5000) vibrating U-tube densitometer in a temperature range of 278.15 to 343.15 K and ambient pressure (100 kPa). density and speed of sound have been measured for furan + MDEA, furan + DEG, furan + TEG, and furan + DMA in a temperature range of 278.15 K to 303.15 K whereas for DMF + DMA, the temperature range is 283.15 K to 343.15 K. excess molar volume have been calculated for all binary systems. The Redlich-Kister model is used to correlate the experimental data. In order to identify the impact of molecular interactions participating significantly in the excess molar volume, the Prigogine-Flory-Patterson model is selected to correlate and predict the deviations for excess molar volumes of the binary mixtures.

Aims Cracks and biopores in compacted soil such as plough pans could aid deep rooting, mitigating constraints to seasonal upland use of paddy fields for rice production. This research investigated how soil macropores through a simulated plough pan affects root growth of contrasting deep and shallow rooting rice genotypes.Methods Deep rooting Black Gora and shallow rooting IR64 rice varieties were grown in packed cores of unsaturated soil in a controlled greenhouse. Artificial biopores and cracks (macropores) were inserted through the plough pan to form treatments with no macropores, biopores, cracks, and combined cracks and biopores. Different root parameters such as root length density (RLD), root volume, root diameter, number of root tips and branches were measured. The number of roots was calculated manually, including the number of roots growing through macropores in the plough pan layer.Results Plough pans with macropores had 25-32 % more roots than with no macropores. RLD was 55 % greater in the plough pan layer if cracks were present compared to biopores. Conversely, RLD was 26 % less in subsoil if the plough pan had cracks compared to biopores. Different root parameters were greatly influenced by the presence of macropores in the plough pan, and deep-rooted Black Gora produced 81% greater RLD, 30 % more root numbers and 103 % more branching than the shallow rooted rice genotype IR64 within the plough pan layer.Conclusions Macropores greatly improve rice root growth through plough pans for a deep rooting but not shallow rooting rice variety. Whereas cracks produce a greater number of roots in the plough pan, biopores result in greater root branching and root numbers deeper in subsoil.

Summary • An infiltrometer device, 0.4 mm in radius was designed specifically to measure the hydraulic characteristics of rhizosphere soil. Its testing and application to the rhizosphere of four plant species–barley (Hordeum vulgare), oil-seed rape (Brassica napus), potato (Solanum tuberosum) and grass (Lolium multiflorum) – was described. • In excavated blocks of field soil, there was a significant influence of plant species on sorptivity and water repellency in the rhizosphere. • Further controlled laboratory tests on young plants in moist, sieved soil showed reduced water sorptivity owing to increased repellency in the rhizosphere compared with bulk soil for barley but not oil-seed rape. • Root exudates may clog pores or become hydrophobic on soil particle surfaces. The slightly higher water repellency measured in rhizosphere soil would have minimal influence on plant water uptake. However, it may provide a buffer against desiccation at lower water contents and reduce structural degradation of rhizosphere soil by slaking.

Engineered water repellent soils have great potential as construction materials for seepage barriers. By adjusting the water repellency of the soil, an impermeable or semi-permeable seepage barrier can be constructed to suit various engineering applications, such as impervious materials to contain water or semi-permeable materials to allow vegetation growth. Industrial clays, geosynthetics and grouting are proven solutions frequently used for similar applications. To provide a sustainable and low-cost solution to create an engineered water repellent soil, this study explored how Tung oil, a Chinese traditional vegetation oil, affected a Hong Kong completely decomposed granite (CDG). Tung oil has already been used in historical structures and suggested as a self-healing agent for concrete. A natural wettable soil from Hong Kong, CDG, was mixed with Tung oil and heated at different temperatures for different durations. The results reveal that the presence of Tung oil developed severe and persistent water repellency with heating, enhancing water repellency until a critical temperature threshold and heating duration was reached. However, a change to soil physical structure due to aggregation was also observed due to the mixing of the Tung oil with the soil. The newly formed Tung-oil impregnated aggregates were found to be (1) stable when immersed in water, regardless of the temperature and heating duration, (2) and to have increasing tensile strength with aggregate size up to a temperature threshold. Based on these findings, not only can Tung oil induce high and persistent water repellency in a natural soil through simple procedures (by mixing of soil with oil), but also aggregation may offer the opportunity to improve soils for other ground applications including to ameliorate erosion on slopes.

Subtropical regions have clay-rich, weathered soils, and long dry periods followed by intense rainfall that produces large fluctuations in soil water content (SWC) and hydrological behavior. This complicates predictions of spatio-temporal dynamics, as datasets are typically collected at too coarse resolution and observations often represent a duration that is too short to capture temporal stability. The aim of the present study was to gain further insights into the role of temporal sampling scale on the observed temporal stability features of SWC order to aid the design of optimal SWC sampling strategies. This focused on both sampling frequency and total monitoring duration, as previous analyses have not considered both of these sampling aspects simultaneously. We collected relatively high resolution data of SWC (fortnightly over 3.5 years) for various soil depths and under contrasting crops (peanuts and citrus) at the red soil region of southeast China. The dataset was split into a three-year training period and a six-month evaluation period. Altogether 13 sampling frequencies (intervals ranging from 15 to 240 days) and eight monitoring duration periods (between three and 36 months) were derived from the training period to identify temporal stability features and the most time stable location (MTSL). The prediction accuracies of these MTSLs were tested using the independent evaluation data. Results showed that vegetation type did affect the spatio-temporal patterns of SWC, whereby the citrus site exhibited a stronger temporal variation and weaker temporal stability than the peanut site. However, the effects of both sampling frequency and observation duration were more pronounced, irrespective of the role of vegetation type or soil depth. With increasing sampling interval or decreasing monitoring duration, temporal stability of SWC was generally overestimated; by less than 10% when sampling interval increased from every 15 to 240 days and by up to 40% with duration decreasing from 36 to 3 months. Our results suggest that sampling strategies and trade-offs between sampling interval and duration should focus on capturing the main variability in hydro-climatological conditions. For subtropical conditions, we found that sampling once every 45 days over 24 months to be the minimum sampling strategy to ensure errors in SWC temporal stability of less than 10%.

The development of soil sustainability is linked to the improved management of soil biota, such as earthworms, and crop residues to improve soil physical structure, enhance microbial activities, and increase nutrient cycling. This study examined the impacts of maize residue (65.8C/N ratio, dry biomass 0.75 kg m−2) incorporation and earthworms (70 g Metaphire guillelmi m−2) on the resistance and resilience of soil C and N cycling to experimentally applied stresses. Field treatments were maize residue incorporation, maize residue incorporation with earthworm addition, and an unamended control. Resistance and resilience of C mineralization, ammonia oxidation, and potential denitrification were investigated over 28 days following a persistent stress of Cu (1 mg Cu soil g−1) or a transient heat stress (50 °C for 16 h). The results indicated that C mineralization was more resistant and resilient than ammonia oxidation and denitrification to either a persistent Cu or a transient heat stress. The application of maize residues significantly increased soil microbial biomass, C mineralization, ammonia oxidation and potential denitrification compared with the unamended control. Maize residues significantly improved the resistance and resilience of N processes to Cu and heat stress. The presence of earthworms significantly increased potential denitrification but had limited positive effect on functional resistance and resilience. This study suggested crop residue incorporation would strongly increase soil functional resistance and resilience to persistent and transient stresses, and thus could be a useful agricultural practice to improve soil ecosystem sustainability.

Plants have a large impact on the physical behaviour of soil, partly due to seed and root exudates that alter mineral:organic matter associations. In this study we explored how the decomposability of residues in soil interacts with seed or root exudate compounds to influence microbial respiration, mechanical behaviour and hydrological properties. Sandy loam and clay loam soils were amended at a rate of 40 t ha-1 with ground green barley (7.13 mg C g-1), barley straw (7.26 mg C g-1) or poultry manure (5.22 mg C g-1), and either chia seed exudate at 1.84 mg C g-1 soil or root exudate compounds at 14.4 mg C g-1 soil. On cores packed to 1.3 g cm-3, uniaxial compression, penetration resistance, water sorptivity, water retention and porosity were measured at time 0, after 14 days of incubation at 20 oC, and then after subjecting incubated soils to three cycles of wetting and drying to simulate weathering. These time increments and weathering were intended to simulate a newly germinated seed or tip of a root, through to a more mature system. Application of seed and root exudate increased carbon dioxide (CO2) emissions from 0.31 ± 0.01 to 15.11 ± 0.71 μg C-CO2 g soil-1 hour-1 for the sandy loam soil and from 0.171 ± 0.01 to 10.56 ± 0.78 C-CO2 g soil-1 hour-1 for the clay loam soil. There were large changes in soil physical properties caused by seed or root exudate amendment coupled with residues, their decomposition and weathering. After incubation and weathering, soils with added seed or root exudates and their interactions with organic residues were more mechanically stable, as measured by penetration resistance (22 to 58% increase) and compression index (25 to 43% decrease) compared to soils amended only with organic residue. Water sorptivity and porosity diminished with the addition of the exudate. Exudates in combination with organic residues better protected soils against structural destabilization by increasing particle cementation and decreasing rapid wetting and porosity.

Nitrate accumulation has been reported in the top 1 m and subsurface soil (> 1 m) across arid to semi-humid regions, but not in humid regions. Nitrate inventories through the whole regolith, referred to collectively as soil and saprolite, in humid regions have received little attention to date, likely due to previously assumed low nitrification rates and large nitrogen (N) losses by severe surface runoff and erosion. In order to understand if and how reactive N exists in the below ground (soil and saprolite) in humid environment, the amount of NO3--N, NH4+-N and dissolved organic N (DON) present in the regolith to a depth of 9 m in a typical red soil Critical Zone was investigated under different land uses (upland, woodland and paddy field). The Red Soil Critical Zone Observatory is located in the subtropical Jiangxi Province, China, with a mean annual precipitation of 1795 mm and mean annual potential evapotranspiration of 1229 mm. The examined regoliths were acidic, highly weathered, and mainly clay loam in texture. Results showed that on average 92% (827 ± 97 kg N ha-1) of NO3--N and 82% (521 ± 153 kg N ha-1) of DON were stored at depth (from a depth of 1 m to the bedrock surface) in the upland regolith, while 92% (283 kg N ha-1) of NO3--N and 78% (820 kg N ha-1) of DON were stored at depth in the woodland regolith. Nitrate N significantly accumulated with depth in the upland regolith from the 1- to 4-m depth interval (p < 0.01), while the inventory (632 ± 75 kg N ha-1) in the top 3-m zone accounted for on average 71% of the total. Dissolved organic N significantly accumulated with depth in the upland regolith from the 0- to 3-m depth interval (p < 0.01), while the inventory (408 ± 75 kg N ha-1) in the top 3-m zone accounted for on average 64% of the total. There was no significant accumulation for NH4+-N throughout the upland regolith (p = 0.35). No substantial accumulation of dissolved N was measured at depth in paddy field regoliths with different cultivation ages. The finding that large reservoirs of reactive N can exist in deep regolith rather than in the routinely investigated solum of subtropical regions shows a missing part of the terrestrial N budget and raises concerns about potential 34 groundwater nitrate pollution.

Long-term fertilization has a considerable effect on the dynamics of soil organic carbon (SOC). However, quantifying the contribution of fertilization practices to SOC is still a challenge. In this study, we selected a 30-yr fertilization experiment planted with a shift from C3 to C4 crops. Our objectives were (i) to determine temporal dynamics of SOC and newly-derived C (fnew) with the cultivation time and their vertical distribution along with soil profile; (ii) to assess the effect of the fertilization on SOC and fnew. Three treatments were involved: no fertilization (Control), NPK application (NPK), and continuously planted with C3 crops adjacent to the experiment as a reference (NAT). The SOC was physically separated into cPOM, fPOM, iPOM, s + c_m and s + c_f fractions, and their δ13C values were determined. Our results show the fnew in the bulk soil and C fractions presented an exponential increase over the cultivation time in the NPK treatment but this was only observed for the bulk soil and the s + c_f fraction in the Control treatment. The fnew had a priority to be stored within microaggregates, and then enriched in the silt and clay sized fraction over time. The SOC and fnew in the bulk soil and C fractions decreased with soil depth so that the difference between the Control and NPK treatments was observed only in the 0–20 cm depth. Our results demonstrate that the long-term fertilization increases the new C proportion in the bulk soil and C fractions but this contribution was limited to the plough layer.

\ud Aims Rhizodeposits collected from hydroponic solutions with roots of maize and barley, and seed mucilage washed from chia, were added to soil to measure their impact on water retention and hysteresis in a sandy loam soil at a range of concentrations. We test the hypothesis that the effect of plant exudates and mucilages on hydraulic properties of soils depend on their physicochemical characteristics and origin.\ud Methods Surface tension and viscosity of the exudate solutions were measured using the Du Noüy ring method and a cone-plate rheometer, respectively. The contact angle of water on exudate treated soil was measured with the sessile drop method. Water retention and hysteresis were measured by equilibrating soil samples, treated with exudates and mucilages at 0.46 and 4.6 mg g−1 concentration, on dialysis tubing filled with polyethylene glycol (PEG) solution of known osmotic potential.\ud Results Surface tension decreased and viscosity increased with increasing concentration of the exudates and mucilage in solutions. Change in surface tension and viscosity was greatest for chia seed exudate and least for barley root exudate. Contact angle increased with increasing maize root and chia seed exudate concentration in soil, but not barley root. Chia seed mucilage and maize root rhizodeposits enhanced soil water retention and increased hysteresis index, whereas barley root rhizodeposits decreased soil water retention and the hysteresis effect. The impact of exudates and mucilages on soil water retention almost ceased when approaching the wilting point at −1500 kPa matric potential.\ud Conclusions Barley rhizodeposits behaved as surfactants, drying the rhizosphere at smaller suctions. Chia seed mucilage and maize root rhizodeposits behaved as hydrogels that hold more water in the rhizosphere, but with slower rewetting and greater hysteresis.

Root tensile strength controls root reinforcement, but a range of factors including root moisture and diameter have such a large impact that it is difficult to make predictions. In this study, we measured how variable root moisture content affects the relationship between root diameter and root tensile strength of herbaceous plants. Fresh roots of two herbaceous plants, Heteropappus altaicus and Poa sphondylodes were divided into four groups: (i) saturated in water, (ii) kept fresh, (iii) or dried for 6 h or (iv) 12 h in air. Root diameter and mechanical failure under tension before and after the moisture treatment were measured. Tensile strength and tensile force of both species decreased linearly while mean root diameter increased linearly with increasing root moisture content. Root moisture content has a large impact on the variability of root tensile strength. This emphasizes the need to avoid desiccation during testing. In field impacts of soil water potential on root strength requires further study. We recommend soaking roots in water before testing to decrease this source of error.

Soil adjacent to roots has distinct structural and physical properties from bulk soil, affecting water and solute acquisition by plants. Detailed knowledge on how root activity and traits such as root hairs affect the 3D pore structure at a fine scale is scarce and often contradictory.\ud \ud Roots of hairless barley (Hordeum vulgare L. cv ‘Optic’) mutant (NRH) and its wildtype (WT) parent were grown in tubes of sieved (

Soils frequently experience environmental stresses that may have transient or persistent impact on important ecosystem services, such as carbon (C) and nitrogen (N) cycling. Microbial communities underpin resistance (the ability to withstand a stress) and resilience (the ability to recover from a stress) of these functions. Whilst functional stability and resilience have been studied extensively, the link to genetic stability is missing. In this study, the resistance and resilience of C mineralization, ammonia oxidation and denitrification, their associated gene abundances (16S rRNA, bacterial amoA, nirK, nirS, nosZ-I and nosZ-II) and bacterial community structures (T-RFLP 16S rRNA) were compared in two managed soils for 28 days after stressing the soils with either a persistent (1 mg Cu soil g−1) or a transient (heat at 40 °C for 16 h) stress. The average resistance of C mineralization to Cu was 60%, which was significantly greater than the resistance of ammonia oxidation (25%) and denitrification (31%) to Cu. Similarly, the average resilience of C mineralization to Cu was 52%, which was significantly greater than the resilience of ammonia oxidation (12%) and denitrification (18%) to Cu. However, this pattern was not significant after heat stress, indicating the critical role of different stressors. Changes in total bacterial community structure rather than abundance of 16S rRNA reflected the responses of C mineralization to Cu and heat. Both Cu and heat significantly decreased functional gene abundance (amoA, nirK, nirS, nosZ-I and nosZ-II), however, a significant recovery of denitrifying gene abundance was observed after 28 days following heat. There were lack of constant relationships between functional and genetic stability, highlighting that soil physiochemical properties, the nature of the stressor, and microbial life history traits combine to confer functional resistance and resilience. Genetic responses on their own are therefore inadequate in predicating changes to soil functions following stresses.

Root hairs represent an attractive target for future crop breeding, to improve resource use efficiency and stress tolerance. Most studies investigating root hairs have focused on plant tolerance to phosphorus deficiency and rhizosheath formation under controlled conditions. However, data on the interplay between root hairs and open-field systems, under contrasting soils and climate conditions, are limited. Although root hairs and rhizosphere are assumed to play a key role in regulating plant water relations, their effect on plant water uptake has been rarely investigated. As such, this study aimed to experimentally elucidate some of the impacts that root hairs have on plant performance under field conditions and water deficit. A field experiment was set up in Scotland for two consecutive years, in 2017 (a typical year) and 2018 (the driest growing season ever recorded at this site), under different soil textures (i.e., clay loam vs. sandy loam). Five barley (Hordeum vulgare) genotypes exhibiting variation in root hair length and density were used in the study. Measurements of root hair density, length and its correlation with rhizosheath weight highlighted trait robustness in the field under variable environmental conditions. Root hairs did not confer a notable advantage to barley under optimal conditions, but under soil water deficit root hairs enhanced plant water status and stress tolerance. This resulted in less negative leaf water potential and lower leaf abscisic acid concentration, while promoting shoot phosphorus accumulation. Specifically, minimum leaf water potential differed significantly (P = 0.021) between the wild type (-1.43 MPa) and its hairless mutant (-1.76 MPa) grown in clay loam, with the mutant exhibiting greater water stress. In agreement with leaf water potential measurements, at the peak of water stress, leaf abscisic acid concentration was significantly (P = 0.023) greater for the hairless mutant (394 ng g-1) than the wild type (250 ng g-1) grown in clay loam soil. Under water deficit conditions, in clay loam soil, shoot phosphorus accumulation in the wild type (2.49 mg P shoot-1) was over twice that in the hairless mutant (1.10 mg P shoot-1). Furthermore, the presence of root hairs did not decrease yield under optimal conditions, while root hairs enhanced yield stability under drought. While yield of the hairless mutant significantly (P = 0.012) decreased from 2017 to 2018 in both clay (-26%) and sandy (-33%) loam soils, no significant differences were found between years in the yield of the wild type. Therefore, selecting for beneficial root hair traits can enhance yield stability without diminishing yield potential, overcoming the breeder’s dilemma of trying to simultaneously enhance both productivity and resilience. To our knowledge, the present findings provide the first evidence of the effect of root hairs under drought in open field conditions (i.e., real agricultural system). Therefore, along with the well-recognized role for P uptake, maintenance or enhancement of root hairs can represent a key trait for breeding the next generation of crops for improved drought tolerance in relation to climate change.

Nitrate accumulated deep (>100 cm) in the regolith (soil and saprolite) threatens groundwater quality, but most studies focus only on nitrate nearer the surface (

Background and Aims Previous laboratory studies have suggested selection for root hair traits in future crop breeding to improve resource use efficiency and stress tolerance. However, data on the interplay between root hairs and open-field systems, under contrasting soils and climate conditions, are limited. As such, this study aims to experimentally elucidate some of the impacts that root hairs have on plant performance on a field scale. Methods A field experiment was set up in Scotland for two consecutive years, under contrasting climate conditions and different soil textures (i.e. clay loam vs. sandy loam). Five barley (Hordeum vulgare) genotypes exhibiting variation in root hair length and density were used in the study. Root hair length, density and rhizosheath weight were measured at several growth stages, as well as shoot biomass, plant water status, shoot phosphorus (P) accumulation and grain yield. Key Results Measurements of root hair density, length and its correlation with rhizosheath weight highlighted trait robustness in the field under variable environmental conditions, although significant variations were found between soil textures as the growing season progressed. Root hairs did not confer a notable advantage to barley under optimal conditions, but under soil water deficit root hairs enhanced plant water status and stress tolerance resulting in a less negative leaf water potential and lower leaf abscisic acid concentration, while promoting shoot P accumulation. Furthermore, the presence of root hairs did not decrease yield under optimal conditions, while root hairs enhanced yield stability under drought. Conclusions Selecting for beneficial root hair traits can enhance yield stability without diminishing yield potential, overcoming the breeder’s dilemma of trying to simultaneously enhance both productivity and resilience. Therefore, the maintenance or enhancement of root hairs can represent a key trait for breeding the next generation of crops for improved drought tolerance in relation to climate change.

Soil degradation is a worsening global phenomenon driven by socio‐economic pressures, poor land management practices and climate change. A deterioration of soil structure at timescales ranging from seconds to centuries is implicated in most forms of soil degradation including the depletion of nutrients and organic matter, erosion and compaction. New soil–crop models that could account for soil structure dynamics at decadal to centennial timescales would provide insights into the relative importance of the various underlying physical (e.g. tillage, traffic compaction, swell/shrink and freeze/thaw) and biological (e.g. plant root growth, soil microbial and faunal activity) mechanisms, their impacts on soil hydrological processes and plant growth, as well as the relevant timescales of soil degradation and recovery. However, the development of such a model remains a challenge due to the enormous complexity of the interactions in the soil–plant system. In this paper, we focus on the impacts of biological processes on soil structure dynamics, especially the growth of plant roots and the activity of soil fauna and microorganisms. We first define what we mean by soil structure and then review current understanding of how these biological agents impact soil structure. We then develop a new framework for modelling soil structure dynamics, which is designed to be compatible with soil–crop models that operate at the soil profile scale and for long temporal scales (i.e. decades, centuries). We illustrate the modelling concept with a case study on the role of root growth and earthworm bioturbation in restoring the structure of a severely compacted soil., This photograph, depicting ant bioturbation, was taken at the compaction recovery experiment at Agroscope, Zurich, Switzerland. Together with other biological processes, faunal bioturbation profoundly influences soil structure and thus soil physical and hydraulic properties, hydrological processes and plant growth. The parsimonious model concept developed in this paper, which is designed to be compatible with profile‐scale soil–crop models, allows simulation of the effects of biological agents (e.g. plant roots and soil‐living organisms) on soil structure dynamics.

The main aim of this global review and systematic analysis was to investigate the impacts of previous land use system, climate zone and forest type and age on soil organic carbon (SOC), total nitrogen (TN) and total phosphorus (TP), in the different soil layers (0-20, 20-60 and 60-100 cm), following afforestation. We collected 85 publications on SOC, TN and TP stock changes, covering different countries and climate zones. The data were classified into groups depending on these investigated parameters and analyzed using R version 3.6.1. We found that afforestation significantly increased SOC and TN stocks in the 0-20 and 20-60 soil layers, with values of 45% and 44% for SOC, 30% and 22% for TN, respectively, but had no impact on TP stock. Previous land use systems had the largest influence on SOC, TN and TP stocks, with greater accumulations on barren land compared to cropland and grassland. Climate zone influenced SOC, TN and TP stocks, with significant accumulations in the moist than in the dry climate zone. Afforestation with broadleaf deciduous and broadleaf evergreen forests led to greater SOC, TN and TP accumulations in each soil layer throughout the investigated profile (0-100 cm), compared to coniferous forests. Afforestation for

A number of critical zone observatories across China have focussed on human impacts caused by agriculture, particularly the sustainability of soil and water resources. Using the CZO approach of measuring from the top of vegetation, through soil, to the bedrock below, joint China/UK projects at these CZOs have quantified large pools of previously undocumented nitrogen stored at depth, pathways for water loss and pollutant transport and drivers of accentuated soil erosion. Socioeconomic studies have found that these challenges to land and water resources tie in well with the concerns of farmers. In two different regions of China, farmers identified fertilisers as their greatest cost and water availability as their biggest challenge. Using large data-sets generated over the past 4 years in these projects, we are developing Decision Support Tools (DSTs) underpinned by CZO science that can guide farmers and policy makers. The work addresses food and water security in the context of climate change and diminishing resources, with an aim to improve livelihoods and sustainable economic development. We have been guided by a review of over 400 DSTs designed for agriculture and the environment, which have been ranked in terms of their outputs and data requirements. A goal at the EGU will be to develop links with other CZO projects to help with our DST development.

Abstract Background and aims Root hairs play a significant role in phosphorus (P) extraction at the pore scale. However, their importance at the field scale remains poorly understood. Methods This study uses a continuum model to explore the impact of root hairs on the large-scale uptake of P, comparing root hair influence under different agricultural scenarios. High vs low and constant vs decaying P concentrations down the soil profile are considered, along with early vs late precipitation scenarios. Results Simulation results suggest root hairs accounted for 50% of total P uptake by plants. Furthermore, a delayed initiation time of precipitation potentially limits the P uptake rate by over 50% depending on the growth period. Despite the large differences in the uptake rate, changes in the soil P concentration in the domain due to root solute uptake remains marginal when considering a single growth season. However, over the duration of 6 years, simulation results showed that noticeable differences arise over time. Conclusion Root hairs are critical to P capture, with uptake efficiency potentially enhanced by coordinating irrigation with P application during earlier growth stages of crops.