Impeded Root Growth Research Articles

Genome-Wide Association study for root system architecture traits in field soybean [Glycine max (L.) Merr.]

Roots play a crucial role in plant development, serving to absorb water and nutrients from the soil while also providing structural stability. However, the impacts of global warming can impede root growth by altering soil conditions that hinder overall plant growth. To address this challenge, there is a need to screen and identify plant genotypes with superior Root System Architecture traits (RSA), that can be used for future breeding efforts in enhancing their resilience to these environmental changes. In this project, 500 mid to late-maturity soybean accessions were grown on blue blotting papers hydroponically with six replicates and assessed seven RSA traits. Genome-Wide Association Studies (GWAS) were carried out with root phenotypic data and SNP data from the SoySNP50K iSelect SNP BeadChip, using both the TASSEL 5.0 and FarmCPU techniques. A total of 26 significant SNP-trait correlations were discovered, with 11 SNPs on chromosome 13. After SNP selection, we identified 14 candidate genes within 100-kb regions flanking the SNPs, which are related to root architecture. Notably, Glyma.17G258700, which exhibited substantial differential expression in root tips and its Arabidopsis homolog, AT4G24190 (GRP94) is involved in the regulation of meristem size and organization. Other candidate genes includes Glyma.03G023000 and Glyma.13G273500 that are also play a key role in lateral root initiation and root meristem growth, respectively. These findings significantly contribute to the discovery of key genes associated with root system architecture, facilitating the breeding of resilient cultivars adaptable to changing climates.

Optimizing the Nitrogen Fertilizer Management to Maximize the Benefit of Straw Returning on Early Rice Yield by Modulating Soil N Availability

Straw returning has gradually been adopted as an effective approach to address the serious degradation of farmland. However, the carbon/nitrogen (C/N) ratio of rice straw is generally too high for microorganisms to decompose the organic materials and release nutrients, which may minimize the benefits of straw returning to the agricultural production system. This study aimed to investigate the effects of straw returning on rice production and propose optimum nitrogen (N) management for early rice production under a straw returning system. The total N fertilizer that was evaluated was 165 kg N ha-1, urea (46% N), applied in different proportions in three stages of rice cultivation: basal, tillering, and panicle. Using no straw returning with the N fertilizer ratio of basal:tillering:panicle = 5:2:3 treatment (T1) as the control, four different N fertilizer ratios of basal:tillering:panicle, including 5:2:3 (T2), 5:2:2 (T3), 5:4:1 (T4), and 5:5:0 (T5) were set under straw returning. The return of straw decreased the available N in the soil at the tillering stage, and impeded root growth and the crop canopy from establishing, which decreased the effective panicles by 10.1% compared with that of T1, limiting the increases in rice grain yield. Increasing the N fertilizer ratio 10–20% (T3 and T4) at the tillering stage effectively increased the content of soil ammonium and nitrate nitrogen, improved the root growth, and increased the root activities by 16.0–40.5% at the tillering stage. As a result, the effective panicle number increased by 5.1–16.2%. Among these, T4 treatment maximized the benefits of straw returning the most. Additionally, increasing the N fertilizer ratio at the tillering stage increased the shoot uptake across the early rice growing season and synchronized crop N uptake with the accumulation of carbon assimilates, which enhanced the crop growth rate and increased the rice yield by 13.5–25.1%. It is concluded that increasing the N fertilizer ratio by 20% at the tillering stage is a promising strategy to increase the availability of N in the phases of high demand for this nutrient.

Detection of plant cadmium toxicity by monitoring dielectric response of intact root systems on a fine timescale.

The root dielectric response was measured on a minute scale to assess its efficiency for monitoring short-term cadmium (Cd) toxicity non-destructively. Electrical capacitance (CR), dissipation factor (DR) and electrical conductance (GR) were detected during the 24 to 168 h after Cd treatment (0, 20, 50 mg Cd2+ kg-1 substrate) in potted maize, cucumber and pea. Stress was also evaluated by measuring leaf chlorophyll content, Fv/Fm and stomatal conductance (gs) in situ, and shoot and root mass and total root length after harvest. CR showed a clear diurnal pattern, reflecting the water uptake rate, and decreased significantly in response to excessive Cd due to impeded root growth, the reduced tissue permittivity caused by accelerated lignification, and root ageing. Cd exposure markedly increased DR, indicating greater conductive energy loss due to oxidative membrane damage and enhanced electrolyte leakage. GR, which was coupled with root hydraulic conductance and varied diurnally, was increased transiently by Cd toxicity due to enhanced membrane permeability, but declined thereafter owing to stress-induced leaf senescence and transpiration loss. The time series of impedance components indicated the comparatively high Cd tolerance of the applied maize and the sensitivity of pea cultivar, which was confirmed by visible shoot symptoms, repeated physiological investigations and biomass measurements. The results demonstrated the potential of single-frequency dielectric measurements to follow certain aspects of the stress response of different species on a fine timescale without plant injury. The approach can be combined with widely used plant physiological methods and could contribute to breeding crop genotypes with improved stress tolerance.

Genotypic differences in systemic root responses to mechanical obstacles.

As roots grow through the soil to forage for water and nutrients, they encounter mechanical obstacles such as patches of dense soil and stones that locally impede root growth. Here, we investigated hitherto poorly understood systemic responses of roots to localised root impedance. Seedlings of two wheat genotypes were grown in hydroponics and exposed to impenetrable obstacles constraining the vertical growth of the primary or a single seminal root. We deployed high-resolution in vivo imaging to quantify temporal dynamics of root elongation rate, helical root movement, and root growth direction. The two genotypes exhibited distinctly different patterns of systemic responses to localised root impedance, suggesting different strategies to cope with obstacles, namely stress avoidance and stress tolerance. Shallower growth of unconstrained seminal roots and more pronounced helical movement of unconstrained primary and seminal roots upon localised root impedance characterised the avoidance strategy shown by one genotype. Stress tolerance to localised root impedance, as exhibited by the other genotype, was indicated by relatively fast elongation of primary roots and steeper seminal root growth. These different strategies highlight that the effects of mechanical obstacles on spatiotemporal root growth patterns can differ within species, which may have major implications for resource acquisition and whole-plant growth.

DEM modelling of root circumnutation-inspired penetration in shallow granular materials

Plant root growth is often accompanied by circumnutative motion consisting of downward helical movement of the root tip. Previous studies indicate that circumnutations allow roots to avoid obstacles that would impede root growth, while other studies show that circumnutations can reduce the penetration resistance mobilised during root growth. Discrete-element modelling (DEM) simulations were performed on probes that employ circumnutation-inspired motion (CIM) to penetrate granular assemblies at shallow depths to evaluate the reduction in penetration resistance. These simulations investigate the effect of the ratio of tangential to vertical velocity of the circumnutative motion (i.e. relative velocity) and of the probe geometry (i.e. tip tilt angle and length). The results indicate that CIM penetration reduces the penetration force and work relative to non-rotational penetration (NRP) by changing the soil fabric and diffusing the force chains around the probe tip. However, the circumnutative motion leads to an increase in torque and associated rotational work. An optimal relative velocity and probe geometry exist for the simulated CIM probes, resulting in a smaller total work than that required for NRP. CIM penetration also mobilises smaller penetration forces and work than rotational penetration (i.e. with a straight tip), particularly at smaller relative velocities. The reduction in penetration forces induced by CIM could facilitate site investigation and monitoring activities.

Effects of microplastics on the phytoremediation of Cd, Pb, and Zn contaminated soils by Solanum photeinocarpum and Lantana camara

Microplastics are emerging pollutants and have become a global environmental issue. The impacts of microplastics on the phytoremediation of heavy metal–contaminated soils are unclear. A pot experiment was conducted to investigate the effects of four additions (0, 0.1%, 0.5%, and 1% w·w−1) of polyethylene (PE) and cadmium (Cd), lead (Pb), and zinc (Zn) contaminated soil on the growth and heavy metal accumulation of two hyperaccumulators (Solanum photeinocarpum and Lantana camara). PE significantly decreased the pH and activities of dehydrogenase and phosphatase in soil, while it increased the bioavailability of Cd and Pb in soil. Peroxidase (POD), catalase (CAT), and malondialdehyde (MDA) activity in the plant leaves were all considerably increased by PE. PE had no discernible impact on plant height, but it did significantly impede root growth. PE affected the morphological contents of heavy metals in soils and plants, while it did not alter their proportions. PE increased the content of heavy metals in the shoots and roots of the two plants by 8.01–38.32% and 12.24−46.28%, respectively. However, PE significantly reduced the Cd extraction amount in plant shoots, while it significantly increased the Zn extraction amount in the plant roots of S. photeinocarpum. For L. camara, a lower addition (0.1%) of PE inhibited the extraction amount of Pb and Zn in the plant shoots, but a higher addition (0.5% and 1%) of PE stimulated the Pb extraction amount in the plant roots and the Zn extraction amount in the plant shoots. Our results indicated that PE microplastics have negative effects on the soil environment, plant growth, and the phytoremediation efficiency of Cd and Pb. These findings contribute to a better knowledge of the interaction effects of microplastics and heavy metal–contaminated soils.

A regional soil classification framework to improve soil health diagnosis and management

AbstractSoil health research has developed soil tests to validate management strategies for creating healthier soils, such as cover crops, compost, and reduced tillage. Missing in this research agenda are soil health management strategies and diagnostics tailored to the systematic variation of soils. The Soil Survey Geographic (SSURGO) database offers comprehensive estimates for many properties linked to soil health indicators. This research uses unsupervised classification of soil surface (0–30 cm) properties and root restrictive horizons in an internationally important agricultural region, the Central and Coastal Valleys of California, covering 5.6 million ha of mostly cropland. K‐means clustering of 10 soil properties derived from SSURGO revealed groups distinct from USDA‐NRCS Soil Taxonomy. Clustering metrics, data visualization, and validation tests justified a seven‐region soil health conceptual model that divided the landscape into two broad classes—those with and without performance limitations. Results revealed three pedogenic conditions limiting soil performance: (a) root restrictive horizons that impede root growth into deeper soil; (b) salinity and alkalinity harmful to crops; and (c) shrink–swell properties making soils challenging to cultivate. Soils without performance limitations, soils with restrictive horizons, and salt‐affected soils are further divided by texture and/or organic matter for a total of seven soil health regions. In reality, variation in soil properties is often continuous across the landscape and sometimes fractal in nature, but this research establishes a testable framework for evaluating soil health diagnostics according to geographically coherent differences in soil properties, demonstrating potential for how soil health management and interpretation can be tailor‐made to the landscape.

Grazing winter rye cover crop in a cotton no‐till system: Soil strength and runoff

AbstractGrazing cover crops (CC) could provide an economic incentive to increase adoption rates in the southeastern United States. However, understanding grazing effects on soil properties is lacking for most soils of the region. Effects of grazing or rolling a cereal rye (Secale cereale L.) CC prior to no‐till planting cotton (Gossypium hirsutum L.) were determined in 2009 after 4 yr on Cecil soil, in the Southern Piedmont near Watkinsville, GA. The four catchments had a previous long history of no‐till cropping with CC. Wet spring conditions in 2009 resulted in visible surface roughness from cattle hooves. Average soil penetration resistance (PR) for the 0‐ to 30‐cm profile was 14% greater following rye CC grazing than rolling (1.95 vs. 1.53 MPa) and was still apparent the following February (1.86 vs. 1.58 MPa) after cotton harvest. Increases in PR at 2.5‐ to 7.5‐ and 7.5‐ to 15‐cm soil depths were observed following CC grazing but not rolling. Depth to 2 MPa resistance, considered sufficient to impede root growth, was similar for CC grazing and rolling treatments in March prior to grazing but decreased in the grazed treatment to 10.7 cm in May and 15.6 cm in February. Seasonal runoff data for 2006–2009 indicated no differences between grazed and rolled CC management. We concluded that grazing CC for short periods under wet conditions presents a risk of short‐term negative effects even for Southern Piedmont soils where a long history of conservation tillage and CC has improved soil quality.

Agronomic and physiological responses of potato subjected to soil compaction and/or drying

AbstractCompact and dry soils impede root growth and restrict plant water availability, respectively, potentially causing leaf water deficit. Although both stresses likely co‐occur in the field and limit yield, little is known about their combined impact on plant growth and physiology over a whole season, especially in a tuberous crop like potato. Field‐grown potato (Solanum tuberosum L. var. 'Maris Piper') was exposed to factorial combination of deficit irrigation (watering when soil moisture deficit reached 60 vs. 25 mm) and soil compaction (compacted with heavy machinery vs. uncompacted), with plant growth and leaf physiology measured weekly. Shoot growth was restricted by adverse soil conditions, while leaf water status, photosynthesis rates and leaf abscisic acid (ABA) levels did not vary significantly between treatments. Across all treatments, final yield was linearly correlated (R2 = 0.71) to mid‐season shoot biomass. Compared to well‐watered plants growing in loose soil, soil compaction, deficit irrigation and their combination decreased final tuber yield similarly, by 23%–34%. Surprisingly, tuber size distribution was more dependent on irrigation management than on soil strength. Plants exposed to deficit irrigation produced more, smaller potatoes than their respective control. Thus, low soil water availability and/or compact soil caused these field‐grown potatoes to restrict shoot growth rather than limit leaf gas exchange. Further research is needed to understand the role of hormonal signalling in regulating tuber growth when plants are exposed to compact and dry soils.

Nonspecific phospholipase C4 hydrolyzes phosphosphingolipids and sustains plant root growth during phosphate deficiency.

Phosphate is a vital macronutrient for plant growth, and its availability in soil is critical for agricultural sustainability and productivity. A substantial amount of cellular phosphate is used to synthesize phospholipids for cell membranes. Here, we identify a key enzyme, nonspecific phospholipase C4 (NPC4) that is involved in phosphosphingolipid hydrolysis and remodeling in Arabidopsis during phosphate starvation. The level of glycosylinositolphosphorylceramide (GIPC), the most abundant sphingolipid in Arabidopsis thaliana, decreased upon phosphate starvation. NPC4 was highly induced by phosphate deficiency, and NPC4 knockouts in Arabidopsis decreased the loss of GIPC and impeded root growth during phosphate starvation. Enzymatic analysis showed that NPC4 hydrolyzed GIPC and displayed a higher activity toward GIPC as a substrate than toward the common glycerophospholipid phosphatidylcholine. NPC4 was associated with the plasma membrane lipid rafts in which GIPC is highly enriched. These results indicate that NPC4 uses GIPC as a substrate in planta and the NPC4-mediated sphingolipid remodeling plays a positive role in root growth in Arabidopsis response to phosphate deficiency.

Evaluation of Recycled Materials as Hydroponic Growing Media

Conventional soilless growing media, such as perlite, are mined from nonrenewable resources and can only be disposed of in landfills after limited use. There is a need to investigate novel, sustainable growing media adapted from waste or engineered to be reused over multiple cycles. This study investigated waste almond shells and a recycled plastic drainage plank as hydroponic growing media alternatives. Physiochemical properties were evaluated, and a germination and greenhouse growth trial was conducted to understand the effect these media have on production and nutritional quality of lettuce (Lactuca sativa L. cv. Catalogna Verde). Drought testing was carried out to understand how the media affected the lettuce’s response to water stress. In comparison to perlite, yields under regular irrigation were reduced by 52% in almond shells and 72% in plastic planks, although lettuce grown in almond shells still obtained commercially relevant yields. Reduced yields in almond shells were likely caused by the shell’s high salinity. Lettuce growth in plastic planks was limited by impeded root growth and low water-holding capacity. In conclusion, with minor alterations, almond shells could be used as a sustainable growing media alternative to perlite in hydroponic lettuce production. More research is needed to manufacture the planks to be conducive to plant growth.

Comparisons with wheat reveal root anatomical and histochemical constraints of rice under water-deficit stress

AimsTo face the challenge of decreasing freshwater availability for agriculture, it is important to explore avenues for developing rice genotypes that can be grown like dryland cereals. Roots play a key role in plant adaptation to dry environments.MethodsWe examined anatomical and histochemical root traits that affect water acquisition in rice (Oryza sativa) and wheat (Triticum aestivum). These traits and root growth were measured at two developmental stages for three rice and two wheat cultivars that were grown in pots under three water regimes.ResultsWheat roots had larger xylem sizes than rice roots, which potentially led to a higher axial conductance, especially under water-deficit conditions. Suberization, lignification and thickening of the endodermis in rice roots increased with increasing water deficit, resulting in stronger radial barriers for water flow in rice than in wheat, especially near the root apex. In addition, water deficit strongly impeded root growth and lateral root proliferation in rice, but only slightly in wheat, and cultivars within a species differed little in these responses. The stress sensitivity of rice attributes was slightly more prominent at vegetative than at flowering stages.ConclusionsRice root characteristics, which are essential for growth under inundated conditions, are not conducive to growth under water deficit. Although rice roots show considerable plasticity under different watering regimes, improving root xylem size and reducing the radial barriers would be required if rice is to grow like dryland cereals.

Chromosome doubling of androgenic haploid plantlets of rice (Oryza sativa) using antimitotic compounds

AbstractThe regeneration of haploid plantlets is considered as a bottleneck in rice anther culture. In this study, an antimitotic chromosome doubling method, simple and efficient, of androgenic haploid plantlets resulted in an efficient doubled haploid obtainment. Through chromosome doubling capacity comparison of the three antimitotic compounds (colchicine, trifluralin and oryzalin), colchicine at 500 and 625 mg/L without supplementing with DMSO was found to be the best antimitotic treatment, with a chromosome doubling capacity of 40%. Furthermore, the in vitro growth of plantlets was followed to analyse the effects of antimitotic compounds. Colchicine treatments were more toxic than dinitroanilines, and colchicine DMSO‐supplemented treatments had significant lower values on shoot growth. On the other hand, dinitroaniline compounds impeded root growth, provoked helical growth of shoot and caused the apparition of white nodules in the base of the plantlet due to sprouting abortion. In this study, a protocol for doubled haploid plant recovery was established taking advantage from androgenic haploid plantlets in order to increase the number of doubled haploid plantlets produced after an anther culture protocol.

Estimation of the impact of precrops and climate variability on soil depth-differentiated spring wheat growth and water, nitrogen and phosphorus uptake

Water and nutrients in the subsoil are valuable resources in crop production but the availability varies with weather conditions and management, in particular the crop rotation. Moreover, constraints such as mechanical resistance or water stress may impede root growth into deeper soil layers. This study presents a simulation-based stochastic approach to investigate the impact of precrops on spring wheat growth and water and nutrient uptake under varying weather conditions. The effect of the three precrops lucerne, chicory and tall fescue on spring wheat growth was investigated extensively in a field trial. For model calibration and evaluation, we selected a year with a dry spell (2010) and one with abundant precipitation (2012) and used field data on biopore densities in the subsoil, crop development, leaf area index, shoot biomass, grain and straw yield, nitrogen (N) and phosphorus in shoot, grain and straw, root length densities, as well as soil moisture and soil N and P concentrations for several soil depths. The modeling framework consisted of the modeling platform SIMPLACE and the stochastic weather generator LARS-WG to consider climate variability. The weather generator was used to generate a synthetic time-series of daily weather data (100 years) based on observed weather data of the experimental site in order to simulate 100 spring wheat growth periods under recent climate conditions for each precrop. Moreover, a 100 year long time-series with annual dry spells in June was generated to analyze the effect of drought during flowering on crop water and nutrient uptake. During the scenario runs, the model was annually reinitialized at sowing to provide identical initial conditions. The experimental data over two years showed that spring wheat growth as well as total N and P uptake were clearly enhanced after precrop lucerne. This was comfirmed by the simulations over 100 years. The simulation runs also prompt that precrop fescue led to higher spring wheat biomass and enhanced subsoil and total water and N uptake in years with normal precipitation pattern compared to precrop chicory, but in drier years, it was vice versa. Because plants compensate for moderate nutrient or water deficiencies, small differences in grain yield may hide significant differences in total and in subsoil N and P uptake.

Electrical characterization of the root system: a noninvasive approach to study plant stress responses

A pot experiment was designed to demonstrate that the parallel, single-frequency detection of electrical capacitance (CR), impedance phase angle (ΦR), and electrical conductance (GR) in root–substrate systems was an adequate method for monitoring root growth and some aspects of stress response in situ. The wheat cultivars ‘Hombar’ and ‘TC33’ were grown in a rhyolite-vermiculite mixture under control, and low, medium, and high alkaline (Na2CO3) conditions with regular measurement of electrical parameters. The photochemical efficiency (Fv/Fm) and SPAD chlorophyll content were recorded non-intrusively; the green leaf area (GLA), shoot dry mass (SDM), root dry mass (RDM), and root membrane stability index (MSI) were determined after harvest. CR progressively decreased with increasing alkalinity due to impeded root growth. Strong linear CR–RDM relationships (R2 = 0.883–0.940) were obtained for the cultivars. Stress reduced |ΦR|, presumably due to the altered membrane properties and anatomy of the roots, including primarily enhanced lignification. GR was not reduced by alkalinity, implying the increasing symplastic conductivity caused by the higher electrolyte leakage indicated by decreasing root MSI. Fv/Fm, SPAD value, GLA, and SDM showed decreasing trends with increasing alkalinity. Cultivar ‘TC33’ was comparatively sensitive to high alkalinity, as shown by the greater relative decrease in CR, SDM, and RDM under stress, and by the significantly lower MSI and higher (moderately reduced) |ΦR| compared to the values obtained for ‘Hombar’. Electrical root characterization proved to be an efficient non-intrusive technique for studying root growth and stress responses, and for assessing plant stress tolerance in pot experiments.

Soil properties and subsoil constraints of urban and peri-urban agriculture within Mahikeng city in the North West Province (South Africa)

PurposeUrban and peri-urban agriculture is becoming increasingly important as a source of income and food for the urban population in South Africa. While most studies on urban agriculture have focused their attention on surface soils, there is dearth of information regarding subsoil properties. This study examined properties of subsoil horizons that may impede root growth and productivity of crops under urban agriculture.Materials and methodsThe properties of topsoil (0–20 cm) and subsoil horizons (20–40 cm) of four profiles from plots within the city of Mahikeng (25° 48′ S and 25° 38′ E) were examined to determine the nature of subsoil constraints that can limit root growth and crop productivity. The plots were selected in an area extending through four residential suburbs of the city, and two plots with a long history of cultivation were purposely selected from each suburb to represent the main cropping systems and soil types. Soil physical (penetrometer resistance, bulk density, hydraulic conductivity), chemical (pH, exchangeable Ca, Mg, K, Na, phosphorus and boron) and biological (root growth, organic carbon, microbial biomass, enzyme activity) properties were measured in the profiles.Results and discussionEven though there was a large variability between profiles, the results revealed high bulk density (mean 2.06 Mg m−3) at the top of the subsoil for all the profiles. The corresponding mean penetrometer resistance was 1.89 MPa implying high mechanical resistance to root growth in this layer. The hydraulic conductivities at saturation were below 12 mm h−1 suggesting low drainage which may result in perched water table and waterlogging leading to depleted oxygen in the root zone. The pH in all the profiles was slightly acid to moderate alkaline (6.1–8.3, in water), and low levels of plant available boron (B) were found in the subsoil layers. Most of the profiles had extreme values of physical properties that would constrain root growth. All the subsoil layers had significantly (p < 0.05) lower root growth, organic carbon, microbial biomass and enzyme activity.ConclusionsIt was concluded that subsoil constraints to root growth appear to be widespread in profiles of soils used for urban and peri-urban agriculture in the city of Mahikeng. Given that studying and ameliorating subsoil constraints is difficult, time-consuming and expensive, it is recommended that periodic deep ploughing and inclusion of plants with roots which are tolerant or resistant to these conditions be considered as part of routine soil management practice in plots used for urban agriculture.

English

Lack of detailed soil data has been a major constraint to hydrological modeling and making of agronomic decisions in the Koupendri Catchment. A soil survey was carried out to characterize and classify the soils of the 11.8 km2 catchment using Soil and Terrain (SOTER) approach. The soils were classified using the soil taxonomy (USDA) and the world reference base for soil resources (WRB) classification systems. The soil map produced at a scale of 1:25000 using FAO/UNESCO legend showed five distinct soil types. The dominant soil type - Dystric Plinthosols - covered about 55% of the area and supports few crop productions but make plantation agriculture almost impossible. The soils are slightly acidic to alkaline, predominantly silty to clayey in texture with good to imperfect drainage, low permeability and high bulk density that impedes root growth. The poor soil organic carbon content, total nitrogen, available phosphorus, cation exchange capacity, base saturation and other basic exchangeable cations with moderately leached horizons indicated low-moderate fertility status of less weathered soils. The soils belong to three major soil orders: Ultisols, Inceptisols and Alfisols (USDA), and reference soil groups: Plinthosols, Cambisols, Luvisols and Gleysols (WRB). The WRB gave a better and detailed soil classification compared to USDA, and thus should be used in subsequent classification of soils in the region. Key words: Soil and terrain (SOTER), ultisols, alfisols, inceptisols, plinthosols, cambisols, luvisols, gleysols.

Floodplain ecohydrology: Climatic, anthropogenic, and local physical controls on partitioning of water sources to riparian trees.

Seasonal and annual partitioning of water within river floodplains has important implications for ecohydrologic links between the water cycle and tree growth. Climatic and hydrologic shifts alter water distribution between floodplain storage reservoirs (e.g., vadose, phreatic), affecting water availability to tree roots. Water partitioning is also dependent on the physical conditions that control tree rooting depth (e.g., gravel layers that impede root growth), the sources of contributing water, the rate of water drainage, and water residence times within particular storage reservoirs. We employ instrumental climate records alongside oxygen isotopes within tree rings and regional source waters, as well as topographic data and soil depth measurements, to infer the water sources used over several decades by two co-occurring tree species within a riparian floodplain along the Rhône River in France. We find that water partitioning to riparian trees is influenced by annual (wet versus dry years) and seasonal (spring snowmelt versus spring rainfall) fluctuations in climate. This influence depends strongly on local (tree level) conditions including floodplain surface elevation and subsurface gravel layer elevation. The latter represents the upper limit of the phreatic zone and therefore controls access to shallow groundwater. The difference between them, the thickness of the vadose zone, controls total soil moisture retention capacity. These factors thus modulate the climatic influence on tree ring isotopes. Additionally, we identified growth signatures and tree ring isotope changes associated with recent restoration of minimum streamflows in the Rhône, which made new phreatic water sources available to some trees in otherwise dry years.Key PointsWater shifts due to climatic fluctuations between floodplain storage reservoirsAnthropogenic changes to hydrology directly impact water available to treesEcohydrologic approaches to integration of hydrology afford new possibilities

Effects of soil density on grass-induced suction distributions in compacted soil subjected to rainfall

Grass is recognized as being beneficial in reducing rainfall infiltration in some kinds of surface cover systems such as landfill cover, because rainwater discharges as surface runoff due to reduced water permeability caused by evapotranspiration-induced soil suction as well as foliage interception. However, the distributions of grass-induced suction in various compacted soils during rainfall are rarely reported. Moreover, it is not straightforward to determine an optimum soil dry density for minimizing rainfall infiltration and at the same time encouraging plant growth. This is because there are conflicting requirements for vegetated cover systems, i.e., compacted soil should not be too dense as to impede root growth, while on the other hand to minimize infiltration. This study thus aims to investigate, quantify, and compare grass-induced suction distributions in silty sand compacted at different densities when subjected to artificial rainfall in the laboratory. A grass species, Cynodon dactylon, which is common in many parts of Asia, was selected for testing. Compacted soil with and without a growing grass patch was tested at three relative compactions (RCs) of 70%, 80%, and 95%, in six test boxes. Test results reveal that at an RC of 95%, suction (40 kPa) retained in vegetated soil after rainfall is 100% higher than that (20 kPa) in bare soil. Among the vegetated soil compacted at the three RCs, suction retained was the highest at an RC of 95% (40 kPa), whereas suction decreased to 0 kPa at an RC of 70% after rainfall. As the average depth of grass roots decreased by 36% due to an increase in RC from 70% to 95%, the depth of influence of suction for vegetated soil at an RC of 95% reduced to less than half of root depth, which was the shallowest among the three compacted soil specimens.

NOTA TÉCNICA: RESISTÊNCIA MECÂNICA DO SOLO À PENETRAÇÃO EM FUNÇÃO DA SUA UMIDADE E DO TIPO DE PENETRÔMETRO - DOI: 10.13083/1414-3984.v22n01a08

Com o advento da mecanização agrícola o solo passou a receber uma maior pressão dos pneus das máquinas, que pode ocasionar zonas de impedimento ao desenvolvimento radicular das plantas. O objetivo do trabalho foi avaliar a resistência mecânica do solo a penetração (RP) com penetrômetro eletrônico e de impacto em condições de umidade em área cultivada anteriormente por sorgo forrageiro. O experimento foi conduzido no Campus das Ciências Agrárias da Universidade Federal do Vale do São Francisco – UNIVASF, Petrolina (PE). A coleta de dados da RP foi realizada com penetrômetro eletrônico e de impacto em condições de umidade (3,5 e 6,7%) nas profundidades de 0,00 a 0,50 m, sendo os penetrômetros posicionados a 0,20 m um do outro para a coleta. Para o penetrômetro de impacto verificaram-se altos valores de RP, e não houve diferença nos valores de RP nas diferentes condições de umidade. Para o penetrômetro eletrônico verificou-se que em baixas condições de umidade não se conseguiu realizar a penetração no solo, e que até a camada de 0,30 m verificou-se diferença nos valores de RP, sendo menor na maior umidade do solo. Ocorreu relação entre a umidade e o valor da RP para o penetrômetro eletrônico.