kPa Matric Potential Research Articles

Comparing impacts of corn residue removal and amelioration practices on soil properties after 3, 6, and 10 years

AbstractInformation on corn (Zea mays L.) residue removal and organic amendment additions to ameliorate removal effects on soil properties is limited. Thus, we compared impacts of corn residue removal at 59% and organic amendments (winter rye [Secale cereale L.]) cover crop and manure every other year at 24 Mg ha−1 on soil organic carbon (SOC) and physical properties after 10 years under irrigated no‐till continuous corn on a silt loam in the western US Corn Belt. We collected soil property data after 10 years and then compared it with earlier results from this experiment (3 and 6 years). Cover crop and manure amendments maintained SOC concentration, but no amelioration practice reduced SOC concentration (−15%) from 3 to 10 years when residues were annually removed in 0‐ to 5‐cm depth. Under residue retention, SOC concentration increased with time with largest increase (+41%) occurring under manure amelioration practice in the 0‐ to 5‐cm depth. Residue removal reduced soil wet aggregate stability by 34%, soil dry aggregate stability by 73%, bulk density by 6%, water content at −33 kPa matric potential by 14%, and plant available water by 17% after 10 years in the 0‐ to 5‐cm soil depth but did not affect infiltration rate. Cover crops increased wet aggregate stability (32%), but manure and cover crops had limited effects on other soil properties. Residue removal increased the susceptibility of the soil to erosion and reduced water retention and SOC after 3 years, but such effects were not fully offset by amendments.

Prediction of water retention properties of French soils using the in situ volumetric water content at field capacity as single input data

The objective of this study was to investigate the relevance of using the in situ volumetric water content at field capacity (θFC) as a predictor of the water retention properties by comparing the performances of pedotransfer functions (PTFs) established using artificial neural networks (ANN-PTFs) and support vector machines (SVM-PTFs) with much simpler PTFs in the form of simple linear regressions (SLR-PTFs). A dataset comprising 456 horizons collected in soils located in France was used. The available data were: the silt and clay contents (SC), the organic carbon content (OC), the bulk density at field capacity (BDFCm), the in situ gravimetric water content at field capacity (WFCm) related to θFC by using BDFCm, and the volumetric water content at –1, –3.3, –10, –33, –100, –330 and –1500 kPa matric potential. The performances of the PTFs studied were compared by using the root mean squared error (RMSE) and the coefficient of determination (R²). Our results showed the relevance of using θFC, which was proved to be close to the volumetric water content at –10 kPa matric potential, as a predictor of the water retention properties. With ANN-PTFs, the best performances were recorded when both θFC and SC were used as input data (RMSE = 0.027 cm3 cm-3 and R2 = 0.92). With SVM-PTFs, the smallest RMSE was recorded when θFC was used as single input data (RMSE = 0.026 cm3 cm-3). As for R2 of SVM-PTFs, it was the highest with θFC and SC as input data (R2 = 0.84). The SLR-PTFs using θFCas single predictor after stratification by texture performed better (RMSE = 0.031 cm3 cm-3 and R2 = 0.88) than the ANN-PTFs using one or two soil characteristics as input data. Comparison of SLR-PTFs with SVM-PTFs showed that the latter performed slightly better than SLR-PTFs after stratification by texture but R2 was smaller when θFCwas used as the single predictor. Use of a predicted value of the bulk density at field capacity to obtain a value of in situ volumetric water content at field capacity led to poorer performances of the SLR-PTFs but after stratification by texture they remained close to those recorded with ANN-PTFs or SVM-PTFs when they used a single soil characteristic as input data. Finally, our results showed that associating OC to the input data did not increase the perfomances of the ANN-PTFs and SVM-PTFs.

Funções de pedotransferência para predição da retenção de água em solo sob Cerrado Brasileiro

Abstract The objective of this work was to determine pedotransfer functions to predict water retention at the -33 and -1500 kPa matric potentials of soils under Cerrado, in the south of the state of Mato Grosso, Brazil. Samples (n=156) were collected for model calibration (n=124) and validation (n=32). A stepwise multiple regression was used to determine pedotransfer functions. Willmott’s index of agreement, root-mean-square error, Pearson’s correlation coefficient, and the confidence index were used to evaluate the performance of the functions and to compare them with those described in the literature. The most efficient variables to estimate water retention were: microporosity, total sand, and clay at -33 kPa; and total sand, silt and clay at -1500 kPa. The regional pedotransfer functions explained more than 94% of water retention variance in the studied soils. The reliability of the functions to predict water retention increased, at -33 kPa, with the use of the structural property microporosity and, at -1500 kPa, with the use of granulometric parameters. The studied regional pedotransfer functions predict water retention at the -33 and -1500 kPa matric potentials of soils under Cerrado, in southern Mato Grosso, better than the functions described in the literature.

Counterions, smectite, and palygorskite increase microstructural stability of saline-sodic soils

Saline-sodic soils are susceptible to wind and water erosion when the dispersive effect of sodium overcomes inter-particle bonds. Rheological parameters of viscoelasticity can help to quantify inter-particle attractive forces and account for the effect of salinity in these soils. The main objective of the present study was to investigate the viscoelasticity behavior of saline-sodic soils of the Sirjan playa in south-central Iran. Three representative pedons were excavated and described by horizon. Soil physicochemical properties and rheological properties were determined, namely the micromechanical parameters flow point (γf), loss factor tan δ, and integral z, with samples analyzed at three matric potentials (0, −6, and −15 kPa). Results showed that soil microstructural stiffness was mainly influenced by soil texture, clay minerals, gypsum, calcium carbonate equivalent (CCE), and matric potential. The dispersive effect of sodium, as indicated by low integral z and γf values, decreased with increasing gypsum content in − 6 and − 15 kPa matric potentials (0.6 < r < 0.8) and CCE percentage in the quasi-saturated (0 kPa) condition (r > 0.8). However, greater microstructural stability (i.e., higher integral z and γf) was observed for fine-textured soils with relatively high amounts of smectite and palygorskite and low pH. Furthermore, integral z and γf increased with lower matric potentials due to the stabilizing effect of menisci forces. Therefore, the viscoelastic behavior of the saline-sodic soils was negatively associated with water content and high sodium concentration, while the presence of smectite, palygorskite, gypsum, and CCE improved the soil physical conditions and thus the rigidity of the porous system. These results demonstrate that rheological measurements can identify saline-sodic soils that have strongly degraded microstructural stability and would most benefit from active management and amelioration.

WITHDRAWN: Counterions, smectite, and palygorskite increase microstructural stability of saline-sodic soils

Abstract Saline-sodic soils are susceptible to wind and water erosion when the dispersive effect of sodium overcomes inter-particle bonds. Rheological parameters of viscoelasticity can help to quantify inter-particle attractive forces and account for the effect of salinity in these soils. The main objective of the present study was to investigate the viscoelasticity behavior of saline-sodic soils of the Sirjan playa in south-central Iran. Three representative pedons were excavated and described by horizon. Soil physicochemical properties and rheological properties were determined, namely the micromechanical parameters flow point (γf), loss factor tan δ, and integral z, with samples analyzed at three matric potentials (0, −6, and −15 kPa). Results showed that soil microstructural stiffness was mainly influenced by soil texture, clay minerals, gypsum, calcium carbonate equivalent (CCE), and matric potential. The dispersive effect of sodium, as indicated by low integral z and γf values, decreased with increasing gypsum content in − 6 and − 15 kPa matric potentials (0.6 0.8). However, greater microstructural stability (i.e., higher integral z and γf) was observed for fine-textured soils with relatively high amounts of smectite and palygorskite and low pH. Furthermore, integral z and γf increased with lower matric potentials due to the stabilizing effect of menisci forces. Therefore, the viscoelastic behavior of the saline-sodic soils was negatively associated with water content and high sodium concentration, while the presence of smectite, palygorskite, gypsum, and CCE improved the soil physical conditions and thus the rigidity of the porous system. These results demonstrate that rheological measurements can identify saline-sodic soils that have strongly degraded microstructural stability and would most benefit from active management and amelioration.

Predicting soil water content using support vector machines improved by meta-heuristic algorithms and remotely sensed data

ABSTRACT Soil water content characteristics included field capacity (FC) and permanent wilting point (PWP) are key soil indicators to study permeability, soil water retention capacity, drainage, irrigation, plant water stress and solute movement. It is necessary to use an appropriate model for predicting these characteristics because of the hardness of their measurement. The present research shows a comparison of intelligent models included ANN, ANFIS, SVM and SVM optimised by firefly and particle swarm meta-heuristic algorithms (SVM-FFA and SVM-PSA) to predict soil water content at −33 and −1500 kPa matric potentials in agricultural soils. Results showed that the SVM-PSA and SVM-FFA hybrid models presented the best performance rather than the others, with predictor variables included geometric mean diameter (dg) of soil particles, bulk density, organic carbon, NDVI and NSMI and the values of R2 and NRMSE in validation dataset, 0.94, 0.081, 0.96 and 0.077 for FC and PWP in SVM-PSA, respectively, and 0.96, 0.079, 0.97 and 0.075 for FC and PWP in SVM-FFA model. Therefore, these intelligent machines are preferable for accurate prediction and could be used to predict soil water content of soils with different soil textures in other regions of Iran or even the world.

Cover crop impacts on soil physical properties: A review

AbstractCover crop (CC) impacts on soil ecosystem services including erosion control, C sequestration, soil productivity, and others have been reviewed. However, CC impacts on soil physical properties, which affect the soil's ability to perform a variety of soil ecosystem services, have not been synthesized. We reviewed 98 peer‐reviewed publications up to 10 June 2020 on CCs and soil physical properties. Our review indicates that, in most studies, CCs reduce soil penetration resistance or compaction by 0–29% (average, 5%). They improve wet aggregate stability by 0–95% (average, 16%) and cumulative infiltration by 0–190% (average, 43%) but have negligible impacts on bulk density, dry aggregate stability, saturated hydraulic conductivity (Ksat), unsaturated hydraulic conductivity (Kunsat), volumetric water content at −10 to −33 kPa matric potential (field capacity), and plant available water. Soils under CCs can be cooler in daytime and warmer at nighttime, and warmer in winter and cooler in the rest of year. Volumetric heat capacity increases and thermal diffusivity decreases, indicating that CCs could moderate heat transport rate. Soil texture, tillage system, CC‐derived soil C concentration, and CC duration affect CC impacts on physical properties. For example, the positive impacts from CCs can increase as CC management duration increases and combining CCs with no‐till can improve water infiltration more than with tilled soils. Long‐term data on hydraulic properties, thermal properties, dry aggregate stability, and pore‐size distribution are scant. In general, CCs improve most soil physical properties, but the magnitude of improvement is highly site‐ and management specific.

Enhanced-efficiency phosphate fertilisers, diffusive flux of phosphorus and matric potential in Acrudox

Enhanced-efficiency phosphate fertilisers may play an important role in phosphorus (P) availability in tropical soils by increasing their concentration in solution and enhancing the diffusive flux of P (DFP). This work evaluated the DFP in soil influenced by polymer-coated phosphate fertilisers and organophosphates (enhanced-efficiency phosphate fertilisers) applied to soil, at two matric potentials. The experiment was conducted using a 4 × 2 × 4 + 2 factorial design in which four phosphate fertilisers (conventional monoammonium phosphate (MAP), polymer-coated monoammonium phosphate (POL), pelletised monoammonium phosphate with filter cake (FC) and granulated monoammonium phosphate with swine compost (SC)), two soil water contents corresponding to two matric potentials (–10 and –50 kPa), four anion exchange resin insertion distances (0.5, 1.0, 1.5 and 2.0 cm from the phosphate fertiliser granules) and two control treatments (matric potential of –10 and –50 kPa without fertiliser) were studied across four replicates. Enhanced-efficiency phosphate fertilisers increased the release of P into the soil solution. The values of DFP (nmol m–2 15 days–1) for MAP were in the range of 0.18–48.69, for POL were 0.19–32.20, for FC were 0.17–19.74 and for SC were 0.17–18.50. For –10 and –50 kPa matric potentials, the values ranged within 0.18–43.07 and 0.17–48.69 nmol m–2 15 days–1 respectively. In relation to the distances 0.5, 1.0, 1.5 and 2.0 cm, DFP (nmol m–2 15 days–1) ranged within 17.56–48.69, 0.42–11.39, 0.22–0.57 and 0.17–0.22 respectively. The decrease in the soil water matric potential decreased DFP in the short term for fertilisers with coating technologies compared to MAP. This result indicates that coating technologies hold promise for maintaining DFP over time.

Crop rotational diversity impacts soil physical and hydrological properties under long-term no- and conventional-till soils

Diversification of crop species and minimum mechanical soil disturbance are the interlinked principles of conservation agriculture that are beneficial in improving soil physical and hydrological properties, and hence crop productivity. The present study was conducted to assess the long-term impacts of crop rotational diversity and tillage on soil water infiltration (qs), soil water retention (SWR), pore size distribution (PSD), bulk density (ρb) and soil penetration resistance (SPR). The study was established in 1991 at Beresford, South Dakota, and included three crop rotation systems (2-year, maize (Zea mays L.)–soybean (Glycine max L.); 3-year, maize–soybean–wheat (Triticum aestivum L.); and 4-year, maize–soybean–wheat–oat (Avena sativa L.)) and two tillage systems (NT, no-tillage; and CT, conventional tillage). Soil samples were collected only under maize and soybean phases of the crop rotations. Our results showed that NT with 4-year rotation had the lowest ρb under maize and soybean phases (1.21 and 1.19 g cm–3 respectively) compared with the CT system. Similarly, NT with 4-year rotation decreased SPR by 20% compared to CT with 4-year rotation in the soybean phase. Soils managed under NT with 4-year rotation in the soybean phase retained 27, 28, 28, 32, 33, 31 and 26% more water compared with CT and 4-year system at 0–7.5 cm depth at 0, –0.4, –1.0, –2.5, –5.0, –10 and –30 kPa matric potentials respectively. A similar trend was observed for qs under the same treatments, in which it was 31% higher under NT than under CT, both with 4-year rotation. Data from this study showed that diversified crop rotation under NT enhanced soil physical and hydrological properties compared with CT with less diverse systems (e.g. maize–soybean).

Recalibration of Sensors in One of The World's Longest Running Automated Soil Moisture Monitoring Networks

Obtaining accurate soil moisture data from sensors in automated monitoring networks is critical as these data are increasingly used for research in soil hydrology, ecohydrology, and related disciplines. One of the earliest such networks is the Oklahoma Mesonet, which monitors soil matric potential using heat dissipation sensors. Various calibration equations have been proposed for those sensors, and there is a need to compare and validate the performance of those equations, especially for matric potentials &lt; –150 kPa. A laboratory experiment was conducted in silt loam soil using a sand‐kaolin box and a pressure plate apparatus with matric potentials ranging from 0 to –1500 kPa. The calibration equations included Starks’ equation, Flint et al.'s equation, Schneider et al.'s equation, and a new logistic equation. The upper limit of the sensors was ‐9 kPa, and the sensors remained responsive at ‐1500 kPa matric potential. The logistic equation produced the lowest root mean squared error (34 kPa), followed by Flint et al.'s equation (192 kPa), Starks’ equation (295 kPa), and Schneider et al.'s equation (463 kPa). After recalibration of the coefficients in the three preexisting equations, their performances improved, with all RMSE values ≤ 251 kPa; however, the logistic equation still provided superior accuracy. The logistic equation effectively removed an ∼ 0.02 cm3 cm−3 positive bias in soil water content that resulted from use of the original parameterization of Schneider et al.'s equation. This logistic equation is recommended for use with past and future data from the Oklahoma Mesonet's heat dissipation sensors.Core Ideas Soil matric potential data from the Oklahoma Mesonet are widely used. Those data are estimated using a calibration equation shown here to be inaccurate. The logistic equation developed here produces more accurate matric potential estimates.

Effect of sepiolite and palygorskite on plant available water in Arenosols of Namaqualand, South Africa

Sepiolite and palygorskite (attapulgite) are fibrous magnesium silicate clay minerals renowned industrially for their water-holding and sorptive capacities. They are only stable in arid region soils, which are regions where water is the limiting factor for agriculture and where ecosystems are the most dependent on soil as a medium for storage and timely release of water. The aim of this study is to determine how the presence of sepiolite and palygorskite affect the plant available water in sandy soils of the Namaqualand region in arid northwestern South Africa, an area where these clay minerals are present and where sepiolite is in some places present in high enough concentration to be detected by XRD in the bulk soil. The data for the water holding capacity of the soils, their mineralogy, organic carbon, CEC, soluble sodium, conductivity, resistivity and texture were extracted from the Land Type Survey records for each horizon and analyzed for statistically significant relationships. The results showed that the plant available water (defined as the difference between the water held at field capacity (−33 kPa matric potential) and water held at −500 kPa, the permanent wilting point) increases significantly with increasing CEC and clay content and decreases significantly with increasing medium sand. The presence of sepiolite in the Namaqualand soils is associated with both higher plant available water and higher amount of water held at wilting point for a given texture class (clay and medium sand) or CEC. This is significant (p > 0.001) for soils where the medium sand content is > 50%, suggesting that the effect of sepiolite on plant available water is positive for plant growth in sandy soils. In contrast, palygorskite-containing Namaqualand soils showed a lower plant available water than for a given texture or CEC, but this was not apparent for the water content at wilting point. Gypsum was not associated with a higher plant available water, even though gypsum-containing soils had significantly higher water at the permanent wilting point. The fact that sepiolite is associated with higher plant available water content in sandy soils signifies that it is a water storing mechanism available to plants in these areas, with a potential for impact on the biodiversity and land use.

Computed tomography as an extension of classical methods in the analysis of soil compaction, exemplified on samples from two tillage treatments and at two moisture tensions

Some soil physical properties can easily be measured using classical laboratory methods. However, explicit valuable information on the real morphology of the pore structure as well as soil physical properties cannot be obtained at the same time with classical methods. This requires non-destructive measurements such as X-ray computed tomography (CT).However, explicit valuable information on the real morphology of the pore structure as well as soil physical properties cannot be obtained at the same time with classical methods.This paper combines parameters obtained from CT analysis (mean macropore diameter, macroporosity, pore connectivity, anisotropy) and classical laboratory methods (dry bulk and aggregate density, saturated hydraulic conductivity, mechanical precompression stress) to analyse soil compaction, exemplified on samples from two tillage treatments (cultivator and plough) and at two moisture states (6 and 1000 kPa matric potential) on a Chernozem collected at a soil depth of 16–22 cm (texture 0–30 cm: silty clay loam).The study shows that the matric potential can have a decisive impact on the mechanical stability of soil. In the loose but less stable plough treatment a more negative matric potential was clearly beneficial to the mechanical stability. In already dense soil structures, as in the cultivator treatment, a reduction of water content was less effective in increasing soil stability.The CT parameters were all closely and uniquely related to each other. The shown CT parameters can be used for a standardized characterization of the soil. Ploughing has a positive effect on soil structure which persists only as long as macroporosity and mean macropore diameter remain high. Plough maintains higher pore connectivity when compacted under dry conditions.

Soil hydrological properties as influenced by long‐term nitrogen application and landscape positions under switchgrass seeded to a marginal cropland

AbstractSwitchgrass (Panicum virgatum L.) has the potential to recover the soil hydrological properties of marginal lands. Nitrogen (N) and landscape position are the key factors in impacting these soil properties under switchgrass. The specific objective of this study was to investigate the responses of N rate (low, 0 kg N/ha and high, 112 kg N/ha) and landscape positions (shoulder and footslope) on near‐surface soil hydrological properties that included: infiltration rate (qs), saturated hydraulic conductivity (Ksat), bulk density (ρb), penetration resistance (SPR), water retention (SWR), pore‐size distribution (PSD), and carbon (C) and nitrogen (N) fractions under switchgrass production. Data showed that, in general, the N and landscape position significantly influenced soil hydrological properties. Higher N rate decreased ρb (1.23 and 1.36 g/cm3 at 0–5 and 5–15 cm, respectively) and SPR (1.06 and 1.53 MPa at 0–5 and 5–15 cm, respectively) at both depths and increased the qs, Ksat and Green–Ampt estimated sorptivity (S) and hydraulic conductivity (Ks) parameters, and SWR (0–5 cm depth) at 0 and −0.4 kPa matric potentials (ψm). Furthermore, footslope position significantly decreased ρb, SPR at 0–5 and 5–15 cm depths, and increased the qs, Ksat, S, Ks, and SWR (0–5 cm depth) at every ψm ranged from 0 to −30.0 kPa. The higher N rate increased the coarse mesopores (60–1,000 μm) and total pores, whereas, footslope position increased the coarse mesopores, micropores (&lt;60 μm), and total pores. Data from this study showed that planting switchgrass with 112 kg N/ha under footslope position helped in improving the soil hydrological properties, those can be beneficial in enhancing the biomass yield under marginal lands.

Impact of Successive Wetting and Drying Cycles on Some Physical Properties of Gypsifereous Soils

A laboratory experiment was carried out to quantify the impact of three wetting-drying cycles onphysical and mechanical properties of gypsifereous soils such as bulk density, penetration resistance, drying index, shrinkage limit and pore geometry changes.The soil gypsum content treatments were 60.0 (G 1 ), 137.6 (G 2 ), 275.2 (G 3 ), 314.2 (G 4 ), 486.0 (G 5 ), 688.3 (G 6 ) and 860.0 (G 7 ) g.kg -1 . Soil samples were equilibrated to a matric potential -4.9, -9.8, -34 and -1500 kPa after saturation for each wetting-drying cycle. Peak cone index values showed that besides water content and bulk density, penetration resistance was positively affected by gypsum content. Drying index values at 1200 kPa matric potential were increased from 79.96% to 96.50% for the soils with gypsum content G 1 to G 7 .

Rhizosphere‐Scale Quantification of Hydraulic and Mechanical Properties of Soil Impacted by Root and Seed Exudates

Core Ideas We hypothesized that plant exudates gel soil particles and on drying enhance water repellency. This has been carried out using rhizosphere‐scale mechanical and hydraulic measurements. Plant exudates enhanced soil hardness and modulus of elasticity as chia seed &gt; maize root &gt; barley root. Plant exudates caused measureable decreases in soil wetting rates through water repellency. Using rhizosphere‐scale physical measurements, we tested the hypothesis that plant exudates gel together soil particles and, on drying, enhance soil water repellency. Barley (Hordeum vulgare L. cv. Optic) and maize (Zea mays L. cv. Freya) root exudates were compared with chia (Salvia hispanica L.) seed exudate, a commonly used root exudate analog. Sandy loam and clay loam soils were treated with root exudates at 0.46 and 4.6 mg exudate g−1 dry soil and chia seed exudate at 0.046, 0.46, 0.92, 2.3 and 4.6 mg exudate g−1 dry soil. Soil hardness and modulus of elasticity were measured at −10 kPa matric potential using a 3‐mm‐diameter spherical indenter. The water sorptivity and repellency index of air‐dry soil were measured using a miniaturized infiltrometer device with a 1‐mm tip radius. Soil hardness increased by 28% for barley root exudate, 62% for maize root exudate, and 86% for chia seed exudate at 4.6 mg g−1 concentration in the sandy loam soil. For the clay loam soil, root exudates did not affect soil hardness, whereas chia seed exudate increased soil hardness by 48% at 4.6 mg g−1 concentration. Soil water repellency increased by 48% for chia seed exudate and 23% for maize root exudate but not for barley root exudate at 4.6 mg g−1 concentration in the sandy loam soil. For the clay loam soil, chia seed exudate increased water repellency by 45%, whereas root exudates did not affect water repellency at 4.6 mg g−1 concentration. Water sorptivity and repellency were both correlated with hardness, presumably due to the combined influence of exudates on the hydrological and mechanical properties of the soils.

Plant exudates may stabilize or weaken soil depending on species, origin and time.

SummaryWe hypothesized that plant exudates could either gel or disperse soil depending on their chemical characteristics. Barley (Hordeum vulgare L. cv. Optic) and maize (Zea mays L. cv. Freya) root exudates were collected using an aerated hydroponic method and compared with chia (Salvia hispanica L.) seed exudate, a commonly used root exudate analogue. Sandy loam soil was passed through a 500‐μm mesh and treated with each exudate at a concentration of 4.6 mg exudate g−1 dry soil. Two sets of soil samples were prepared. One set of treated soil samples was maintained at 4°C to suppress microbial processes. To characterize the effect of decomposition, the second set of samples was incubated at 16°C for 2 weeks at −30 kPa matric potential. Gas chromatography–mass spectrometry (GC–MS) analysis of the exudates showed that barley had the largest organic acid content and chia the largest content of sugars (polysaccharide‐derived or free), and maize was in between barley and chia. Yield stress of amended soil samples was measured by an oscillatory strain sweep test with a cone plate rheometer. When microbial decomposition was suppressed at 4°C, yield stress increased 20‐fold for chia seed exudate and twofold for maize root exudate compared with the control, whereas for barley root exudate decreased to half. The yield stress after 2 weeks of incubation compared with soil with suppressed microbial decomposition increased by 85% for barley root exudate, but for chia and maize it decreased by 87 and 54%, respectively. Barley root exudation might therefore disperse soil and this could facilitate nutrient release. The maize root and chia seed exudates gelled soil, which could create a more stable soil structure around roots or seeds.Highlights Rheological measurements quantified physical behaviour of plant exudates and effect on soil stabilization.Barley root exudates dispersed soil, which could release nutrients and carbon.Maize root and chia seed exudates had a stabilizing effect on soil.Physical engineering of soil in contact with plant roots depends on the nature and origin of exudates.

Plant exudates improve the mechanical conditions for root penetration through compacted soils

Background and aimPlant exudates greatly affect the physical behaviour of soil, but measurements of the impact of exudates on compression characteristics are missing. Our aim is to provide these data and explore how plant exudates may enhance the restructuring of compacted soils following cycles of wetting and drying.MethodsTwo soils were amended with Chia (Salvia hispanica) seed exudate at 5 concentrations, compacted in cores to 200 kPa stress (equivalent to tractor stress), equilibrated to −50 kPa matric potential, and then compacted to 600 kPa (equivalent to axial root stress) followed by 3 cycles of wetting and drying and recompression to 600 kPa at −50 kPa matric potential. Penetration resistance (PR), compression index (CC) and pore characteristics were measured at various steps.ResultsPR decreased and CC increased with increasing exudate concentration. At 600 kPa compression, 1.85 mg exudate g−1 soil increased CC from 0.37 to 0.43 for sandy loam soil and from 0.50 to 0.54 for clay loam soil. After 3 wetting-drying cycles the clay loam was more resillient than the sandy loam soil, with resilience increasing with greater exudate concentration. Root growth modelled on PR data suggested plant exudates significantly eased root elongation in soil.ConclusionPlant exudates improve compression characteristics of soils, easing penetration and enhancing recovery of root induced soil compaction.

PORE SIZE DISTRIBUTION AND SOIL HYDRO PHYSICAL PROPERTIES UNDER DIFFERENT TILLAGE PRACTICES AND COVER CROPS IN A TYPIC HAPLUSULT IN NORTHERN NIGERIA

&lt;p&gt;Tillage practices influence soil physical, chemical and biological qualities which in-turn alters plant growth and crop yield. In the Northern Guinea Savanna (NGS) ecological zone of Nigeria, agricultural production is mainly constrained by low soil nutrient and water holding capacity, it is therefore, imperative to develop appropriate management practices that will give optimal soil hydro-physical properties for proper plant growth, effective soil and water management and environmental conservation.&lt;strong&gt; &lt;/strong&gt;This study investigated the effect of three tillage practices (no till, reduced till and conventional till) and four cover crops (&lt;em&gt;Centrosema pascuorum, Macrotyloma uniflorum, Cucurbita maxima &lt;/em&gt;and &lt;em&gt;Glyine max&lt;/em&gt;) and a bare/control (no cover crop) on some soil physical properties of a Typic Haplusult during the rainy seasons of 2011, 2012 and 2013 in Samaru, NGS ecological zone of Nigeria. The field trials were laid out in a split plot arrangement with tillage practices in the main plots and cover crops in the subplots, all treatments were replicated three times. Auger and core soil samples were collected at the end of each cropping season each year in three replicates from each treatment plot at four depths (0-5, 5-10, 10-15 and 15-20 cm). Particle size distribution, bulk density, total pore volume and water retention at various soil matric potentials were determined using standard methods. Data obtained were compared with optimum values and fitted into a RETC computer code for quantifying soil hydraulic behavior and physical quality. Results showed that different tillage practices had varied effect on soil physical properties. No-till had the highest water holding capacity at most suction points evaluated, it had 4.3 % and 12.9 % more soil moisture than the reduced till and conventionally tilled systems across all matric potentials while &lt;em&gt;Centrosema pascuorum&lt;/em&gt; (3.1%) and &lt;em&gt;Cucurbita maxima&lt;/em&gt; (5.5%) were best among evaluated cover crops in retaining soil moisture content compared to the bare plots at -33kPa matric potential. Generally the Dexter S value used as an index for soil physical quality ranged within the limits of very good to good soil physical quality irrespective of the tillage practice, cover crops grown or depth of soil sampling. However the conventional tillage practice and soil under no cover crop had adverse effect on soil structural stability, placing them at a high risk of soil degradation. Indicators like Macro porosity, Air capacity, relative field capacity and Plant available water capacity were all within the optimal range for normal plant growth. The RETC computer code well described soil hydraulic parameter regardless of the treatments imposed on the soil. &lt;/p&gt;

Rice straw biochar affects water retention and air movement in a sand-textured tropical soil

ABSTRACTDespite the current global attention on biochar (BC) as a soil amendment, knowledge is limited on how BC impacts the physical properties of coarse-textured soils (sand > 95%), particularly in tropical regions. A two-season field-study was conducted to investigate the effect of rice straw BC (3% w/w) on water retention, gas transport and structure of a sand-textured tropical soil. We sampled 3 months and 15 months after BC application and measured wet- and dry-region soil water retention, air permeability and gas diffusivity at selected matric potentials. At all measured potentials and for both sampling times, soil water retention was significantly higher (20–150%) for the BC treatment due to increased fraction of smaller pores (< 30 µm) at the expense of macropores (< 100 µm). Although there was no consistent effect of BC on air-filled porosity, BC significantly reduced air permeability and gas diffusivity (~20%) at −30 kPa matric potential. After 15-months, air permeability decreased by ~15% after BC amendment, but analyses of the pore structure revealed a more tortuous and complex soil structure. Thus, application of rice straw BC to similar coarse-textured soils will improve soil-water relations and over time provide better structure for agricultural purposes.

Response of Dry Seeded Rice to Sowing Dates, Irrigation Regimes and Cultivar Duration

Direct dry-seeded rice (DSR) is a resource conservation technology as it consumes less water, incurs low labour expenses and is suitable for mechanization. The aim of this study was to examine the combined effects of sowing time, irrigation regimes and cultivars on paddy yield and water productivity under dry-seeded rice in a semi-arid sub-tropical environment of north-west India. The treatments included combination of two sowing times (1st and 20th June) in main plots, three irrigation regimes-IW/Pan-E ratio of 2.4, 1.6 and-20 kPa matric potential in subplots and two cultivars (PR114/PR121 and PR115) in sub-sub plots. Paddy yield was 20 per cent higher with I2.4 and I20kPa irrigation regimes over I1.6 while utilizing 248 mm more irrigation water. The cultivar PR115 was found to be suitable for dry direct seeding rice being highest yielder among tested cultivars under both of the sowing dates in addition to saving 110 mm irrigation water. PR115 accumulated higher biomass, and had more number of grains per panicle and grain weight compared to PR114. The irrigation water productivity was higher by 5.9 kg ha−1 mm−1 in PR115 than PR114/PR121 which registered 3.1/2.7 kg ha−1 mm−1. Among irrigation regimes, it was higher in I1.6 as compared with I2.4 and I20kPa. The optimum irrigation schedule for dry-direct seeded rice was found to be I2.4 and I20kPa in terms of paddy yield.