Lowest matric potential in quartz: Metadynamics evidence

The lowest matric potential is an important soil property characterizing the strength of retaining water molecules and a key parameter in defining a complete soil water retention curve. However, the exact value of the lowest matric potential is still unclear and cannot be measured due to the limitation of current experimental technology. In this study, a general theoretical framework based on metadynamics was proposed to determine the lowest matric potential in quartz minerals. The matric potential was derived from partial volume free energy and can be further calculated by the difference between the adsorption free energy and self‐hydration free energy. Metadynamics was employed to enhance molecular dynamics for determination of the adsorption free energy. In addition to the water‐mineral interaction, the adsorptive water layer structure was identified as an important mechanism that may lower the free energy of water molecules. The lowest matric potential for quartz mineral was found as low as −2.00 GPa

Wappfruit: a project for the optimisation of water use in agriculture

The WAPPFRUIT project is related to the optimisation of irrigation techniques in the Piemonte Region, Northwest Italy. The main goal is to control irrigation to understand if it is possible to reduce the volume of water used for irrigation and also save energy. The project involves several stakeholders, among which Politecnico and the University of Torino, Piemonte Region, Agrion Foundation for research in agriculture, and three farms (two apple orchards and one Actinidia orchard). The optimisation relies on soil matric potential measurements at several soil depths. The irrigation will be triggered using a particular algorithm which is based on a system of matric potential thresholds at the depths of 20 and 40 cm. These thresholds are based on soil texture, and vegetation species (including root depth). Each orchard is divided into two parts: an “experimental area” where the irrigation algorithm will be tested, and an area that will be irrigated as usual by farmers. Each orchard is equipped with four to six measurement nodes, with soil water content and soil matric potential profile having measures at 20, 40, and 60 cm of depth. The retention curves, as well as the spatial and temporal variability of soil water content and soil matric potential, can be inferred from measures, which reveal high volumes of water used for irrigation (frequently the soil was near saturation conditions). In addition, all the soils show, in the retention curves, a hysteresis due to wetting/drying cycles. The farmers continued to irrigate as usual in the two parts of the fields up to October 2022. Hence, to investigate the matric potential behavior and identify good estimates of thresholds, modeling approaches are important for the simulation of soil without irrigation, to understand when water stress conditions could occur. To this purpose, two models are used to simulate the water fluxes in the atmosphere and the soil (and, particularly, the matric potential). The two models adopted are the hydrological model Hydrus 1D and the land-surface model CLM5. Forcing the models with the precipitation summed to irrigation of the fields, Hydrus, in its 1D formulation did not yield reliable results, although more studies are needed to fully understand the causes for the misrepresentation. The CLM model yields instead more reliable outcomes. The CLM model is then used to simulate the behavior of the soil matric potential under the hypothesis of no irrigation. The results illustrate that the matric potential threshold for triggering irrigation could be around -50 kPa at 20 cm, whereas the threshold at 40 cm for the deactivation of irrigation could be around -40 kPa for the sites with apple orchards. The site with Actinidia could have the aforementioned thresholds equal to -40 kPa at 20 cm and -30 kPa at 40 cm

Evaluating the Effect of Woodchips on Soil Matric Potential, Temperature, Weed Biomass, and Yield of Selected Crops

Organic mulches are very popular for weed control in sustainable agricultural systems where the application of synthetic herbicides is restricted. A study was conducted to evaluate the effectiveness of organic mulch in controlling weeds, enhancing soil matric potential, and soil temperature. Blended hardwood mulch was applied to the soil surface at a thickness of 10 cm. The experimental design was laid out as a completely randomized design with two treatments, viz., mulch and no-mulch, replicated 5 times. Data were collected during the growing period for weed biomass, soil matric potential, soil temperature, and yield of selected crops. Results from a two-way ANOVA revealed that the mulch treatments significantly (p≤0.50) reduced weed biomass, and soil temperature while increasing the soil matric potential and yields of okra, tomatoes, squash, and basil. It was concluded that the use of organic mulch was beneficial for weed control and increasing crop yield

An estimate of energy dissipation due to soil-moisture hysteresis

Processes of infiltration, transport and outflow in unsaturated soil necessarily involve the dissipation of energy through various processes. Accounting for these energetic processes can contribute to modelling hydrological and ecological systems. The well-documented hysteretic relationship between matric potential and moisture content in soil suggests that one such mechanism of energy dissipation is associated with the cycling between wetting and drying processes. Working from a time-series of soil moisture content data (taken in the south-west of Ireland), and making rather straightforward assumptions regarding the hysteretic relationship mentioned, the average rate of energy dissipation was found to be O(10−5)

Prediction of biopore- and matrix-dominated flow from X-ray CT-derived macropore network characteristics

Peer reviewedPublisher PD

Effects of osmotic and matric potential on radial growth and accumulation of endogenous reserves in three isolates of Pochonia chlamydosporia

For the first time, the effects of varying osmotic and matric potential on fungal radial growth and accumulation of polyols were studied in three isolates of Pochonia chlamydosporia. Fungal radial growth was measured on potato dextrose agar modified osmotically using potassium chloride or glycerol. PEG 8000 was used to modify matric potential. When plotted, the radii of the colonies were found to grow linearly with time, and regression was applied to estimate the radial growth rate (mm day-1). Samples of fresh mycelia from 25-day-old cultures were collected and the quantity (mg g-1 fresh biomass) of four polyols (glycerol, erythritol, arabitol and mannitol) and one sugar (glucose) was determined using HPLC. Results revealed that fungal radial growth rates decreased with increased osmotic or matric stress. Statistically significant differences in radial growth were found between isolates in response to matric stress (P<0.006) but not in response to osmotic stress (P=0.759). Similarly, differences in the total amounts of polyols accumulated by the fungus were found between isolates in response to matric stress (P<0.001), but not in response to osmotic stress (P=0.952). Under water stress, the fungus accumulated a combination of different polyols important in osmoregulation, which depended on the solute used to generate the stress. Arabitol and glycerol were the main polyols accumulated in osmotically modified media, whereas erythritol was the main polyol that was accumulated in media amended with PEG. The results found that Pochonia chlamydosporia may use different osmoregulation mechanisms to overcome osmotic and matric stresses

Seasonal variation in soil and plant water potentials in a Bolivian tropical moist and dry forest

We determined seasonal variation in soil matric potentials (¿soil) along a topographical gradient and with soil depth in a Bolivian tropical dry (1160 mm y-1 rain) and moist forest (1580 mm y-1). In each forest we analysed the effect of drought on predawn leaf water potentials (¿pd) and drought response (midday leaf water potential at a standardized ¿pd of -0.98 MPa; ¿md) of saplings of three tree species, varying in shade-tolerance and leaf phenology. ¿soil changed during the dry season and most extreme in the dry forest. Crests were drier than slopes and valleys. Dry-forest top soil was drier than deep soil in the dry season, the inverse was found in the wet season. In the moist forest the drought-deciduous species, Sweetia fruticosa, occupied dry sites. In the dry forest the short-lived pioneer, Solanum riparium, occupied wet sites and the shade-tolerant species, Acosmium cardenasii drier sites. Moist-forest species had similar drought response. The dry-forest pioneer showed a larger drought response than the other two species. Heterogeneity in soil water availability and interspecific differences in moisture requirements and drought response suggest great potential for niche differentiation. Species may coexist at different topographical locations, by extracting water from different soil layers and/or by doing so at different moments in tim