Many soils and other porous media exhibit dual- or multi-porosity type features. In a previous study (Seki et al., 2022) we presented multimodal water retention and closed-form hydraulic conductivity equations for such media. The objective of this study is to show that the proposed equations are practically useful. Specifically, dual-BC (Brooks and Corey)-CH (common head) (DBC), dual-VG (van Genuchten)-CH (DVC), and KO (Kosugi)1BC2-CH (KBC) models were evaluated for a broad range of soil types. The three models showed good agreement with measured water retention and hydraulic conductivity data over a wide range of pressure heads. Results were obtained by first optimizing water retention parameters and then optimizing the saturated hydraulic conductivity (Ks) and two parameters (p, q) or (p, r) in the general hydraulic conductivity equation. Although conventionally the tortuosity factor p is optimized and (q, r) fixed, sensitivity analyses showed that optimization of two parameters (p + r, qr) is required for the multimodal models. For 20 soils from the UNSODA database, the average R2 for log (hydraulic conductivity) was highest (0.985) for the KBC model with r = 1 and optimization of (Ks, p, q). This result was almost equivalent (0.973) to the DVC model with q = 1 and optimization of (Ks, p, r); both were higher than R2 for the widely used Peters model (0.956) when optimizing (Ks, p, a, ω). The proposed equations are useful for practical applications while mathematically being simple and consistent.
Lowered stability of soil aggregates governed by insufficient organic matter levels has become a major concern in Sri Lanka. Although the use of organic manure with water repellent properties lowers the wetting rates and improves the stability of soil aggregates, its effects on soil hydrophysical properties are still not characterized. Therefore, the objective of this study was to examine the relation of water repellency induced by organic manure amendments to the water entry value and water retention of a Sri Lankan Ultisol. The soil was mixed with ground powders of cattle manure (CM), goat manure (GM), Gliricidia maculata (GL) and hydrophobic Casuarina equisetifolia (CE) leaves to obtain samples ranging from non-repellent to extremely water repellent, in two series. Series I was prepared by mixing GL and CE with soil (5, 10, 25, 50%). Series II consisted of 5% CM, GM, and GL, with (set A) and without (set B) intermixed 2% CE. Water repellency, water entry value, and water retention of samples were determined in the laboratory. Soilwater contact angle increased with increasing organic matter content in all the samples showing positive linear correlations. Although the samples amended with CE showed high soil-water contact angles in series I, set A (without 2% CE) and set B (with 2% CE) in series II did not show a noticeable difference, where >80% of the samples had soilwater contact angles <90°. Water entry value (R2 = 0.83-0.92) and the water retention at 150 cm suction (R2 = 0.69-0.8) of all the samples increased with increasing soil-water contact angles showing moderate to strong positive linear correlations. However, set A (without 2% CE) and set B (with 2% CE) in series II did not differ noticeably. Water entry value of about 60% the samples was <2.5 cm. Mixing of a small amount (2%) of hydrophobic organic matter with commonly used organic manures slightly increased the water repellency of sample soils, however not up to detrimental levels. It did not generate adverse effects on water entry and increased the water retention. It was clear that intermixing of small quantities of hydrophobic organic manure with organic manures commonly used in Sri Lankan agriculture, would not generate unfavorable impacts on soils.
Detailed data on the long-term performance of bioretention cells (BC) for stormwater management are sparse. This research aimed at setting up and testing an infrastructure that will provide the data on hydrologic and chemical performance of BC. Two identical experimental BC’s were built. The monitoring methodology monitoring was developed and tested during a first growing season with the first BC supplied with natural rainfall, while the second BC was used for ponding experiments. Key layer of the BCs, a biofilter, was composed of sand, compost and topsoil. Both BCs are equipped with sensors monitoring the components of water balance and the water potential of the biofilter. High levels of total suspended solids were detected in the outflow. The runoff coefficient for the entire period of the growing season was 0.72 in the first BC and 0.86 in the second BC, while the peak outflow reduction for individual rainfall episodes ranged between 75% to 95% for the first BC and 19% to 30% for the second BC. Saturated hydraulic conductivity of the biofilter in the first BC decreased by two orders of magnitudes after the first year of operation. Retention curves of the biofilter changed due to material consolidation.
Vodní retenční kapacita půd závisí na mnoha faktorech, z nichž nejdůležitější jsou textura, struktura, obsah a kvalita organické hmoty, aktivita a diverzita půdních organismů, pórovitost a hloubka půdního profilu. Článek je zaměřen na roli půdní organické hmoty a půdních organismů. Ukazuje, že v České republice jsou zemědělské půdy ochuzeny o organickou hmotu v průměru o 50%. Půdy z horských a podhorských oblastí jsou na ochuzení náchylnější než půdy v nižších nadmořských výškách. Diskutuje opatření vedoucí ke zvýšení kvality půd., Water retention capacity depends on many factors, of which soil texture, structure, organic matter content and quality, functioning of soil fauna and microflora, pore size and distribution, soil depth and properties of subsurface horizons are of the highest importance. We discuss the importance of soil organic matter and the key role played by soil microflora and fauna. We also document a reduction in organic matter and microbial biomass contents in the arable soils of the Czech Republic. On average, soil organic matter in arable soils is depleted by 50 %. The possibilities of improving the quality of arable soils are discussed., and Hana Šantrůčková, Stanislav Malý, Emil Cienciala.