Soil texture is an important factor governing a range of physical properties and processes in soil. The clay and fine fractions of soil are particularly important in controlling soil water retention, hydraulic properties, water flow and transport. Modern soil texture analysis techniques (x‐ray attenuation, laser diffraction and particle counting) are very laborious with expensive instrumentation. Chilled‐mirror dewpoint potentiameters allows for the rapid measurement of the permanent wilting point (PWP) of soil. As the PWP is strongly dictated by soil texture, we tested the applicability of PWP measured by a dewpoint potentiameter in predicting the clay, silt and sand content of humid tropical soils. The clay, silt, and sand content, organic matter and PWP were determined for 21 soils. Three regression models were developed to estimate the fine fractions and validated using independent soil data. While the first model showed reasonable accuracy (RMSE 16.4%; MAE 13.5%) in estimating the clay, incorporating the organic matter into the equation improved the predictions of the second model (RMSE 17.3%; MAE 10.9%). When used on all soil data, the accuracy of the third model in predicting the fine fraction was poor (RMSE 31.9%; MAE 24.5%). However, for soils with silt content greater than 30%, the model prediction was quite accurate (RMSE 7–12%; MAE 7–9%). The models were used to estimate the sand content and soil textures of soils, which proved relatively accurate. The dewpoint potentiometer can serve a dual purpose of rapidly estimating the PWP and the clay, fine fraction, and soil texture of soils in a cost efficient way. 相似文献
The cationic bridging effect of the calcium ion (Ca2+) and the flocculating ability of clay and organic matter are crucial in the formation and stability of soil aggregates. They are therefore likely to influence the soil's saturated hydraulic conductivity ( K s). We tested the individual effects of these factors on aggregate stability and related hydraulic properties, and studied the influence of clay mineralogy also. Samples from the surface (0–10 cm) of three contrasting soils in Trinidad were used. The soils were treated with three levels of Ca2+ and three levels of organic matter in a 3 × 3 × 3 factorial design and incubated for 14 days. Both aggregate stability and saturated hydraulic conductivity were influenced by all factor combinations. Interactions between soil type and Ca2+ revealed the importance of polyvalent cations in aggregate stability of soils with low activity minerals. The influence of organic matter varied with quantity; the more there was, the more stable the soil became, particularly in the soil containing little clay. Clay dispersion and slaking of expanding minerals occurred even with large additions of Ca2+ and organic matter, emphasizing the overall influence of mineralogy in determining the response of soils to stability treatments. 相似文献
Journal of Soils and Sediments - The unsustainable use of soil natural capital and ecosystem services is of global concern due to damage and losses on a worldwide scale. This situation is further... 相似文献
In the humid Caribbean region characterized by high-intensity tropical rainfall, soil aggregate breakdown and pore blocking due to slaking pressures are major land degradation mechanisms. In this research, we investigated the susceptibility of soils to slaking pressures under rapid wetting as influenced by soil properties and the depositional origin from which the soil is formed using water-stable aggregates (WSAr) and percolation stability (PSc) as indices of the strength of aggregate inter-particle cohesion.
Materials and methods
Wet sieving and percolation stability analyses were employed to investigate WSAr and pore blocking, respectively. The combined effect of soil properties of clay, organic matter (OM), cation exchange capacity (CEC), and exchangeable sodium percentage (ESP) was used to determine the slaking sensitivity score (SSc) of 14 physiogeographically important soils in Trinidad, comprising of nine alluvial and five residual soils.
Results and discussion
Results showed that irrespective of alluvial or residual depositional nature of the parent material, samples had high SSc with an average WSAr of 37.8% and PSc of 6.0 mm/10 min. The linear relationships between SSc with WSAr (r2?=???0.12) and SSc with PSc (r2?=???0.012) of all the 14 soils although negative were weak. Clay content accounted for 94.0% of the variation in CEC in alluvial soils and had strong negative relationships with WSAr (r2?=???0.74) and PSc (r2?=???0.79) in residual soils. Additionally, OM with WSAr (r2?=?0.52) and PSc (r2?=?0.24), and CEC with WSAr (r2?=?0.46) and PSc (r2?=?0.39) showed significant positive linear relationships in residual soil.
Conclusions
The predominantly micaceous and kaolinitic clay mineralogy of these soils, coupled with the low OM contents, increases the proneness of the soils to slaking. This suggests that clay mineralogy is responsible for the high slaking sensitivity rather than clay content or just the depositional origin of the soils. As CEC increases, an accompanying increase in OM is required to increase inter-particle cohesion and to impart partial hydrophobicity, which in turn decreases mineralogically induced susceptibility of individual aggregates to slaking.