Micromorphological and mineralogical components of surface sealing in loess soils from different geographic regions

Mineralogy of clay sized particles and rainstorm characteristics are among the major factors that determine the nature of soil sealing. This research was designed to further our knowledge about the role of clay mineralogy and rainstorm characteristics on crust formation. Four loess soils from different geographic locations (Canada, USA, China, and Belgium) were used in this study. Preliminary studies were carried out on Grenada Bt (USA), Lishi (China), and Bierbeek Bt (Belgium) horizons. Detailed infiltration and microscopic studies were performed only on the Bm1 horizon of the Saskatchewan soil, Canada and the Ap horizon of the Grenada soil, Mississippi, USA. Two levels of rainstorm were applied (∼ 40 and 80 mm h-1). While smectite was the major component in the Saskatchewan Bm 1 horizon, vermiculite and illite were found to be the dominant clay minerals in the Bt horizon of the Grenada soil. Formation of the washed layer together with thin lamellar crust coincided with the preferential movement of clay sized particles through runoff in both the Saskatchewan Bm1 and Grenada Ap horizons. The higher initial infiltration rate with higher rainfall intensity in both soils were likely due to higher matric suction, but rapid reduction in infiltration in this treatment was due to rapid aggregate destruction and a dense packing of the fundamental soil particles. No washed-in zone could be observed in the Bm1 horizon of the Saskatchewan soil in both rainstorm intensities. However, drastic reduction in infiltration, especially with high rainstorm intensity (after 7-8 min), was attributed mainly to the swelling of smectite in this soil material. Washed-in materials were visible in the Ap horizon of Grenada under high rainstorm intensity. Due to the presence of iron oxides and clay coatings, aggregates were stable and no sealing could be observed in the Grenada Bt and Bierbeek Bt materials. The degree of seal development in the Lishi soils was low. This was due to low clay and high carbonate contents. This study shows clearly that higher and continuous rainstorm intensity causes rapid seal development and as a result more erosion would occur, especially in the soils with high smectite content. © 1995.status: publishe

Micromorphological and mineralogical components of surface sealing in loess soils from different geographic regions

Mineralogy of clay sized particles and rainstorm characteristics are among the major factors that determine the nature of soil sealing. This research was designed to further our knowledge about the role of clay mineralogy and rainstorm characteristics on crust formation. Four loess soils from different geographic locations (Canada, USA, China, and Belgium) were used in this study. Preliminary studies were carried out on Grenada Bt (USA), Lishi (China), and Bierbeek Bt (Belgium) horizons. Detailed infiltration and microscopic studies were performed only on the Bm1 horizon of the Saskatchewan soil, Canada and the Ap horizon of the Grenada soil, Mississippi, USA. Two levels of rainstorm were applied (∼ 40 and 80 mm h-1). While smectite was the major component in the Saskatchewan Bm 1 horizon, vermiculite and illite were found to be the dominant clay minerals in the Bt horizon of the Grenada soil. Formation of the washed layer together with thin lamellar crust coincided with the preferential movement of clay sized particles through runoff in both the Saskatchewan Bm1 and Grenada Ap horizons. The higher initial infiltration rate with higher rainfall intensity in both soils were likely due to higher matric suction, but rapid reduction in infiltration in this treatment was due to rapid aggregate destruction and a dense packing of the fundamental soil particles. No washed-in zone could be observed in the Bm1 horizon of the Saskatchewan soil in both rainstorm intensities. However, drastic reduction in infiltration, especially with high rainstorm intensity (after 7-8 min), was attributed mainly to the swelling of smectite in this soil material. Washed-in materials were visible in the Ap horizon of Grenada under high rainstorm intensity. Due to the presence of iron oxides and clay coatings, aggregates were stable and no sealing could be observed in the Grenada Bt and Bierbeek Bt materials. The degree of seal development in the Lishi soils was low. This was due to low clay and high carbonate contents. This study shows clearly that higher and continuous rainstorm intensity causes rapid seal development and as a result more erosion would occur, especially in the soils with high smectite content. © 1995.status: publishe

Variability in the properties of soils on two toposequences in northern Ghana

The variability in the properties of five Lixisols _Tingoli, Tolon and Kumayili series on toposequence 1; Kpelesawgu and Changnalili series on toposequence 2 _ was studied to ascertain the natural differences in the soils. The Tingoli and Tolon series accumulate more in situ formed nodules with greater bulk density. Moisture storage is greater in the toposequence 2 soils because of poor internal drainage. Kaolinite is the dominant clay mineral in the toposequence 1 soils. Illite is dominant in the toposequence 2 soils, especially in the Changnalili series, serving as K reserve source. The nodules have high concentrations of haematite and goethite, implying greater maturity. Soils on toposequence 1 are more weathered with more pronounced desilication. Organic carbon accumulation and effective CEC in the toposequence 2 soils are relatively greater because of poor internal drainage, which hinders organic matter decomposition. The toposequence 1 soils show reddish colouration because of better internal drainage. Ghana Jnl agric. Sci. Vol.30(2) 1997: 115-12

Amounts of distribution of some forms of phosphorus in ferruginous soils of the interior savanna zone of Ghana l

The forms and distribution of phosphorus in three well-drained and two poorly drained, widely cultivated Lixisols on two landscapes in the interior savanna zone of Ghana were studied. Total phosphorus (TP) and dithionite-citrate-bicarbonate extractable P (DCB-P) concentrations increase with depth in all the soils and are related to profile maturity in the well-drained soils. In the low-lying soils, however, the concentration is governed by drainage. The greatest amounts of TP occur in the topsoils of the Tingoli series on Catena 1, which were 132, 92, 744, and 700 mg/kg in the fine earth, silt, clay, and nodule fractions, respectively. The Kpelesawgu series on Catena 2, however, has the least TP accumulation of 78, 159, and 50 mg/kg in the fine earth, silt, and clay fractions, respectively. The large concentration of TP and DCB-P in the nodules and clays is due to their greater sesquioxide contents. The available P concentration is extremely low because of the low content of P-bearing parent material. The amounts of clay, silt, and DCB-P may be used to estimate the accumulation of TP concentration in the soils. Variations in TP saturation correspond with changes in clay accumulation in the soils on Catena 1 and in silt content in the Catena 2 soils. Ghana Jnl agric. Sci. Vol.30(2) 1997: 135-14