Peter, Prince Chinedu2021-11-242021-11-242015http://hdl.handle.net/20.500.11837/1918Soil structure and its associated physical properties are essential soil components. Soil texture and mineralogy are inherent soil properties that influence soil management. This study assessed the implication of tillage, texture and mineralogy on soil sieving, aggregate stability indices and physical fractions of organic matter in soils of Eastern Cape Province of South Africa. An Iris FTLVH – 0200 digital electromagnetic sieve shaker (Filtra Vibraciόn SL Spain), was used to determine settings for sieving efficiency. Mean weight diameter (MWD), water stable aggregate (WSA), state of aggregation (SA), dispersion ratio (DR), water dispersible clay (WDC), clay dispersion ratio (CDR), clay flocculation index (CFI), and potential structural deformation index (PSDI) were aggregate stability indices evaluated to check for sensitivity in evaluating aggregate stability of soils under two tillage systems and physical fractions of carbon and nitrogen in soils of Eastern Cape Province. The T4I3P2 and T4I4P3 settings were sensitive under tillage and T4I1P4, T3I4P3 and T4I4P3 were sensitive under mineralogical considerations for sieving efficiency. The total carbon in soils under conventional tillage (CT) was 17.7 g/kg and in soils under no tillage (NT) it was 15.8 g/kg. The total carbon content in the clay fraction of soils under CT was 24.1 % higher than the total carbon content in the clay fraction of soils under NT. The total nitrogen content in the clay fraction of soils under CT was 5.4 % higher than the total nitrogen content in the soils under NT. The total carbon in the sandy loam (SL) textured soils was 17.4 g/kg and in the sandy clay loam (SCL) textured soils it was 17.1 g/kg. The total nitrogen in SL soils was 3.7 g/kg and in SCL soils it was 3.7 g/kg. The clay fraction had higher total carbon than other fractions in Sl and SCL soils. The higher values of nitrogen were observed in the silt fraction for SL soils and clay fraction for SCL soils. The total carbon in the soils dominated with kaolinite was 17.3 g/kg and in quartz dominated soils the value was 16.9 g/kg. The total nitrogen in the soils dominated with kaolinite was 3.7 g/kg and in the soils dominated with quartz the value was 3.7 g/kg. For soils under NT the WDC was 135.8 g/kg and for soils under CT it was 139.7 g/kg. The ASC was 72.5 for soils under NT and 92.0for soils under CT. The DR was 0.9 for soils under NT and 0.8 for soils under CT. The CFI was 0.5 for soils under NT and 0.5 for soils under CT. The CDR was 0.5 for soils under NT and 0.5 for soils under CT. The MWDw was 1.6 mm for soils under NT and 1.4 mm for soils under CT. The MWDd was 4.0 mm for soils under NT and 4.0 for soils under CT. The % WSA > 0.25 mm was 61.7 % for soils under NT and 56.2 % for soils under CT. The PSDI was 55.2 % for soils under NT and 61.15 % for soils under CT. The SA was 43.2 % for soils under NT and 37.89 % for soils under CT. The WDC was 125.7 g/kg for SCL soils and 151.4 g/kg for SL soils. The CDR was 0.5 for both SCL and SL soils. The DR was 0.9 for SCL soils and 0.8 for SL soils. The CFI was 0.5 for both SCL and SL soils. The ASC was 56.2 g/kg for SCL soils and 115 g/kg for SL soils. The MWDw was 1.5 mm for SCL soils and 1.4 mm for SL soils. The MWDd was 3.6 mm for SCL soils and 3.6 mm for SL soils. The % WSA > 0.25 mm was 53.0 % for SCL soils and 62.5 % for SL soils. The PSDI was 59.2 % for SCL soils and 59.7 % for SL soils. The SA was 33.6 % for SCL soils and 45.2 % for SL soils. The WDC was 313.3 g/kg for kaolinitic soils and 120.7 g/kg for quartz dominated soils. The CDR was 0.5 for kaolinitic soils and 0.5 for quartz dominated soils. The DR was 0.9 for kaolinitic soils and 0.8 for quartz dominated soils. The CFI was 0.5 for kaolinitic soils and 0.5 for quartz dominated soils. The ASC was 110.0 g/kg for kaolinitic soils and 101.7 g/kg for quartz dominated soils. The WSA > 0.25 mm was 57.3 % for quartz dominated soils and 68.4 % for kaolinitic soils. The MWDw was 1.6 mm for quartz dominated soils and 0.8 mm for kaolinitic soils. The MWDd was 3.6 mm for quartz dominated soils and 3.4 mm for kaolinitic soils. The PSDI was 56.3 for quartz dominated soils and 76.0 for kaolinitic soils. It was concluded that Tillage, texture and mineralogy influenced the result of the sieving operation using Iris FTLVH – 0200 digital electromagnetic sieve shaker (Filtra Vibraciόn SL Spain). Sieving efficiency attained for these soils varied with tillage and mineralogy. The aggregate size composition and distribution in soils of these ecotopes are a function of mineralogy rather than tillage. Tillage influenced Nitrogen in the physical fractions of these soils. Changes in nitrogen content due to tillage were expressed more in the silt fraction of the soils. Soils in these ecotopes showed tendency for slow nitrogen accumulation. Texture influenced the accumulation of carbon and nitrogen in these soils. Clay fraction was prominent in determining the amount of carbon and nitrogen in these soils. Tillage influenced the sensitivity of different aggregate stability indices in these soils. The indices WSA > 0.25 mm, SA, and MWDw were sensitive to detect differences in macro aggregate stability among tillage system in these soils. Micro aggregate stability indices were generally not sensitive in detecting expected differences among tillage systems in these soils. The micro aggregate stability indices DR and ASC were more sensitive in soils of different texture. The macro aggregate stability indices MWDw, MWDd and PSDI were not sensitive to detect difference in stability with texture. The SA and WSA > 0.25 mm indices were sensitive to detect differences in the stability of the soils with texture. The micro aggregate stability indices DR and WDC were sensitive in soils of different mineralogy. Clay fraction influenced the carbon content of these soils irrespective of mineralogy. The soils responded to different indices differently under different conditions of tillage, texture and mineralogy. Therefore caution must be exercised in adopting any index; it is however suggested to use the response of more than one index for any given conclusion. Further research on site specific measures to improve soil nitrogen retention in these soils is suggested to forestall green house gas emission. Also proper delineation of these ecotopes according to carbon response to tillage, texture and mineralogy for enhanced carbon sequestration measures is recommended.en-USThesis