Aggregates are part of the structure of the soil and are the way in which sand silt and clay all bond together. They can consist of fine single grains or dense masses or material bonded together. Inside aggregates there are pores and these vary in size depending on the structure (the way in which the soil material is arranged). The way the soil is structure has a profound effect on the way processes take place and their pace (Ashman & Puri, 2002, p. 31).
‘Cations’ and ‘Anions’ are released into the soil after weathering and decomposition have taken place. Cations are positive and anions are negative (Ashman & Puri, 2002, p. 55), the ability of the soil to absorb cations is referred to as the Cation Exchange Capacity (CEC). CEC is the total negative charge per unit weight of soil. Soils that have high CEC are more likely to have high concentrations of colloidal particles, particularly clay minerals and organic matter and a neutral to high pH (>7) (Ashman & Puri, 2002, p. 56). Soil colloids include clay minerals, hydrous oxides or iron and aluminium, amorphous material and humus. Cation exchange occurs where these particles have large surface areas and an electrostatic charge which is negative. Positive cations K+, Ca2+ and Mg2+ are known as the base metals and these are the nutrients that are supplied to plants through cation exchange (Ashman & Puri, 2002, p. 57) as they bond with the negative anions. Base saturation is the % of the CEC occupied by these cations. There are many variables that can affect the CEC of a soil and these are further explained using pine and oak ecosystems.
Field Methodology
Figure 2. Pine Forest Figure 3. Oak Forest
Figure 4. 15m x 15m Plot
Figure 5. Measuring Tree Height
Figure 6. Removing Excess Vegetation Figure 7. Shovel Width to Dig Sample Site
Figure 8. Change in Soil Horizons Figure 9. Soil Sample Removed For Horizon ‘A’
Figure 10. Obtaining Horizon ‘B’ Soil Figure 11. Soil Samples
Laboratory Methodology
Figure 12. Variety of Samples before Weighing
Figure 13. 5g of Soil ready for Tube
Figure 14. The Shaker
Figure 15. Separating the Sand from Silt and Clay Figure 16. Separated Soils
Figure 17. Oven Dried Sand Figure 18. Laser to Determine Material Size
Data Description and Analysis
Pine Forest Description
Oak Forest Description
The above two tables provides brief descriptions about the sites and their soil horizons. The colour of the soils was described used the Munsell Colour Chart which provides us with the hue (spectral colour), value (lightness/darkness) and chroma (strength/purity) of the soil. The colour descriptions suggest that for both ecosystems there is intimate mixing of organic and inorganic soils but in some small areas there are high levels of organic content, peat and manganese crystals. The two sites begin to differ for their B horizons. Pine soil shows little organic matter suggesting there is a domination of quartz sand but there is still both organic and inorganic matter. Oak B suggests there is strong mixing of the organic and inorganic material. Our observations suggest that the soil in the pine ecosystem is coarser that that of the oak soil. Pine soil consists of individual grains of sand while in the oak ecosystem there is a thick consistency of clay. Roots in the oak forest could be due to small shrubs and plants on the ground while the thick layer of material on the surface of the ground in the pine forest suggests the litter is most likely to have fallen from the pine trees. In general there were more clasts in the pine forest rather than the oak; this indicates the presence of aggregates which also suggests there is a wider combination of soil types and structure in the pine forest. The nearest neighbour analysis suggests that both forests have a random distribution of trees even though the pine forest has over 5 times the amount.
Graph 1 Graph 2
Graph 1 shows that on average the A horizons in both woodland horizons have a much higher mean than that of the B horizons with much larger spreads. This shows that there was more organic content in the A horizons for both woodlands because there is a significant loss in variation between the A and B horizons and the mean is much lower in the B horizons, a decrease by approximately 11% organic matter in oak and a vast approximate 24% decrease for pine. Across all of the soil samples there was a much larger range of % organic matter for the A horizons showing that there wasn’t an equal amount of organic matter in each 15m2 area, however oak A shows a positive distribution. B horizons have a very small spread meaning the amount of organic matter in the B horizon for roughly the same throughout the soil samples.
Graph 2 shows the level of CEC (meq/100g of soil) for each woodland horizon. Generally the spread for this data is much smaller for the A horizons but larger for the B horizons. The data however, follows a similar pattern as the previous graph suggesting that the amount of organic matter in the soil affects the CEC. Apart from one outlier in pine A, Oak A has the highest level of CEC and Oak B has a significant amount of CEC as well. This could be down to the material in the soil as it is primarily clay material which supports Ashman and Puri’s (2002, p.57) theory that the positive base metals are attracted to the negative anions, and clay being a major negative colloidal material attracts these nutrients increasing the level of CEC.
Graph 3
Graph 4
Graph 5
Scatter Plot 1
Scatter Plot 2
Scatter Plot 3
Scatter Plot 4
Scatter Plot 5
Discussion of Findings
(process links between CEC and other soil variables.
IS PINE SOIL ACIDIC?!
Lower levels of microbial activities, coupled with organic matter that is difficult to compose can led to teh accumulation of plant residues in a black coloured layer in the top few centimetres of the soil (page 10 ashman and puri.
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oak in clay because it retains more water for the oak to suck up. HOW COLOUR SUGGETS AMOUNT OF ORGANIC AND INORGANIC MATERIAL!!
A clay rich pasture soil will have a far higher CEC than an acidic sandy textured soil (Ashman & Puri, 2002, p. 56)
Soils have varied retentive properties depending on their texture, organic matter content, and cation exchange capacity (CEC). ABOUT WATER IN THE OAK PLACE!!
Soil texture effect on nitrate leaching in soil percolates
Communications in Soil Science and Plant Analysis
1994, Pages 2561 - 2570
Authors: T. P. Gainesa; S. T. Gainesa
DOI: 10.1080/00103629409369207
Conclusions
References
Ashman, M.M., & Puri, G. (2002). Essential Soil Science. Oxford: Blackwell Publishing.
Oak Tree Culture. 2010. Retrieved May 5, 2010, from Garden Action website: http://www.garden
action.co.uk/trees/quercus/oak-trees-1.asp
Leeper, G.W., & Uren, N.C. (1993). Soil Science (5th ed.) Victoria: Melbourne University Press.
McBride, M.B. (1994). Environmental Chemistry of Soils. Oxford: Oxford University Press.