Part A: Physical Properties of Soil – Soil Colour, Soil Texture, and Soil Struct
ID: 289744 • Letter: P
Question
Part A: Physical Properties of Soil – Soil Colour, Soil Texture, and Soil Structure 1. Explain how soil texture is related to soil surface area? Why is this relationship important? (5 marks) 2. Referring to the textural triangle on the right. What approximate range in percentage silt could each of the textural classes contain if: (10 marks)
HC is 70% clay % silt =
SiC is 50% clay % silt =
C is 30% sand % silt =
SiCL is 30% clay % silt =
CL is 30% clay % silt =
Si is 10% clay % silt =
SiL is 10% clay % silt =
SL is 10% clay % silt =
LS is 10% clay % silt =
S is 90% sand % silt =
Explanation / Answer
Soil texture refers to the proportion of sand, silt and clay sized particles that constitute the mineral fraction of the soil, and it is determined by the size and type of the particle that makesup.
Sandy Soils are sonsist of sand particle (coarse sand 0.2-2mm in diameter and fine sand 0.02-0.2mm in diameter), in general these particles are large, hence the surface area is small, therefoe sand drains easly(poor ability to retain moisture) and little nutrient bonding.
2)
silt particles has a limited surface area which is greater than the sandy soil, particle size is between 0.02 mm and 0.002 mm in diameter. it will compact under heavy silt soils are poor in air and water movement also little nutrient bonding.
clay soils consisted by clay particle which are small in size and hence a large surface area, therefore water adhers very well with clay/ which has high ability to retain moisture and there are good in nutrient bonding.
these properties are very important in the case of vegetation, water flow etc. rather than a one type, soil is a combination of sand silt and clay.
2)
type sand% silt% Clay% High clay(HC) 10 30 60 silty clay (SiC) 5 45 50 clay 30 20 50 silty clay loam 10 60 30 clay loam 36 31 33 silt 7 83 10 silty loam 10 80 10 sand loam 70 20 10 loamy sand 85 5 10 sand 90 5 5