SOIL PHYSICS (Rabi 2020-21)
Exp: 1. TO STUDY THE RELATIONSHIP BETWEEN THE PHYSICAL PROPERTIES
OF SOIL AND DEPTH
Introduction
Soil physics is the study of soil’s physical properties and processes. It is applied to
management and prediction under natural and managed ecosystems [1]. Soil physics deals with
the dynamics of physical soil components and their phases as solid, liquids and gases. It draws
on the principles of physics, physical chemistry, engineering and meteorology [2]. Soil physics
applies these principles to address practical problems of agriculture, ecology and engineering
[1].
The quality of dry land is generally low due to low soil organic amendments (OA)
which is pivotal to the soil quality. OA affect the soil’s ability to provide nutrients for plants [3].
A good indicator of the soil quality is soil aggregation as it relates to microbial and the carbon
and nitrogen ratio. It is also important to increase the soil’s carbon and nitrogen which is an
indicator of soil fertility [4].
Since OA have low bulk density and higher porosity, addition of organic
amendments to soil improves soil physical properties [5].
Objectives
The aim of the experiment is to study the effect of depth on soil bulk density, porosity and
particle density. “Bulk density” is defined as the dry weight of soil per unit volume of soil.
Mathematically,
𝜌=
𝑊
(1), where ρ = bulk density
𝑉
“Particle density” is the weight of an individual soil particle per unit volume.
𝜌𝑝 =
𝑤
(2), where 𝜌𝑝 = particle density
𝑣
“Porosity” refers to the volume of soil voids that can be filled by water and/or air. It is inversely
related to the bulk density. Generally,
𝜙=
𝑉𝑣
𝑉𝑇
× 100%
(3)
where ϕ = porosity, 𝑉𝑉 = 𝑉𝑜𝑖𝑑 𝑣𝑜𝑙𝑢𝑚𝑒 and 𝑉𝑇 = 𝑇𝑜𝑡𝑎𝑙 𝑣𝑜𝑙𝑢𝑚𝑒
Materials and Method
 Soil samples will be collected from the field of Agriculture Research Institute Tarnab,
Peshawar.
 The samples will be collected from the following depths:
0-15cm, 15-30cm,30-45cm and 45-60cm.
 These samples will then be sent to the laboratory for processing.
 After the completion of processing, the volume of a sample of known mass will be found
with the help of a measuring cylinder. And the bulk density will be calculated using
equation (1).
 Then a known volume of water will be taken in measuring cylinder, and a certain amount
of soil from the collected sample will be poured till it reaches a certain known height.
The difference in both the volumes will give us the particle density.
 Now the porosity can be calculated as
𝜙 = (1 − 𝜌 𝜌𝑝−1 ) × 100%
References
[1]. Hillel, D. Environmental Soil Physics, Academic Press: San Diego, 2004. pp. 5-87.
[2]. Lal, R.; Shukla, M. Principles of soil physics, New York: M. Dekker, 2004. pp. 50-102.
[3]. Richards, P. Soil, Physical Properties and Crop Production in the Tropics. Journal of
Arid Environments, 1980, 3(4), pp.350-352.
[4]. Letey, J. Advanced Soil Physics. Soil Science, 1973, 115(5), p.399.
[5]. Boivin, P., Schäffer, B. and Sturny, W. Quantifying the relationship between soil
organic carbon and soil physical properties using shrinkage modelling. European Journal of
Soil Science, 2009, 60(2), pp.265-275