Soil Density

 

 

    Soil density, denoting the mass of soil per unit volume, holds paramount significance as it profoundly shapes the physical, chemical, and biological attributes of the soil, thereby playing a pivotal role in determining its capacity to facilitate plant growth, maintain ecosystems, and withstand environmental degradation.
Soil density as points out the mass or weight of soil per unit volume, is expressed in the unit grams per cubic centimeter (g/m³).It is explained by the formula    D=M/V
Where
D= Density
M= Mass
V= Volume
    However, healthy soil is made up of 50% soil solids, while the remaining 50% is composed of pore spaces. When considering soil density, you can either focus on the volume of soil solids (particle density) or consider the entire soil, which includes soil solids and pore spaces (bulk density). The ideal bulk density for plant growth on average is 1.6gm³ but depends on soil texture, while the particle density range in the soil is 2.65gm³ is commonly used.
Each soil bulk density or particle density has its significance.
Particle Density:
    Particle density refers to the mass of soil particles (excluding pore space) per unit volume. It contributes to understanding soil composition, mechanics, and porosity, providing complementary insights into different aspects of soil behavior.
Soil Bulk density:
    Soil Bulk density refers to the mass of soil particles (including pore spaces) per unit volume. Bulk density is vital for assessing soil compaction, water movement, and nutrient availability. From a plant growth point of view, it is of key significance, because it affects soil aeration, and influences uptake of water and nutrients. The excess of 1.6gm³ restricts root penetration and results in poor hydraulic conductivity. Moreover, it is used to convert mass water content to volumetric water content, to determine the weight of soil per unit area for a particular depth as well as the quantity of nutrients present in soil.
Example
A soil sample with a volume of 550 cm³ weighs 900 g at a depth of 30 cm and has a nitrogen content of 0.20%. Calculate the bulk density, determine the amount of nitrogen in kilograms present in a 30 cm-depth hectare of soil, and assess whether this bulk density is suitable for the crop.

Step 1. Bulk density = Mass/Volume
Bulk density = 900/550
Bulk density = 1.63 gcm³ 

Step 2. Nitrogen content= 0.20%
Bulk Density = 1.63 gcm³= 1.63 Mgcm³
1 Hectare =10000 m2
Volume of 30 cm-ha= 10000 m2 x 0.3m = 3000m³
Weight of 30 cm-ha= 3000 x 1.63 = 4890 Mg
N in 30 cm-ha= 0.20 x 4890 / 100
N in 30 cm-ha= 9.78Mg = 9780kg

The calculated bulk density is 1.63 g/cm³, which is equivalent to 1.63 Mg/cm³. The nitrogen content in a 30 cm-depth hectare of soil is 9780 kg. To assess whether this bulk density is suitable for the crop, additional information about the specific crop's requirements and ideal soil conditions is needed. Generally, for most crops, a bulk density between 1.6g/cm³ is considered suitable.