Final answer:
The aeration porosity of the soil is estimated to be approximately 25%, and the volume of air present in the top 20 cm of a hectare of land is estimated to be around 250 cubic meters.
Step-by-step explanation:
To estimate the aeration porosity and volume of air present in a hectare of soil, we must consider the given composition of the soil. Given that about 50% of the soil volume is occupied by water and air, and the rest by inorganic matter (40-45%) and organic matter (5%), we will approximate that water and air occupy equal volume unless otherwise specified, so air and water would each take up about 25% of the soil volume. Since porosity refers to the volume of pores or spaces in the soil, we're interested in the air part of the 50%.
The volume of the top 20 cm of soil in a hectare (10,000 square meters) can be calculated by multiplying the area by the depth:
V = Area × Depth = 10,000 m2 × 0.2 m = 2,0000 m3
Assuming a 50-50 distribution between water and air, we can then estimate the volume of air is half the total pore space, therefore:
Volume of Air = Total Soil Volume × Porosity × Fraction of Air = 2,000 m3 × 0.25 × 0.5 = 250 m3
The aeration porosity, in this case, is approximately 25%, and the estimated volume of air is 250 cubic meters in the top 20 cm of the root zone for a hectare of land.