Final answer:
Pore spaces in soil are primarily occupied by water and air, which are essential for soil structure and plant growth. The ideal soil composition includes equal parts solid material and pore space, with water and air filling the pore space equally.
Step-by-step explanation:
Pore spaces in the soil are shared by variable amounts of water and air. The soil composition ideally consists of 50 percent solid material and 50 percent pore space, with approximately equal parts water and air within that pore space. The inorganic mineral matter makes up about 40 to 45 percent of the soil volume while organic matter accounts for about 5 percent. Together, water and air fill the remaining 50 percent, which is vital for soil's structural integrity and its ability to support plant life. Optimal soil structure allows for adequate oxygenation and water availability to plants, a consideration crucial for agriculture and horticulture. Biological factors such as the presence of microorganisms, plant roots, and animals contribute to the formation and structure of soil by producing pores and affecting soil composition.