NOCTI Plant Science Practice Test

Porosity is the fraction of a soil’s volume that is made up of pore spaces where air and water reside. The size of the soil particles determines how large those gaps between particles are. Larger particles create bigger spaces, increasing the overall pore space and thus porosity. Fine-textured soils with very small particles tend to pack more tightly, leaving less room for voids, which lowers porosity. Color, pH, and organic matter affect other soil properties—color reflects mineral content and oxidation, pH governs acidity or alkalinity, and organic matter improves structure and water retention—but they do not directly set the proportion of void space in the soil like particle size does.