Abstract

Acidity is an environmental pressure shaping the fitness of soil for plants including turfgrasses. Details on pH and its measurement appear in the plant literature but specifics on the chemical-physical nature and behavior of hydrogen ions (H+) are lacking. Filling this knowledge gap may increase understanding of soil acidity. If understanding of the chemical-physical nature and behavior of H+ can be increased, then perspective of soil acidity may be broadened. The objective of this review is to describe the chemical-physical nature and behavior of H+. The objective is augmented by recapping the concept of acidity, explaining why H+ are acidity, identifying sources of H+ contributing to acidity, examining water’s role in H+ behavior, and evaluating the link between H+ and aluminum (Al3+). Physically, H+ are protons, composite particles comprised of quarks bound together by gluons; hydrogen nuclei absent neutrons and electrons (e-). Due to e- deficiency and high charge density, H+ polarize the orbital e- distribution of hydroxyl anion (OH-) explaining dissolution of hydroxy-Al minerals like gibbsite (-Al(OH)3) at low pH releasing Al3+ to soil solution. Solution Al3+ induces plant stress and nutrient imbalance via oxidative effects on roots and impacts on CEC. Both H+ and Al3+ are Lewis-acids. Understanding the Lewis-acid behavior of H+ and Al3+ helps explain the nature of acidity and its effects on plants and soils. Describing the chemical-physical nature and behavior of H+ helps shape the evolution of thinking about intrinsic soil characteristics like pH, which is a goal of plant and soil sciences.