INTRODUCTION

A plant’s growth is affected to a large degree by the relative concentrations of hydrogen ions (H+) and hydroxyl ions (OH-) in the surrounding soil solution (soil pH). Acid soils (pH<7) have higher concentrations of H+ ions, while alkaline or "basic" soils have more OH- ions. A neutral soil (pH=7) has equal concentrations of both. Soil pH is measured on a logarithmic scale resulting in a ten-fold change between each whole pH number. Soil pH is important because it influences (1) nutrient availability (especially micronutrients), (2) solubility of toxic ions, and (3) microbial activity.

A plant’s ability to endure various pH levels depends largely on it’s ability to take in and utilize nutrients at varying concentrations in the soil solution. Some plants are able to assimilate nutrients existing in minute quantities, whereas others require an abundance of an element in order to assimilate enough for their growth. These plants may show clear nutrient deficiency symptoms as a result of an extreme pH level. The maximum availability of the primary nutrients required for plant growth is greatest at a pH value between 6.5 and 7.5.

High pH extremities are often corrected using elemental sulfur or acid forming fertilizer, while low pH values are increased by the addition of hydrated lime (slaked lime) which is the most soluble of the liming products. The value of a liming material depends on molecular composition, purity, and degree of fineness.

Soil pH may be affected by several factors including:

-leaching of basic cations as a result of rainfall

-absorption of cations by plants

-acid or base forming fertilizers

-soil texture

-elemental composition of plants decaying in the soil

-irrigation water quality

-the presence of free lime as a buffering agent against change in pH

-cation exchange capacity which acts as a buffering mechanism in the soil