Evaluation of Soil Liming Materials.

Acid soils in the southeastern Coastal Plain require ground limestone or some other liming materials to reduce acidity.  There are limited high-quality limestone deposits used for agricultural purposes in this region.  Some industrial byproducts (e.g., paper mill sludge and steel slag) are potential alternative liming materials, but their neutralizing ability is highly variable and may not be addressed by state lime laws regulating ground limestone.  Relative neutralizing value (RNV) represents percentage of effective constituent in liming materials based on particle size and total alkalinity.  The objective of this study is to evaluate the liming potential of 9 industrial byproducts and 11 ground agricultural limestones and to determine if RNV is indicative of the actual neutralizing ability.  The pH, moisture content, total elements, total alkalinity expressed as calcium carbonate equivalent (CCE), and particle size were analyzed for each product.  Three acid soils in Alabama were collected for an incubation study.  The amount of each product needed to bring soil pH to 6.5 (“X” rate) was calculated according to soil pH buffer curves and RNV of each product.  Each product was mixed thoroughly with soil at 0, 1/2X, X, and 2X rates and incubated for 6 wk.  Results indicated that lime mud and ash from paper and pulp industry and K-lime (a mixture of lime and ash) may be used as alternative liming agent because of their high CCE and fine particle size.  The stainless steel slag has sufficient alkalinity, but is high in Cr (1087 mg kg^-1).   During the incubation study, soil pH initially increased within the first wk and remained fairly stable afterward.  The wide range in properties of the liming materials resulted in various abilities to raise pH even when based on the pH buffer curve.  When applied at X rate, few evaluated liming materials brought soil pH to 6.5.  For most products, the 2X rate was necessary to improve soil pH to the target pH.   Possible explanations are that the pH buffer curve may underestimate the soil natural acidity.  Relative neutralizing value of liming materials may be used to evaluate all soil liming materials if adjustments are made to the calculations.