Evaluating Potential Agricultural Use of Industrial Byproducts

Abstract

The large quantity of byproducts produced by the U.S. industry requires environmentally friendly and economical means of disposal. Integration of certain byproducts (e.g., papermill lime mud and calcium silicate slag) into agriculture may provide mutually beneficial solutions to the disposal problem. However, industrial byproducts significantly vary in chemical (e.g., calcium carbonate equivalent and trace contaminants) and physical (e.g., particle size) properties and may not meet the current regulations for liming materials and/or sludge and biosolids. As a result of these factors, several studies were conducted to evaluate beneficial effects and environmental risks of selected industrial byproducts. Soil incubation and rice culture studies were conducted at the Plant Science Research Center at Auburn University, AL, in 2015 and 2016. Eleven ground limestones, 6 papermill byproducts, 2 slags from steel industry (steel slag), and 1 slag from phosphorus fertilizer industry (P slag) were evaluated for their liming ability. The P slag was further analyzed for rates (0, 1000, 2000, and 4000 mg kg-1) and application method (surface application and incorporation) using two typical soils (Sharkey clay and Pahokee muck) for rice/sugarcane production. Results indicated that the relative neutralizing value (RNV) is an adequate indicator of actual liming ability for ground limestones and industrial byproducts, if particle size can be accurately analyzed. Papermill mud is a suitable alternative liming agents. The P slag may also serve as a liming material if the particle size is reduced. Applied P slag increased plant available Si and rice biomass in both soils and Si in plant tissues in the organic soil. Plant available Mn and Mn in plant tissues decreased with increasing slag rate, possibly due to the liming effect; however, deficiency was not observed. Trace contaminants (e.g., Cd, Cr, and Pb) and radioactivity in soils and rice grain were not affected by P slag application. The P slag increased transpiration and photosynthesis rates, canopy density, soluble sugars (i.e., glucose, fructose, and sucrose), and carbon isotope discrimination (Δ13C), and decreased proline accumulation of drought-stressed rice leaf. These results suggest that Si in the P slag is available to plant, and trace contaminants are unlikely to cause environmental risks for rice production. The P slag may also provide benefits on mitigating drought stress.