Exploitation of Coal Fly Ash Based Synthetic Aggregates as a Granular Fertilizer Medium and a Soil Amendment to Improve Crop Production in Low Productive Red Soil in Okinawa, Japan.

This work proposes a new potential way of developing synthetic aggregates (SA) using waste coal fly ash, paper waste, starch waste and ammonium sulfate, as a granular fertilizer medium and their utilization to improve the crop production in low productive red soil in Okinawa, Japan. Ammonium sulfate was obtained during the process of entrapping carbon dioxide gas originated from coal combustion in electricity generation. Carbon dioxide is converted into calcium carbonate and ammonium sulfate using calcium sulfate and ammonia. Three different SA with three different nitrogen percentages were developed by changing the quantities of ammonium sulfate and incorporated to the acidic red soil in a pot experiment as a granular fertilizer and a soil amendment. Chemical fertilizer only was considered as the control. Produced SA showed low bulk density, high water holding capacity, high saturated hydraulic conductivity, alkaline pH, high electrical conductivity compared with the original red soil. SA showed high aggregate strength in the range of 3.67-3.83 kg/cm². SA showed low decomposition rates, when incorporated to the soil compared with the commercial granular fertilizer (CGF). Scanning electron microscopic study revealed that the SA is a dual composite material, which is having a higher surface area where the more or less round shape coal fly ash particles were embedded into the fibrous paper waste matrix with the assistance of the starch waste by creating porous spaces within the aggregate. Incorporation of these SA to the low productive red soil in Okinawa, Japan not only enhanced the soil fertility but also improved the soil physical and chemical properties such as water holding capacity, hydraulic conductivity, bulk density, particle size distribution, pH, electrical conductivity, carbon content, and cation concentration compared to the chemical fertilizer control. Incorporation of these SA increased the growth and yield parameters of Japanese mustard spinach (Brassica rapa Var.Pervidis) compared to the chemical fertilizer control. Moreover, production of these SA can be regarded as an effective waste management practice in Okinawa, Japan.
Key words: coal fly ash, paper waste, fertilizer, red soil, synthetic aggregates, soil amendment