Abstract
The application of agrichar derived from organic feedstocks has the potential to improve soil fertility and crop production by providing major nutrients like phosphorus (P) to the crop, and in some cases also reducing P leaching. The effect of agrichar on the leaching of P in soils is not uniform and can vary depending on the type of agrichar and amount applied. The objective of this study was to (i) evaluate the behavior of four agrichars (rice hulls RH, palm fronds PF, horse bedding HB, and bagasse BG) for their ability to retain/release P and (ii) determine the effect of wet sonication on P sorption behavior. The feedstocks were torrefied at 500 °C using a top-lit updraft gasifier and used in multiple batch incubation experiments to evaluate equilibrium phosphorus concentration, maximum P sorption capacity (Smax), and adsorption/desorption potential. Both, RH (12.6 g kg-1) and HB (11.5 g kg-1) contained 10-15 times higher total P concentration than PF and BG, rendering RH and HB as potentially suitable products to be used as soil amendments. However, this initial P content of the agrichar seemed to have an overriding effect on the P sorption behavior of the agrichar. PF had Smax of 676 (±127) mg kg-1 for the non-sonicated agrichar, and 237 (±91) mg kg-1 following sonication. There was significant increase in CEC for PF and BG agrichar upon sonication. PF agrichar increased from 27 (±3) cmolc kg-1 to 41 (±4) cmolc kg-1 with sonication. Similarly, BG agrichar CEC increased from 21 (±2) cmolc kg-1 to 45 (±5) cmolc kg-1 with sonication. Initial total P and Ca concentration and their ratios was found to play significant roles on P adsorption and desorption. Major cations like Ca, Fe, Al and Mn are found to act as active sorption site for phosphorus controlling its fate and mobility along with compounding effects of other physicochemical parameters.
Highlights
Developing effective technologies to retain nutrients in soils is important because they can increase soil fertility and reduce repeated fertilizer application cost
Cation exchange capacity values for both sonicated and non-sonicated horse bedding (HB) agrichar samples was 39 (±4) cmolc kg-1 showing no effect of sonication for HB agrichar
The sonication of samples for palm fronds (PF) and BG agrichar might have resulted in breakdown of agrichars leading to increase in specific surface area and more exchange sites contributing to higher cation exchange capacity (CEC)
Summary
Developing effective technologies to retain nutrients in soils is important because they can increase soil fertility and reduce repeated fertilizer application cost. Sometimes referred to as “agrichar”, has received attention over the past decade to improve soil properties and improve overall soil quality (Van Zwieten et al, 2009) Enhancing soil properties such as water holding capacity, organic matter content, and nutrient retention dynamics are key to improving soil quality. The application of agrichar derived from organic feedstocks has the potential to improve soil fertility and crop production by reducing the leaching of nutrients, and in most cases by supplying nutrients to the plants (Ding et al, 2016; Gao, Hoffman-Krull, Bidwell, & DeLuca, 2016; Glaser, Lehmann, & Zech, 2002; Madiba, Solaiman, Carson, & Murphy, 2016; Major, Rondon, Molina, Riha, & Lehmann, 2010; Ngatia, Hsieh, Nemours, Fu, & Taylor, 2017; Randolph et al, 2017). The nature of change in soil characteristics following char application is dependent on native biogeochemistry (Streubel et al, 2011; Zhu, Peng, & Huang, 2015), feedstock characteristics (Windeatt et al, 2014), temperature of torrefaction, inherent levels of major cation, anion http://sar.ccsenet.org
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