Effects of fresh and aged chars from pyrolysis and hydrothermal carbonization on nutrient sorption in agricultural soils

Abstract

Abstract. Leaching of nutrients from agricultural soils causes major environmental problems that may be reduced with amendments of chars derived from pyrolysis (pyrochars) or hydrothermal carbonization (hydrochars). Chars are characterized by a high adsorption capacity -i.e. they may retain nutrients such as nitrate and ammonium. However, the physicochemical properties of the chars and hence their sorption capacity likely depend on feedstock and the production process. We investigated the nutrient retention capacity of pyrochars and hydrochars from three different feedstocks (digestates, Miscanthus, woodchips) mixed into different soil substrates (sandy loam and silty loam). Moreover, we investigated the influence of char degradation on its nutrient retention capacity using a 7-month in situ field incubation of pyrochar and hydrochar mixed into soils at three different field sites. Pyrochars showed the highest ability to retain nitrate, ammonium and phosphate, with pyrochar from woodchips being particularly efficient in nitrate adsorption. Ammonium adsorption of pyrochars was controlled by the soil type of the soil-char mixture. We found some ammonium retention on sandy soils, but no pyrochar effect or even ammonium leaching from the loamy soil. The phosphate retention capacity of pyrochars strongly depended on the pyrochar feedstock with large phosphate leaching from digestate-derived pyrochar and some adsorption capacity from woodchip-derived pyrochar. Application of hydrochars to agricultural soils caused small, and often not significant, effects on nutrient retention. In contrast, some hydrochars did increase the leaching of nutrients compared to the non-amended control soil. We found a surprisingly rapid loss of the chars' adsorption capacity after field application of the chars. For all sites and for hydrochar and pyrochar, the adsorption capacity was reduced by 60-80 % to less or no nitrate and ammonium adsorption. Thus, our results cast doubt on the efficiency of char applications to temperate zone soils to minimize nutrient losses via leaching.

Optimum rates of surface‐applied coal char decreased soil ammonia volatilization loss

“…Ventura, Sorrenti, Panzacchi, George, and Tonon (2013) observed a reduction in NO 3 -N leaching only in the second year after biochar application, suggesting an increase in biochar sorption properties over time, possibly due to the oxidation and interaction of biochar and soil particles and an increase in the adsorbing surface due to particle fragmentation with aging (Hagemann et al, 2017;Singh, Hatton, Singh, Cowie, & Kathuria, 2010). In contrast, Gronwald, Don, Tiemeyer, and Helfrich (2015) observed that the adsorption capacity of biochar decreased by 60-80% to less or observed no NO 3 /NH 4 -N adsorption after 7 mo of aging in the field compared with the fresh char. A similar trend of decreasing adsorption capacity with biochar from beetroot chips was reported from a laboratory study on loam soil (Bargmann, Martens, Rillig, Kruse, & Kücke, 2014).…”

Soil Reserves of Potassium: Release and Availability to Lolium perenne in Relation to Clay Minerals in Six Cropland Soils from Eastern China

“…Agriculture is one of the main causes of the desertification of the land, and this is partially due to the exhaustion of the soil nutrients (Kraaijvanger & Veldkamp, 2015;Lü et al, 2016;Lucas-Borja et al, 2016;Udeigwe et al, 2016). There is a need to restore the degraded lands (Chen et al, 2016;Costantini et al, 2016), and the recovery of the nutrients is a key strategy (Gronwald et al, 2015;Silvestri et al, 2016;Wang et al, 2016a). Potassium (K) is an essential element for higher plants; it plays a particularly crucial role in a number of physiological processes vital to growth, yield, quality and stress resistance of all crops (Pettigrew, 2008;Römheld & Kirkby, 2010;Zörb et al, 2014).…”

The Influence of Organic Carbon and pH on Heavy Metals, Potassium, and Magnesium Levels in Lithuanian Podzols

“…In recent years, derivatives of organic carbon such as composts (Srinivasarao et al, 2014b;Mahmoud & El-Kader, 2015;Montiel-Rozas et al, 2016) and biochar have been considered to be a productive solution to various environmental problems, including soil that has been contaminated with potentially toxic elements (Sohi, 2012;Paz-Ferreiro et al, 2014). Biochar is a high-carbon and fine-grained residue which is produced from organic carbon under thermal decomposition in the absence of oxygen (Lehmann, 2009;Gronwald et al, 2015). Biochar as a soil amendment is used to improve soil quality over both the long and short term (Khaledian et al, 2013;Krause et al, 2016).…”