Mineral nitrogen captured in field-aged biochar is plant-available

Abstract

Biochar may serve as a tool to sustainably mitigate climate change via carbon sequestration and by improving soil fertility. Biochar has shown to retain nitrate in its pores, which increases with an organic coating of the inner surfaces and residence time in soil ("aging"). Here we investigated the plant accessibility of the captured nitrate in field-aged biochar, as a prerequisite for developing carbon-based N fertilization techniques with environmental benefits. Based on previous results, we hypothesized that part of the biochar-captured nitrate would remain unavailable for plants. A twofactorial greenhouse experiment was designed, where the N was applied either as Ca(NO 3) 2 or as n captured in field-aged biochar at five increasing N doses to quinoa and perennial ryegrass in pots. Interestingly, the biochar-captured N was as plant available as the mineral nitrate, except for the highest dosage. Refuting our hypothesis, no significant amounts of N were extractable at the end of the study from the biochar-soil mixtures with repeated-extraction protocols. Thus, N captured by biochar may improve the N use efficiency in agriculture. Further research should evaluate the role of biochar particle size, root morphology, mycorrhization, and soil moisture (variations) for nitrate retrieval from biochar particles by plants because the captured biochar N was less available in the field as under present controlled conditions. Abbreviations BC Biochar BC-aged Field-aged biochar Since preindustrial times (ca. 1,750), anthropogenic CO 2 emissions have increased atmospheric CO 2 mixing ratios by approximately 150% to more than 410 ppm to date, at an unprecedented rate of increase of currently 2.24 ppm per year 1. In December 2015, the COP21 stated in the Paris Agreement that humanity intends 'to keep atmospheric temperature rise to well below the 1.5 °C by 2050'. To achieve this goal, it is not only necessary to curb anthropogenic CO 2 emissions drastically within the next 30 years but also to additionally remove about 300 Gt of carbon from the atmosphere until 2,100 (using negative emission technologies, NETs, e.g. 2,3 ; see also www.4per1 000.org). Among various NETs, natural climate solutions (NCS) such as afforestation/reforestation, combustion/pyrolysis 4,5 and soil C sequestration (SOC stock increase; biochar) offer multiple co-benefits, supporting the UN's sustainable development goals (SDGs 3). NCS involving soil management strategies play an important role among the available spectrum of NETs. It is estimated that if the full potential of carbon sequestration in the biosphere (vegetation and soil 155 and 178 Pg respectively

Biochar alters hydraulic conductivity and inhibits nutrient leaching in two agricultural soils

“…SW500, however, significantly inhibited the flow of nitrate, despite not exhibiting chemical affinity in sorption trials. This suggests the physical retention mechanism known as nitrate capture, which is believed to be facilitated by increased surface area and porosity (Haider et al, 2016(Haider et al, , 2020Kameyama et al, 2012;Kammann et al, 2015). Indeed, SW500 had a substantially larger surface area than AS500 (93.5 compared to 54.7 m 2 g -1 ).…”

“…Despite increased interest and investigation, there remains uncertainty regarding the ability of biochar to deliver these agronomic benefits. While many studies show promising results where nutrient retention and soil water dynamics are concerned (Blanco-Canqui, 2017;Glaser et al, 2002Glaser et al, , 2015Glaser and Lehr, 2019;Haider et al, 2020;Hestrin et al, 2019), others have demonstrated no or only minor effects (Griffin et al, 2017;Jones et al, 2012;Martos et al, 2020). Several authors have concluded that, due to differences in biochar production parameters and those of the soil environment, material and site-specific investigation is required before conclusions can be drawn about the potential of biochar to provide agricultural benefits (Hassan et al, 2020;Jeffery et al, 2011;Zhang et al, 2016).…”

“…While exceptions have been observed, biochar has largely been shown to decrease the ability of a saturated soil to transmit water (saturated hydraulic conductivity (Ksat)) in coarse textured soils and increase Ksat in finer soils (Blanco-Canqui, 2017). The impact of biochar on these soil physical properties may influence nitrate retention through a mechanism known as "nitrate capture," in which nitrate molecules become physically entrapped within biochar pores (Haider et al, 2016), potentially leading to increased residence time in crop rooting zones and a greater opportunity for plant uptake (Haider et al, 2020;Kameyama et al, 2012;Kammann et al, 2015).…”

Short term effects of Municipal Solid Waste compost, Khat-Derived Biochar and Co-composted Biochar on Soil quality and Faba bean Yield and Protein content

“…According to the report by 51 , there is a signi cant increasing in the N content after the applications of different organic amendments such as dairy cattle manure, fresh white clover, vegetable, fruit, and yard waste compost, and poplar tree compost as a result of mineralization of organic nitrogen in the organic amendments. Some studies also reported that reduced N (nitrate) leaching when biochar was applied to soil combined with mineral or organic N fertilizer 52 . Our results also showed that soil residual available P content was increased in the control compost, 5% co-composted biochar, 15% co-composted biochar, 25% co-composted biochar, khat biochar and 50% NPF + compost by 3.1% − 12.7%, while in the 100% NPF and control soil residual available P reduced by 6.2% and 2.8% respectively compared to the value before harvesting.…”

Biochar induced improvement in root system architecture enhances nutrient assimilation by cotton plant seedlings

“…Biochar has been proposed as a soil amendment to enhance nutrient retention, reduce nutrient losses, improve soil fertility and crop growth, and sequestrate carbon [ 7 , 8 ]. In some cropping systems, biochar addition helps to reduce nitrogen fertiliser input while maintaining productivity [ 9 ] as biochar serves as a good complement to site preparation techniques that are frequently used for capturing nitrogen from nitrate so as to increase rhizosphere nitrogen bioavailability in alkaline soils [ 10 ]. According to other reports, biochar application level influences soil nutrient and plant root phenotype [ 11 , 12 ].…”