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Standard Extraction Methods May Underestimate Nitrate Stocks Captured by Field‐Aged Biochar
Author(s) -
Haider Ghulam,
Steffens Diedrich,
Müller Christoph,
Kammann Claudia I.
Publication year - 2016
Publication title -
journal of environmental quality
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.888
H-Index - 171
eISSN - 1537-2537
pISSN - 0047-2425
DOI - 10.2134/jeq2015.10.0529
Subject(s) - nitrate , chemistry , leaching (pedology) , subsoil , environmental chemistry , soil water , ammonium , topsoil , biochar , calcareous , environmental science , soil science , botany , organic chemistry , pyrolysis , biology
Biochar (BC) has been shown to increase the potential for N retention in agricultural soils. However, the form of N retained and its strength of retention are poorly understood. Here, we examined if the N retained could be readily extractable by standard methods and if the amount of N retained varied with BC field ageing. We investigated soil and field‐aged BC (BC aged ) particles of a field experiment (sandy soil amended with BC at 0, 15, and 30 t ha −1 ) under two watering regimes (irrigated and rain‐fed). Throughout the study, greater nitrate than ammonium retention was observed with BC addition in topsoil (0–15 cm). Subsoil (15–30 cm) nitrate concentrations were reduced in BC treatments, indicating reduced nitrate leaching (standard 2 mol L −1 KCl method). The mineral‐N release of picked BC aged particles was examined with different methods: standard 2 mol L −1 KCl extraction; repeated (10×) extraction in 2 mol L −1 KCl at 22 ± 2°C and 80°C (M 0 ); electro‐ultrafiltration (M 1 ); repeated water + KCl long‐term shaking (M 2 ); and M 2 plus one repeated shaking at 80°C (M 3 ). Nitrate amounts captured by BC aged particles were several‐fold greater than those in the BC‐amended soil. Compared with M 0 , standard 2 mol L −1 KCl or electro‐ultrafiltration extractions retrieved only 13 and 30% of the total extractable nitrates, respectively. Our results suggest that “nitrate capture” by BC may reduce nitrate leaching in the field and that the inefficiency of standard extraction methods deserves closer research attention to decipher mechanisms for reactive N management. Core Ideas Biochar reduced nitrate leaching from temperate sandy soil in the field. Biochar particles captured nitrate amounts several‐fold greater than found in soil. Standard extraction methods may not retrieve all biochar‐captured nitrate. Field‐aged biochar captured much more nitrate than ammonium. Captured nitrate amounts were independent of the biochar particle size.