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

Ghulam Haider,Sarasadat Taherymoosavi,Stephen Joseph,David Mitchell,Diedrich Steffens,Christoph Müller,Claudia I. Kammann

doi:10.1038/s41598-020-70586-x

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 pre-requisite 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 two-factorial greenhouse experiment was designed, where the N was applied either as Ca(NO3)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.

Highlights

Biochar may serve as a tool to sustainably mitigate climate change via carbon sequestration and by improving soil fertility
It has been proposed as a carbon sequestration strategy with environmental co-benefits when used in s oils[8,9,10,11,12] and is considered to be one of the potential NETs in the IPCC 1.5 °C special report published in 2 0182,13
This study aimed to test for the first time if N captured in field-aged biochar particles would be bioavailable to plants under controlled conditions

Summary

Introduction

Biochar may serve as a tool to sustainably mitigate climate change via carbon sequestration and by improving soil fertility. Biochar is a solid by-product of pyrolysis, the thermal conversion of biomass at temperatures of 350–900 °C at low to absent oxygen conditions It has been proposed as a carbon sequestration strategy with environmental co-benefits when used in s oils[8,9,10,11,12] and is considered to be one of the potential NETs in the IPCC 1.5 °C special report published in 2 0182,13. A global meta-analysis of 105 studies revealed that the use of pure biochar, applied in large doses of ≥ 10 t ha−1 to soils, resulted in no yield increases in temperate latitudes and an average 25% yield increase in the subtropics and tropics[14] Another meta-analysis of 153 peer-reviewed studies reported that crop plant productivity is dependent on the consortium of biochar and soil properties[15]. A successful commercial strategy has been to create a compound fertilizer that comprises 20% biochar, 5% clay, and 75% NPK with application rates of the biochar at approximately 100 kg ha−123,24

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