Characterization, Stability, and Plant Effects of Kiln-Produced Wheat Straw Biochar

Abstract

Biochar is a promising technology for improving soil quality and sequestering C in the long term. Although modern pyrolysis technologies are being developed, kiln technologies often remain the most accessible method for biochar production. The objective of the present study was to assess biochar characteristics, stability in soil, and agronomic effects of a kiln‐produced biochar. Wheat‐straw biochar was produced in a double‐barrel kiln and analyzed by solid‐state 13C nuclear magneticresonance spectroscopy. Two experiments were conducted with biochar mixed into an Ap‐horizon sandy loam. In the first experiment, CO2 efflux was monitored for 3 mo in plant‐free soil columns across four treatments (0, 10, 50, and 100 Mg biochar ha−1). In the second experiment, ryegrass was grown in pots having received 17 and 54 Mg biochar ha−1 combined with four N rates from 144 to 288 kg N ha−1. Our kiln method generated a wheat‐straw biochar with carbon content composed of 92% of aromatic structures. Our results suggest that the biochar lost <0.16% C as CO2 over the 90‐d incubation period. Biomass yields were not significantly modified by biochar treatments, except for a slight decrease at the 144 kg N ha−1 rate. Foliar N concentrations were significantly reduced by biochar application. Biochar significantly increased soil water content; however, this increase did not result in increased biomass yield. In conclusion, our kiln‐produced biochar was highly aromatic and appeared quite recalcitrant in soil but had no overall significant impact on ryegrass yields.

Miscanthus Biochar had Limited Effects on Soil Physical Properties, Microbial Biomass, and Grain Yield in a Four-Year Field Experiment in Norway

“…As biochar is a material with high C content, some farmers may be concerned that adding large amounts to their soils (the amount of biochar in BC25 applied in our experiment is 10 times that of yearly straw produced from the same land area) may lead to a microbial immobilization of N and, thus, reduce plant yields. While some studies have shown short-term N immobilization that restricts plant growth [62,63], we did not observe this under field conditions over four years where even the higher BC treatment did not reduce grain, straw yields, and grain protein or increase Microbal C or N. A lack of yield response after the biochar amendment concurs with other studies in boreal and temperate regions. Reference [64] found no yield differences in wheat or faba bean after applying spruce and pine biochar at 10 t ha −1 in a three-year field experiment in Finland and a similar absence of yield effect was found in a two-year field ring trial carried out in seven different countries in Northern Europe [65].…”

Biochar Affects Essential Nutrients of Carrot Taproots and Lettuce Leaves

“…It was possible that the general lower leaf Ca and Mg concentrations we found in lettuce could be due to excess Zn in the biochars. O'Toole et al (2013) suggested that the Zn in galvanized metal containers used during their studies likely increased biochar Zn, which reduced plant Ca and Mg. However, we used ceramic bowls to make biochar, and, thus we did not have a metal container factor.…”

A Review of Biochar and Soil Nitrogen Dynamics

“…More recently, O'Toole et al [37] reported on a pot experiment growing ryegrass under 4 rates of N fertiliser with 2 rates of a wheat-straw biochar (500-600 °C) and found foliar N concentrations were reduced, possibly due to adsorption or immobilisation of N being stimulated with biochar addition, but with unaffected yields. Kammann et al [16] also observed reductions in foliar N concentrations in a pot trial with a relatively nutrient-rich peanut hull biochar, but in this case the reduction likely resulted from increased N use efficiency since the authors reported biomass increases of up to 60%.…”