Pyrolysis Temperature Effects on Biochar–Water Interactions and Application for Improved Water Holding Capacity in Vineyard Soils

Abstract

Grapevine cane and stalks were considered for pyrolysis at 400 to 700 °C to produce biochar for increasing the water holding capacity of vineyard soil. Feedstocks were pyrolysed using a continuous feed reactor and the resulting biochars characterized in terms of physico-chemical properties, including water retention performance. Hydrophobicity was found in biochar from both feedstocks pyrolysed at 400 °C, but not at higher temperatures. At low soil matric potential, the pyrolysis temperature was the defining variable in determining water retention whereas at higher pressures, the feedstock was the more important variable. Available water content (AWC) of biochar increased with increasing pyrolysis temperatures, with optimal results obtained from grapevine cane at a pyrolysis temperature of 700 °C, which had an AWC 23% higher than a typical clay type soil. Principal component analysis showed variability in water retention of these biochars to be closely associated with the zeta potential, as well as the carbon and ionic content, suggesting that surface charge and hydrophobicity are key properties determining water holding capacity. Pure biochars were superior in water retention performance to typical sandy soils, and so biochar amendment of these soil types may improve water holding (particularly at field capacity). Further study with pot or field trials is recommended to confirm water retention behaviour and assess the feasibility of application under different viticultural scenarios.

Effects of Biochar Application in a Sorghum Crop under Greenhouse Conditions: Growth Parameters and Physicochemical Fertility

“…Numerous studies have demonstrated that biochar amendment improves WHC [3,57,58]; the present study reports a direct relationship between WHC and pyrolysis final temperature, which is directly correlated with WHC values already measured for individual biochar analyses (see Table 2). In agreement with Marshall et al [39], who also reported a high hydrophobicity in vine shoots-derived biochar produced at 400 • C, it could be an important parameter to take into account, and not only the macroporous structure of biochar which could led to attribute higher WHC at lower pyrolysis peak temperatures. Accordingly, the dependence of this parameter on pyrolysis temperature is an aspect that could be of interest for agronomic contributions.…”

“…Approximately 500 g of vine shoots were heated at an average heating rate of 5 • C min −1 to the final temperature (400 and 600 • C) with a soaking time of 60 min at this temperature. The mass flow rate at standard temperature and pressure (STP) conditions of the carrier gas (N 2 ) was adjusted to keep a constant real flow rate of N 2 within the reactor (at the corresponding final temperature) of 1.8 L min −1 , which corresponds to a carrier gas residence time of 180 s. The particle size adopted resulted appropriate to improve the carbonization efficiency (i.e., higher fixed-carbon content in the resulting biochar) during pyrolysis process because of the enhancement of secondary charring reactions at an intra-particle level [18,39].…”

“…Since relatively little information is available regarding the application of this type of biochar as an organic amendment [37][38][39], our study aims at achieving a wide understanding on the influence of different factors (such as the final pyrolysis temperature, biochar application rate, and soil texture) on the crop response variables. Outcomes from this kind of assessment studies will help researchers and agricultural advisors to make decisions concerning the viability of using biochar as a soil amendment in agricultural lands.…”

Biochar - A Panacea for Agriculture or Just Carbon?

“…Plant-available water in fine-textured soils could be enhanced through management or manipulation of hydrophobic properties of BC, thereby improving BC-soil interactions [74]. For example, it has been reported that grapevine feedstocks subjected to low pyrolysis temperatures (~400°C) yield BC with a 23% higher available water content in clay soils [75].…”

Differences in Water Vapor Adsorption-Desorption of Non Aged and 3-Year Aged Biochar in Sandy Spodosols

“…Current hydrophysical studies of biochars are mainly focused on measurements of their water retention curves and available water contents at high matric potentials (>-15 MPa) using pressure plate chambers (Marshall et al, 2019). Less attention has been paid to the assessment of water vapor adsorption-desorption characteristics of biochar surface while ageing in soils.…”