Biochar application does not improve the soil hydrological function of a sandy soil

Abstract

a b s t r a c tBiochar application to soil is currently being widely posited as a means to improve soil quality and thereby increase crop yield. Next to beneficial effects on soil nutrient availability and retention, biochar is assumed to improve soil water retention. However, evidence for such an effect in the primary literature remains elusive. Therefore, we studied the effect of biochar on soil hydrological characteristics in two separate field experiments on a sandy soil in The Netherlands. In Experiment I, biochar produced through slow pyrolysis of herbaceous feedstock at two temperatures (400°C and 600°C) was applied to soil at a rate of 10 t ha −1 . In Experiment II, the 400°C biochar was applied at rates of 1, 5, 20 and 50 t ha −1 . Soils were analysed for soil water retention, aggregate stability and other soil physical parameters after three growing seasons and one growing season for Experiment I and Experiment II, respectively. We characterised the pore structure of the biochar using X-ray computed micro-tomography (XRT) and hydrophobicity using contact angle measurements. We found no significant effects of biochar application on soil water retention in either experiment. Aggregate stability was also not significantly affected, nor was field saturated hydraulic conductivity. XRT analysis of the biochars showed that they were highly porous, with 48% and 57% porosity for the 400°C and 600°C biochar respectively. More than 99% of internal pores of the biochar particles were connected to the surface, suggesting a potential role for biochars in improving soil water retention. However, the biochars were highly hydrophobic. We postulate that this strong hydrophobicity prevented water from infiltrating into the biochar particles, prohibiting an effect on soil water retention. Our results suggest that, in addition to characterising pore space, biochars should be analysed for hydrophobicity when assessing their potential for improving soil physical properties.

Impact of Different Agricultural Waste Biochars on Maize Biomass and Soil Water Content in a Brazilian Cerrado Arenosol

“…This is in agreement with Jeffery et al [33], who did not observe either a biochar effect on water retention nor differences between the biochars at 400 • C and 600 • C, despite the biochar 600 • C having higher porosity. Although temperature of pyrolysis is considered the most important factor determining physical changes of biochar, feedstock type determines the temperature range under which changes occur [15].…”

Behavior the Water in Typical Yellow Oxisoil of Central Amazon Under Biochar Application

“…Authors such as Novak et al (2012), Carvalho et al (2014) and Sun and Lu (2014) evidenced the increase in available water in the soil, as well as the improvement in its retention with biochar application. Studies conducted by Major et al (2012) and Jeffery et al (2015) did not show significant results with the application of biochar in the soil as an alternative of water use efficiency. It is believed that the influence of the use of biochar in the increase of water availability is related to the applied dose and the morphological characteristics of the soil, such as mineralogy and granulometry (TEIXEIRA et al, 2017).…”

“…Other studies have demonstrated the lack of positive results in this aspect (MAJOR et al, 2012;JEFFERY et al, 2015), while others have observed limitations in water availability (TEIXEIRA et al, 2017).…”

Effect of Corn Residue Biochar on the Hydraulic Properties of Sandy Loam Soil

“…The biochar produced at high temperatures possesses pores unclogged by volatile/mobile matter and converts the biochar surface to be more hydrophilic [71]. However, Jeffery et al [72] reported no significant impact on soil water retention and K sat after the application of hay biochar produced at 400 and 600 • C to sandy soil.…”