Can biochar improve agricultural water use efficiency?

Fischer, Benjamin; Manzoni, Stefano; Morillas, Laura; Garcia, Monica; Johnson, Mark S.; Lyon, Steve W.

To sustain and increase agricultural production under increasingly water-limited conditions,there is an urgent need to develop agricultural methods that balance water supply and demandwhile improving resilience to climate variability. A promising approach to address this needis biochar – a charcoal made from pyrolyzed organic material. Laboratory, pot-scaleand some field studies have shown that biochar retains soil water and nutrients,supports root growth soil, and helps sequester organic carbon. However, does biocharimproves soil water availability, plant water consumption rates and crop yields?To address this question, we synthesized literature-derived observational data andassessed how biochar affects evapotranspiration using a minimal soil water balancemodel.Our data analysis showed that relative to control conditions, biochar additions increase thesoil water holding capacity and have a variable but generally positive impact on soil waterretention. Our modeling results demonstrated that biochar additions, by increasing soil waterholding capacity, can increase long-term evapotranspiration rates, especially indry regions. Empirical and model results support assertions that biochar generallyimproves water availability (and stability) for plants. However, biochar effects on plantproductivity, crop yield, and water use efficiency are surprisingly variable. Empiricaldata showed that biochar amendments generally increased crop yields (75% of thecompiled studies). In 35% of the cases, biochar simultaneously increased crop yield andimproved water use efficiency. However, in some studies yield did not improve,and/or evapotranspiration rates increased (i.e., water use efficiency worsened). Thissuggests that less water might be available to plants in some biochar amended soils, orthat some indirect (and poorly quantified) negative effects of biochar on plants canoccur. Identifying the biochar properties that are most influential on improvingsoil moisture content (and subsequent yields) for crops, remains challenging, inparticular due to the different variables being reported in the literature and low samplesizes.Hence, while biochar amendments are promising, the variable impacts found in the literaturehighlight the need for targeted research on how biochar affects the soil-plant-water cycle.Specifically, at the pot or field scale, conservative tracers such as stable water isotopes 18Oand 2H in combination with hydrometric measurements could be particularly useful toidentify the effect of biochar on plant subsurface water sources, and how water is partitionedin the vadose zone.

BIOCHAR; STABLE isotope tracers; WATER supply; WATER efficiency; CHARCOAL; WATER consumption; CROP yields

Geophysical Research Abstracts, 2019, Vol 21, p1

1029-7006

Academic Journal