Articles | Volume 5, issue 2
Solid Earth, 5, 939–952, 2014

Special issue: Environmental benefits of biochar

Solid Earth, 5, 939–952, 2014

Research article 03 Sep 2014

Research article | 03 Sep 2014

Biochar increases plant-available water in a sandy loam soil under an aerobic rice crop system

M. T. de Melo Carvalho1,2,3, A. de Holanda Nunes Maia4, B. E. Madari1, L. Bastiaans2, P. A. J. van Oort2,5, A. B. Heinemann1, M. A. Soler da Silva1, F. A. Petter6, B. H. Marimon Jr.7, and H. Meinke2,3 M. T. de Melo Carvalho et al.
  • 1Embrapa Rice and Beans, Santo Antônio de Goiás, Goiás, Brazil
  • 2Wageningen University, Centre for Crop Systems Analysis, Wageningen, the Netherlands
  • 3Tasmanian Institute of Agriculture, University of Tasmania, Hobart, Australia
  • 4Embrapa Environment, Jaguariúna, SP, Brazil
  • 5Africa Rice Centre, Cotonou, Benin
  • 6Federal University of Mato Grosso, Sinop, Mato Grosso, Brazil
  • 7State University of Mato Grosso, Nova Xavantina, Mato Grosso, Brazil

Abstract. The main objective of this study was to assess the impact of biochar rate (0, 8, 16 and 32 Mg ha−1) on the water retention capacity (WRC) of a sandy loam Dystric Plinthosol. The applied biochar was a by-product of slow pyrolysis (∼450 °C) of eucalyptus wood, milled to pass through a 2000 μm sieve that resulted in a material with an intrinsic porosity ≤10 μm and a specific surface area of ∼3.2 m2 g−1. The biochar was incorporated into the top 15 cm of the soil under an aerobic rice system. Our study focused on both the effects on WRC and rice yields 2 and 3 years after its application. Undisturbed soil samples were collected from 16 plots in two soil layers (5–10 and 15–20 cm). Soil water retention curves were modelled using a nonlinear mixed model which appropriately accounts for uncertainties inherent of spatial variability and repeated measurements taken within a specific soil sample. We found an increase in plant-available water in the upper soil layer proportional to the rate of biochar, with about 0.8% for each Mg ha−1 biochar amendment 2 and 3 years after its application. The impact of biochar on soil WRC was most likely related to an effect in overall porosity of the sandy loam soil, which was evident from an increase in saturated soil moisture and macro porosity with 0.5 and 1.6% for each Mg ha−1 of biochar applied, respectively. The increment in soil WRC did not translate into an increase in rice yield, essentially because in both seasons the amount of rainfall during the critical period for rice production exceeded 650 mm. The use of biochar as a soil amendment can be a worthy strategy to guarantee yield stability under short-term water-limited conditions. Our findings raise the importance of assessing the feasibility of very high application rates of biochar and the inclusion of a detailed analysis of its physical and chemical properties as part of future investigations.