Nutrient leaching below the rooting zone is reduced by biochar, the hydrology of a Colombian savanna

1
Nutrient leaching below the rooting zone is
reduced by biochar, the hydrology of a Colombian
savanna Oxisol is unaffected
by Julie Major1, Johannes Lehmann1, Marco Rondon2
and Susan J. Riha1 1Department of Crop and Soil
Sciences, Cornell University, Ithaca NY 14853
2International Development Research Centre,
Ottawa, ON K1G 3H9, Canada (formerly Centro
Internacional de Agricultura Tropical (CIAT),
A.A. 6713 Cali, Colombia) Contact
jm322_at_cornell.edu

• Relevance
• The mechanisms that underlie crop yield
  improvements with biochar remain poorly
  understood.
• Laboratory and pot studies indicated that biochar
  is efficient at sorbing inorganic nutrients
  (Downie et al. 2007 Dünisch et al. 2007 Lehmann
  et al., 2003).

• Objectives
• This work was undertaken to assess the effect of
  biochar application on soil water movement and
  nutrient leaching in the field, by saturated as
  well as unsaturated flux, over two years.

Summary of Materials and Methods
A field experiment was established on an Oxisol
at Matazul farm in the Oriental savanna region of
Colombia. Wood biochar made commercially using
traditional techniques was ground and
incorporated to 10 cm in a randomized complete
block design with 3 replicates in Dec. 2002.
Application rates were 0, 8 and 20 t biochar
ha-1. In Dec. 2004, free-draining as well as
suction cup lysimeters and datalogged
tensiometers were installed from a soil pit
giving access to one replicate of application
rates 0 and 20 t ha-1.
Free-draining lysimeters
Free-draining lysimeters were installed at 15,
30, 60 and 120 cm depths, with one lysimeter per
depth, per treatment. Water accumulated in
bottles was measured and collected weekly during
the 2005 and 2006 rainy seasons, while all plots
were cropped to a maize-soybean rotation and
fertilized with inorganic fertilizer according to
standard practices. Suction cup lysimeters were
inserted at 15, 30, 60, 120 and 200 cm depths,
with 2 lysimeters for each depth in each
replicate plot. Vacuum was applied constantly
using battery-powered pumps. Water was analyzed
for nutrients by atomic emission spectrometry
(ICP), for NO3-N by ion chromatography, and for
NH4-N colorimetrically by the phenate method.
Suction cup lysimeters
Water movement through the soil profile was
modeled using HYDRUS-1D, and soil surface
infiltration was measured.
Results and discussion
Between plots receiving 0 or 20 t biochar ha-1,
NO significant or ecologically relevant
difference in
Moisture retention curve
Surface infiltration
Matric potential over time
Soil moisture content
This is not surprising, given the soil was a
heavy clay

• Leaching by saturated flux over 2 years
• Flux reductions were key in reducing total
  leaching only at 15 cm.
• At 30 and 60 cm, concentrations of nutrients were
  generally lower when biochar was applied. At 0.6
  m, total nutrient amounts leached were reduced
  despite greater flux with biochar.
• With 20 t biochar ha-1, leaching was reduced for
• Ca by 27-77
• Mg by 37-80
• NO3-N by 18-78
• P by 4-46
• Sr by 2-82
• K by 0-71

The big picture With biochar, over 2 years in
the field, we saw -less leaching of important
nutrients -more crop uptake of nutrients -greater
soil availability of nutrients
Greatest reductions occurred below the rooting
zone at 1.2 m, however small total amounts were
leached at that depth

• Leaching by unsaturated flux over 2 years
• With 20 t biochar ha-1, leaching below the
  rooting zone was reduced for
• Ca by 14
• Mg by 22
• NO3-N by 2
• Sr by 15
• K by 31
• No differences in unsaturated flux between
  treatments
• Nutrient concentrations reduced with biochar

-All these occurring simultaneously indicate that
biochar retains nutrients in the soil
References Dünisch, O., V.C. Lima, G. Seehann, J.
Donath, V.R. Montoia, and T. Schwarz. 2007.
Retention properties of wood residues and their
potential for soil amelioration. Wood Sci Technol
41169-189. Downie, A., Van Zwieten, L., Chan,
K.Y., Dougherty, W. and Joseph, S. (2007)
Nutrient retention characteristics of agrichar
and the agronomic implications, poster presented
at the International Agrichar Initiative
Conference, April 2007, Terrigal, NSW
Australia. Lehmann, J., J.P. da Silva Jr., C.
Steiner, T. Nehls, W. Zech, and B. Glaser. 2003.
Nutrient availability and leaching in an
archaeological Anthrosol and a Ferralsol of the
Central Amazon basin fertilizer, manure and
charcoal amendments. Plant Soil 249343-357.