Phosphorus availability in soils amended with biochar
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Date
2017
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Punjab Agricultural University, Ludhiana
Abstract
The current system of agricultural crop production is severely constrained by soil available P
deficiency in soils and costs associated with mineral P fertilizers to address this constraint in
arable lands. Thermo-chemical conversion of surplus biomass to produce biochar is an
emerging ameliorating strategy in the context of sustainable P and biomass waste
management. Two incubation studies (90 and 60 days respectively) were conducted to
investigate the interactive effects of rice residue biochar and the inorganic-P fertilizer on
phosphorous availability in soils with varying P status and contrasting pH. For the first
incubation study, four rates of the rice residue biochar (0, 10, 20 and 40 g kg-1) in
combination with three levels of the inorganic-P (KH2PO4) (0, 25 and 50 mg kg-1) were added
into the medium and the high P status soils. Increasing biochar addition rates alone or in
combination with the inorganic-P resulted in significant increase in the P pools (plant
available Olsen-P, microbial biomass P and the inorganic-P fractions), greater so in the high P
than the medium P status soils. In the second incubation experiment, two rates of rice residue
biochar (0 and 20 g kg-1) with three rates of inorganic-P (KH2PO4) (0, 25 and 50 mg kg-1)
were added into the three contrasting pH soils (acidic, neutral and alkali soils). Biochar
addition alone or in combination with inorganic-P resulted in significant increase in organic
and inorganic P pools (microbial biomass-P, plant available Olsen-P and mineral bound
inorganic-P fractions) and followed the order neutral soil > alkali soil > acid soil. The biochar
mediated changes in P availability in both experiments were attributed to: 1) high available P
content in the biochar itself and; 2) biochar induced reduction in the P sorption capacity of
soils due to increase in competition for the P sorption sites by the released P and the surface
functional groups present in the biochar. Further, lower alkaline and acid phosphatase activity
with increasing rates of biochar addition in the soils of both experiments elucidates biochar’s
ability to act not only as a source but also as a sink of P. Therefore, it may be concluded that
the rice residue biochar can be used as a promising amendment in meeting the crop P demand,
and thus has the potential to supplement or replace the exhaustible mineral P fertilizers.