Abstract:
Biochar amendment to cropping lands is a promising management tool to increase crop
productivity while mitigating soil degradation. Biochar application influences the nutrient
availability in soil and other soil properties. Rhizosphere is the root-soil interface that plays a
predominant role in nutrient uptake by plants. Rhizosphere nutrient dynamics and its relation to
nutrient uptake of crops as influenced by biochar amendment remains poorly understood. A pot
experiment was conducted in a greenhouse to investigate the impact of Gliricidia biochar
application and incubation period on plant growth and nutrient uptake of soybean (Glycine max
L.). Plants were grown with (2.5% weight basis) or without biochar amendment coupled with
(one month incubation period) or without an incubation period. Rhizosphere nutrient
availability, plant growth, uptake of nitrogen (N), phosphorus (P) and potassium (K), and yield
parameters were measured. A soil column leaching experiment was conducted separately to test
the soil nutrient retention ability of biochar-applied soil. Irrespective of the incubation
condition, pod dry weight was significantly increased (P< 0.05) when plants were cultivated in
biochar-amended soil. There was a tendency of increasing rhizosphere concentration of N, P,
and K in biochar-treated soil compared to soil without biochar at physiological maturity of
soybean. Further, concentrations of the same nutrients were lower in rhizosphere soil than
those in non-rhizosphere soil indicating the plant uptake. Total plant uptake of N, P, and K
greatly enhanced under biochar amendment compared with the plants grown without biochar.
Without incubation, soybean plant increased its P and K uptake, respectively by 52% and 48%
with biochar amendment compared to those without biochar. With incubation, the relevant
increases were 42% and 32%, respectively. The results from soil column leaching experiment
suggest that the application of biochar in planting media could be an effective way to retain soil
N through reducing the leaching losses. At six weeks after planting, N leaching from soil under
biochar amendment was reduced by 57% compared to that of soil without biochar. Hence, the
results confirm that the application of biochar could increase nutrient availability in rhizosphere
and their subsequent root uptake.
