Biochar as A Liming Agent and Phosphorus Source to Enhance the Growth of Soya Bean in Two Acid Soils.

Abstract

Unavailability and high cost of conventional liming materials have contributed largely to low food production in acid soils of Ghana. Biochar produced from agricultural waste materials have high concentration of basic cations and available P that could be exploited for use as liming material and/or P source. However, the biochar type that will provide a conducive soil pH vis-à-vis P availability for food crop production in acid soils of Ghana has received little attention. Consequently, two typical acid soils, Ankasa series (Plinthic Acrudox) and Tikobo series (Typic Hapludult) were amended with corn cob and rice husk biochar types charred at 500 and 700 oC at a rate of 80 tons/ha in a screen house experiment to ascertain the efficacy of the biochar types as substitutes for agricultural lime and sources of P. The Ca equivalent of the biochar types from CaCO3 was amended to the soils to serve as a realistic control. The amended soils in addition to their un-amended counterparts were all kept at 80% field capacity in a completely randomized design in the screen house to allow for pH equilibration amidst weekly pH and bi-weekly exchangeable Al and basic cations monitoring. After pH equilibration, inoculated soya bean seeds were sown at stake. Nitrogen was applied at rates of 0 kg/ha and 10 kg/ha. Phosphorus was applied at zero and the biochar P equivalent from triple super phosphate was applied to the non-biochar-amended soils. Extra 30 kg P/ha from TSP was applied to some of the biochar amended soils to ascertain if any, the combined effect of synthetic P and biochar on growth and nodulation of soya bean. At flower initiation, crops were harvested, nodules counted, root volume, shoot and root dry matter and P uptake were determined. Results showed that corn cob charred at 700 oC was able to raise pH from 4.2 to 5.2 in Ankasa Series and from 4.9 to 6.2 in Tikobo Series within a six-week incubation and equilibraation period. Rice husk charred at 700 oC was able to raise pH from 4.2 to 5.0 Ankasa Series and 4.9 to 5.8 in Tikobo Series within the incubation period. All the biochar types reduced Al concentration from 0.4 cmol/kg to undetectable levels in the Tikobo Series with the element being reduced from 1.31 cmol/kg to 0.45 cmol/kg in the rice husk and corn cob at 700 oC biochar amended Ankasa soils within the six-week equilibration period. Soya bean nodulated in the rice husk biochar charred at 700 oC amended Tikobo Series without any form of synthetic fertilization. There was no nodulation in the Ankasa series. Shoot P uptake of soya bean was 1.5 and 1.4 times more in Ankasa and Tikobo Series, respectively when amended with rice husk biochar charred at 700 oC than the same soils amended with conventional lime and equivalent biochar P from triple super phosphate. Apparent nutrient recovery efficiency was higher in biochar amended soils than the CaCO3 amended soils. The biochar amended soils showed an increase in organic carbon contents. The residual total P increased from 101.4 mg/kg to 257.8 mg/kg when rice husk biochar charred at 700 oC was applied to Tikobo Series whilst there was an increase from 164.0 mg/kg to 344.9 mg/kg when corn cob biochar charred at 500 oC was added to Ankasa Series. There was high increase in residual available P after amending the soils with the liming materials. The study concludes that corn cob and rice husk biochar can be used as liming materials and P source in acid soils, particularly Tikobo Series for growth of soya bean.