Biochar Application To A Colombian Savanna Oxisol: Fate And Effect On Soil Fertility, Crop Production, Nutrient Leaching And Soil Hydrology Volume I

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Biochar, or biomass-derived black carbon (BC), is being considered as a tool for improving soil fertility, crop yields and for C sequestration in the soil. Biochar has been widely shown to be beneficial in agriculture, but the mechanisms underlying such effects are often not clearly demonstrated. Similarly, the fate of biochar after deliberate soil application has rarely been studied in the field. Two field experiments were undertaken on an Oxisol of the oriental savanna region of Colombia: one to study the effect of biochar application on soil fertility, crop yields, nutrient leaching and soil hydrology, and another to observe the fate of soil-applied BC as well as nonBC through soil respiration, leaching and changes in soil C stocks. The application of 20 t ha-1 of biochar resulted in maize yield increases of 28, 30 and 140% in the second, third and fourth year after biochar application. These yield increases were associated with greater nutrient uptake by the crop where biochar had been applied. Leaching below the rooting zone was reduced by 17% for P, 19% for Sr, 8% for NO3-N, 23% for Ca, 28% for Mg, and 36% for K, over two years, with biochar application. Simultaneously, soil availability of Ca and Mg was also greater, although these were limiting for maize production. The retention of nutrients by biochar and greater pH thus resulted in reduced leaching and greater crop uptake, with the greatest effect observed with Ca and Mg. In this heavy clay soil, biochar application did not modify soil hydrological parameters. In a separate experiment using stable isotope techniques to attribute sample C to its source, the mean residence time of biochar applied at a rate of 23.2 t ha-1 was found to be ~600 years at 26 ?C. Losses by respiration amounted to 2.2% of BC applied, while losses by leaching amounted to less than 1%. Small amounts of BC migrated downward below the application depth. Black C application caused a 189% increase in above ground biomass, which quantitatively explains greater amounts of non-BC also being respired, leached and found as a soil C stock.
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