Implications of Acidified and Non-Acidified Biochars on N and K Availability and their Uptake by Maize Plants

Maize is one of the important crops in Egypt that can be grown successfully on light textured soils. Although amending these soils with biochar may increase the efficiency of nutrient utilization by plants; yet both biochars and Egyptian soils exhibit alkaline nature. The current study investigates to what extent can biochar modified with either sulfuric acid or with elemental sulfur (S) (an acidifying agent) surpass the effect of adding biochar solely to a sandy soil (93% sand), with emphasis on the increase of N and K availability in soil and their uptake and distribution within maize plants. A greenhouse experiment was conducted in a complete randomized design comprising (1) no biochar application (control), (2) biochar applied at a rate of 10g kg-1, (3) biochar (10g kg-1) + elemental sulfur (2 g kg-1) and (4) biochar acidified with H2SO4 (10g kg-1). These treatments were added 2 weeks prior to maize sowing. Thereafter, all pots were planted for 60 days and soil moisture was kept at 80% of the water holding capacity throughout the period of this investigation. Results indicate that only “acidified bioachar” and “biochar+S” treatments raised significantly SO42- content in soil; thus they both decreased soil pH. On the other hand, application of non-acidified biochar solely raised soil pH. All treatments decreased soil bulk density and improved soil moisture characteristics (field capacity, permanent welting point and available water content). This, in turn, significantly raised N- and K- available contents in soil and consequently increased their uptake by maize plants. In particular, the non-acidified biochar recorded the highest increases in N-uptake by plants while acidified biochar recorded the highest K uptake followed by biochar+S. Overall, all biochars significantly boosted root and shoot biomass, especially the acidified one, followed by the combined biochar+S treatment. Furthermore, these treatments recorded the highest N and K utilization efficiencies by maize plants. In conclusion, using elemental sulfur with biochar may effectively increase the efficiency of applied biochar via increasing nutrient use efficiencies; yet this dual application might not be as efficient as acidified biochar for enhancing plant growth.