Impact of MgCl2 Modified Biochar on Phosphorus and Nitrogen Fractions in Coastal Saline Soil

Biochar application is claimed to improve nutrient availability in many problem soils; however, pristine biochars are often reported to produce inconsistent results. Therefore, appropriate biochar modification techniques are required to retain soil nutrients at an optimum level. To increase Nitrogen (N) and Phosphorus (P) availability in coastal saline soil, two slow pyrolyzed biochars viz domestic organic waste (DWB) and farmyard manure (FMB) were modified with MgCl2. Ten different treatments comprising the biochars (pristine and modified) with and without the recommended fertilizer were applied (2% w/w) to the soil and incubated for ninety days. The soils were analyzed for pH, EC, available , and different phosphorus fractions sequentially extracted by NH4Cl, NaHCO3, NaOH, and HCl. During the incubation period, biochar treatments increased all phosphorus and nitrogen fractions than the control and recommended fertilizer treatment. The application of FMB significantly (p 4Cl, NaHCO3, and NaOH extractable P fractions from DWB, while HCl soluble fraction was enhanced (p > 0.05) by DWB. The increased Al and/or Fe bound phosphate after 60 days of incubation had significant correlations to decreasing soil pH and NaHCO3-P, indicating reduced availability with time. Further Mg modification slightly increased P availability only after 60 days of incubation. The modification also improved both nitrogen fractions but significantly (p 3-N content which could be the result of electrostatic attraction between Mg2+ and ions. Overall, Mg-modified biochar may retain both phosphates and nitrates in soil. However, the magnitude of retention will vary depending on biochar type, nutrient species, and aging in soil.