Soil carbon and nitrogen dynamics as affected by lipid-extracted algae application

• Lipid-extracted algae (LEA) soil application increased SOC and SMBC.
• LEA application may be a means of mitigating SOC losses from soil.
• Soil application of LEA increased plant available N.
• Increased soil salinity may be problematic with repeated LEA applications.

Algae are being intensively researched as a potential bioenergy feedstock. Although algae are more productive per area of cultivation compared to first-generation biofuel feedstocks, its production may not be economically sustainable without high-value coproducts. One of many possible coproducts is algal residue following lipid extraction that might be used as a soil amendment for agricultural production. This experiment was aimed at determining, under laboratory conditions, the effects of lipid-extracted algae (LEA) (Nannochloropsis salina) amendment on soil C and N mineralization, soil microbial biomass, and soil pH and salinity over time. Soil organic C measured 392-d after amending soil with 1.5% or 3.0% LEA (dry weight basis) was increased by approximately 0.2% and 0.3% organic C (OC), respectively, compared to the control. Approximately 50% of added LEA-C was mineralized compared with 65% of added wheat (Triticum aestivum L.) straw-C. Lipid-extracted algae application may be one means of increasing OC; however, problems with excess soil salinity, sodicity, and nitrate-N may occur at high (3.0% or greater) addition rates.