Soil Carbon Stock and Total Nitrogen in Hawaiian Sugarcane Commercial Plantations.

There has been a recent, renewed interest in Hawaiian sugarcane as a biofuel feedstock.  However, there is little information on how much soil carbon (C) and nitrogen (N) is stored in Hawaiian sugarcane fields under normal, monoculture operations. Soil C and N data are needed to assess the life cycle impacts of this biofuel system.

Because of lack of quantitative and qualitative information on soil C and N , we collected soil samples from fields with different texture [i.e. sandy clay loam (scl), clay (c), clay loam (cl)], management practices [i.e. burning before  harvest (BH) vs. green harvest (GH)], sugarcane varieties (H65-7052, H78-3567, H86-3792, H87-4319) and sugarcane growing stages. Collected soil samples were dried, ground and analyzed for dissolved organic carbon (DOC), total organic carbon (TOC), total carbon (TC) and total nitrogen (TN).

Preliminary results showed that scl soils had higher TC compared to clay and cl soils under BH practices. GH practices, higher TC was found under clay soils than cl soils. In addition, there was no consistent response for TN and DOC.  For the four sugarcane varieties, higher TC and TN and lower DOC were found on soils growing H65-7052 and H86-3792 compared with H78-3792 and H87-4319 varieties. Also, increases in TOC were found at 6 months after planting at deeper depths due to root presence. The research is ongoing and additional results will help further elucidate the soil C and N status for this growth environment.