Soil Carbon Stock and Total Nitrogen of Different Hawaiian Sugarcane Varieties Used On 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 under the different Hawaiian sugarcane varieties commonly used 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 loam (cl), loam (l)], sugarcane varieties (H65-7052, H78-3567, H86-3792 and H87-4319) and sugarcane growing stages (Tillering, grand growth and maturity). Collected soil samples were dried, ground and analyzed for dissolved organic carbon (DOC), total carbon (TC), total nitrogen (TN) and nitrates (NO3-N).

Preliminary results showed that scl soils had higher TC compared to cl soils. 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 12 mo. 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.