Spatial and Temporal Distribution of Soil Moisture in Drip Irrigated Tropical Grasses Grown in Hawaii.

Recently, bioenergy has been identified as capable of playing an important role in the economy of Hawaii. Because its scarcity is an acute problem in the state water issue must be always addressed in all agricultural practices. To find a cost effective and environmental sustainable way to produce bioenergy, we evaluated three tropical grasses; sugarcane, energy cane and bana grass for their bioenergy potential under three drip irrigation regimes; farmer irrigation rate (FIR) 100%, 75% of FIR and 50% of FIR. The impact of the tree irrigation regimes on the soil moisture profiles were examined through the use of capacitance probes installed to 160 cm depth in the soil under the drip line (Wet)  and between the drip line (Dry). Measurement were taken daily.  Soil moisture varied by depth, and by distance away from the drip line. Soil moisture profiles indicated that in the Dry zone most of the irrigation water moved to lower soil depth, beyond 70 cm, while in the Wet zone water retained in the 30 cm depth area never moved beyond 70 cm, indicating active plant water absorption. The differences in soil moisture between the two zones were greatest at 30cm where soil moisture reached near 40% in the Wet zone while it was only about 20% in the Dry zone. The trend were reversed  in the 70cm depth.