Effects of Land Use On Soil Properties in a Hawaiian Volcanic Ash Soil.

Soils on the mid-elevation (325 to 1200 meters asl) northeastern slopes of the Island of Hawaii developed from volcanic ash parent material in a warm and humid climate. These soils were used continuously for sugar cane cultivation at elevations below 650 meters for approximately 100 years between the late 1800s and the closure of the last sugar cane plantation in 1996. Pasture and forest were the major land uses for these soils at higher elevations. Current land uses include pasture, forest, timber plantations, housing, crops, and unmanaged grass fallow. We propose that historical land use has caused changes in soil physical and chemical properties that are evident today. We analyze differences observed between former sugar cane, pasture, and forest soils of the Honokaa soil series (Hydrous, ferrihydritic, isothermic Acrudoxic Hydrudands). Data collected from pedon samples and field descriptions across the landscape indicate that former sugar cane areas consistently have lower surface organic matter content, higher bulk density, and slower infiltration rates than soils that were used for pasture or remained under natural vegetation. Differences in other chemical and physical properties are also evident. Comparison of samples from natural and pasture areas to those collected in sugarcane lands in the 1960s and more recently suggests that mechanization of sugarcane cultivation in the 1940s and 1950s intensified soil changes. Our analysis indicates that land use, specifically sugar cane, can change soil properties over time.  The changes we observe in soil properties between former sugar cane, pasture, and forest soils of the Honokaa series are important because of their impact on present day management of these areas. Future investigations will explore if current land use has any effect on reversing the changes back to a state similar to the pasture and natural vegetation areas.