Get reliable science

The eight main Hawaiian Islands show a tremendous diversity of soil types despite their small combined land area of approximately 6,420 mi2 (16,628 km2). Ten of the twelve soil orders are represented exemplifying Hawaii's tremendous biodiversity. Soils vary dramatically over small distances in Hawaii because the factors contributing to their formation also vary dramatically. The effect of time on soil diversity is evident when we compare the soils on Kauai with the soils on the island of Hawaii. At about 5 million years old, Kauai is the oldest island and it shows the greatest diversity with ten soil orders, whereas Hawaii is the youngest at 500,000 years old and has six soil orders represented. Likewise, the effect of rainfall on soil differentiation is clearly exhibited as you move from the dry coastal lowlands to the moist ridges of most islands. This diversity presents several challenges, but also opportunities, for rangelands. Judicious management of Hawaii's rangeland and pasture for grazing requires an understanding of soil diversity and its implications for soil fertility and forage production. With the significant reduction of land in sugarcane there is a unique opportunity for the Hawaii livestock industry to expand. Most of these lands, once abandoned, developed into grasslands where Guinea grass (Panicum maximum Jacq.) is now the dominant species. The soils on former sugarcane lands tend to be strongly acidic and deficient in important plant nutrients like N, P, K, and Ca and thus may limit the productivity of forages. Field trials show that despite low fertility, Guinea grass can be productive with careful grazing management and highly productive with added N fertilizer. Understanding animal and plant responses to soil management is key for prioritizing improvements especially in Hawaii's diverse soil environment.