The island of Hawaii is one the eight major islands of the State of Hawaii (fig. 1). It has an area of 2,579,000 acres or about 4,030 square miles. Although its land area is 62.7 percent of the Sate, its population of 65,941 is only 8 percent. The island is a county. Hilo, the county seat, is about 216 miles southeast of Honolulu, the State capital.

Farming is the main source of income, and the highly mechanized production of sugarcane has been the main industry. Farming is now diversified, however, and other enterprises, including the production of macadamia nuts, papaya, and truck crops and the culture of orchids, anthuriums, and ornamental foliage are increasing rapidly. The only coffee grown in the United States is produced in the Kona District. The island leads the State of Hawaii in the production of cattle. Parker Ranch, the second largest in the United States, is in the Kohala District. Tourism also is a growing source of income.

The Island of Hawaii is commonly called the "Volcano Isle," the "Orchid Isle," or the "Big Island" (13). It has the only active volcanoes in the State, one of the most extensive orchid cultures in the world (fig.2), and the largest land mass in the State. Its lush, green rain forest, its warm, sunny coastal areas, and its snow-covered mountain peaks (fig. 3) provide a variety of scenery and climate.

Soil scientists made this survey to learn what kinds of soil are on the Island of Hawaii, where they are located, and how they can be used. The soil scientists went on the island knowing they likely would find many soils they had already seen and perhaps some they had not. They observed the steepness, length, and shape of slopes, the size and speed of streams, the kinds of native plants or crops, the kinds of rock, and many facts about the soils. They dug many holes to expose soil profiles. A profile is the sequence of natural layers, or horizons, in a soil; it extends from the surface down into the parent material that has not been changed much by leaching or by the action of plant roots.

The soil scientists made comparisons among the profiles they studied, and they compared these profiles with those on islands nearby and in places more distant. They classified and named the soils according to nationwide, uniform procedures.

Soils that have profiles almost alike make up a soil series. Except for different texture in the surface layer, all the soils of one series have major horizons that are similar in thickness, arrangement, and other important characteristics. Each soil series is named for a town or other geographic feature near the place where a soil of the series was first observed and mapped. Hilo and Honokaa, for example, are the names of two soil series. All the soils in the United States having the same series name are essentially alike in those characteristics that affect their behavior in the undisturbed landscape.

Soils of one series can differ in the texture of their surface layer, and according to such a difference, they are divided into types. Hilo silty clay loam, for example, is a soil type in the Hilo series. Most of the series in this survey have only on soil type. Some soil types vary so much in slope, degree of erosion, stoniness, or some other feature affecting their use that practical suggestions about their management could not be made if they were shown on the soil map as one unit. Such soil types are divided into phases. The name of a soil phase indicates a feature that affects management. Hilo silty clay loam, 0 to 10 percent slopes, is a phase of Hilo silty clay loam.

After a guide for classifying and naming the soils had been worked out, the soil scientists drew the boundaries of the individual soils on aerial photographs. These photographs show woodlands, buildings, field borders, trees, and other details that help in drawing boundaries accurately. The soil map at the back of this publication was prepared from aerial photographs.

The areas shown on a soil map are called mapping units. On most maps detailed enough to be useful in planning the management of farms and fields, a mapping unit is nearly equivalent to a soil phase. It is not exactly equivalent, because it is not practical to show on such a map all the small, scattered bits of soil of some other kind that have been seen within an area that is dominantly of recognized soil phase.

Some mapping units are made up of soils of different series. One such mapping unit is the soil association. A soil association is made up of adjacent soils that occur as areas large enough to be shown individually on the soil map but are shown as one unit because the time and effort of delineating them separately cannot be justified. There is a considerable degree of uniformity in pattern and relative extent of the dominant soils, but the soils may differ greatly one from another. The name of an association consists of the names of the dominant soils, joined by a hyphen. Amalu-Rough broken land association is and example.

In most areas surveyed there are places where the soil material is so rocky, so shallow, or so severely eroded that it cannot be classified by soil series. These places are shown on the soil map and are described in the survey, but they are called land types and are given descriptive names, such as Fill Land.

While a soil survey is in progress, samples of soils are taken, as needed, for laboratory measurements and for engineering tests. Laboratory data from the same kinds of soil in other places are assembled. Data on yields of crops under defined practices are assembled from farm records and from yield or plot experiments on the same kinds of soil. Yields under defined management are estimated for all the soils.

But only part of a soil survey is done when the soils have been named, described, and delineated on the map, and the laboratory data and yield data have been assembled. The mass of detailed information then needs to be organized in such a way as to be readily useful to different groups of users, among them engineers, farmers, and managers of woodland, pasture, and wildlife.

On the basis of yield and practice tables and other data, the soil scientists set up trial groups. They test these groups by further study and by consultation with farmers, agronomists, engineers, and others, then adjust the groups according to the results of their studies and consultation. Thus, the groups that are finally evolved reflect up-to-date knowledge of the soils and their behavior under present methods of use and management.