Ammonium fixation in Hawaiian soils

Abstract

The physical and chemical nature of the soils that occur in the State of Hawaii are unique as compared to soils found in other parts of the world. The soils of the wet area of the Hilo-Hamakua coast on the Island of Hawaii, maintain a moisture level around 300% for the most part .of the year. These soils which developed from volcanic ash and under high rainfall are very active in ion fixation. Their mineral composition consists mainly of amorphous colloidal hydrated oxides of aluminum and iron. Allophane and gibbsite are found in considerable quantities (4,41), while magnetite, maghemite, and quartz are a minor portion of the constituents of these soils. The fixation of ammonium in these and other Hawaiian soils has been investigated very briefly, and all reported studies were quantitative in nature. Due to the developments in technology and the availability of modern equipment, like the X-ray diffractometer, qualitative studies of NH4 fixation in Hawaiian soils became possible. The major interest of this study was to determine the nature of NH4 fixation in Hawaiian soils, with emphasis on the soils that are predominantly amorphous in nature. The soils were kept under field conditions with the exception of the additions of NH4 carriers. No quantitative analysis was attempted due to the complexities and the unlimited sources of error that could result when tremendously large quantities of NH4 carriers were added to the soil. The very high concentration of NH4 carriers that were added to the soil was selected to simulate conditions that might prevail in the field when the fertilizer is applied in a band. When a solid NH4 fertilizer is added to the soil, the area surrounding the fertilizer granule will have a very high concentration of NH4 , and that is where any initial reaction between the NH4 carrier and the soil might occur.