Units, are shown nested within provinces, the smallest unit of the ecoregion level. Sections are delineated primarily by evaluation and integration of physical and biological components including climate, physiography, lithology, soils, and potential natural communities. Not shown on the front cover map are subsection ecological units, which are subdivisions of sections. Together, sections and subsections form subregions that may be used for planning and assessments at regional scales.

In 1996, nine federal agencies with mandates to inventory and manage the nation's land, water, and biological resources signed a memorandum of understanding entitled "Developing a Spatial Framework of Ecological Units of The United States." This spatial framework is the basis for interagency coordination and collaboration in the development of ecosystem management strategies. One of the objectives in this memorandum is the development of a map of common ecological regions for the conterminous United States. The regions defined in the spatial framework will be areas within which biotic, abiotic, terrestrial, and aquatic capacities and potentials are similar. The agencies agreed to begin by exploring areas of agreement and disagreement in three federal natural-resource spatial frameworks--Major Land Resource Areas of the US Department of Agriculture (USDA) Natural Resources Conservation Service, National Hierarchy of Ecological Units of the USDA Forest Service, and Level III Ecoregions of the US Environmental Protection Agency. The explicit intention is that the framework will foster an ecological understanding of the landscape, rather than an understanding based on a single resource, single discipline, or single agency perspective. This paper describes the origin, capabilities, and limitations of three major federal agency frameworks and suggests why a common ecological framework is desirable. The scientific and programmatic benefits of common ecological regions are described, and a proposed process for development of the common framework is presented.

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Soil solution P concentration was monitored at weekly intervals during the vegetative growth of Rice (Oryza sativa L. var. ‘Bluebelle’) on flooded soils from the gulf coast region of Texas. Significant increases in dry matter production were obtained from application of phosphate fertilizer. Average soil solution P concentration ranged from 0.02 to 5.28 ppm when all soils and P fertilization rates were considered. A linear relationship was obtained between the logarithm of the average soil solution P concentration and the P concentration or P uptake of the plant. Yields were greater than 90% of maximum when the average soil solution P concentration was greater than 0.1 ppm. The concentration of P in the plant tissue at 0.1 ppm soil solution P was 0.25%.

A number of acidic ammonium polyphosphate fertilizers which varied in pH (2.20-4.20) and nonorthophosphate content were evaluated as potential carriers of manganese (Mn). Fertilizer residues recovered after reacting ammonium polyphosphate-MnSOfH20 blends with soil contained from 6 to 82% of the applied Mn. Reaction and precipitation of the Mn with the fertilizer phosphate increased with increasing fertilizer pH. X-Ray analysis of the residues identified only one reaction product, MnafNHiMPaOT^• 2H2O within the pH range studied. Manganese uptake by oats in the growth chamber from a point application of the fertilizer blends was dependent upon the fertilizer pH and distance of Mn diffusion from the point of application. The data indicate that under-ammoniated polyphosphates with a saturated pH less than 2.65 would be most effective as Mn carriers.