Differential effect of carbon sources on nitrogen transformation in Hawaiian soils
SummaryMineralization of native N was curtailed by addition of carbon sources in all soils tested. A readily available energy source, sucrose, accelerated and increased the immobilization of native as well as added N more than a slowly available energy source, sugar cane bagasse. Addition of N as ammonium sulfate increased CO2 production in only one out of five soils when no energy source was added. With energy source addition, N addition enhanced CO2 production in most soils. Without any treatment, the immobilization of added N was related to the C:N ratio of the soil; maximum immobilization occurred in the soil with the widest C:N ratio.
Effects of sugarcane trash and pineapple residue incorporation on soil nitrogen, pH and redox potential
SummarySugarcane trash and pineapple residue, in a finely ground state, were mixed with soil at different levels with and without nitrogen fertilization. The nitrogen treatments received 112 kg N/ha as ammonium sulfate. The samples were incubated for different lengths of time (up to 16 weeks) and analyzed for total, ammonium, nitrate and nitrite nitrogen, pH and redox potential.There was no noticeable loss of nitrogen from the samples due to denitrification. The concentration of ammonium and nitrate nitrogen remained very low throughout the incubation study, probably due to immobilization by soil microflora. After 12 weeks, there was some indication of the release of mineral nitrogen from immobilized reserves. The redox potential was found to be between 400–600 mv during this study and nitrates became unstable below 400 mv redox potential.
Studies on root enamel (2). Enamel pearls. A review of their morphology, localization, nomenclature, occurrence, classification, histogenesis and incidence.
Enamel pearls are one of a number of different enamel structures that can be found on the roots of deciduous and permanent teeth. They have a distinct predilection for the furcation areas of molar teeth, particularly the maxillary third and second molars. They can consist primarily of enamel, but in most instances, a core of dentin is contained within them. On rare occasions, even pulpal tissues can be found. Enamel pearls usually occur singularly, but up to 4 enamel pearls have been observed on the same tooth. Depending on the study, enamel pearls on permanent molar teeth have an incidence rate of between 1.1%-9.7% with distinct differences among racial and national groups. The incidence of enamel pearls increases greatly in histological studies, suggesting that they are often obscured by a covering of cementum.