Studies on nitrogen transformation and nitrate adsorption in soils Nitrogen transformation and nitrate adsorption in soils

Singh, Budh Ram
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Studies on nitrogen transformation and nitrate adsorption were conducted with Hawaiian soils belonging to the Akaka, Wahiawa, Paaloa, Koko, and Lualualei series. There was no definite or conclusive trend of NH4- or NO3-N accumulation with time in the Akaka (virgin), Akaka (cultivated), Wahiawa "A", and Wahiawa "B" soils in situ. However, under laboratory conditions both NH4- and NO3-N were affected. The Akaka (virgin), Akaka (cultivated), and Wahiawa "A", stored In polyethylene bags at room temperature, showed a substantial increase in NO3-N with time but practically no change in NH4-N. In contrast, when two of the above soils [Akaka (virgin) and Wahiawa "A"] were oven dried at 90°C, NH4-N increased with time but N03-N remained unchanged during the entire course of oven drying. Possibly, increased NH4-N resulted from the splitting of ammonium from the proteinaceous parts of organic matter. The Akaka (virgin) and Wahiawa "c" soils were treated with chloride salts. NH4-N mineralization was generally a direct function of salt concentration and length of incubation. Probably NH4-N release resulted from microbial cell breakdown and/or chemical processes. Presumably once the NH4 ions were released from soil organo-inorganic complexes, the subsequent exchange reaction between cations in soil solution and NH4 ions on surface was mainly involved with bringing NH4 ions in the soil solution. A consideration of the overall effect of cations on NH4-N release in the two soils led to the series, Al > Fe> Ca > Mg > K > Na, in order of decreasing NH4 replacing power. However, the series was true only to a concentration of O. 1 M. Beyond this, Al and Fe ions were probably complexed in the soil. The added salts had little or no effect on NO3-N content of the two soils. The Akaka (virgin), Wahiawa "C", Paaloa, Koko, and Lualualei soils were subjected to varying dosages of gamma radiation. The release of NH4-N generally increased with increasing dosages in all soils, while NO3-N decreased in the first three soils, possibly due to certain chemical reactions rendering the loss of nitrate. The rate of NH4-N mineralization in irradiated soils was highest during the first seven days and declined during subsequent incubation periods. Irradiation decreased the recovery of added NH4-N in the Koko and Lualualei soils and N03-N in all soils. In another series three acid soils, Akaka (virgin), Wahiawa "C", and Paaloa, were limed before irradiation. Liming decreased the recovery of added NH4- N and increased the recovery of added NO3-N. Possibly chemical reactions responsible for nitrate loss were inhibited by liming. The adsorption of NO3 was studied with the Akaka (virgin) and Wahiawa "e" soils. Adsorption increased with increasing concentration and decreasing pH of the electrolyte solution. The nitrate adsorption in the two soils followed the Freundlich type of isotherm.
Bibliography: leaves [97]-105.
xiii, 105 l graphs, tables
Soils -- Nitrogen content, Soils -- Hawaii
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