http://www.loc.gov/mods/v3 http://www.loc.gov/standards/mods/v3/mods-3-2.xsd
Ammonium availability as influenced by clay minerals in Texas rice-producing soils
In the Texas Gulf Coast, there are about two million acres of Beaumont and Lake Charles soils (Pelluderts) that require regular N-fertilization to yield a satisfactory rice crop. Nada (Typic Albaqualf) and other similar soils can frequently supply enough native N to produce 4,000 kg/ha or more rice grain. This study proposes to determine whether NH4 fixation is one of the reasons why Beaumont and Lake Charles soils require more nitrogen fertilization for rice production. The potential for NH4 fixation in Beaumont soil was established when a yield reduction occurred upon KCl addition to experimental plots. Equivalent amounts of NaCl did not reduce plot yields, indicating that the yield reduction was the result of entrapment of NH4 in clay minerals when K was added. Characterization of the clay minerals showed that Beaumont soil could potentially fix more NH4 than Nada soil because of its: 1) greater content of high-charge (0.76 per formula unit) smectite, 2) greater portion of charges located in the tetrahedral sites, and 3) greater amount of exchangeable K. Two-month incubation of Beaumont soil samples, chemically treated to increase the amount of fixed NH4, in the root zone only showed partial release when the sample was Ca-saturated. Nitrogen isotope analysis showed that the released NH4 came from the added fraction. The native fixed NH4 level was little affected by either the fixation or the incubation procedures. When the Beaumont sample was K-saturated the added NH4 was not released at all. Nada soil did not fix any more NH4 than its native level during the NH4 solution washings nor did it release any upon incubation. Lake Charles soil showed clay and fixation characteristics similar to that of Beaumont. The presence of a 2:1 layer silicate in Beaumont and Lake Charles soils with x-ray diffraction characteristics of a smectite and NH4 fixation characteristics of a vermiculite is recognized.
Includes bibliographical references (leaves 56-59).