Influence of Flooding, Soil Ph, Copper, and Zinc on Growth and Chemical Composition of Rice Plants.

Investigations were conducted in the greenhouse, field, and laboratory to evaluate eight different chemical methods for estimating the availability of Cu in air-dried and flooded soils, and to determine the influence of flooding, soil pH, and applications of Cu and Zn on the growth and chemical composition of rice (Oryza sativa L. cultivar Saturn) plants grown on selected soils in Louisiana. DTPA-TEA extractant generally removed smaller amounts of Cu and Zn and larger amounts of Mn and Fe from flooded soils than from air-dried soils. In general, levels of soil Ca, Mg, and K were significantly correlated with extractable Cu. No significant relationships were found between extractable Cu and soil pH or soil organic matter content. The DTPA-TEA, pH 7.3, 0.1N HCl, and 1N NH(,4)OAc, pH 4.8 extractable Cu were significantly related to the concentration of Cu in rice tissue. A significant negative correlation was found between Cu concentration in rice tissue and soil organic matter content. Multiple regressions consisting of extractable Cu and soil organic matter accounted for over 53% of the variations in predicted concentration of Cu in rice tissue. In general, Cu uptake by rice plants was significantly correlated with extractable Cu. Flooding the Lafitte muck significantly increased the production of dry matter, total leaf chlorophyll content, and the concentrations of Cu, Fe, and P, and significantly decreased the concentrations of Zn, Mn, Ca, and K in rice tissue. The dry matter production and nutrient concentration and uptake by rice plants were greatly reduced when soil pH was adjusted to over 5.9 by application of CaCO(,3). The concentrations of Cu, Zn, Mn, and Fe in rice tissue were significantly higher at pH 4.8 than at pH 4.2. The application of 5ppm of Cu significantly increased the production of dry matter, total leaf chlorophyll content, and concentrations of Cu, Fe, and Ca, and significantly decreased the concentrations of P and K in rice tissue. The concentration of Cu in the tissue of rice plants grown on Lafitte muck without applied Cu tended to be lower under flooded conditions than under nonflooded conditions. When Cu was applied, it was significantly higher under flooded conditions. The soil pH levels did not significantly influence the concentration of Cu in plants grown on the soil that did not received Cu. Application of Cu resulted in a significantly higher Cu concentration in rice tissue at pH 4.8, 5.4, and 5.9. The concentration of Zn in rice tissue was significantly increased at pH (LESSTHEQ) 5.4, and decreased at pH (GREATERTHEQ) 5.9 by application of Cu. Cu and Zn applied to Crowley silt loam under field conditions did not significantly influence the grain yields, although consistently higher yields were obtained on plots that received Cu and Zn in each of the two years. The application of Cu significantly increased the leaf concentrations of Cu and Zn. Applied Zn significantly increased the concentration of Zn, but did not significantly influence the concentration of Cu in rice leaves at first joint. The data obtained from laboratory, greenhouse, and field investigations indicate that there is not a critical need for supplemental Cu fertilization of rice on the mineral soils. The data suggest that Cu may be beneficial to rice plants growing on soils that contain more than approximately 4% of organic matter and less than 0.2 ppm of DTPA-TEA extractable Cu