Search

Temporal and spatial availability of K can influence soybean [Glycine max (L.) Merr.] productivity. This study quantified the impact of initial soil K concentrations, soil-water content, and soybean K uptake on soil K pools (water-extractable solution-phase K [[K.sub.sol]], 1 mol [L.sup.-1] N[H.sub.4]OAc-extractable K, referred to as exchangeable K ([K.sub.exch]), and 5-min sodium tetraphenylboron [NaTPB] extractable K [[K.sub.TPB]]) and compared predictions of plant K availability using the NaTPB vs. N[H.sub.4]OAc tests. Soil and soybean samples were collected five times between the VE and R6 development stages in 2003 and 2004 from fallow and cropped notill Toronto--Millbrook silt loam Alfisols at the Throckmorton Purdue Agricultural Center. Gravimetric soil water content was measured weekly during the growing season. Low-, medium-, and high-K fertility plots were replicated four times. Initial [K.sub.exch] levels ranged from 60 to 290 and from 50 to 90 mg [kg.sup.-1] at the 0- to 10- and 10- to 20-cm depths, respectively. Medium- and high-fertility soils had the highest grain yields. The 0- to 5-cm soil layer had the highest [K.sub.exch] levels, water availability, and soybean K uptake. Compared with [K.sub.exch], [K.sub.sol] levels were less stratified and the surface layer was less dynamic. The NaTPB extraction was a better predictor of soybean K uptake in 1 yr, but across both years, N[H.sub.4]OAc was superior. Potassium measurements in the 0- to 10-cm soil layer provided slightly better estimates of plant K uptake than those in the 0- to 20-cm layer. Greater water availability and K uptake in the 0- to 5-cm soil layer suggest that under evenly distributed, intermittent rainfall conditions in somewhat poorly drained soils, vertical soil K stratification might not be a concern for no-till soybean production. Abbreviations: ET, evapotranspiration; [K.sub.exch], exchangeable potassium; [K.sub.fix], fixed potassium; [K.sub.sol], solution-phase potassium; [K.sub.TPB], 5-min sodium tetraphenylboron extractable potassium; NaTPB, sodium tetraphenylboron.

Simultaneous determination of the amounts of Na and K inside single human erythrocytes was accomplished by laser vaporization and monitoring the atomic emission produced. By using a modified sheath-flow arrangement, detection of 8 fg (0.35 fmol) of Na is possible with one laser pulse. By using Poisson statistics, one can obtain single-cell information even when multiple cells are vaporized per laser pulse. The intracellular contents for a given individual were found to vary significantly. The + or - 55% and + or - 155% variations for Na and K, respectively, cannot be explained by changes in cell volume. There is only a weak correlation between the Na and K contents in single cells. The results reflect the age distribution of erythrocytes in the sample. Presumably, the enzymes regulating ion transport lose their activities in the older cells.

A simple setup for measuring the amount of potassium in foods is described. A 3-in. NaI detector is used to measure samples that are 3000 [cm.sup.3] in size. With moderate shielding, the potassium content can be measured down to a detection limit of a few pans per 10 000.

A new and accurate measurement of the isotopic abundance of potassium in samples from the different parts of the world has been reported by Munir Humayun and Robert Clayton. The composition of the inner rocky planets does not match with that of original rocky components of the nebula. Earth, Mars, Venus, and the Moon have very little potassium. This had made measurement of potassium very difficult. Humayun and Clayton have attained a precision of plus or minus 0.5 parts per thousand in measuring the 41K/39K ratio which is considerably better than the previous results.

The medical slogan 'no one is dead until (he is) warm and dead' is meant to signify that victims of hypothermia (abnormally low body temperatures) can often be resuscitated if dramatic measures are used. However, heroic methods are worthwhile only if they have a reasonable chance of success. The physiological variables associated with a favorable prognosis have not been clearly identified for hypothermic patients. An article in the October 10, 1990 issue of The Journal of the American Medical Association reports that blood potassium levels may used as a guide when considering the advisability of attempting cardiorespiratory resuscitation of hypothermic patients. The study compared potassium levels in avalanche victims in cardiorespiratory arrest (cessation of heart and lung activity) with levels in a group of hypothermic people, most of whom were not in a state of arrest. Additional control groups should have been included. Physiological factors that affect blood potassium levels are discussed. In spite of its weak points, the study shows that a person can be cold and dead. The avalanche victims may have died from trauma and asphyxiation, rather than hypothermia; more data are needed to determine the cause of death. Although potassium levels can be taken into account in some cases, a better-formulated study will have to appear before current resuscitative practice changes. Resuscitation attempts must be instituted when signs of life are present, and not as a consequence of a value on a blood test. (Consumer Summary produced by Reliance Medical Information, Inc.)