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Byline: Sims, J. R. This article discusses a new approach and spreadsheet tool for engineers that can be used to provide operating pressure limits as a function of vessel-metal temperatures. [...]

Farming practices such as stubble mulching are known to influence surface soil temperatures. This study was conducted to determine the effect of temperature variations in the shallow surface zone that normally contains the crown node on early growth, nutrient uptake, and nutrient translocation of spring wheat (Triticum aestivumL.). Surface soil temperatures below optimum, about 19 C, significantly decreased top growth but not root growth. When surface soil temperature was increased, total nutrients accumulated in the tops increased. Under low surface soil temperature roots appeared to accumulate Cu and Zn. Translocation of 80Rb from the roots to the tops was significantly greater when the surface soil was warm than when it was cold. Thus, translocation of nutrients from the roots to the tops may be restricted by low soil surface temperatures. Fertilization with N, P, and K appears to modify the detrimental effect of low surface soil temperatures. However, nutrients did not completely alleviate the detrimental effect of low surface soil temperatures. The crown node (transition region) of the plant appears to be the plant component most sensitive to low surface soil temperatures. When the crown node was located above the cold zone, dry weight was nearly equal with cold and warm surface soil temperatures. Unlike the crown node, the shoot growing point (meristematic region) was not affected by low, surface‐soil temperatures.

Boron retention as a function of pH was determined for Fe‐ and Al‐coated layer silicates using a previously described procedure (15). Treating the Na+and K+forms of South Africa vermiculite material with Al3+prior to B treatment resulted in equivalent B retention by the two forms. Coating kaolinite with hydroxy iron compounds initially decreased B retention in comparison to uncoated kaolinite. However, as the amount of coating was increased to 4.2% Fe2O3the amount of B retained was slightly greater than that retained by uncoated kaolinite. Boron retention by the Al‐coated kaolinite and by both Fe‐ and Al‐coated montmorillonite was significantly greater than B retention by the uncoated clays. A single regression line represented B retention as a function of Fe2O3content for both clays. Boron retention as a function of Al2O3content for the two coated clays fell on two lines which led to the conclusion that hydroxy Fe and Al compounds in the layer silicates dominate over clay mineral species per sein determining B retention characteristics and that B retention characteristics may be conditioned by clay mineral species. Boron retention at pH 6 by nine soil materials was determined from the difference in the initial and final B concentrations of the saturating solutions. Relationships between B retention and various chemical properties of the soil materials were examined statistically. The highest correlations with B retention were found with free iron oxide content and 1.0NKCl (pH2) extractable Al2O3. It was concluded that B retention by these soil materials was in response mainly to their free iron oxide and Al2O3contents.

Boron retention by hydroxy iron and aluminum materials was found to be pH dependent with maximum retention occurring in the alkaline range. The hydroxy aluminum materials retained B in amounts that were an order of magnitude greater than the amounts retained by the hydroxy iron materials. Boron retention by these materials was significantly reduced by aging on a steam bath prior to being treated with B. Iron and aluminum were precipitated from solutions in the presence of B in application of the “mole ratio” method of determining the formulas of complexes. Evidence was obtained indicating Fe(III) or Al(III) and B were precipitated in stoichiometric proportions. Considering these precipitated forms as “solid complexes” with the general formula, MXn, a greater variety of complexes was found in the Al(III) systems than in the Fe(III) systems. In the Fe(III)‐B systems, values of n for the most part were ≤1.0; in the Al(III)‐B systems, values of n were ≥1.0. Samples of similar constitution to those used in the “mole ratio” study were prepared for each metal at three pH levels. The amount of B combined in the precipitate was determined as a function of aging. The amount of B combined in the precipitate of the pH 6 samples remained relatively unchanged throughout the course of the 42‐day aging period whereas the amount of B combined in the pH 9, 10, and 11 samples decreased with time. Since the observed decreases in the amounts of B combined in the precipitates were limited to the pH 9, 10, and 11 samples, it was concluded that the ready source of hydroxyl ion in these suspensions promoted hydrolysis of the hydroxy iron and aluminum precipitates, resulting in expulsion of B from the precipitates probably as borate ions.

The characteristics of boron retention by layer silicates were studied. Boron retention was determined by a procedure developed for use with solution concentrations ranging from zero up to several hundred parts per million B, which consisted of treatment of the adsorbent with B solutions, washing with methanol to remove excess B, and extracting the retained B with 0.01NNaCl (pH 3). Vermiculite, kaolinite, montmorillonite, and hydrobiotite all exhibited a pH‐dependent affinity for B with maxima in the alkaline range. Access to the interlayer surfaces of the expanding lattice clays was necessary for maximum B retention by these clays. Boron retention by these layer silicates was, in the main, attributed to hydroxy iron and aluminum compounds occurring in the samples as impurities.

Studies were conducted on the retention of Cu and Zn by H‐montmorillonite in relation to associated anion, salt concentration reaction time, pH of the equilibrium solution, and techniques. Under conditions where the pH of the equilibrium solution was too acid for formation of Cu(OH)2, the amounts of Cu and Zn retained were similar for Cl, NO3, and SO4salts and equal to the cation‐exchange capacity (CEC) as measured with NH4+. Detailed studies of metal retention in relation to pH of equilibrium solutions for Cl systems revealed no retention of Cu or Zn in excess of the CEC provided the pH of the system was below 5.5 to 6.5. The exact pH favoring excess retention varied according to salt concentration and the metal in question. Retention of the metals in excess of the CEC was explained in terms of precipitation of Cu(OH)2and Zn(OH)2in the clay systems. In the acetate systems, Cu and Zn retention was usually greater than the CEC even under acid conditions. As the pH of the systems increased, metal retention increased. In addition to metal retention, acetate retention was measured. Acetate retention was found to be related to the concentration of acetate and essentially independent of the quantity of metal retained.