Under three managements, stockpiled (no summer cut), hay (one summer cut), and pasture (three summer cuts), significant differences were noted in percent dry matter, crude protein, and crude fiber in the leaves, stems, and heads of ‘Piper’ sudangrass (Sorghum sudanense (Piper) Stapf) and ‘RP30F’ forage sorghum (Sorghum bicolor (L.) Moench) with advancing maturity. These changes were particularly striking when the forage was saved for fall use. Generally, sudangrass analyzed significantly higher in percent dry matter and crude fiber but lower in percent crude protein than forage sorghum. Percent dry matter in the leaves, steins, and heads of both species differed significantly with management and increased with maturity, except in the heads of sudangrass under the stockpiled management where percent dry matter increased until full maturation and decreased abruptly thereafter, possibly because of seed shattering and loss. In both sudangrass and forage sorghum, the heads were highest in percent dry matter, the leaves intermediate, and the stems lowest. Percent crude protein and crude fiber differed significantly between species, plant parts within each species, and dates of sampling. Percent crude protein generally decreased as the date of sampling was delayed. The leaves of both species were highest in percent crude protein, the heads intermediate, and the stems lowest. Percent crude fiber increased in the leaves and stems of sudangrass, but decreased in the leaves and stems of forage sorghum as plants matured. Percent crude fiber decreased in the heads of both species with advancing maturity.

Corn (Zea mays L.) and sorghum (Sorghum vulgare Pers.) plants were grown in a controlled environmental growth chamber in 12 medium- to coarse-textured soils with two levels of Zn for each soil. These levels were the native amount in each soil and with 2.5 ppm added. After 4 weeks plants were harvested and Zn concentration and total Zn uptake were measured. Each soil was extracted with three different solutions: (i) 0.05N HCl plus 0.025N H₂SO₄, (ii) 0.1N HCl, and (iii) 0.05N EDTA at pH 7.0. Zinc uptake by the plants was correlated with the level of soil Zn determined by each extractant. The highest correlation was obtained for corn and sorghum with extractant (i). Correlation coefficients for corn for extractants (i), (ii), and (iii) were 0.89, 0.82, and 0.62, respectively. Correlation coefficients for sorghum for extractants (i), (ii), and (iii) were 0.70, 0.63, and 0.44, respectively.

A greenhouse experiment using nutrient solution culture with graded levels of K was used to determine the concentration of K required in grain sorghum leaves for optimum growth. It was determined that growth of grain sorghum is reduced if the leaf K concentration is much below 1.5% at the full bloom stage. A field study was made to relate soil K parameters from eight different soils to concentration of K in grain sorghum leaves at the full bloom stage of growth. The best method of predicting K uptake by plants included both solution K and exchangeable K. A correlation coefficient of 0.890 was obtained between percent K in leaves and solution K + log (1 + exchangeable K).

Two sources of beta radiation, carbon-14 (C¹⁴) and promethium-147 (Pm¹⁴⁷), were investigated for determination of leaf water content of three plant species over a range of water stress conditions. The plant species used were soybean (Glycine max L.), sorghum (Sorghum vulgare L.), and barley (Hordeum vulgare L.). Results obtained with both sources gave high correlations of relative turgidity with attenuated radiation. However, for relative turgidities above 60% in the plants studied, higher correlation coefficients were obtained using the C¹⁴ source. Results indicated that the C¹⁴ method appeared to be more sensitive to small changes in relative turgidity than was the Pm¹⁴⁷ method. Leaf disc sections taken from sorghum and barley leaves gave more uniform response to water stress changes than did whole leaves.

Measurements of meteorological parameters were made at St. Paul, Minnesota, on four different types of days. The data obtained were analyzed by an energy—balance technique which yielded daily trends of light intensity and temperature for individual plant leaves. The computed leaf temperatures were verified experimentally. Together with the light—intensity data they were then used to construct typical net photosynthetic rate curves which would have been characteristic of maize and sorghum growing under these conditions. On a clear—acool day the net photosynthetic rates of maize and sorghum both rose gradually to a sharp peak near solar noon and then declined. On a clear, warm day, however, net photosynthesis in sorghum rose rapidly to establish an enduring high rate throughout the major portion of the day, while maize showed a midday slump with photosynthetic rates depressed almost to zero. On a cool, cloudy day both species had only a nominal net CO₂ fixation and a day with broken cumulus clouds resulted in an oscillation of the net photosynthetic rates of both species between quite high and medium values.

The gelatinization temperatures of starches from 85 samples of sorghum grain of diverse origin and type were determined by a standard microscopic procedure. In general, waxy starches had higher gelatinization temperatures than regular starches. The sweet, juicy stalk characteristic of forage sorghums seemed to depress gelatinization temperature of both waxy and regular starch types. Two commercial grain sorghums and two commercial waxy grain sorghums were grown in each of three locations in the warm, humid Coastal Bend region of South Texas and at a single location in the cooler and less humid High Plains of North Texas. Starch synthesized by plants grown in North Texas consistently gelatinized at a lower temperature (average, 4 C) than starch from the same variety grown in South Texas. Gelatinization end-point temperatures of the waxy starches were 2 to 3 C higher than those of the regular starches. A 6-year breeding program to transfer the property of low starch gelatinization temperature from the forage varieties 'Atlas' and 'Hoti' to acceptable grain types was unsuccessful. Waxy derivatives from this program had a higher starch gelatinization temperature than derivatives with regular starch. Two commercial maize hybrids and their waxy counterparts were grown in central Illinois. In each case the waxy starch had a gelatinization temperature higher than that of the regular starch counterpart. Waxy starch from another corn hybrid had a 3 C higher gelatinization temperature when the grain was produced in Texas than when it was grown in central Illinois.

Grain is ground finely and refluxed in CaCl2 solution and protein is precipitated with zinc uranyl acetate. The percentage of starch in the grain is calculated from the optional rotation of the filtrate, taking the specific rotation of starch as 200 at 20°0.1°C and correcting for the volume of the filter paper, which goes into the volumetric flask. The method is rapid and at least 99.6% of the starch is recovered.-M. S.

Under irrigation, removal of the surface 10, 20, 30, and 41 cm of soil decreased N yields 40.6, 47.5, 58.7, and 64.7%, respectively. Respective decreases under limited moisture were 20.0, 36.3, 53.9, and 62.4%. Total N in the surface 15 cm of soil and N yields were closely related. Relationships among drymatter yields of grain sorghum (Sorghum vulgare), associated N uptake, and N treatments (soil NO₃-N + fertilizer N) were used to estimate maximum yields attainable and to determine the internal N requirement of grain sorghum. That requirement was almost a constant (1.0%) despite the widely different yield maxima attained under the contrasting moisture regimes. Under irrigation, similar yield potentials were attained on all except the treatment with the greatest topsoil removal (41 cm). Undefined factors, other than N, P, or water, reduced the yield potential on that treatment. Under limited moisture, fertilizer treatments did not restore drymatter yields on any depth of soil removal. Differences are attributed to differences in water storage and use. Efficiency of uptake of available N was not directly affected by topsoil removal but was affected by the N status of the plants. It remained relatively constant until the plant N requirement was met, and then declined.

Measurements of temperature and diffusion resistance of leaves and of micrometeorological factors in a wellwatered sorghum field during June in central Arizona show that the stomata regulate transpiration only during the periods of darkness and low light. This was concluded from a comparison of the values for the canopy resistance as derived from direct measurement on leaves and as calculated from the environmental data. This finding predicts that, during the main part of the daylight period, neither an increase in number or aperture of stomata nor a wetting of the entire foliage would increase the evaporative flux. The action of the sorghum plant is then like that of a wick. We also found that, in a hot and dry environment, the sorghum foliage will constantly be several degrees cooler than the ambient air, even in the middle of the day when radiant energy input is large. Finally, the energy equivalent of the evaporative flux exceeded the net radiant flux significantly at all times, and by 80% over a 24-hour period. All three findings are at variance with common generalizations concerning the energetics and mechanics of crop transpiration. However, we recognize that our findings cannot be generalized to include other crop plants without specific studies.