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Plant population of soybean [Glycine max (L.) Merr.] may influence the residual N contribution to a cropping system and yield benefits to following cereals. Field studies were conducted from 1994 to 1996 on a N-depleted Sharpsburg silty clay loam soil at Mead, NE to: (i) determine soybean yield at different plant populations; (ii) investigate residual N, chlorophyll-N-yield relations, and yield benefits from these different soybean populations to a following maize (Zea mays L.) crop; (iii) and compare N credits from soybean assessed with fallow and cereal plots as references. Eight soybean populations froml4 000 to 544 000 plants ha -1 in narrow 50-cm rows, a fallow plot, and a maize plot were followed by maize in a rotation study. Soybean yield was highest at populations of ≥129 000 plants ha 1 . Maize grain yields were highest following fallow and soybean populations

Pearl millet [Pennisetum glaucum (L.) R. Br.] is a staple grain crop in the arid and semiarid regions of Africa and India, and a new grain crop in the USA. A 2-year field experiment was conducted near Mead, NE, in 1995 and 1996 on a Sharpsburg silty clay loam (fine, smectitic, mesic Typic Argiudoll) soil with approximately 29 g kg -t organic matter, 35 kg ha -1 NO 3 -N, and pH of 6.0. The objective was to determine the influence of hybrid and N on grain yield, dry matter accumulation and partitioning, and growth rates throughout the growing season. Nitrogen concentrations, uptake, and use efficiency were also determined. Treatments were a factorial combination of the pearl millet dwarf hybrids (59022A × 89-0083, 1011A × 086R, and 1361M × 6Rm) and N levels (0 and 78 kg ha -1 ) in a randomized complete block design. Two plants per plot were sampled at 2-wk intervals and partitioned into plant parts, dried, weighed, and analyzed for N concentration. Applied N increased grain yield by 0.4 to 0.5 Mg ha ', but had only a small effect on dry matter accumulation and partitioning. Hybrid differences were small for grain yield. Pearl millet dry matter accumulation increased cubically in both years, with maximum crop growth rates among hybrids ranging from 0.48 to 0.57 g m - 2 per growing degree day (GDD) in 1995 and ranging from 1.9 to 3.1 g m -2 GDD -1 maximum in 1996. The relative growth rate among hybrids declined from 0.012 to 0.020 g -1 m -2 GDD -1 in both years to near zero at physiological maturity. Nitrogen concentrations were higher during the vegetative stages and decreased with plant age. Applied N decreased N use efficiency for aboveground biomass (NUE 1 ) by 18 to 25 g DM g -1 N, and N use efficiency for grain (NUE 2 ) by 7 to 12 g grain g 1 N. Environmental variability due to years had a greater effect on yield, growth, and N levels than hybrid and applied N.

Pearl Millet [Pennisetum glaucum (L.) R. Br.] plays an important role as a staple food grain in many developing countries, but is relatively new to the Great Plains of the USA. This study was conducted for 2 yr to evaluate the effects of a preceding soybean [Glycine max (L.) Merr.] crop and/or applied N fertilizer on pearl millet yield and N uptake, and to quantify the amount of residual soil NO 3 -N resulting from the cropping system. The experiment was conducted on a fine montmorillonitic, mesic, Typic Argiudoll soil at the University of Nebraska Research Center near Mead, NE. The experiment included three treatments consisting of 0, 45, and 90 kg N ha −1 applied to continuous pearl millet, and two treatments consisting of 0 and 45 kg N ha −1 applied to pearl millet following soybean [...]

Plant breeding and hybrid seed production of maize require good parent lines; however, little attention has been given to pollen production and relationships among its components. The objectives of this study were: to identify presence of phenotypic plasticity on pollen traits, their contribution to total pollen production, and the relationships among them. During 1994, in the summer nursery, the four parent lines: 93Nex306, LN9638, WF9, and Hex301 were evaluated and increased for their use next seasons. Direct and reciprocal F1 single crosses between early lines (WF9×Hex301, Hex301×WF9) and late lines (LN9638×93Nex306, 93Nex306× LN9638) were also made. The F2 generation was obtained by selfing F1 single crosses during the winter season in a greenhouse. Thus, in 1995 twelve genotypes: four parental lines, four F1 single crosses, including the reciprocals, and four F2 generations from the single crosses were evaluated. They were evaluated using a split-plot arrangement of treatments in a randomized blocks design with four replications, where planting dates were the whole plots, and genotypes the subplots. Measurements were made on tassel length, branch number, main spike size, branch size, main spike flowers, flowers per branch, anther size, total male flowers, pollen size, shedding period and pollen production. Phenotypic relationships and identification of morphological traits as pollen production components were estimated using principal component analysis and Gabriel’s plots. The first two principal components (PC) explained 70% of variation. Cumulative proportions of phenotypic variability ranged from 14% in PC1 to 54% in PC2. Proportion of variation by PC showed that total male flowers, flowers per branch, main spike flowers and branch number were the best morphological traits for predicting pollen yield. Lack of constancy of PC scores, different magnitude of variation and degree of associations among traits in parents, indicated presence of phenotypic plasticity, since the expression of these traits changed over years. Year differences and genotypic variation of tassel morphological traits indicated that these traits rely on both phenotypic plasticity and genetic variation.

Recent emphasis on energy problems has stimulated efforts to identify crops capable of producing high yields of biomass that can be converted into ethanol. The sorghum [ Sorghum bicolor (L.) Moench] crop includes cultivars and hybrids that vary widely in the relative amounts of grain and stalks produced, and also in the sugar content of the stalks. N39 × Wray, a relatively sweet hybrid with good grain potential, and Wray, a cultivar with sweet stalks, were compared for their grain and sugar yields, alcohol production potential, and other related characters. The hybrid produced heavier seeds, more seeds per head, and more heads per ha than the Wray. This resulted in a grain yield of 6630 kg/ha, about 3.4 times that of Wray. Wray produced about 10% more biomass with the stalk sugars accounting for about 80% of the total alcohol potential as compared to 45% for the hybrid. The total alcohol production potential (stalk plus grain) was 1.11 times as great for the hybrid as for Wray.

Most plant canopy and solar radiation studies have comprised theoretical considerations, assuming a randomly oriented leaf arrangement. Lacking are field measurements concerning culturally arranged plant canopies in relation to interception of solar radiation. The purpose of this study was to describe the light environment under field conditions below and within grain sorghum (Sorghum bicolor (L.) Moench) canopies. Visible radiation was measured in sorghum using sensors mounted on a traversing system and having about the same sensitivity to direction and spectrum as does a leaf. As much as 89% more light was transmitted to a sensor when it moved, between rows rather than across them. Therefore, measurement across rows is recommended. Light transmission profiles of sorghum canopies on clear and cloudy days were similar. Differences between transmission values over a diurnal period were less on cloudy than on clear days indicating more uniform light distribution. Visible radiation transmitted through sorghum canopies of .51-m rows as compared to sorghum canopies of .76- and 1.02-m rows or sorghum, canopies of .76-m rows as compared to sorghum canopies of 1.02-m rows was less. This would indicate more visible radiation would be available for photosynthesis with narrower row spacings. Extinction coefficients (K) for canopy layers were calculated and for each layer proceeding downward K decreased. Extinction coefficients of sorghum canopies of different row spacings decreased as row spacing increased. Differences between hourly values of K were less on the cloudy day than on the clear day. For all conditions minimum values of K occurred at solar noon. These results agree with theoretical data

Growth-promoting action of simazine and other s-triazine herbicides was detected by the use of sorghum (Sorghum bicolor [L]. Moench) callus tissue and the chlorophyll retention test. Soil application of simazine [2-chloro-4, 6-bis(ethylamino)-s-triazine] at sublethal levels nearly doubled the growth-promoting action of sorghum root exudates. Treated plants yielded up to 26% more total protein than untreated plants. This indicated that the level of callus growth-promoting action in the root exudate of the plant has a positive effect on its final total protein yield and confirms a positive effect of simazine on total protein content in certain instances. The results may provide a new understanding of the mode of action of s-triazines applied at sublethal levels in increasing protein content and certain enzymic activities of treated plants. It is speculated that the growth-promoting action of these herbicides is hormonal in nature and most likely kinetin-like.

A need to study the effect of a wide range of temperatures on early plant growth as well as seed germination of a wide range of sorghum [Sorghum bicolor (L.) Moench] germplasm led to the construction of a sand thermogradient sand table. The table was constructed so heat was transferred between water baths of two different temperatures. A continuous, linear thermogradient was established when the water baths were at 15 and 45 C. Other temperature differentials produced nearly linear gradients. Temperature deviation at any depth during the experiments never exceeded 1 C and usually was less. Germination and early growth of sorghum and corn (Zea mays L.) were measured to demonstrate the type of response curves that could be obtained with this apparatus. The table lends itself to many applications for physiological studies, including screening genetic material for temperature tolerance

A method has been developed to measure concentrations of CO(2) in gases rapidly. A gas sample is injected into a flowing carrier gas that passes through an infrared CO(2) analyzer. A strip chart recorded peak response is obtained which is proportional to the CO(2) concentration. A resolution of better than 2 microliters of CO(2) per liter of gas was obtained. Seven to 10 seconds were required for sample analysis once the sample was obtained. Sorghum bicolor plant respiration was determined at different temperatures by measuring CO(2) using this system and by using a conventional system. The correlation between techniques was 0.996, and about the same variation occurred within each method. This technique greatly increased the efficiency of the infrared CO(2) analyzer in our laboratory for use in plant respiration and photosynthetic studies.

An improved light sensor with a spectral response based on photon absorption between 400 and 700 nm was developed for both field and environmental chamber use. The indicated sensor response was selected because it approximates the photosynthetic response of plants for which data are available. A silicon photo cell with high response in the visible range was used as a sensor. The spectral response was controlled by use of a Kodak Gelatin Wratten Filter. A visible bandpass interference filter produced a sharp cutoff at 700 nm. Heat—absorbing glass eliminated transmission beyond 1,000 nm, and a diffusing plastic and filters were mounted in a miniaturized cosine—corrected head that was fitted with a collimating system to eliminate spectral shifts which arise when light enters the interference filter at oblique angles. Error calculations indicate that under sun—and—sky radiation and various artificial light sources the errors are smaller than those associated with available standard calibration lamps. The device also includes a battery—operated meter circuit suitable for making measurements over a wide range of intensities.