A method has been developed to measure concentratons of CO2 in gases rapidy. A gas sample is injected into a flowing carrier gas that passes through an Inrared CO2 analyzer. A strip chart recorded peak respome is obtained which is proportional to the CO2 concentration. A resolution of better than 2 microliters of CO2 per liter of gas was obtained.Seven to 10 seconds were required for sample analysis once the sample was obtained. So bum iclor plant respirto was deterned at different temperatures by measuring CO2 using this system ad by using a conventonl system. The correlaton between tehqs was 0.996, and about the same variation occurred within each method. This te ue greatly increased the efficiency of the infrared CO2 analyr in our laboratory for use in plant resprato d photosynthetic studies.The concentration of CO2 in gases is frequently measured in environmental and biological studies. Both respiration and photosynthesis can be monitored by measuring CO2 exchange. Because analysis of a large number of samples is often necessary, the method for measurement should be rapid and sensitive. The IR gas analyzer is the instrument most commonly used to measure CO2 concentrations. Flow-through systems which monitor CO2 exchange of plants or plant parts enclosed in a chamber usually depend on the detection of a 10 to 30 pl C02/1 concentration differential between input and exhaust air (3,(7)(8)(9)12). The CO2 differentials can be related to net photosynthesis or respiration. CO2 concentrations of the air surrounding photosynthesizing plants can also be monitored and a concentration level maintained by automatically injecting CO2. The amount of CO2 added is equal to net photosynthesis (5,11). In the field, photosynthesis may be determined aerodynamically by determining the CO2 gradients within the crop canopy (4, 6, 10).In many photosynthetic studies determination of CO2 concentrations requires an IR gas analyzer to monitor continuously a single CO2 exchange chamber, or several chambers may be monitored consecutively with a sample switching device at the analyzer while continually purging the sampling lines. After switching, I to several min equilibration time is usually necessary to stabilize the analyzer and obtain a reliable reading (13).A method for measuring CO2 in small volumes of gas has been described which was used in a working range generally between 1,000 and 15,000 1s1/1 CO2 (1 MATERIALS AND METHODSThe basic system consisted of an IR gas analyzer, mv recorder, flow meter, and drying columns (Fig. 1). Tygon2 tubing was used to connect the system. The tubing lengths from the tee connector to the IR gas analyzer were the same to balance line resistance. The flow rate of the carrier gas (usually N2) was adjusted to approximately 0.6 I/min. At this flow, a narrow based peak was recorded on the strip chart recorder and only measurement of peak heights was necessary to obtain the CO2 concentration ofthe injected gas sample. A 10-ml or less sample was injected with a syringe through a short section of sur...

Crop rotation of soybean [Glycine max (L.) Merr.] with grain sorghum [Sorghum bicolor (L.) Moench], and application of N fertilizer or manure generally increases grain sorghum yield. Little is known about rotation and fertilization effects on soybean yield in the Great Plains. Grain yields were measured from 1981 to 1987 in a cropping experiment started in 1980 on a Sharpsburg silty clay loam (fine, montmorillonitic, mesic Typic Argiudoll). The cropping treatments included continuous soybean, continuous grain sorghum, and grain sorghum‐soybean rotation. Fertilizer treatments consisted of control, manure (15.8 Mg dry matter ha−1 yr−11) and N (45 kg ha−1 for soybean and 90 kg N ha−1 for sorghum). Volumetric soil water content was determined with a neutron probe in 1985, 1986, and 1987. Soil water content was unaffected by fertilizer treatment. Water content in the upper 30 cm was generally greatest with continuous grain sorghum and least with continuous soybean. Soil water depletion to 120 cm in September was 10 to 36 mm greater with soybean than with grain sorghum. Crop rotation increased soybean yield, but N application did not. Manure application reduced soybean yield in 1986, but had no effect in the other years. Rotation and fertilization increased sorghum grain yield. The soybean yield advantage from crop rotation decreased as 1 April to 31 May rainfall increased. Cropping‐system induced differences in soil water content early in the growing season may be partly responsible for higher soybean yield with crop rotation.

Environmental factors such as temperature and available moisture significantly affect the development of yield components in grain sorghum [Sorghum bicolor (L.) Moench]. However, effect of these factors may vary among plant growth stages. This study was conducted in the field to determine the relative importance of yield components and the effects of environmental factors in two growth periods, planting to bloom (Period 1) and bloom to physiological maturity (Period 2), on yield and its components in 46 sorghum hybrids tested in contrasting field environments. Number of seed was the major contributing component of yield, but the relative importance of seed weight to yield compared to number of seed increased from lownight‐temperature to high‐night‐temperature environments. Number of seeds head−1 was more important than number of heads in affecting variation in number of seed and yield among sorghum hybrids. Rate of grainfill day−1 accounted for more variation in seed weight than rate of fill per growing degree unit (GDU), but both were more important than the length of grainfill period. The relationship between the mean yield and the total GDU of environments was quadratic (R2=0.70), and GDU in the range of 1250 to 1350 favored development of high yields. Slow rate of GDU accumulation in Period 1 coupled with a relatively high rate in Period 2 was associated with high sorghum yields in high‐night‐temperature environments. In low‐night‐temperature environments, high GDU accumulation rate in both Period 1 and Period 2 favored high yields. Within an environment, the GDU accumulation rate was important to yield through its effects on seed weight. Although rain accounted for a significant proportion of variability in yield and its components in most environments, its effects generally were less important than those of GDU and GDU accumulation rate. The results indicate the importance of GDU and rate of GDU accumulation to yield and yield component development across diverse environments, and they demonstrate the need to exploit genetic variation of metabolic efficiency in grainfill in breeding programs designed for stress environments.

Corn (Zea mays L.) grain yield is sensitive to water availability from emergence to maturity. Using early‐maturing corn hybrids might avoid the late‐season stress that frequently occurs with dryland culture. This research was conducted to determine whether early‐maturing corn hybrids could yield similarly to late‐maturing hybrids under dryland conditions. Field studies were conducted at Mead, NE, on a Sharpsburg silt clay loam (fine, montmorillonitic, mesic Typic Argiudolls) in 1991 and 1992. In Lincoln, NE, the soils were a Kennebec silt loam (fine‐silty, mixed, mesic Cumulic Hapludolls) in 1991 and a Crete silt loam (fine, montmorillonitic, mesic Pachic Argiustolls) 1992. Three early‐maturing (95 to 99 d) hybrids and three late‐maturing (114 to 118 d) hybrids were grown at 10 000, 18 000, 26 000, and 34 000 plants /acre. Little late‐season water stress occurred in 1992, thus, hybrids produced high yields that increased with increasing population up to 26 000 plants/acre and even 34 000 plants/acre. However, substantial late‐season water stress occurred in 1991. Environments dominated by late‐season water stress caused yield reduction at high plant populations for all three late‐maturing hybrids and one early‐maturing hybrid. Two of the three early‐maturing hybrids produced similar yield responses to increased plant population, independent of degree of late‐season water stress. This indicates use of well adapted early‐maturing hybrids might improve yield stability, since their response was not dependent upon yearly weather conditions, in contrast to the late‐maturing hybrids. Two early‐maturing corn hybrids did not consistently yield comparably to late‐maturing hybrids. These two early maturing hybrids appeared to lack the water stress tolerance and yield potential required to consistently yield comparably with late‐maturing hybrids. However, the early‐maturing hybrid, Pioneer 3737, produced grain yields comparable to late‐maturing hybrids in nearly every instance. These results indicate a well adapted early‐maturing hybrid can produce yields comparable to or better than late‐maturing hybrids, particularly where late‐season water stress is prevalent. However, the optimum plant population may be higher for early‐maturing compared to late‐maturing hybrids. Research Question Corn grain yield is sensitive to water availability from plant emergence to maturity. The water stress that often occurs late in the growing season with dryland corn culture might be avoided by using early‐maturing corn hybrids. Producers often are reluctant to accept this strategy, because late‐maturing hybrids generally have greater yield potential than early‐maturing hybrids. This study was conducted to determine the yield of early‐maturing and late‐maturing hybrids in a dryland environment. Literature Summary Conventional corn production practices assume light is the limiting production factor and uses the entire growing season. This practice of maximizing light interception often increases late season plant water stress and causes unstable...

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.

Seed size is highly influential in determining germinability and seedling vigor of grain sorghum (Sorghum bicolor L. Moench), but whether this factor is predominate over seed density (i.e. specific gravity) has not been established. A 2‐year study was conducted to determine to what extent seed size and density influence germination and subsequent field performance. Large and small seed lots from the same genotype were compared to “more dense” and “less dense” seed lots which were separated using either urea‐phosphate or sucrose solutions. The results indicated that seed lots with larger and denser seeds had a higher percent germination. The data also supported the conclusion that a higher percentage of viable seeds could be selected from seed lots with low average germinability by using specific gravity separations. However, the establishment of seedlings, final stands, and grain yields were not a function of size or density when the same number of viable seeds were planted in the field.

nutrient-poor soil and low rainfall conditions, yet it is capable of rapid and vigorous growth under favorable Pearl millet [Pennisetum glaucum (L.) R. Br.] is a staple grain conditions (Maiti and Bidinger, 1981). Pearl millet is a crop in the arid and semiarid regions of Africa and India, and a new potential alternative grain crop for areas of the Great 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, Plains with sandy soil, low rainfall, and a short growing smectitic, mesic Typic Argiudoll) soil with approximately 29 g kg Ϫ1 season since dwarf hybrids with good yield potential organic matter, 35 kg ha Ϫ1 NO 3 -N, and pH of 6.0. The objective was have been developed. A better understanding of pearl to determine the influence of hybrid and N on grain yield, dry matter millet growth and its N concentration and accumulation accumulation and partitioning, and growth rates throughout the growis necessary to improve pearl millet grain yield and ing season. Nitrogen concentrations, uptake, and use efficiency were promote its adoption by farmers in the Great Plains. also determined. Treatments were a factorial combination of the pearl Growth rate is a physiological trait associated with millet dwarf hybrids (59022A ϫ 89-0083, 1011A ϫ 086R, and 1361M ϫ increased grain yield in cereal crops. Growth is generally 6Rm) and N levels (0 and 78 kg ha Ϫ1 ) in a randomized complete a function of environmental factors (such as temperablock design. Two plants per plot were sampled at 2-wk intervals ture and solar radiation) and mineral nutrition, along 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 Ϫ1 , with genotype and production practices. General asbut had only a small effect on dry matter accumulation and partipects of growth and development of pearl millet plants tioning. Hybrid differences were small for grain yield. Pearl millet dry were reported by Maiti and Bidinger (1981) and Bramelmatter accumulation increased cubically in both years, with maximum Cox et al. (1984). Dry matter accumulation by pearl crop growth rates among hybrids ranging from 0.48 to 0.57 g m Ϫ2 permillet under different management conditions have growing degree day (GDD) in 1995 and ranging from 1.9 to 3.1 g m Ϫ2 been reported in Africa (Azam-Ali et al., 1984), Austra-GDD Ϫ1 maximum in 1996. The relative growth rate among hybrids lia (Coaldrake and Pearson, 1985), and India (Craufurd declined from 0.012 to 0.020 g Ϫ1 m Ϫ2 GDD Ϫ1 in both years to near and Bidinger, 1989; Carberry et al., 1985). zero at physiological maturity. Nitrogen concentrations were higherMineral nutrition is one of the most important factors during the vegetative stages and decreased with plant age. Applied affecting plant productivity (Clark, 1990), and N is the N decreased N use efficiency for aboveground biomass (NUE 1 ) by 18 to 25 g DM g Ϫ1 N, and N use efficiency for grain (NUE 2 ) by 7 to major nutrient...

findings that, when available, soil N is the main source of N for soybean growth rather than N fixation (Her-Plant population of soybean [Glycine max (L.) Merr.] may influridge and Brockwell, 1988). Thus, growing soybean can ence the residual N contribution to a cropping system and yield beneresult in a net depletion of soil N (Zapata et al., 1987). fits to following cereals. Field studies were conducted from 1994 to 1996 on a N-depleted Sharpsburg silty clay loam soil at Mead, NE High amounts of N are removed by harvested soybean to: (i) determine soybean yield at different plant populations; (ii) seeds (144 and 169 kg N ha Ϫ1 , Clement et al., 1992; investigate residual N, chlorophyll-N-yield relations, and yield bene-150-200 kg N ha Ϫ1 , Varvel and Peterson, 1992). This fits from these different soybean populations to a following maize 12678. Work supported in part by the Canadian Int. Dev. Agency (CIDA).