Sorghum Canopy Research Articles

Fractional coefficient for estimating physiologically meaningful and diurnal transpiration cycle weighted VPD from daily ambient environmental data

Appropriate representation of environmental conditions via meaningful metrics is critical for their effectiveness in modeling crop physiological and resource use processes. Vapor pressure deficit (VPD) is a primary determinant of crop water use efficiency, commonly reported as daily average. However, VPD can vary substantially during the day in relation to diurnal cycle of transpiration, in which case daily average VPD may not suffice. In such scenarios, integrating VPD over the course of diurnal transpiration cycle into a weighted VPD (VPDw) can be physiologically meaningful as a metric. The goal of this research is to characterize the fractional coefficient (Frac) that can be used to effectively calculate VPDw from daily temperature and relative humidity data without the need for sub-daily environmental data. Site-specific and seasonal estimates of Frac, which represent the relative positioning of VPDw to diurnal extremes of saturation vapor pressure are currently lacking for semi-arid regions. To address this, we quantified Frac at 101 sites in the U.S. Central Plains using long-term (1982–2019) hourly and daily radiation and VPD datasets. Frac varied substantially across the region, with growing season mean values ranging from 0.59 to 0.92. Summer months had the highest Frac values with relatively lower uncertainty as compared to lower Frac during winter. Local observations of Frac deviated significantly from previously assumed stationary estimates implying that site-specific and month-specific Frac may be necessary for robust water use estimations. VPDw measured at an experimental site in Central U.S. Plains explained greater variance in daytime crop transpiration than daily mean VPD in maize, soybean, and sorghum canopies. Site-specific Frac was also assessed to perform better than commonly used Frac estimate of 0.75 to explain day-to-day variation in transpiration, demonstrating effective use of long-term mean Frac values presented here to estimate VPDw using daily datasets.

Optimal time of plant growth regulator application to Sorghum canopy according to BBCH and Kuperman crop growth scales

The relevance of the study is due to the problem of choosing the optimal scale for identifying the phases of plant development in order to determine the best timing of agronomic operations for sorghum plant care. The aim of the experiment was to use a plant growth regulator with higher efficiency during the stages of crop development 21, 31, 37 (BBCH) and III, IV, VI-VII on the Kupperman scale. Field and laboratory research methods were used in the study. The experiment was conducted in the Forest-Steppe zone of Ukraine on two sorghum varieties - Sorghum bicolor and Sorghum saccharatum, which were treated with PGR. Foliar application of PGR (0.5 l/ha) at 21 and 31 stages of BBSH provides 2.8 and 4.9% better results than at III and IV stages according to the Kuperman scale (the latter is based on a comprehensive morphophysiological analysis to identify I-VII CGS). Foliar application of PGR at microstage 21 (BBCH) contributed to faster development and increased grain yield in sorghum varieties (0.19 t/ha in Odesskyi 205 and 0.12 t/ha in Lan 59) compared to application at stage III (according to Cooperman). A similar effect of PGR application at microstage 21 (BBCH) compared to stage III (Kuperman) was recorded for two sugar sorghum hybrids: in Dovista variety, the increase in biomass yield was 1.6 t/ha, dry matter - 0.7 t/ha, and sugar content in stem juice - 0.0%, while in Gulliver variety these indicators were 1.6 t/ha, 0.7 t/ha and 0.2%, respectively. Thus, it is recommended to use the BBCH scale for the application of PPP, and foliar fertilization with PPP should be carried out at 21 and 31 days. The practical value of the work lies in the selection of the scale of growth and development of sorghum crops and the timing of foliar fertilization, which is optimal for the conditions of Ukraine. The study is useful from the practical point of view of foliar nutrition of plants in production and as a theoretical assessment of the scale of plant growth and development for students and scientists.

Planting System Effects on Intercropping of Gardenpea and Sorghum

The field experiment was conducted at Agronomy Research Field, Joydebpur and RARS, Burirhat, Rangpur, BARI during Rabi season of 2018-2019 and 2019-2020 to find out suitable combination of sorghum and gardenpea intercropping for higher productivity and monetary advantage. Treatments included in the experiment were: T1 = Sorghum normal row (SNR) + 1 row gardenpea (GP), T2 = SNR + 2 rows GP, T3 = Sorghum paired row (SPR) + 2 rows GP, T4 = SPR + 3 rows GP, T5 = SPR + 4 rows GP, T6 = Sole sorghum (60 cm ´ 10 cm) and T7 = Sole GP (30 cm ´ 10 cm). Light availability on gardenpea decreased with the increase of shade produced by sorghum canopy over the time up to 60 DAS. The lowest light availability on gardenpea was observed in T2 treatment and the highest was observed in sole gardenpea (T7) followed by T3 treatment in both the years. The maximum grain yield of sorghum was observed in T6 and it was decreased (6-10% in 2018-2019 and 1-12% in 2019-2020) at Joydebpur and (5-11% in 2018-2019 and 6-14% in 2019-2020) at Burirhat. The highest sorghum equivalent yield (SEY) of 10.93 t ha-1 in 2018-2019 and 12.02 t ha-1 in 2019-2020 at Joydebpur and 12.06 t ha-1 in 2018-2019 and 11.77 t ha-1 in 2019-2020 at Burirhat and also the highest land equivalent ratio (LER) of 1.77 in 2018-2019 and 1.93 in 2019-2020 at Joydebpur and 1.79 in 2018-2019 and 1.81 in 2019-2020 at Burirhatwere observed in T5 treatment. The highest gross margin of Tk.146600 ha-1 in 2018-2019 and Tk.168400 ha-1 in 2019-2020 at Joydebpur and Tk. 169200 ha-1 in 2018-2019 and Tk.163400 ha-1 in 2019-2020 at Burirhat and also the benefit cost ratio (BCR) of 3.04 in 2018-2019 and 3.34 in 2019-2020 at Joydebpur and 3.35 in 2018-2019 and 3.27 in 2019-2020 at Burirhat were also found in the same treatment. The results revealed that sorghum paired row + 4 rows gardenpea might be agronomically feasible and economically profitable for sorghum + gardenpea intercropping system at Joydebpur and Burirhat region.
 Bangladesh Agron. J. 2020, 23(2): 59-68

Responses of photosynthetic characteristics and dry matter formation in waxy sorghum to row ratio configurations in waxy sorghum-soybean intercropping systems

Abstract In intercropping systems, microclimate environment, especially light environment induced by row ratio configurations, is crucial to crop productivity. However, little information is available on how waxy sorghum canopy light environment is affected by row ratio configurations in waxy sorghum-soybean intercropping systems. Hence, field experiments were conducted in 2019 and 2020 to study the responses of photosynthetic characteristics, dry matter formation, and yield performance of waxy sorghum to seven treatments: sole waxy sorghum (SW), sole soybean (SS), two rows of waxy sorghum alternated with one row of soybean (2W1S), two rows of waxy sorghum alternated with two rows of soybean (2W2S), three rows of waxy sorghum alternated with one row of soybean (3W1S), three rows of way sorghum alternated with two rows of soybean (3W2S), and three rows of way sorghum alternated with three rows of soybean (3W3S). The results showed that intercropping increased the photosynthetically active radiation (PAR) and leaf area index (LAI) of waxy sorghum compared to SW treatment. This increase in PAR and LAI increased the photosynthetic characteristics of waxy sorghum canopy, including chlorophyll content (SPAD value), net photosynthetic rate (Pn), stomatal conductance (Gs), transpiration rate (Tr), and stomatal limitation value (Ls). These changes resulted in increased dry matter accumulation, its distribution, and promoted the dry matter transportation from vegetative organs to grain in waxy sorghum. Likewise, intercropping increased the grain number per spike and 1000-grain weight of waxy sorghum, and ultimately increased the land equivalent ratio (LER). Moreover, the 2W1S treatment showed the most suitable light environments and greatest resource utilization to obtain the highest LER and economic benefits. Based on the present results, we suggested that the 2W1S should be used as optimal row ratio configuration of waxy sorghum-soybean system to attain maximum benefits.

Sweet Sorghum Canopy Development in Relation to Radiation and Water Use

The present work deals with sweet sorghum canopy development in relation to the radiation capture and water demand. Two experimental sites and four cultivation periods with sweet sorghum (var. Keller and var. MN1500) were used in a plain of Central Greece. The water consumption by the crops, the aerial biomass production, the Leaf Area Index (LAI), as well as the radiation interception under various irrigation rates were monitored and analyzed. Key findings of the work include: (a) canopy penetration of Photosynthetic Active Radiation (PAR) is 10 times less than the global solar radiation, indicating that practically all PAR is intercepted by the leafage; (b) LAI values higher than 6.0 lead to no extra PAR capture and non-significantly higher biomass production; (c) rapid canopy development by rational use of water and fertilizer would attain capture and use of radiation at its maximum availability; (d) for the well watered plots, the Radiation Use Efficiency ranged from 2.8 to 3.63 g dry matter/MJ intercepted and the Water Use Efficiency (WUE) from 43 to 56.5 kg ha−1 mm−1, whereas the corresponding actual cumulative evapotranspiration ranged from 601 to 662 mm. In addition, the crop coefficient Kc values for the various cultivation stages of sorghum were evaluated.

Water use and productivity of a sorghum–cowpea–bottle gourd intercrop system

Water is the main factor affecting crop production in sub-Saharan Africa. It was hypothesized that intercropping sorghum (S) with either cowpea (C) or bottle gourd (B) would result in better productivity and water use efficiency (WUE). This was evaluated using a split-plot design with sub-plots arranged in a randomised complete block manner within the main plot, replicated thrice. Water regimes [full irrigation (FI), deficit irrigation (DI) and rainfed (RF)] were allocated to the main plots. Sub-plots comprised intercrop combinations, SS (sole), C (sole), B (sole), SC (intercrop) and SB (intercrop). Data collected included soil water content (SWC), plant height (PH)/vine length, leaf number (LN), tillering (T)/branching, leaf area index (LAI), relative leaf water content (RWC), stomatal conductance (gs) and chlorophyll content index (CCI) as well as biomass accumulation and partitioning. Yield and yield components, water use (WU) and WUE for grain (WUEg) were calculated at harvest. Land equivalent ratio (LER) was used to evaluate productivity of the intercrop. Sorghum canopy size decreased (P<0.05) (−6.7%, −10.6%, −89% and −79% for PH, LN, T and LAI, respectively) with decreasing water availability. Sorghum growth and development were unaffected by intercropping. Intercropping sorghum with cowpea improved gs (23%) and CCI (6.56%) of sorghum under low water availability. Productivity of sorghum across varying water regimes and cropping systems was stable with final biomass, yield and harvest index of 2.4tha−1, 0.98tha−1 and 35%, respectively. Overall, LER showed a 46% increase in productivity across all intercrop systems. Intercropping marginally increased WU (5.64%). Improvements of WUEg were observed under SC and SB (54.65% and 46.98%, respectively) relative to SS. Intercropping sorghum with cowpea is recommended for semi-and arid environments since it promoted efficient use of water.

Harnessing Genetic Variation in Leaf Angle to Increase Productivity of Sorghum bicolor.

The efficiency with which a plant intercepts solar radiation is determined primarily by its architecture. Understanding the genetic regulation of plant architecture and how changes in architecture affect performance can be used to improve plant productivity. Leaf inclination angle, the angle at which a leaf emerges with respect to the stem, is a feature of plant architecture that influences how a plant canopy intercepts solar radiation. Here we identify extensive genetic variation for leaf inclination angle in the crop plant Sorghum bicolor, a C4 grass species used for the production of grain, forage, and bioenergy. Multiple genetic loci that regulate leaf inclination angle were identified in recombinant inbred line populations of grain and bioenergy sorghum. Alleles of sorghum dwarf-3, a gene encoding a P-glycoprotein involved in polar auxin transport, are shown to change leaf inclination angle by up to 34° (0.59 rad). The impact of heritable variation in leaf inclination angle on light interception in sorghum canopies was assessed using functional-structural plant models and field experiments. Smaller leaf inclination angles caused solar radiation to penetrate deeper into the canopy, and the resulting redistribution of light is predicted to increase the biomass yield potential of bioenergy sorghum by at least 3%. These results show that sorghum leaf angle is a heritable trait regulated by multiple loci and that genetic variation in leaf angle can be used to modify plant architecture to improve sorghum crop performance.

Eclipse Effects on CO2 Profile within and above Sorghum Canopy

We analyzed the effects of a partial solar eclipse (22 July 2009) on microclimate including vertical gradients of CO2 concentrations ([CO2]), so called [CO2] profile, in a mature sorghum canopy. Together with CO2 measurement, major photosynthetic drivers of microclimate, light intensity, temperature and atmospheric H2O concentration ([H2O]) were also measured simultaneously at the same place and height. [CO2] at 6.0, 3.2, 2.1, 1.4, 0.7, 0 m above the ground (canopy height was 3.2 m) increased by 5.8, 4.8, 9.0, 7.8, 6.4, 7.6μmol mol-1, respectively, from 1 hour before the eclipse maximum to the eclipse maximum, during which theincident solar radiation above the canopy dropped by 1473 μmol photons m-2 s-1. However, it declined by 3.4, 10.6, 10.8, 6.0, 5.4, and 5.8μmol mol-1, respectively, from the eclipse to 1 hour later,during which the incident radiation increased by 1350μmol photons m-2 s-1. The [CO2] profile during the eclipse was uniform except for higher [CO2] near the ground. Comparative analysis of theeffect of light intensity on the microclimate during the eclipse-induced light decreasing phase (ELDP) and eclipse-induced light increasing phase (ELIP) revealed that [CO2], [H2O], temperature and relative humidity (RH) are significantly correlated with the light intensity above the canopy in a nearly linear fashion. Furthermore it indicated that detected less light-reacted canopy photosynthesis at a higher layer within the canopy during ELIP might be due to slower response of stomatal opening (than closing) to the light intensity above the canopy.

Evaluation of a turbid medium model to simulate light interception by walnut trees (hybrid NG38×RA and Juglans regia) and sorghum canopies (Sorghum bicolor) at three spatial scales.

Light is one of the most important components to be included in functional-structural plant models that simulate the biophysical processes, such as photosynthesis, evapotranspiration and photomorphogenesis, involved in plant growth and development. In general, in these models, light is treated using a turbid medium approach in which radiation attenuation is described by the Beer-Lambert law. In the present study, we assessed the hypothesis of leaf random dispersion in the Beer-Lambert law at the whole-canopy, horizontal-layer and local scales. We compared two calculation methods of radiation attenuation: a 3D turbid medium model using the Beer-Lambert law and the other based on a projective method. The two models were compared by applying the calculations to two walnut trees and two sorghum canopies, which have contrasting structural characteristics. The structures of these canopies were measured in 3D to take into account the arrangement and orientation features of the plant elements. The assumptions made by the Beer-Lambert law allowed adequate simulation of light interception in a structure with little overlapping at the horizontal-layer and whole-canopy scales. At the local scale, discrepancies between the turbid medium model and the model based on a virtual plant were reduced with an adequate choice of structural parameters, such as the leaf inclination distribution function.

Estimation of evapotranspiration, transpiration ratio and water-use efficiency from a sparse canopy using a compartment model

Using the Shuttleworth and Wallace (S–W) model, evapotranspiration (ET); transpiration ratio ( T/ET), which is the ratio of transpiration ( T) to ET; and water-use efficiency (WUE) were estimated for a sparsely planted sorghum canopy that was well irrigated. That model is designed to estimate separately the evaporation from soil and transpiration from crops. The evapotranspiration estimates for both short- and long-term measurement periods coincided closely with the Bowen ratio energy balance (BREB) measurements. The transpiration ratios were affected by the canopy resistances and the soil surface resistances during the day. The regression curve between leaf area index (LAI) and transpiration ratio suggests that LAI, less than 1.6, determined the transpiration ratio in the absence of water stresses by soil water drought and extreme weather condition. The WUEs for transpiration (WUEt) and evapotranspiration (WUEet), which are the total dry matter (TDM) production for 1 kg T and ET, reached the peaks of 9.0 and 4.5 g kg −1 H 2O, respectively, in the end of July when the total dry matter increasing rate was greatest. These two WUEs degraded to less than zero in the end of August when the plant biomass decreased due to drying and death. The WUEs are largely affected by the TDM seasonal increment rate. Thus, in a sparse crop, the crop growth properties (i.e. LAI and TDM increment) mainly determine the crop water uses (i.e. the transpiration ratio and water-use efficiency) in the absence of water stresses.

Correcting eddy-covariance flux underestimates over a grassland

Independent measurements of the major energy balance flux components are not often consistent with the principle of conservation of energy. This is referred to as a lack of closure of the surface energy balance. Most results in the literature have shown the sum of sensible and latent heat fluxes measured by eddy covariance to be less than the difference between net radiation and soil heat fluxes. This under-measurement of sensible and latent heat fluxes by eddy-covariance instruments has occurred in numerous field experiments and among many different manufacturers of instruments. Four eddy-covariance systems consisting of the same models of instruments were set up side-by-side during the Southern Great Plains 1997 Hydrology Experiment and all systems under-measured fluxes by similar amounts. One of these eddy-covariance systems was collocated with three other types of eddy-covariance systems at different sites; all of these systems under-measured the sensible and latent-heat fluxes. The net radiometers and soil heat flux plates used in conjunction with the eddy-covariance systems were calibrated independently and measurements of net radiation and soil heat flux showed little scatter for various sites. The 10% absolute uncertainty in available energy measurements was considerably smaller than the systematic closure problem in the surface energy budget, which varied from 10 to 30%. When available-energy measurement errors are known and modest, eddy-covariance measurements of sensible and latent heat fluxes should be adjusted for closure. Although the preferred method of energy balance closure is to maintain the Bowen–ratio, the method for obtaining closure appears to be less important than assuring that eddy-covariance measurements are consistent with conservation of energy. Based on numerous measurements over a sorghum canopy, carbon dioxide fluxes, which are measured by eddy covariance, are underestimated by the same factor as eddy covariance evaporation measurements when energy balance closure is not achieved.

２次のクロージャーモデルを用いたソルゴー群落内外の乱流特性に関する研究

２次のクロージャーモデルを用いたソルゴー群落内外の乱流特性に関する研究

Grain Sorghum Response to Row Spacings and Seeding Rates in Kansas

Previous research suggests that reducing row spacings increased grain sorghum's [Sorghum bicolor (L.) Moench.] yield potential. However, most of this research was conducted in environments with lower yield potentials than currently found in northeast Kansas. The objectives of this study were to determine the impact that reducing row spacing had on grain sorghum grain yields and yield components. Research was conducted over five location-years in northeast Kansas to evaluate the effects of row spacings and plant populations on grain sorghum yields. Two hybrids were planted in 10, 20, and 30 in. rows at 30 000, 60 000, and 90 000 plants/acre. In environments where yields exceeded 100 bu/acre, yields were approximately 10% higher from the 10 and 20 in, rows than from the 30 in. rows. When moisture and temperature stress limited grain yields, no yield differences occurred among the row-spacing treatments. Grain yields responded little to changes in plant populations throughout the study. Reducing spacing per plant (reducing row spacing or plant populations) reduced panicles per plant. Caryopses per panicle and caryopses weights were affected primarily by growing conditions during their respective development periods. These results suggest that decreasing sorghum row spacing below 30 in, will increase grain yields under high yielding environments with little risk of reducing yields in lower yielding environments. This study also indicates that seeding rates do not have to be altered as narrow row systems are adopted.

Measurement of radiant interception of crop canopies with the LAI-2000 plant canopy analyzer

The performance of the plant canopy analyzer (PCA), model LAI-2000 (LI-COR, Lincoln, NE, USA), has been tested in two separate field trials for 18 annual crop and pasture species. The objective was to recommend appropriate techniques for reliable estimates of fractional interception of radiation (Fl), leaf area index (LAI) and canopy extinction coefficients. At least six below-canopy measurements and the use of 180° view restriction masks are recommended for row crops. Measurements should preferably be carried out before 8:00. Alternatively, shading of the sensor and sampling area is recommended during sunshine hours. The PCA's fisheye sensor proved to be more suitable than the sunfleck ceptometer (Decagon Devices, Pullman, WA, USA) for a daily estimation of canopy cover. The ceptometer would be preferable for the estimation of hourly Fl which is affected by solar orientation. The PCA's indirect, non-destructive and time saving measurement can accurately estimate LAI of soybean, sorghum, pearl millet and small canopies of wheat and milkvetch (LAI < 1.5). LAI of maize, cow- peas, rye, oats, triticele, ryegrass and perennial grasses obtained with the PCA should be corrected using the derived empirical functions. Potential users should investigate specific measurement techniques for other crops to determine whether the PCA provides reliable data. Fl and LAI measurements with the PCA were used to generate a database of extinction coefficients for photosynthetically active and global solar radiation.

Performance of Seedigated and Conventionally Planted Crops

Seedigation is the use of a moving sprinkler irrigation system to broadcast seeds on the soil surface. Seed germination, plant characteristics and yield for grain sorghum, winter wheat and soybeans that were seedigated and conventionally planted are compared. When the seeding rates for seedigation were increased above that for conventional planting, and adequate moisture was available for germination, grain sorghum and wheat seedigated on tilled surfaces produced yields similar to conventionally planted crops. Seedigation of soybeans into fallow conditions, or when used as a relay crop, was unsuccessful. Shallow disking following seedigation did not improve germination or yield of grain sorghum or winter wheat. Using seedigation to plant wheat into soybeans offers good potential. Seedigating wheat into dense grain sorghum canopies was less successful.

Short-term estimation of sorghum evapotranspiration from canopy temperature

This study was conducted to compare calculated evapotranspiration ( ET c) values using canopy and aerodynamic resistances derived by two methods with measured evapotranspiration ( ET) from a weighing lysimeter. Grain sorghum ( Sorghum bicolor (L.) Moench) mean potential canopy (r̄ cp) and aerodynamic (r̄ ap) resistances were estimated from the linear relationship between sorghum canopy minus air temperature and air vapor pressure deficit. Additionally, wind speed-dependent aerodynamic resistance ( r a) estimates were used. High-frequency short-term (10 min) estimates of crop evapotranspiration were made under clear and partly cloudy sky conditions. The agreement between ET c and measured ET from the lysimeter was optimum when r̄ cp and the wind speed-dependent r a were utilized ( r=0.95, RMSE=0.06 mm h −1, MB=−0.042 mm h −1) during clear sky conditions. On a day with partly cloudy sky conditions, the relationship was slightly less correlated ( r=0.81, RMSE=0.12 mm h −1, MB=−0.036 mm h −1) but the method's ability to track rapidly changing ET rates was notable. Short-term or high-frequency estimates of ET could be useful for crop-level physiological studies of response to water stress, and irrigation water management research.

Canopy leaf display effects on absorbed, transmitted, and reflected solar radiation

Diurnal measurements of reflected, transmitted, and absorbed solar radiation, over an 80–280° solar azimuth range, were compared for wheat, corn, cotton, and sorghum canopies to study the effects of crop leaf display on light penetration into plant stands. The diurnal transmitted radiation (400–700 nm) differed for these four crops, apparently due to inherent canopy architecture and stand structure differences. Diurnal reflectance curves for visible (630–690 nm) and near infrared (760–800 nm) were flat except for the infrared reflectance curve of wheat. Thus, transmitted radiation contained most of the spectral information about canopy architecture of the four crops. Measurements several times during the day may be needed to reliably estimate daily absorbed photosynthetically active radiation (APAR) for generally erectophile crops such as wheat whereas for planophile crops such as cotton, whose leaves are closely and compactly spaced in the canopy, measurements close to solar noon may characterize the canopy. These results suggest that APAR estimates used in crop growth models may be in error, depending on canopy characteristics if based solely on reflectance and transmittance measurements near solar noon.

Chlorpyrifos Applications for Greenhug (Homoptera: Aphididae) Control with a New Multifunction Irrigation System

A new multifunction irrigation system (MFIS) was evaluated in 1983, 1985, and 1986 as a tool for chlorpyrifos applications to grain sorghum for greenbug, Schizaphis graminum (Rondani), control. The unique MFIS chemical nozzling system was evaluated for efficacy or chlorpyrifos rates applied through nozzles either held stationary above or moving within the sorghum canopy, and for efficacy of chlorpyrifos application with and without a nonemulsifiable oil in the spray mixture. Greenbug control was achieved when one-eighth to one-sixteenth of the registered rate of chlorpyrifos was applied through the MFIS. Applications through MFIS nozzles moving within the canopy were more effective with lower chlorpyrifos rates than applications through stationary nozzles. Nonemulsifiable oil need not be added with chlorpyrifos when applying treatments through the MFIS.

Comparative Predation of the Sugarcane Borer (Lepidoptera: Pyralidae) on Sweet Sorghum and Sugarcane

Arthropod predator composition was the same for sweet sorghum and sugarcane, but the numbers of predators in sugarcane were 4-fold and 16-fold greater than those found in sweet sorghum during 1985 and 1986, respectively. Predator habitat disruption associated with cultivation practices in sweet sorghum and sugarcane is important in this relationship because sugarcane, a ratoon crop, receives minimal cultivation compared with the annual crop of sweet sorghum. The red imported fire ant, Solenopsis invicta Buren, was the dominant arthropod species found in pitfall traps and canopy samples for both crops. Carabid larvae, cicindelids, and the Araneae were predators with significantly greater populations in sweet sorghum compared with sugarcane based on pitfall trap estimates during both years. Carabid larvae, chrysopids, and Orius spp. also had significantly greater populations in sweet sorghum canopy samples. Reduced damage by the sugarcane borer, Diatraea saccharalis (F.), resulted in 22.4 and 18.6%greater yield of total sugars in sweet sorghum and sugarcane plots, respectively, without predator suppression during 1986. Survival of Diatraea saccharalis larvae inside stalk tunnels (third instar through prepupa) was significantly greater in sweet sorghum than in sugarcane during 1985. Predators reduced D. saccharalis moth emergence in both crops by ca. 50% in 1986.

Within-canopy temperature patterns of sorghum at two row spacings

The assumptions that conditions are horizontally homogeneous in a canopy and that concentration differences are of a small scale relative to the scale of turbulence have been made in within-canopy studies, but some recent studies have shown that these assumptions are invalid under particular circumstances. The effect of changing row spacing on temperature patterns within a grain sorghum canopy was investigated to study the nature of conditions in the canopy and to help evaluate mechanisms of within-canopy transfer. Within-canopy temperature patterns were monitored in fields with 0.76- and 1.52-m row spacings. Thermopiles were located in a grid at four positions across a row and at five heights. The junctions of each thermopile were uniformly distributed along 1 m of row to obtain a spatial average. Within-canopy air temperature patterns were relatively more one-dimensional in the narrow-row (0.76 m) field and two-dimensional in the wide-row (1.52 m) field. Horizontal temperature gradients were larger and more persistent in the wide-row field. A cool mid-cavity region occurred at midday between the wide rows suggesting gust penetration of air from above the canopy. Daytime temperature patterns suggest a circulation between the wide rows.