West Central Nebraska Research Articles

Evaluation of artificial intelligence algorithms with sensor data assimilation in estimating crop evapotranspiration and crop water stress index for irrigation water management

Irrigation water management using automated irrigation decision support system (IDSS) as a smart irrigation scheduling tool can improve water use efficiency and crop production, especially under circumstances of limited water supply. The current study evaluated the performance of different artificial intelligence (AI) algorithms and their ensembles in forecasting Crop Evapotranspiration (ETc) and Crop Water Stress Index (CWSI) against calculated single crop coefficient FAO56 ETc and Jackson's theoretical CWSI, respectively. Soil moisture, canopy temperatures (Tc) and Normalized Difference Vegetation Index (NDVI) were all measured from irrigated and non-irrigated maize plots in West Central Nebraska during 2020 and 2021 growing seasons. There were fifteen and twelve input combinations used for ETc and CWSI predictions, respectively, having input variables such as weather and soil moisture as well as ancillary variables, including NDVI, reference evapotranspiration (ETr), and cumulative growing degree days (CGDDs). While evaluating the models, four statistical performance indicators including coefficient of determination (r2), root mean square error (RMSE), mean absoluter error (MAE), and mean absolute percentage error (MAPE) were used. Furthermore, ranking scores were performed on statistical results to find the overall best model across all the input combinations. Based on total ranking scores, CatBoost (RMSE ranging between 0.06 – 0.09 unitless) was the best model in predicting CWSI, while Stacked Regression (RMSE ranging between 0.27 – 0.72 mm d−1) was the best model for ETc estimation. Future research will consider designing and evaluating an IDSS using identified best machine learning models to establish soil water and plant stress feedback for automated irrigation scheduling.

Crop water stress index computation approaches and their sensitivity to soil water dynamics

There is a growing interest of using canopy temperature (Tc) based methods, including crop water stress index (CWSI), for irrigation management. However, different approaches exist to normalize Tc to microclimatic conditions, which can influence the accuracy and suitability of CWSI for irrigation scheduling. This study evaluated the performance of CWSI computation approaches and their sensitivity to changes in soil water depletion under different water stress levels. There were six different approaches – two empirical methods using developed lower baseline (i.e., CWSI-EB1, CWSI-EB2), two empirical methods using either artificial (CWSI-EA) or actual/natural (CWSI-EN) canopy reference surfaces, and two theoretical approaches which differ by how aerodynamic and canopy resistances are determined (CWSI-Th1, CWSI-Th2). Stationary infrared thermometers (IRTs) provided continuous Tc to calculate CWSI-EB, CWSI-Th, and CWSI-EN; whereas mobile IRTs and a thermal camera provided one-point-in-time Tc and temperatures of artificial canopy reference surfaces to calculate CWSI-EA. These measurements were all collected from full and deficit irrigated and rainfed maize plots in West Central Nebraska. Day-to-day variations within and across CWSI approaches were evident and their sensitivity to soil water depletion varied. Greater sensitivity and correlation strength to depletion (Dr,i) were observed with CWSI-Th and CWSI-EB under severe stress (i.e., Dr,i > 80%) at deeper soil depths of 1.8 and 2.1 m, producing r2 which ranged from 0.61 to 0.80 (slope: 0.03–0.05) and 0.69–0.79 (slope: 0.03–0.04), respectively. Observed differences in stress magnitudes among approaches and treatments, warrants a specific irrigation triggering threshold for each approach. Additionally, developing a robust index coupling both CWSI and soil water depletion is desirable to improve irrigation water management by accounting for both soil and plant water status.

Molecular Gut-Content Analysis of Adult Ground Beetles (Coleoptera: Carabidae) Provides No Evidence of Predation of Western Corn Rootworm (Coleoptera: Chrysomelidae) in a Nebraska Corn Agroecosystem

Abstract This study was conducted to characterize the ground beetle (Coleoptera: Carabidae) community in Nebraska continuous cornfields and investigate the potential for predation of the western corn rootworm, Diabrotica virgifera virgifera LeConte, a key root-feeding insect pest that is an annual management challenge in this system. Seven collection dates were conducted at five commercial cornfields in west central Nebraska during the growing season of 2014. In each field, carabids were sampled using five 24-h pitfall traps. Carabid specimens were placed in 95% ethanol in the field and stored at –20°C to preserve DNA. After identification to the species level, DNA was extracted and polymerase chain reaction was conducted for gut-content analysis using D. v. virgifera-specific primers. Data from single-plant emergence cages and yellow sticky cards showed high abundance of D. v. virgifera prey in three of the five fields sampled. Sixteen genera and 36 carabid species were found in pitfall traps. Of the total 235 carabid specimens tested in this study, zero tested positive for D. v. virgifera DNA. The lack of positive results for the presence of D. v. virgifera DNA in the gut-contents of carabids, despite abundant pest populations, indicates that, in this system, ground beetles may not be a strong mortality agent of D. v. virgifera. However, results presented here contribute to our knowledge of carabid diversity in agroecosystems and indicate that future D. v. virgifera biological control efforts in this region should focus on other natural enemies and/or other life stages of carabids, such as larvae.

Differences in soil water changes and canopy temperature under varying water × nitrogen sufficiency for maize

Crop nitrogen (N) status is known to affect crop water status and crop water use. To investigate further the N effects on soil water changes and on canopy temperature, three water levels × four N levels were imposed on two growing seasons of maize in west central Nebraska, USA. Soil water changes were measured using a neutron probe, whereas canopy temperature was measured using infrared thermometers on a ground-based mobile platform. At all water levels, soil water losses over month-long intervals were generally greater as N levels increased. Given equal water levels, early afternoon canopy temperatures were usually lower with higher N levels, but no trend or even the opposite trend was occasionally observed. Jointly considering canopy reflectance and soil water depletion shows potential to explain much of the variation in estimated instantaneous water use among plots. However, determining the relative contributions of the canopy and soil factors on a particular day may require season-to-date knowledge of the crop. Further research on assimilating such sensor data for a combined stress coefficient would improve crop modeling and irrigation scheduling when variable water sufficiency and variable N sufficiency are simultaneously significant.

Variable Rate Irrigation of Maize and Soybean in West-Central Nebraska Under Full and Deficit Irrigation

Variable rate irrigation (VRI) may improve center pivot irrigation management, including deficit irrigation. A remote-sensing-based evapotranspiration model was implemented with Landsat imagery to manage irrigations for a VRI equipped center pivot irrigated field located in West-Central Nebraska planted to maize in 2017 and soybean in 2018. In 2017, the study included VRI using the model, and uniform irrigation using neutron attenuation for full irrigation with no intended water stress (VRI-Full and Uniform-Full treatments, respectively). In 2018, two deficit irrigation treatments were added (VRI-Deficit and Uniform-Deficit, respectively) and the model was modified in an attempt to reduce water balance drift; model performance was promising, as it was executed unaided by measurements of soil water content throughout the season. VRI prescriptions did not correlate well with available water capacity (R2 < 0.4); however, they correlated better with modeled ET in 2018 (R2 = 0. 69, VRI-Full; R2 = 0.55, VRI-Deficit). No significant differences were observed in total intended gross irrigation depth in 2017 (VRI-Full = 351 mm, Uniform Full = 344). However, in 2018, VRI resulted in lower mean prescribed gross irrigation than the corresponding uniform treatments (VRI-Full = 265 mm, Uniform Full = 282 mm, VRI-Deficit = 234 mm, and Uniform Deficit = 267 mm). Notwithstanding the differences in prescribed irrigation (in 2018), VRI did not affect dry grain yield, with no statistically significant differences being found between any treatments in either year (F = 0.03, p = 0.87 in 2017; F = 0.00, p = 0.96 for VRI/Uniform and F = 0.01, p = 0.93 for Full/Deficit in 2018). Likewise, any reduction in irrigation application apparently did not result in detectable reductions in deep percolation potential or actual evapotranspiration. Additional research is needed to further vet the model as a deficit irrigation management tool. Suggested model improvements include a continuous function for water stress and an optimization routine in computing the basal crop coefficient.

Water effects on optical canopy sensing for late-season site-specific nitrogen management of maize

The interpretation of optical canopy sensor readings for determining optimal rates of late-season site-specific nitrogen application to corn (Zea mays L.) can be complicated by spatially variable water sufficiency, which can also affect canopy size and/or pigmentation. In 2017 and 2018, corn following corn and corn following soybeans were subjected to irrigation × nitrogen fertilizer treatments in west central Nebraska, USA, to induce variable water sufficiency and variable nitrogen sufficiency. The vegetation index-sensor combinations investigated were the normalized difference vegetation index (NDVI), the normalized difference red edge index (NDRE), and the reflectance ratio of near infrared minus red edge over near infrared minus red (DATT) using ACS-430 active optical sensors; NDVI using SRS-NDVI passive optical sensors; and red brightness and a proprietary index using commercial aerial visible imagery. Among these combinations, NDRE and DATT were found to be the most suitable for assessing nitrogen sufficiency within irrigation levels. While DATT was the least sensitive to variable water sufficiency, DATT still tended to decrease with decreasing water sufficiency in high nitrogen treatments, whereas the effect of water sufficiency on DATT was inconsistent in low nitrogen treatments. A new method of quantifying nitrogen sufficiency while accounting for water sufficiency was proposed and generally provided more consistent improvement over the mere averaging of water effects as compared with the canopy chlorophyll content index method. Further elucidation and better handling of water-nitrogen interactions and confounding are expected to become increasingly important as the complexity, automation, and adoption of sensor-based irrigation and nitrogen management increase.

Heifer development systems: A comparison of grazing winter range or corn residue1

Two experiments at 2 Nebraska locations evaluated effects of heifer development system on growth and pregnancy rate. In Exp. 1, heifers (n=270, BW=225 ± 2 kg) grazed winter Sandhills range (WR) or west central Nebraska corn residue (CR) with a supplement (0.45 kg/animal; 31% CP; 80 mg·animal(-1)·d(-1) of monensin). In Exp. 2, heifers (n=180, BW = 262 ± 3 kg) grazed eastern Nebraska WR or CR with a supplement (0.45 to 0.90 kg/d; 31% CP; 80 to 160 mg·animal(-1)·d(-1) of monensin). The CR heifers tended to have less (P=0.10) ADG compared with WR heifers before breeding in Exp. 1; however, prebreeding ADG was similar (P=0.77) in Exp. 2. Prebreeding BW, percentage of mature BW at breeding, and pregnancy determination BW were similar (P ≥ 0.14) for CR and WR in both experiments. Percentage of heifers pubertal at breeding, AI conception, and AI pregnancy rate (Exp. 2) and final pregnancy rate in both experiments were also similar (P ≥ 0.27) for CR and WR heifers. Precalving BW, percentage of calves born in the first 21 d, calf birth date, calf birth BW, and dystocia score were all similar (P ≥ 0.21) for CR and WR heifers in both experiments. Cow BW at weaning, calf weaning BW, adjusted 205-d calf BW, and second season pregnancy rates were not affected (P ≥ 0.16) by treatment. Heifer development system did not affect (P ≥ 0.56) the cost of producing 1 pregnant heifer in Exp. 1 or 2. Development on CR may reduce ADG before breeding, but did not affect pregnancy rate. Heifer development using CR or WR postweaning resulted in similar reproductive performance and development cost.

Environment and Hybrid Influences on Rapid‐Visco‐Analysis Flour Properties of Food‐Grade Grain Sorghum

ABSTRACTGrain processors would benefit from information about the production environment and the influences of the sorghum [Sorghum bicolor (L.) Moench] hybrid on food‐grade flour properties. The objective of this study was to determine the effects of environment and hybrid on rapid‐visco‐analysis (RVA) flour properties of commercially available food‐grade sorghum. A randomized complete block experiment was planted in 12 environments, which included the 2004 and 2005 growing seasons and irrigated and dryland water regimes in eastern, central, and west central Nebraska, and a dryland, low‐N environment in eastern Nebraska. The environment accounted for 71–85% of the total variation in RVA parameters, while the hybrid accounted for 11–23% and the environment‐by‐hybrid interaction, 1–3%. Unfortunately, the results of this experiment suggest that it is difficult to predict the effect that environment will have on resulting sorghum‐flour parameters. Although of secondary importance in terms of total variation in sorghum‐flour RVA properties, the choice of hybrid predictably and significantly contributes to sorghum‐starch viscosity properties. Food‐grade hybrids were grouped based on viscosity properties into those best suited for dry‐mill and alkaline‐cooked products (Asgrow Orbit; Sorghum Partners NK1486) and those best suited for porridge, consumable alcohol, and ethanol production (Kelly Green Seeds KG6902; NC+ Hybrids 7W92; Asgrow Eclipse; and Fontanelle W‐1000). These results were consistent with those previously reported for grain density.

Environment and Hybrid Influences on Food‐Grade Sorghum Grain Yield and Hardness

Few studies have examined grain quality of food‐grade sorghum hybrids. The objective of this study was to determine the effects of environment and hybrid on grain quality of commercially available food‐grade sorghums. A randomized complete block experiment with three replications was planted in 12 environments, which included the 2004 and 2005 growing seasons and irrigated and dryland water regimes in eastern, central, and west central Nebraska and a dryland low‐N environment in eastern Nebraska. Environment accounted for 5 to 140 times greater variation in measured parameters than hybrid, and the hybrid × environment interaction accounted for less than 2% of the total variation. Grain yield and kernel mass varied, with low yields of 1.4 Mg ha−1 and kernels weighing 9.5 g 1000 kernels−1 in the low‐N 2004 environment, high grain yields of 10.5 Mg ha−1 under irrigated conditions in central Nebraska in 2005, and kernels weighing 27.8 g 1000 kernels−1 in the eastern Nebraska dryland 2005 environment. Harder grain was produced in 2005 than in 2004, with the west central and central 2005 environments having the lowest tangential abrasive dehulling device (TADD) removals of 14%. Non‐food‐grade hybrids produced higher grain yields and kernel mass than food‐grade hybrids. Grain hardness was greater for non‐food‐grade and medium maturity hybrids when environmental means were lower (i.e., softer) but showed little or no difference in hardness when environmental means were high. Nebraska production environments have the capability to produce high quality food‐grade sorghums for specific food uses to benefit both the producer and the food processor.

Crop Residue Cover Effects on Evaporation, Soil Water Content, and Yield of Deficit-Irrigated Corn in West-Central Nebraska

Competition for water is becoming more intense in many parts of the U.S., including west-central Nebraska. It is believed that reduced tillage, with more crop residue on the soil surface, conserves water, but the magnitude of water conservation is not clear. A study was initiated on the effect of residue on soil water content and corn yield at North Platte, Nebraska. The experiment was conducted in 2007 and 2008 on plots planted to field corn (Zea mays L.). In 2005 and 2006, soybean was grown on these plots. There were two treatments: residue-covered soil and bare soil. Bare-soil plots were created in April 2007. The residue plots were left untreated. In April 2008, bare-soil plots were recreated on the same plots as in 2007. The experiment consisted of eight plots (two treatments with four replications each). Each plot was 12.2 m 12.2 m. During the growing season, soil water content was measured several times in each of the plots at six depths, down to a depth of 1.68 m, using a neutron probe. The corn crop was sprinkler-irrigated but purposely water-stressed, so that any water conservation in the residue-covered plots might translate into higher yields. In 2007, mean corn yield was 12.4 Mg ha-1 in the residue-covered plots, which was significantly (p = 0.0036) greater than the 10.8 Mg ha-1 in the bare-soil plots. Other research has shown that it takes 65 to 100 mm of irrigation water to grow this extra 1.6 Mg ha-1, which may be considered water conservation due to the residue. In 2008, the residue-covered soil held approximately 60 mm more water in the top 1.83 m compared to the bare soil toward the end of the growing season. In addition, mean corn yield was 11.7 Mg ha-1 in the residue-covered plots, which was significantly (p = 0.0165) greater than the 10.6 Mg ha-1 in the bare-soil plots. It would take 30 to 65 mm of irrigation water to produce this additional 1.1 Mg ha-1 of grain yield. Thus, the total amount of water conservation due to the residue was 90 to 125 mm in 2008. Water conservation of such a magnitude will help irrigators to reduce pumping cost. With deficit irrigation, water saved by evaporation is used for transpiration and greater yield, which may have even greater economic benefits. In addition, with these kinds of water conservation, more water would be available for competing needs.

Effect of irrigation amounts applied with subsurface drip irrigation on corn evapotranspiration, yield, water use efficiency, and dry matter production in a semiarid climate

Quantifying the local crop response to irrigation is important for establishing adequate irrigation management strategies. This study evaluated the effect of irrigation applied with subsurface drip irrigation on field corn ( Zea mays L.) evapotranspiration (ETc), yield, water use efficiencies (WUE = yield/ETc, and IWUE = yield/irrigation), and dry matter production in the semiarid climate of west central Nebraska. Eight treatments were imposed with irrigation amounts ranging from 53 to 356 mm in 2005 and from 22 to 226 mm in 2006. A soil water balance approach (based on FAO-56) was used to estimate daily soil water and ETc. Treatments resulted in seasonal ETc of 580–663 mm and 466–656 mm in 2005 and 2006, respectively. Yields among treatments differed by as much as 22% in 2005 and 52% in 2006. In both seasons, irrigation significantly affected yields, which increased with irrigation up to a point where irrigation became excessive. Distinct relationships were obtained each season. Yields increased linearly with seasonal ETc ( R 2 = 0.89) and ETc/ETp ( R 2 = 0.87) (ETp = ETc with no water stress). The yield response factor (ky), which indicates the relative reduction in yield to relative reduction in ETc, averaged 1.58 over the two seasons. WUE increased non-linearly with seasonal ETc and with yield. WUE was more sensitive to irrigation during the drier 2006 season, compared with 2005. Both seasons, IWUE decreased sharply with irrigation. Irrigation significantly affected dry matter production and partitioning into the different plant components (grain, cob, and stover). On average, the grain accounted for the majority of the above-ground plant dry mass (≈59%), followed by the stover (≈33%) and the cob (≈8%). The dry mass of the plant and that of each plant component tended to increase with seasonal ETc. The good relationships obtained in the study between crop performance indicators and seasonal ETc demonstrate that accurate estimates of ETc on a daily and seasonal basis can be valuable for making tactical in-season irrigation management decisions and for strategic irrigation planning and management.

Wicked Curve: The Life and Troubled Times of Grover Cleveland Alexander (review)

Reviewed by: Wicked Curve: The Life and Troubled Times of Grover Cleveland Alexander Lee Lowenfish John C. Skipper. Wicked Curve: The Life and Troubled Times of Grover Cleveland Alexander. Jefferson, NC: McFarland, 2006. 238 pp. Paper, $29.95. The photo on the cover of John Skipper's absorbing new biography of Grover Cleveland Alexander is worth at least a thousand words. Taken late in the career of the future Hall-of-Fame pitcher, he is pictured on the floor of a dugout with his back resting against a wall. Clasping his right hand firmly with his left, the look of dour contemplation on Alexander's face strongly suggests his ongoing battle against demons inside. The story of the Nebraska farm boy who had unprecedented control on the mound but little control off of it is one of baseball's most tragic tales, and Skipper has done an admirable job in researching and writing it. Born in 1887 in Elba, Nebraska, a farming town that took its name from the elbow created by the Union Pacific railroad tracks, Grover Cleveland Alexander was one of thirteen children, twelve boys, five of whom died in infancy. Skipper informs us that he could find no particular reason for Alexander's presidential given names except that perhaps his parents ran out of alternatives. As a youth, Grover, or Dode as he was nicknamed, quickly earned a reputation for his prodigious ability to shuck corn and to throw a baseball. By his midteens, Alexander's powerful arm became widely known in the surrounding towns of west-central Nebraska, but he wasn't signed to a professional contract until 1909 when he won 15 games for a team in Galesburg, Illinois. His season was cut short when he was hit on the head by a second baseman's throw while trying to break up a double play. He suffered from double vision for some time thereafter but recovered enough to win 29 games in 1910 for a team in Syracuse, New York. However, he was not signed for the next season, probably because he was already drinking heavily. Skipper does not say so definitively, but it seems that his weakness for what sportswriters of the time lightly called "John Barleycorn" was also a factor in Alexander's not being offered a pro contract until his early twenties. Regardless of his off-field problems, a talent like Alexander's did not go [End Page 89] unnoticed for long. He was signed by the Philadelphia Phillies in 1911, and he enjoyed what Skipper boldly states was "the greatest rookie season of all time" (29). Surely the numbers are impressive: a 28-13 record in 367 innings with an ERA of 2.57 and nearly a 2:1 strikeout-walk ratio of 227:129. For the next eighteen years, Alexander—probably the greatest control pitcher of all time—never walked more than seventy-six men. From 1915 through 1917, Alexander put together three unprecedented seasons in which he won more than 30 games each year with ERAs below 2 runs per game. In 1915 he won the only game that the Phillies would win in a World Series until 1980. In 1916 his 33 wins included an amazing 16 shutouts. Phillies team ownership, however, was in disarray. Horace Fogel initially signed Alexander, but because of his close connection to professional gambling—Skipper informs us that he actually wanted to change the name of the team to the Live Wires—he was forced to sell the team to local investor William Locke. When Locke died suddenly, his partner, William F. Baker (a former New York City police commissioner), took over the team but was not interested in paying top dollar for his stars. Alexander held out before the 1917 season, taking a job in a traveling circus to make ends meet. Skipper notes perceptively, "The fact that Alexander would even consider being a sideshow for a circus for huge money [$1,000 a week for thirty-five weeks] was an indication of how much his life was worth to others and of his own self-worth" (64). Alexander eventually did sign with the Phillies in 1917 and won another 30 games...

Construction, installation, and performance of two repacked weighing lysimeters

Weighing lysimeters are the standard method for directly measuring evapotranspiration (ET). This paper discusses the construction, installation, and performance of two (1.52 m × 1.52 m × 2.13-m deep) repacked weighing lysimeters for measuring ET of corn and soybean in West Central Nebraska. The cost of constructing and installing each lysimeter was approximately US $12,500, which could vary depending on the availability and cost of equipment and labor. The resolution of the lysimeters was 0.0001 mV V−1, which was limited by the data processing and storage resolution of the datalogger. This resolution was equivalent to 0.064 and 0.078 mm of ET for the north and south lysimeters, respectively. Since the percent measurement error decreases with the magnitude of the ET measured, this resolution is adequate for measuring ET for daily and longer periods, but not for shorter time steps. This resolution would result in measurement errors of less than 5% for measuring ET values of ≥3 mm, but the percent error rapidly increases for lower ET values. The resolution of the lysimeters could potentially be improved by choosing a datalogger that could process and store data with a higher resolution than the one used in this study.

Comparison of irrigation strategies for surface-irrigated corn in West Central Nebraska

Many farmers in West Central Nebraska have limited irrigation water supplies, and need to produce crops with less water. This study evaluated the impact of four water management strategies on grain yield of surface-irrigated corn (Zea mays L.) at North Platte, Nebraska. Treatments included: (1) no irrigation (DRYLAND), (2) one irrigation prior to tassel formation (EARLY), (3) one irrigation during the silk stage (LATE), and (4) irrigation following farmer’s practices (FARMER). The study included three wet years (1992, 1993, and 1996) and 2 years with average annual rainfall for the area (1994 and 1995). Significant yield differences among treatments, and a yield response to irrigation, were only observed during the 2 years with average rainfall. During all years, the FARMER treatment was over-irrigated and resulted in considerable water losses by runoff and deep percolation. Grain yield response to irrigation during the three wet years was insignificant among the treatments, but significant during the dry years. The results of this study suggest that inducing stress is not a good strategy for increasing crop water productivity (yield per unit ETd) for corn and point out the need to minimize irrigation water losses and improve irrigation scheduling.

Survival and Growth of Wildflowers with Buffalo Grass or Blue Grama Grass

Two studies in west-central Nebraska to determine the survival of wildflowers planted with buffalo grass [Buchloe dactyloides (Nutt.) Engelm.] and blue grama grass [Bouteloua gracilis (H.B.K.) Lag. ex Steud.)] were conducted in 6 and 10 year studies. In total, 19 forbs and 1 grass were transplanted with `Texoka' buffalo grass in the first study, and 16 forbs were planted in a split-plot design into 3 buffalo grass selections, blue grama or a clean cultivated plot in the second study. Survival between transplants in both studies varied significantly. In the first study, survival was significantly higher for little bluestem (Schizachyrium scoparium Michx.) (85%), bouncing bet (Saponaria officinalis L.) (100%), and stiff goldenrod (Solidago rigida L.) (100%) over the 6 years of the study. In the second study, there were significant differences between species for survival, with grayhead prairie coneflower [Ratibida pinnata (Vent.) Barnh.] (85%) and pitcher sage (Salvia azurea Lam.) (80%) having the highest survival at the end of the 10-year study. There were significant differences in height and number of flower stalks within S. rigida, R. pinnata, and S. azurea between years and between main plots. This study demonstrates differences in survival and growth of wildflowers when planted in conjunction with buffalo grass and blue grama grass.

RESPONSE OF SOYBEAN TO DEFICIT IRRIGATION IN THE SEMI-ARID ENVIRONMENT OF WEST-CENTRAL NEBRASKA

Several factors, including multi-year drought, declining aquifer levels, and new water regulations, are contributing to reduced availability of irrigation water in the semi-arid area of west-central Nebraska. Since many farmers in this area do not have enough water to meet the seasonal water requirements of crops like corn and soybean, maximizing yield produced per unit of water under deficit irrigation conditions is becoming increasingly important. This study was conducted to quantify the grain yield response of soybean [Glycine max (L.) Merr.] to deficit irrigation, and to determine which seasonal water variables correlated best to soybean grain yield under deficit irrigation. The study was conducted during 2002 at Curtis, and 2003 and 2004 at North Platte, Nebraska. Nine deficit irrigation treatments, including different irrigation amounts and timings, were studied in 2002 and 2003, and eight treatments were studied in 2004. Soybean grain yields across years and sites were best related to the seasonal ratio of the actual crop evapotranspiration and the crop evapotranspiration when soil water was not limiting (ETd/ETw), and to the seasonal ratio of actual crop transpiration and crop transpiration when soil water was not limiting (Td/Tw). Both of these seasonal ratios were linearly related to grain yield with R2 = 0.91 when combining data for all seasons. The crop water productivity (CWP) (yield per unit of seasonal ETd) linearly increased with both ETd/ETw (R2 = 0.72) and Td/Tw (R2 = 0.72), but was best correlated to the daily positive difference between the actual and the theoretical fraction of total available soil water in the root zone that can be depleted before crop water stress occurred, accumulated for the entire season (seasonal pdiff) (R2 = 0.77). A linear relationship between the cumulative ETw and fraction of season (function of days after emergence) was found. This relationship developed for a given location could be used to extrapolate seasonal ETw for in-season irrigation management. Poor correlation was found between CWP and other variables such as total irrigation, rain + irrigation, and total water. The results of this study can provide useful information for soybean irrigators to make better management decisions under deficit irrigation conditions.

Effects of stable flies (Diptera: Muscidae) on weight gains of grazing yearling cattle.

Differences in weight gains caused by stable flies, Stomoxys calcitrans (L.), on grazing yearling steer/calves averaged 0.2 kg per steer in a 3-yr study on canyon range pastures in West Central Nebraska, Stable fly numbers averaged 0.85 per front leg on treated calves and 3.64 per front leg on control calves. In 2 of the 3 yr after the grazing trials were completed, the calves were placed in a feedlot and fed a finishing ration. Compensatory gain did not occur in the feedlot after the stable fly stress was removed.

Characteristics of nest soil, but not geographic origin, influence cold hardiness of hatchling painted turtles

We investigated environmental factors influencing cold hardiness in hatchling painted turtles ( Chrysemys picta) indigenous to northeastern Indiana and the Sandhills of west-central Nebraska. In both locations, hatchlings overwinter in their natal nests. Survival of hatchlings chilled to minimum temperatures between –2.5 and –6.0°C inside explanted natal nests ranged from 30 to 100%. Mortality likely was caused by freezing of the turtles that was induced by contact with ice nuclei in the surrounding soil. Susceptibility to inoculative freezing was strongly influenced by moisture content (7.5–25%, w/w) of the frozen soil in which hatchlings were cooled. When chilled in soil containing 15% moisture, turtles from Indiana resisted inoculative freezing better than hatchlings from Nebraska, but this variation was due to physical characteristics of the soils indigenous to each locale rather than genetic differences between populations. Soil in which the Indiana turtles nested contained relatively higher amounts of clay and organic matter, and bound more moisture, than the loamy sand at the Nebraska site. Soil collected from both locales contained potent ice nuclei that may constrain supercooling of the hatchlings, even in the absence of soil moisture. In addition to temperature and precipitation, local and regional variation in soils is an important determinant of overwintering survival of hatchling C. picta.

Vegetation Response to Late Growing-Season Wildfire on Nebraska Sandhills Rangeland

This study examined the effects of late growing-season (September) wildfire on the subsequent production and species composition of upland Nebraska Sandhills prairie vegetation. Three paired-plots (burn and control), 0.5 ha in size were established in 1995 on sands range sites on each of 3 replications in west-central Nebraska. Soil temperature data were collected the following growing season and herbage standing crop and species composition data were collected for 3 growing seasons following the burn. During March through May of the 1996 growing season, soil temperature in the burn treatment was an average of 1.6 degrees C higher at both 15 and 30 cm depths compared to the control (P 0.05). Little bluestem [Schizchyrium scoparium (Michx.) Nash] was the species most adversely affected by burning. Percentage composition by weight of little bluestem in August 1996 averaged 8% under the burn treatment compared to 47% in the control. Other species and species groups, however, were more abundant in burned plots, thus offsetting the lesser amounts of little bluestem. Little bluestem exhibited a marked recovery during the second and third growing seasons after the burn. During the third growing season, percent composition of little bluestem averaged 46% and was not different between treatments (P > 0.05). Forbs were more abundant under the burn treatment compared to the control only during the first growing season following the burn (P < 0.05). DOI:10.2458/azu_jrm_v53i4_volesky

Vegetation response to late growing-season wildfire on Nebraska Sandhills rangeland

This study examined the effects of late growing-season (September) wildfire on the subsequent production and species composition of upland Nebraska Sandhills prairie vegetation. Three paired-plots (burn and control), 0.5 ha in size were established in 1995 on sands range sites on each of 3 replications in west-central Nebraska. Soil temperature data were collected the following growing season and herbage standing crop and species composition data were collected for 3 growing seasons following the burn. During March through May of the 1996 growing season, soil temperature in the burn treatment was an average of 1.6 degrees C higher at both 15 and 30 cm depths compared to the control (P &lt; 0.05). This small increase in spring soil temperature under the burn treatment did not appear to result in earlier growth or to increase herbage standing crop in May. Total herbage standing crop in August averaged 143, 142, and 185 g m-2 in 1996, 1997, and 1998, respectively, and did not differ between the burn treatment and control (P &gt; 0.05). Little bluestem [Schizchyrium scoparium (Michx.) Nash] was the species most adversely affected by burning. Percentage composition by weight of little bluestem in August 1996 averaged 8% under the burn treatment compared to 47% in the control. Other species and species groups, however, were more abundant in burned plots, thus offsetting the lesser amounts of little bluestem. Little bluestem exhibited a marked recovery during the second and third growing seasons after the burn. During the third growing season, percent composition of little bluestem averaged 46% and was not different between treatments (P &gt; 0.05). Forbs were more abundant under the burn treatment compared to the control only during the first growing season following the burn (P &lt; 0.05).