@article{sermons_wherley_zhang_bowman_rufty_2017, title={The role of internal and external nitrogen pools in bermudagrass growth during spring emergence from dormancy}, volume={40}, ISSN={["1532-4087"]}, DOI={10.1080/01904167.2016.1264424}, abstractNote={ABSTRACT As bermudagrass (Cynodon dactylon (L.) Pers.) transitions from winter dormancy to active growth in spring, nitrogen is essential for new tissue growth. We examined the relative contributions of internally stored nitrogen and that taken up by preexisting and newly produced roots. Field-collected dormant bermudagrass was transferred to a nutrient solution culture system in a growth chamber. Cultures were provided either a non-nitrogen-containing solution or one amended with nitrate labeled with the 15N isotope of nitrogen, which allowed tracking of endogenous and exogenous N pools in all tissues as growth began. Nitrogen in stolon internodes was the largest N source for early growth. Though mass increased at the same rate in both N treatments over 3 weeks of growth, the unfertilized treatment showed early signs of nitrogen deficiency: low tissue N, slowed leaf elongation, and fewer but longer roots. Preexisting roots were active in absorption almost immediately; new roots were produced quickly and had even higher N uptake rates.}, number={10}, journal={JOURNAL OF PLANT NUTRITION}, author={Sermons, Shannon M. and Wherley, Benjamin G. and Zhang, Chenxi and Bowman, Daniel C. and Rufty, Thomas W.}, year={2017}, pages={1404–1416} }
 @article{riar_carley_zhang_schroeder-moreno_jordan_webster_rufty_2016, title={Environmental Influences on Growth and Reproduction of Invasive Commelina benghalensis}, volume={2016}, ISSN={1687-8159 1687-8167}, url={http://dx.doi.org/10.1155/2016/5679249}, DOI={10.1155/2016/5679249}, abstractNote={Commelina benghalensis(Benghal dayflower) is a noxious weed that is invading agricultural systems in the southeastern United States. We investigated the influences of nutrition, light, and photoperiod on growth and reproductive output ofC. benghalensis. In the first experimental series, plants were grown under high or low soil nutrition combined with either full light or simulated shade. Lowered nutrition strongly inhibited vegetative growth and aboveground spathe production. Similar but smaller effects were exerted by a 50% reduction in light, simulating conditions within a developing canopy. In the second series of experiments,C. benghalensisplants were exposed to different photoperiod conditions that produced short- and long-day plants growing in similar photosynthetic periods. A short-day photoperiod decreased time to flowering by several days and led to a 40 to 60% reduction in vegetative growth, but reproduction above and below ground was unchanged. Collectively, the results indicate that (1) fertility management in highly weathered soils may strongly constrain competitiveness ofC. benghalensis; (2) shorter photoperiods will limit vegetative competitiveness later in the growing seasons of most crops; and (3) the high degree of reproductive plasticity and output possessed byC. benghalensiswill likely cause continual persistence problems in agricultural fields.}, journal={International Journal of Agronomy}, publisher={Hindawi Limited}, author={Riar, Mandeep K. and Carley, Danesha S. and Zhang, Chenxi and Schroeder-Moreno, Michelle S. and Jordan, David L. and Webster, Theodore M. and Rufty, Thomas W.}, year={2016}, pages={1–9} }
 @article{zhang_pinnix_zhang_miller_rufty_2017, title={Evaluation of Key Methodology for Digital Image Analysis of Turfgrass Color Using Open-Source Software}, volume={57}, ISSN={["1435-0653"]}, DOI={10.2135/cropsci2016.04.0285}, abstractNote={Digital image analysis is a frequently used research technique to provide an objective measure of turfgrass color, in addition to the traditional visual rating. A commonly used method relies on commercial software package SigmaScan Pro to quantify mean hue angle, saturation, and brightness values from turf images, and to calculate a dark green color index as the measure of color. To enable turf image analysis to function on an open‐source platform, a method was developed within ImageJ to batch process turf images for color parameters. This Java‐based ImageJ plugin quantifies hue angle, saturation, and brightness values and calculates a dark green color index. In addition, information on the variability of these color parameters can be simultaneously acquired. This new method was used to quantify color parameters of turf images collected from field plots of tall fescue (Schedonorus arundinacea Shreb. Dumort.), Kentucky bluegrass (Poa pratensis L.), ryegrass (Lolium ssp.), hybrid bermudagrass (Cynodon dactylon (L.) Pers. × C. transvaalensis Burtt‐Davy), and creeping bentgrass (Agrostis stolonifera L.). While color parameter values differed little between ImageJ and SigmaScan, the time saved in processing images using ImageJ was considerable. Aside from software, analysis of color parameters acquired from the five turfgrass species indicated that hue angle alone can adequately measure turf color in digital images. Results also demonstrated that, in addition to light source, camera settings should remain fixed during photo capture to avoid introducing errors. The ImageJ plug‐in developed in this study is made available at www.turffiles.ncsu.edu.}, number={2}, journal={CROP SCIENCE}, author={Zhang, Chenxi and Pinnix, Garland D. and Zhang, Zheng and Miller, Grady L. and Rufty, Thomas W.}, year={2017}, pages={550–558} }
 @article{zhang_miller_rufty_bowman_2013, title={Nitrate Leaching from Two Kentucky Bluegrass Cultivars as Affected by Nitrate Uptake Capacity and Subsurface Soil Compaction}, volume={53}, ISSN={["1435-0653"]}, DOI={10.2135/cropsci2012.10.0600}, abstractNote={ABSTRACTThere are a number of strategies to minimize NO3– leaching from turfgrass, including planting turfgrass cultivars with higher NO3– absorption abilities. This column lysimeter study was conducted to examine NO3– leaching from two Kentucky bluegrass (Poa pratensis L.) cultivars differing in NO3– uptake capacity. Subsurface soil compaction was included as a second factor. Tillers of Julia and Midnight Kentucky bluegrass, previously identified as having high and low NO3– uptake capacity, respectively, were grown in column lysimeters. Each column was filled with Wagram loamy sand with or without a subsurface compaction layer 8.5 cm below the surface. The two cultivars were established and then treated to impose moderate N deficiency. Potassium nitrate was applied in solution at 49 kg N ha–1 followed by daily heavy irrigation. Leachate was collected and analyzed for NO3–‐N. Cumulative N leaching loss of applied N ranged from 2.6 to 19% and 2.8 to 21% for Julia and Midnight, respectively. In two out of three trials, both cultivars absorbed NO3– very efficiently in noncompacted soil, with only trace amounts of NO3– leaching. While NO3–‐N loss averaged 4.7% of applied N in noncompacted soil across all trials, subsurface soil compaction increased that to 8.9%. Results indicated that despite being identified as more efficient for NO3– uptake, NO3– leaching from Julia was generally similar to that from Midnight. Soil conditions and differences in root morphology and/or architecture may played a more important role than root uptake capacity in determining NO3– leaching from these Kentucky bluegrass genotypes.}, number={4}, journal={CROP SCIENCE}, author={Zhang, Chenxi and Miller, Grady L. and Rufty, Thomas W. and Bowman, Daniel C.}, year={2013}, pages={1722–1733} }
 @article{zhang_rufty_miller_bowman_2013, title={Nitrate Uptake Rates of Kentucky Bluegrass Genotypes and Their Effect on Nitrate Absorption under Competitive Conditions}, volume={53}, ISSN={["1435-0653"]}, DOI={10.2135/cropsci2012.10.0597}, abstractNote={ABSTRACTNitrate leaching from turfgrasses continues to be a concern. It is proposed that selecting turfgrass genotypes with higher NO3− absorption abilities could reduce NO3− leaching. This study examined the intraspecific difference in NO3− absorption among Kentucky bluegrass (Poa pratensis L.) genotypes and how such a difference affects N absorption when roots are in competition for soil N. A nutrient solution screening procedure was used to identify Kentucky bluegrass genotypes having high vs. low NO3− uptake capacity. Tillers of 60 Kentucky bluegrass cultivars were rooted and transferred to a continuous flow solution culture system. After establishment, plants were treated to develop moderate N deficiency. Isotopically labeled (15N) KNO3 was introduced at high (1 mM) and low (0.05 mM) concentrations to screen for differences in NO3− uptake. After a brief uptake period, plants were harvested, dried, and analyzed for 15N content to determine N uptake rate. There were significant differences among genotypes for uptake rate at both high and low N concentrations. The 60 genotypes exhibited a wide range of uptake rates, with strong correlation between rates at high and low N. The cultivars Julia and Midnight were selected as representing cultivars with efficient and inefficient NO3− uptake, respectively. Julia had NO3− uptake rates averaging 56% higher than Midnight. A subsequent lysimeter study examined whether higher NO3− uptake capacity would translate into increased N absorption under competitive conditions. Tillers of the two cultivars were planted as a mixed stand in soil or sand column lysimeters. After establishment, 15N‐labeled KNO3 solution at high (2 or 1mM) and low (0.05mM) concentrations was applied to each column. After an uptake period, individual plants of each cultivar were harvested for 15N analysis. Results indicated that Julia absorbed 20 to 50% more NO3− than Midnight at the high N concentration and 25 to 71% more NO3− more than Midnight at the low N concentration. Most differences were statistically significant. This indicates that differences in NO3− absorption by Kentucky bluegrass identified in solution culture translate into differences in absorption of soil N.}, number={3}, journal={CROP SCIENCE}, author={Zhang, Chenxi and Rufty, Thomas W. and Miller, Grady L. and Bowman, Daniel C.}, year={2013}, month={May}, pages={1179–1188} }
 @article{riar_spears_burns_jordan_zhang_rufty_2014, title={Persistence of Benghal dayflower (Commelina benghalensis) in sustainable agronomic systems: Potential impacts of hay bale storage, animal digestion, and cultivation}, volume={38}, DOI={10.1080/21683565.2013.839486}, abstractNote={Experiments were conducted to evaluate factors affecting persistence of the invasive, federal noxious weed Benghal dayflower in sustainable agronomic systems. Seeds were exposed to a range of temperatures simulating those found in hay bales in the field and periodically tested for viability over 21 days. Seeds were nonviable after one day at 65 °C and after 14 days at 50 or 45 °C. A second series of experiments examined the effects of simulated rumen digestion on germination and viability of Benghal dayflower seeds and the response was compared to that with seeds of five other common weed species. Time courses revealed that seeds from the other weeds were acutely damaged by digestion and viability depressed after 48 and 96 h, but germination of Benghal dayflower seeds was increased at 48 h, and only a slight decrease occurred after 96 h. In the third experimental series, stem fragments of Benghal dayflower were buried in soil at 2 and 6 cm depths and exposed to aerial temperatures of 20, 25, 30, and 35 °C for 30 days. Root development occurred at both depths, but leaf development was restricted at 6 cm and subterranean spathe development was not found at 2 cm. Temperatures higher than 25 °C favor regeneration at both depths. The results, collectively, show the difficulty encountered when trying to control or eradicate Benghal dayflower in sustainable farming systems. Farms must avoid using fresh hay as animal feed when Benghal dayflower is present in hay fields, as little restraint on seed viability will be exerted during digestion and generation of manure. Cultivation is unlikely to be an effective control strategy during summer months when Benghal dayflower is growing most aggressively, because soil temperatures are optimal for vegetative regeneration.}, number={3}, journal={Agroecology and Sustainable Food Systems}, author={Riar, M. K. and Spears, J. F. and Burns, J. C. and Jordan, D. L. and Zhang, C. X. and Rufty, T. W.}, year={2014}, pages={283–298} }