Milon F. George

Shade effects on forage crops with potential in temperate agroforestry practices

Thirty forages, including eight introduced cool-season grasses, four native warm-season grasses, one introduced warm-season grass, eight introduced cool-season legumes, five native warm-season legumes, and four introduced warm-season legumes, were grown in 7.6 L (two gallon) pots in full sun, 50%, and 80% shade created by shade cloth over a greenhouse frame. Experiments were conducted during summer--fall 1994, spring--early summer 1995, and summer--fall 1995. A complete randomized experimental design was used and above ground dry weight was measured in each shade environment. Tukeys studentized range test was used to compare mean dry weights (MDW) within a species. Warm-season grasses displayed significant reductions in MDW under shade regardless of growing season. All cool-season forages grown during spring--early summer showed a decrease in MDW under shade; however, the reductions in dry weights of ‘Benchmark’ and ‘Justus’ orchardgrass, ‘KY 31’ tall fescue, Desmodium canescens and D. paniculatum were not significant under 50% shade. Cool-season grasses showed more shade tolerance when grown during the summer--fall than when grown during the spring--early summer. Seven of the selected cool-season grasses grown during the summer--fall did not display significant reductions in MDW under 50% shade as compared to full sun. Smooth bromegrass grown under 50% shade showed a significantly increased MDW production compared to growth in full sun. With the exception of Justus orchardgrass and smooth bromegrass, growth of cool-season grasses was inhibited at 80% shade. Among the legumes harvested during the fall, the dry weights of both Desmodium species tested and hog peanut (Amphicarpaea bracteata L.) increased significantly under 50% and 80% shade. In addition, ‘Cody’ alfalfa, white clover, slender lespedeza and ‘Kobe’ lespedeza showed no significant reductions in MDW under 50% shade.

Freezing avoidance by deep undercooling of tissue water in winter-hardy plants

Abstract Freezing avoidance by deep undercooling of tissue water to near its homogeneous nucleation temperature (approximately −40 °C) has recently been shown to be an important survival mechanism in reproductive and vegetative parts of many winter-hardy plants. Biophysical experiments which support the concept of undercooling of the tissue water include thermal analyses, nuclear magnetic resonance spectroscopy, and low-temperature microscopy of tissue freezing. All these experiments suggest that in plant parts that undercool, tissue water is compartmentalized and is not removed to extracellular ice as tissue temperature declines. When freezing takes place at low temperature, it occurs rapidly and appears to be intracellular, resulting in instant death. Analyses of freezing and injury of winter-hardy plants at the northern limits of the deciduous forest in North America and near timberline in the Rocky Mountains of the western United States indicate that freezing survival by deep undercooling is an important factor in limiting plant distribution.

Bioremediation of atrazine-contaminated soil by forage grasses: transformation, uptake, and detoxification.

A sound multi-species vegetation buffer design should incorporate the species that facilitate rapid degradation and sequestration of deposited herbicides in the buffer. A field lysimeter study with six different ground covers (bare ground, orchardgrass, tall fescue, timothy, smooth bromegrass, and switchgrass) was established to assess the bioremediation capacity of five forage species to enhance atrazine (ATR) dissipation in the environment via plant uptake and degradation and detoxification in the rhizosphere. Results suggested that the majority of the applied ATR remained in the soil and only a relatively small fraction of herbicide leached to leachates (<15%) or was taken up by plants (<4%). Biological degradation or chemical hydroxylation of soil ATR was enhanced by 20 to 45% in forage treatment compared with the control. Of the ATR residues remaining in soil, switchgrass degraded more than 80% to less toxic metabolites, with 47% of these residues converted to the less mobile hydroxylated metabolites 25 d after application. The strong correlation between the degradation of N-dealkylated ATR metabolites and the increased microbial biomass carbon in forage treatments suggested that enhanced biological degradation in the rhizosphere was facilitated by the forages. Hydroxylated ATR degradation products were the predominant ATR metabolites in the tissues of switchgrass and tall fescue. In contrast, the N-dealkylated metabolites were the major degradation products found in the other cool-season species. The difference in metabolite patterns between the warm- and cool-season species demonstrated their contrasting detoxification mechanisms, which also related to their tolerance to ATR exposure. Based on this study, switchgrass is recommended for use in riparian buffers designed to reduce ATR toxicity and mobility due to its high tolerance and strong degradation capacity.

Methods for Measuring Cold Hardiness of Conifers

Cold hardiness testing methods have developed from the search to understand the many thermodynamic, physiological, anatomical, and biochemical features of plants involved in acclimation and deacclimation to freezing temperatures. These methods have further evolved from a need to quickly monitor cold hardiness to ensure successful production of conifer nursery stock for reforestation. Cold hardiness is measured by exposing plant tissue to controlled freezing temperatures, then quantifying tissue damage by one or more methods. Adherence to well-defined, standardised testing protocols and evaluation methods is key to our ability to accurately estimate cold hardiness and compare data from different testing methods or times.

Incorporating forage grasses in riparian buffers for bioremediation of atrazine, isoxaflutole and nitrate in Missouri

Multi-species tree-shrub-grass riparian buffer systems have been recognized as one of the most cost-effective bioremediation approaches to alleviate nonpoint source agricultural pollution in heavily fertilized systems. However, highly concentrated herbicides in surface and subsurface water and shade cast by trees along the stream bank usually compromise the effectiveness of these systems. Greenhouse trials and field lysimeter studies were conducted to evaluate the tolerance of orchard grass (Dactylis glomerata), smooth bromegrass (Bromus inermis), tall fescue (Festuca arundinacea), timothy (Phleum pratense), and switchgrass (Panicum virgatum) ground covers to atrazine and Balance™ (isoxaflutole) plus their capacity to sequester and degrade these herbicides and their metabolites. Their ability to remove soil nitrate was also quantified. Concentrations of atrazine, Balance™ and their metabolites in the leachate, soil and plant samples were determined by solid phase extraction followed by high performance liquid or gas chromatographic analyses. Distribution of the herbicides and metabolites in the system was calculated using a mass balance approach. Herbicide bioremediation capacity of each lysimeter treatment was determined by the ratio of metabolites to parent herbicide plus metabolites. Bioremediation of nitrate was quantified by comparing nitrate reduction rates in grass treatments to the bare ground control. Based on this herbicide tolerance, bioremediation data and shade tolerance determined in a previous study, it was established that switch grass, tall fescue and smooth bromegrass are good candidates for incorporation into tree-shrub-grass riparian buffer systems designed for the bioremediation of atrazine, Balance™ and nitrate.

Improved GC-MS/MS method for determination of atrazine and its chlorinated metabolites in forage plants- : Laboratory and field experiments

Abstract Analytical procedures using gas chromatography–ion trap tandem mass spectrometry (GC‐MS/MS) were developed to analyze atrazine (ATR) and its dealkylated metabolites in four forage species (switchgrass, tall fescue, smooth bromegrass, and orchardgrass). Atrazine, deethylatrazine (DEA), and deisopropylatrazine (DIA) were extracted with methanol (CH3OH) followed by liquid–liquid extraction and partitioning into chloroform, with additional cleanup by C18 solid‐phase extraction (SPE). Through the optimization of ionization conditions and ion storage voltages, the background noise of product ion spectra (MS/MS) was reduced dramatically, providing sub‐µg/kg detection limits. Mean recoveries of ATR, DEA, and DIA were 94.3, 105.6, and 113.1%, respectively. The estimated limit of detection (LOD) was 0.6 µg/kg for ATR, 1.3 µg/kg for DEA, and 0.3 µg/kg for DIA. These LODs were one to two orders of magnitude lower than those reported for other GC‐MS, GC‐MS/MS, high pressure liquid chromatography (HPLC)‐UV, or HPLC‐MS/MS procedures designed for food‐safety monitoring purposes. To validate the developed method, a field experiment was carried out utilizing three replications of four forage treatments (orchardgrass, tall fescue, smooth bromegrass, and switchgrass). Forage plants were sampled for analyses 25 days after atrazine application. DEA concentrations in C3 grasses ranged from 47 to 96 µg/kg, about 10‐fold higher than in switchgrass, a C4 species. The ATR and DIA concentrations were similar, ranging from 1.5 to 13.2 µg/kg. The developed method provided sufficient sensitivity to determine the fate of ATR and its chlorinated metabolites via plant uptake from soil or dealkylation within living forage grasses. It also represented significant improvements in sensitivity compared to previous GC methods.

Supercooling of tissue water to extreme low temperature in overwintering plants

Abstract In the past ten years there have been numerous reports of overwintering plants surviving freezing by the deep supercooling of tissue water 1–3 . In many cases, supercooling of cellular solutions to temperature approaching −50°C has been observed. The tissues in which deep supercooling occurs can tell us something of the mechanisms involved.

Ability of Forage Grasses Exposed to Atrazine and Isoxaflutole to Reduce Nutrient Levels in Soils and Shallow Groundwater

Abstract Successful implementation of vegetative buffers requires inclusion of plant species that facilitate rapid dissipation of deposited contaminants before they have a chance to be transported in surface runoff or to shallow groundwater. Thirty‐six field lysimeters with six different ground covers [bare ground, orchardgrass (Dactylis glomerata L.), tall fescue (Festuca arundinacea Schreb.), smooth bromegrass (Bromus inermis Leyss.), timothy (Phleum pratense L.), and switchgrass (Panicum virgatum L.)] were established to evaluate the ability of grasses to reduce nutrient levels in soils and shallow groundwater. Nitrate (NO3 −) and orthophosphate (PO4 3−) were uniformly applied to each lysimeter. In addition, half of the lysimeters received an application of atrazine, and the other half received isoxaflutole (Balance™) at levels indicative of surface runoff from cropland. The leachate from each lysimeter was collected after major rainfall events during a 25‐day period, and soil was collected from each lysimeter at the end of the 25‐day period. Water samples were analyzed for NO3‐N and PO4‐P, and soil samples were analyzed for NO3‐N. Grass treatments reduced NO3‐N levels in leachate by 74.5 to 99.7% compared to the bare ground control, but timothy was significantly less effective at reducing NO3‐N leaching than the other grasses. Grass treatments reduced residual soil NO3‐N levels by 40.9 to 91.2% compared to the control, with tall fescue, smooth bromegrass, and switchgrass having the lowest residual levels. Switchgrass decreased PO4‐P leaching to the greatest extent, reducing it by 60.0 to 74.2% compared to the control. The ability of the forage grasses to reduce nutrient levels in soil or shallow groundwater were not significant between herbicide treatments. Quantification of microbial NO3 − dissipation rates in soil suggested that denitrification was greatest in switchgrass, smooth bromegrass, and tall fescue treatments. The overall performance of these three grasses indicated that they are the most suitable for use in vegetative buffers because of their superior ability to dissipate soil NO3 − and reduce nutrient transport to shallow groundwater.