Bruce Vasilas - Academia.edu (original) (raw)
Papers by Bruce Vasilas
Managing Watersheds for Human and Natural Impacts, 2005
Federal and state regulatory programs in the Chesapeake Bay watershed require wetland mitigation ... more Federal and state regulatory programs in the Chesapeake Bay watershed require wetland mitigation to obtain a permit for wetland impacts. The loss of wetlands in a watershed through permitted activities diminishes its capacity to perform important habitat, water retention and dissipation, and biogeochemical cycling functions. Past attempts at wetland mitigation have produced wetlands that meet the three parameters (a predominance of wetland plants, wetland hydrology, and wetland soils) of a jurisdictional wetland, but little thought was put into whether the mitigation site was providing similar wetland functions to those wetlands impacted. Current research on wetland hydrogeomorphic (HGM) setting as well as HGM functional assessment models and other functional assessment approaches have provided incite on important characteristics that allow wetlands to provide certain functions. These characteristics are starting to be incorporated into wetland restoration and creation site design in hope that the mitigation site will not just mitigate for acreage, but also mitigate for loss of wetland function. Criteria for proper wetland mitigation design incorporate appropriate HGM setting, ability to reproduce hydroperiod and hydrodynamics, inputs of organic matter in forms that are partially decomposed and as coarse woody debris, macro- and micro-topography, and other characteristics that affect specific wetland functions. Mitigation criteria can be adjusted to address problems in a watershed by concentrating on characteristics that affect wetland functions that can help alleviate that problem.
Wetlands, 2011
Piers may impact the health of coastal wetlands by altering vegetation, soil organic matter accre... more Piers may impact the health of coastal wetlands by altering vegetation, soil organic matter accretion, and sediment deposition or erosion. Permit requests for piers have recently increased in the U.S. leading to concern by environmental regulatory agencies on potential impacts. In response, a project was conducted in Maryland to assess the impacts of long piers on plant communities, soils, and
Wetlands, 2004
Ectomycorrhizae are symbiotic relationships between soil fungi and higher plants. Evidence of the... more Ectomycorrhizae are symbiotic relationships between soil fungi and higher plants. Evidence of the symbiosis is the presence of a 'mantle,' a hyphal layer that covers root tips, and a change in root morphology. The potential use of ectomycorrhizal mantles as hydrology indicators for wetland determinations was evaluated on the Delmarva Coastal Plain (Delaware and eastern shores of Maryland and Virginia, USA) over three seasons. In theory, the distribution of mantles with soil depth should vary from uplands to wetlands in most years, as mantle development is considered to be impeded by anaerobic conditions. At four forested locations, plots were set up in seasonally-saturated wetlands and adjacent uplands and drained wetlands (twelve sub-sites). Plots were evaluated according to the Corps of Engineers Wetlands Delineation Manual for soils, plant community, and hydrology to identify a jurisdictional classification. Hydrology was further addressed using automated monitoring wells (twice daily readings), and anaerobic conditions were confirmed via platinum electrodes. Plant roots (Pinus taeda was targeted) were sampled via spade slices in March and August each year and separated by depth: O horizon, 0-5 cm, 5-10 cm, 10-15 cm, and 15-20 cm. Roots were evaluated for the presence of mantles. A threshold depth of 5 cm was identified. From a total of 892 roots with mantles in uplands (including effectively-drained wetland sub-sites), 253 (28%) were found below the threshold depth. For wetlands (including one ineffectively-drained wetland), seven of 331 roots with mantles (2%) were found below the threshold depth. Temporal and spatial variability in mantle data was common; however, mantles consistently occurred at greater depths where seasonally high water tables were lower. We concluded that mantle depth has potential as a hydrology indicator.
Plant Physiology, 1987
In maize (Zea mays L.) large decreases in kernel number result when low water potentials (',,) an... more In maize (Zea mays L.) large decreases in kernel number result when low water potentials (',,) and high temperatures occur during pollination. To gain insight into the basis for the decreased seed set, silk, pollen, and ear-leaf 'I.',,, the capability for silk osmotic adjustment, and pollen appearance were measured to determine their relationship to seed set. A multiple-eared or prolific (high carbohydrate availability to the pistillate inflorescence) hybrid (B73 x FR25), a heat sensitive hybrid (WF9 x A632), and a commercial hybrid (B73 x Mol7) were studied. A crosspollination experiment, with pollination limited by pollen amount, was conducted to determine the impact on seed set of water and heat stressing the tassel and water stressing the ear. At low I,,, silk I,, and seed set were decreased whereas pollen I,,, appearance, and viability were unaffected. High temperature resulted in a 2 megapascal decrease in pollen
Biotronics, 1992
Nitrogen partitioning and net photosynthesis in soybean genotypes differing in seed filling durat... more Nitrogen partitioning and net photosynthesis in soybean genotypes differing in seed filling duration and N source. BIOTRONICS 21, 1-10, 1992. Four soybean cultivars differing in the duration of the seed filling period (SFP) were evaluated in the field for Nand dry weight accumulation, Nz-fixation and net leaf photosynthetic CO z exchange rates (CER). Nz-fixation was measured by isotope dilution, using a non-nodulating (non-nod) near-isogenic line of the cultivar Harosoy as a control. There were consistent differences between the non-nod and its sister cultivar for seed yield, N accumulation and N redistribution, but both genotypes had the same SFP duration and final shoot biomass. Reduced N accumulation in the non-nod resulted in less dry weight partitioned to seeds but no reduction in the length of the SFP. Cultivars with long SFP's had greater yield, more N and dry weight accumulation between the beginning of seed fill and maturity, and a slower decline in leaf CER during seed fill, compared to short SFP cultivars. However cultivars varied with respect to vegetative dry weight, N accumulation, N redistribution, the proportion of total N allocated to seeds, and the peak CER, independent of differences in SFP. Neither the amounts of accumulated N or fixed Nz explained differences in the SFP.
Agronomy Journal, 1985
Hail damage to corn (Zea mays L.) is assessed with the use of loss charts derived primarily from ... more Hail damage to corn (Zea mays L.) is assessed with the use of loss charts derived primarily from research conducted with hybrids. Little data are available on the relative responses of inbreds vs. hybrids to defoliation. Therefore, field experiments were conducted at the University of Illinois on a Drummer silty clay loam (Typic Haplaquoll) in 1982 and a Flanagan silt loam (Aquic Argiudoll) in 1983 to compare the response to defoliation of two corn inbred lines, FRMol7 rh and FR2Th, and their singlecross hybrid. Defoliation treatments of 0,50, and 100% were conducted by hand at the 7-leaf, ldleaf, anthesis, late-milk, and soft-dough stages in 1982 and the 7-leaf, ldleaf, anthesis, milk, and dent stages in 1983. Data were taken on grain yield, kernel sue, kernel number, and percentage barrens, doubles, and nubbins. The response of the inbreds was quite d8erent than that of the hybrid and showed greater yearly variation because of differences in the growing seasons. Complete defoliation at anthesis reduced grain yield 100% in all cases. The greatest genetic variability was observed with 100% defoliation at the ldleaf stage, which reduced FRMol7-and FR27h X F R M O~~'~ grain yields by 90 and 40%, respectively, and increased FR27'b grain yields by 2%. In many cases, defoliation increased grain yields by decreasing transpiration or delaying flowering until irrigation water was applied. Yield reductions were due to decreases in kernel size and kernel number. Kernel size was af€ected most by defoliation at the milk and late-milk stages. Kernel number was affected most by defoliation at anthesis and the 14-leaf stage. Additwnal index wonis: Zea mays L., Leaf removal, Yield components. AIL STORMS in the USA annually effect consid-' Contnbution.fr0.m the Dep. of Agronomy, ,Illionis Agric. Exp.
Agronomy Journal, 1985
Yield loss due to defoliation prediction charts have been developed for corn (Zeu mays L.) hybrid... more Yield loss due to defoliation prediction charts have been developed for corn (Zeu mays L.) hybrids, but not for inbreds. The latter is needed by the hail-loss insurance industry. Field experiments were conducted at the University of Illinois on a Drummer silty clay loam (Typic Haplaquoll) in 1982 and a Flanagan silt loam (Aquic Argiudoll) in 1983 to evaluate the response of six corn (Zeu mays L.) inbreds to 0, 50, and 100% defoliation at the 144eaf stage with respect to grain yields and yield components. One inbred, F R M O I~'~, produced yield responses quite different from the other five. Complete and 50% defoliation reduced grain yields of five inbreds by an average of 45.5 and 2.5%, respectively; and FRMol7'" by 86.0 and 17.0%, respectively. With the exception of F R M O~~'~, yield decreases were due more to a reduction in kernel number than kernel size. Yield reductions with 50% defoliation were due to a reduction in ear number as opposed to kernels per ear; whereas complete defoliation affected both yield components. Ear number was reduced both by decreasing the number of plants with double ears and increasing the number of barren plants. In general, genotypic differences in the yield response to complete defoliation coincide with genotypic differences in final leaf number and the effect of defoliation on increasing the interval between anthesis and silking.
Agronomy Journal, 1990
(...) A 2-yr experiment was conducted on a Flanagan silt loam (fine, montmorillonitic, mesic Aqui... more (...) A 2-yr experiment was conducted on a Flanagan silt loam (fine, montmorillonitic, mesic Aquic Argiudoll) to determine if genotypic differences in plant N derived from fixation (N 2 fixed) and percentage of plant N derived from fixation (% Ndfa) could be detected by isotope dilution or difference (total N) method analysis of whole plant samples (whole plant sample including abscised material), shoot samples (whole plant samples-abscised material), or seed samples. Five experimental soybean lines derived from a «Williams» X «Kanrich» cross and «Harosoy» were tested (...)
Agronomy Journal, 1988
There are exceptions to the positive relationship between seedfilling period (SFP) and seed yield... more There are exceptions to the positive relationship between seedfilling period (SFP) and seed yield in soybean [ (L.) Merr.]. Studying genotypes that do not show a positive relationship between SFP and yield may aid in identifying factors that influence seed yield or SFP, or both. The objective of this research was to analyze groups of soybean genotypes that differed in their SFP-yield relationship, and determine which factors affected seed yield. Eight experimental lines were selected from a ‘Williams’ ✕ ‘Kanrich’ cross to represent the four SFP-yield combinations of long or short SFP and high or low yield. Replicated field plots were grown in 1984 and 1985 at Urbana, IL, on a Flanagan silt loam (fine, montmorillonitic, mesic Aquic Argiudoll). Data taken in each year included: SFP, seed yield, harvest indices for dry matter and N, total flowers, total pods at three stages (5 mm long, pod containing a seed 3 mm long, and mature pod), and total N and dry matter at the beginning and end of SFP. Early flowering was related to SFP, but not to yield. Rate as well as duration of seed fill can influence seed yield. Total N in the plant at the end of SFP was related to yield, but not to SFP. Total N and dry matter assimilated during SFP, harvest indices for N and dry matter, and final seed yield were all related.
Canadian Journal of Plant Science, 1992
A positive relationship generally exists between the duration of seed-fill period (SFP) and seed ... more A positive relationship generally exists between the duration of seed-fill period (SFP) and seed yield in soybean, but exceptions have been reported. The objective of this research was to determine if differences in N2 fixation or N accumulation could explain inconsistent relationships between duration of SFP and seed yield in soybean. For this study, five experimental soybean (Glycine max L. [Men.]) lines were selected on the bases of differences in SFP and seed yield in previous experiments. The experiment was designed to compare lines differing in both SFP and seed yield, differing in SFP but not seed yield, and differing in seed yield but not SFP. Total N2 fixation, using 15N-dilution techniques; total N accumulation, using a semi-micro-Kjeldahl procedure; and total dry matter accumulation, including all vegetative material abscised before maturity were measured on these lines grown in a Flanagan silt loam (fine, montmorillonitic, mesic Aquic Argiudolls) in 1984 and 1985 at Urba...
Soil Biology and Biochemistry, 1989
Frontiers in Environmental Science, Dec 14, 2018
Mobile colloids, 1-1,000 nm particles, are ubiquitous in every ecosystem. They have small size, l... more Mobile colloids, 1-1,000 nm particles, are ubiquitous in every ecosystem. They have small size, large specific surface area, and high mobility in the subsurface, and thus can regulate the fate and transport of sorbing constituents such as nutrients, contaminants, and organic carbon (OC). The movement of colloids and colloidal OC (COC) through soils is an important process in mass and energy transport (including carbon) both within and between ecosystems, e.g., from terrestrial to aquatic ecosystems, and likely contribute to the ecosystem-or global-scale carbon balance given their ubiquitous distribution and unique environmental functions. However, despite their importance for terrestrial and aquatic carbon transport and balance, colloids, and COC have not been adequately accounted for because of the current operational definition uses 0.45 µm as the cutoff size for colloids. In this study, we quantified and characterized loadings of colloids and COC in aqueous samples collected from agricultural, forestry, freshwater wetland, and estuary ecosystems. Results reveal that, in all samples regardless of sampling sources, the total colloidal loads were underestimated by ≥50% and considered as "dissolved" solutes when the (cutoff size of 0.45 µm) was used. Together with a large number of data from the literature, our results further demonstrate that colloids are quantitatively substantial, carbon-dense and that as much as 8-19% of operationally defined DOC is in fact COC. Conservatively, this suggests that COC potentially accounts for 13.6 TgC year −1 as a riverine flux and 530 ± 25 TgC of global DOC pool in the ocean in global carbon cycles. In addition, freshwater wetland was found to be a hotspot, which released more colloids and COC compared to the other sampled ecosystems. These findings clearly demonstrate the limitations of using the operational definition for colloids and DOC and highlight the need for improving quantification and characterization of size-dependent colloidal and OC loads. Such effort will allow direct fundamental research into questions toward microbial access to "protected" carbon by minerals and more accurate assessment of global carbon cycles.
Soil Science Society of America Journal
Soil Biology and Biochemistry
<p>In this ... more <p>In this study we used oxygen sensitive optodes, or optical sensor devices, to observe oxygen depletion by soil microbes. Depletion served as a reference for microbial activity along three artificially constructed preferential flow paths consisting of coarse sand in the center surrounded fine sand. Following a flow event with glucose addition, images showed that oxygen depletion is greatest along the boundary between preferential flow paths (coarse sand) and the bulk matrix (fine sand). Oxygen gradients as well as nutrient gradients are commonly attributed to shaping soil bacterial communities, however, these mechanisms have not been studied in the specific soil architecture of preferential flow paths. A separate experiment was performed in which the fine sand matrix was replaced with a sandy soil containing its native microbial community. An addition of glucose and DOM was flowed through the columns containing real soil. Oxygen depletion was again monitored using oxygen sensor foils. To assess changes in the microbial community in time 16S rRNA analysis was performed on soil samples taken from different locations within the chambers. By monitoring the levels of oxygen depletion in time, we are able to gain an understanding of how this dynamic process alters microbial community structure. Additionally, zymography was performed to elucidate the locations where enzyme activity was greatest. By studying the microbial community in time along with oxygen depletion and enzyme activity, we are able to gain insight into structure-function relationships that take place within preferential flow paths. Furthering our understanding of processes taking place within preferential flow paths will allow for better estimation of how these entities function biogeochemically.</p>
<p&amp... more <p>Understanding the mechanisms governing the composition and stability of organo-mineral associations is critical to predicting the dynamics of soil organic matter (SOC) and the related global carbon cycling. Redox-induced biogeochemical transformations are the key processes that control the stabilization of SOC via association with metal oxides in terrestrial environments such as wetlands. Despite its high C content (20-30% of terrestrial C), size-dependent organo-mineral associations and their dynamic changes in the redox-dynamic wetlands are poorly understood. Here we present size distribution, concentration, and composition of organo-mineral associations in pore water samples from a depressional wetland located at the Delmarva Bay in Delaware, USA, as influenced by seasonal fluctuations in water table level. The samples were collected from piezometers installed at multiple depths (50 cm, 100 cm, and 200 cm) and in three zones (upland, transitional, and wetland), respectively. Four size fractions were analyzed: dissolved (<2.3 nm), natural nanoparticle (2.3-100 nm, NNP), fine colloid (100-450 nm), and particulate (450-100 nm). Our results revealed that dissolved, NNP, fine colloid and particulate fractions comprised 47 ± 4%, 37 ± 4%, 8 ± 3% and 8 ± 3% of  the bulk organic C (<1000 nm) concentration, respectively. Relative percentages of respective Al, Mn, and Fe were 47 ± 24%, 30 ± 22%, 50 ± 18% at 2.3-450 nm and 22 ± 16%, 17 ± 12%, 25 ± 19% at 450-1000 nm size fraction. The main finding from this study are 1) dissolved and NNP fractions contain higher amount of C than colloidal and particulate fractions and 2) organo-mineral associations have significant differences in their elemental concentrations among different size fractions within colloidal size range. Additionally, the results clearly indicate that the commonly used operational definition for dissolved organic matter (DOM, <450 nm) significantly overestimates the dissolved phase C concentration by including the NNP and colloidal fractions, which contain mineral-associated C. This has important implications in the estimation of SOC decomposition rate in soils, particularly in redox sensitive wetlands, thus in assessing terrestrial C cycling and the transport of OC as well as the associated elements.</p>
Managing Watersheds for Human and Natural Impacts, 2005
Federal and state regulatory programs in the Chesapeake Bay watershed require wetland mitigation ... more Federal and state regulatory programs in the Chesapeake Bay watershed require wetland mitigation to obtain a permit for wetland impacts. The loss of wetlands in a watershed through permitted activities diminishes its capacity to perform important habitat, water retention and dissipation, and biogeochemical cycling functions. Past attempts at wetland mitigation have produced wetlands that meet the three parameters (a predominance of wetland plants, wetland hydrology, and wetland soils) of a jurisdictional wetland, but little thought was put into whether the mitigation site was providing similar wetland functions to those wetlands impacted. Current research on wetland hydrogeomorphic (HGM) setting as well as HGM functional assessment models and other functional assessment approaches have provided incite on important characteristics that allow wetlands to provide certain functions. These characteristics are starting to be incorporated into wetland restoration and creation site design in hope that the mitigation site will not just mitigate for acreage, but also mitigate for loss of wetland function. Criteria for proper wetland mitigation design incorporate appropriate HGM setting, ability to reproduce hydroperiod and hydrodynamics, inputs of organic matter in forms that are partially decomposed and as coarse woody debris, macro- and micro-topography, and other characteristics that affect specific wetland functions. Mitigation criteria can be adjusted to address problems in a watershed by concentrating on characteristics that affect wetland functions that can help alleviate that problem.
Wetlands, 2011
Piers may impact the health of coastal wetlands by altering vegetation, soil organic matter accre... more Piers may impact the health of coastal wetlands by altering vegetation, soil organic matter accretion, and sediment deposition or erosion. Permit requests for piers have recently increased in the U.S. leading to concern by environmental regulatory agencies on potential impacts. In response, a project was conducted in Maryland to assess the impacts of long piers on plant communities, soils, and
Wetlands, 2004
Ectomycorrhizae are symbiotic relationships between soil fungi and higher plants. Evidence of the... more Ectomycorrhizae are symbiotic relationships between soil fungi and higher plants. Evidence of the symbiosis is the presence of a 'mantle,' a hyphal layer that covers root tips, and a change in root morphology. The potential use of ectomycorrhizal mantles as hydrology indicators for wetland determinations was evaluated on the Delmarva Coastal Plain (Delaware and eastern shores of Maryland and Virginia, USA) over three seasons. In theory, the distribution of mantles with soil depth should vary from uplands to wetlands in most years, as mantle development is considered to be impeded by anaerobic conditions. At four forested locations, plots were set up in seasonally-saturated wetlands and adjacent uplands and drained wetlands (twelve sub-sites). Plots were evaluated according to the Corps of Engineers Wetlands Delineation Manual for soils, plant community, and hydrology to identify a jurisdictional classification. Hydrology was further addressed using automated monitoring wells (twice daily readings), and anaerobic conditions were confirmed via platinum electrodes. Plant roots (Pinus taeda was targeted) were sampled via spade slices in March and August each year and separated by depth: O horizon, 0-5 cm, 5-10 cm, 10-15 cm, and 15-20 cm. Roots were evaluated for the presence of mantles. A threshold depth of 5 cm was identified. From a total of 892 roots with mantles in uplands (including effectively-drained wetland sub-sites), 253 (28%) were found below the threshold depth. For wetlands (including one ineffectively-drained wetland), seven of 331 roots with mantles (2%) were found below the threshold depth. Temporal and spatial variability in mantle data was common; however, mantles consistently occurred at greater depths where seasonally high water tables were lower. We concluded that mantle depth has potential as a hydrology indicator.
Plant Physiology, 1987
In maize (Zea mays L.) large decreases in kernel number result when low water potentials (',,) an... more In maize (Zea mays L.) large decreases in kernel number result when low water potentials (',,) and high temperatures occur during pollination. To gain insight into the basis for the decreased seed set, silk, pollen, and ear-leaf 'I.',,, the capability for silk osmotic adjustment, and pollen appearance were measured to determine their relationship to seed set. A multiple-eared or prolific (high carbohydrate availability to the pistillate inflorescence) hybrid (B73 x FR25), a heat sensitive hybrid (WF9 x A632), and a commercial hybrid (B73 x Mol7) were studied. A crosspollination experiment, with pollination limited by pollen amount, was conducted to determine the impact on seed set of water and heat stressing the tassel and water stressing the ear. At low I,,, silk I,, and seed set were decreased whereas pollen I,,, appearance, and viability were unaffected. High temperature resulted in a 2 megapascal decrease in pollen
Biotronics, 1992
Nitrogen partitioning and net photosynthesis in soybean genotypes differing in seed filling durat... more Nitrogen partitioning and net photosynthesis in soybean genotypes differing in seed filling duration and N source. BIOTRONICS 21, 1-10, 1992. Four soybean cultivars differing in the duration of the seed filling period (SFP) were evaluated in the field for Nand dry weight accumulation, Nz-fixation and net leaf photosynthetic CO z exchange rates (CER). Nz-fixation was measured by isotope dilution, using a non-nodulating (non-nod) near-isogenic line of the cultivar Harosoy as a control. There were consistent differences between the non-nod and its sister cultivar for seed yield, N accumulation and N redistribution, but both genotypes had the same SFP duration and final shoot biomass. Reduced N accumulation in the non-nod resulted in less dry weight partitioned to seeds but no reduction in the length of the SFP. Cultivars with long SFP's had greater yield, more N and dry weight accumulation between the beginning of seed fill and maturity, and a slower decline in leaf CER during seed fill, compared to short SFP cultivars. However cultivars varied with respect to vegetative dry weight, N accumulation, N redistribution, the proportion of total N allocated to seeds, and the peak CER, independent of differences in SFP. Neither the amounts of accumulated N or fixed Nz explained differences in the SFP.
Agronomy Journal, 1985
Hail damage to corn (Zea mays L.) is assessed with the use of loss charts derived primarily from ... more Hail damage to corn (Zea mays L.) is assessed with the use of loss charts derived primarily from research conducted with hybrids. Little data are available on the relative responses of inbreds vs. hybrids to defoliation. Therefore, field experiments were conducted at the University of Illinois on a Drummer silty clay loam (Typic Haplaquoll) in 1982 and a Flanagan silt loam (Aquic Argiudoll) in 1983 to compare the response to defoliation of two corn inbred lines, FRMol7 rh and FR2Th, and their singlecross hybrid. Defoliation treatments of 0,50, and 100% were conducted by hand at the 7-leaf, ldleaf, anthesis, late-milk, and soft-dough stages in 1982 and the 7-leaf, ldleaf, anthesis, milk, and dent stages in 1983. Data were taken on grain yield, kernel sue, kernel number, and percentage barrens, doubles, and nubbins. The response of the inbreds was quite d8erent than that of the hybrid and showed greater yearly variation because of differences in the growing seasons. Complete defoliation at anthesis reduced grain yield 100% in all cases. The greatest genetic variability was observed with 100% defoliation at the ldleaf stage, which reduced FRMol7-and FR27h X F R M O~~'~ grain yields by 90 and 40%, respectively, and increased FR27'b grain yields by 2%. In many cases, defoliation increased grain yields by decreasing transpiration or delaying flowering until irrigation water was applied. Yield reductions were due to decreases in kernel size and kernel number. Kernel size was af€ected most by defoliation at the milk and late-milk stages. Kernel number was affected most by defoliation at anthesis and the 14-leaf stage. Additwnal index wonis: Zea mays L., Leaf removal, Yield components. AIL STORMS in the USA annually effect consid-' Contnbution.fr0.m the Dep. of Agronomy, ,Illionis Agric. Exp.
Agronomy Journal, 1985
Yield loss due to defoliation prediction charts have been developed for corn (Zeu mays L.) hybrid... more Yield loss due to defoliation prediction charts have been developed for corn (Zeu mays L.) hybrids, but not for inbreds. The latter is needed by the hail-loss insurance industry. Field experiments were conducted at the University of Illinois on a Drummer silty clay loam (Typic Haplaquoll) in 1982 and a Flanagan silt loam (Aquic Argiudoll) in 1983 to evaluate the response of six corn (Zeu mays L.) inbreds to 0, 50, and 100% defoliation at the 144eaf stage with respect to grain yields and yield components. One inbred, F R M O I~'~, produced yield responses quite different from the other five. Complete and 50% defoliation reduced grain yields of five inbreds by an average of 45.5 and 2.5%, respectively; and FRMol7'" by 86.0 and 17.0%, respectively. With the exception of F R M O~~'~, yield decreases were due more to a reduction in kernel number than kernel size. Yield reductions with 50% defoliation were due to a reduction in ear number as opposed to kernels per ear; whereas complete defoliation affected both yield components. Ear number was reduced both by decreasing the number of plants with double ears and increasing the number of barren plants. In general, genotypic differences in the yield response to complete defoliation coincide with genotypic differences in final leaf number and the effect of defoliation on increasing the interval between anthesis and silking.
Agronomy Journal, 1990
(...) A 2-yr experiment was conducted on a Flanagan silt loam (fine, montmorillonitic, mesic Aqui... more (...) A 2-yr experiment was conducted on a Flanagan silt loam (fine, montmorillonitic, mesic Aquic Argiudoll) to determine if genotypic differences in plant N derived from fixation (N 2 fixed) and percentage of plant N derived from fixation (% Ndfa) could be detected by isotope dilution or difference (total N) method analysis of whole plant samples (whole plant sample including abscised material), shoot samples (whole plant samples-abscised material), or seed samples. Five experimental soybean lines derived from a «Williams» X «Kanrich» cross and «Harosoy» were tested (...)
Agronomy Journal, 1988
There are exceptions to the positive relationship between seedfilling period (SFP) and seed yield... more There are exceptions to the positive relationship between seedfilling period (SFP) and seed yield in soybean [ (L.) Merr.]. Studying genotypes that do not show a positive relationship between SFP and yield may aid in identifying factors that influence seed yield or SFP, or both. The objective of this research was to analyze groups of soybean genotypes that differed in their SFP-yield relationship, and determine which factors affected seed yield. Eight experimental lines were selected from a ‘Williams’ ✕ ‘Kanrich’ cross to represent the four SFP-yield combinations of long or short SFP and high or low yield. Replicated field plots were grown in 1984 and 1985 at Urbana, IL, on a Flanagan silt loam (fine, montmorillonitic, mesic Aquic Argiudoll). Data taken in each year included: SFP, seed yield, harvest indices for dry matter and N, total flowers, total pods at three stages (5 mm long, pod containing a seed 3 mm long, and mature pod), and total N and dry matter at the beginning and end of SFP. Early flowering was related to SFP, but not to yield. Rate as well as duration of seed fill can influence seed yield. Total N in the plant at the end of SFP was related to yield, but not to SFP. Total N and dry matter assimilated during SFP, harvest indices for N and dry matter, and final seed yield were all related.
Canadian Journal of Plant Science, 1992
A positive relationship generally exists between the duration of seed-fill period (SFP) and seed ... more A positive relationship generally exists between the duration of seed-fill period (SFP) and seed yield in soybean, but exceptions have been reported. The objective of this research was to determine if differences in N2 fixation or N accumulation could explain inconsistent relationships between duration of SFP and seed yield in soybean. For this study, five experimental soybean (Glycine max L. [Men.]) lines were selected on the bases of differences in SFP and seed yield in previous experiments. The experiment was designed to compare lines differing in both SFP and seed yield, differing in SFP but not seed yield, and differing in seed yield but not SFP. Total N2 fixation, using 15N-dilution techniques; total N accumulation, using a semi-micro-Kjeldahl procedure; and total dry matter accumulation, including all vegetative material abscised before maturity were measured on these lines grown in a Flanagan silt loam (fine, montmorillonitic, mesic Aquic Argiudolls) in 1984 and 1985 at Urba...
Soil Biology and Biochemistry, 1989
Frontiers in Environmental Science, Dec 14, 2018
Mobile colloids, 1-1,000 nm particles, are ubiquitous in every ecosystem. They have small size, l... more Mobile colloids, 1-1,000 nm particles, are ubiquitous in every ecosystem. They have small size, large specific surface area, and high mobility in the subsurface, and thus can regulate the fate and transport of sorbing constituents such as nutrients, contaminants, and organic carbon (OC). The movement of colloids and colloidal OC (COC) through soils is an important process in mass and energy transport (including carbon) both within and between ecosystems, e.g., from terrestrial to aquatic ecosystems, and likely contribute to the ecosystem-or global-scale carbon balance given their ubiquitous distribution and unique environmental functions. However, despite their importance for terrestrial and aquatic carbon transport and balance, colloids, and COC have not been adequately accounted for because of the current operational definition uses 0.45 µm as the cutoff size for colloids. In this study, we quantified and characterized loadings of colloids and COC in aqueous samples collected from agricultural, forestry, freshwater wetland, and estuary ecosystems. Results reveal that, in all samples regardless of sampling sources, the total colloidal loads were underestimated by ≥50% and considered as "dissolved" solutes when the (cutoff size of 0.45 µm) was used. Together with a large number of data from the literature, our results further demonstrate that colloids are quantitatively substantial, carbon-dense and that as much as 8-19% of operationally defined DOC is in fact COC. Conservatively, this suggests that COC potentially accounts for 13.6 TgC year −1 as a riverine flux and 530 ± 25 TgC of global DOC pool in the ocean in global carbon cycles. In addition, freshwater wetland was found to be a hotspot, which released more colloids and COC compared to the other sampled ecosystems. These findings clearly demonstrate the limitations of using the operational definition for colloids and DOC and highlight the need for improving quantification and characterization of size-dependent colloidal and OC loads. Such effort will allow direct fundamental research into questions toward microbial access to "protected" carbon by minerals and more accurate assessment of global carbon cycles.
Soil Science Society of America Journal
Soil Biology and Biochemistry
<p>In this ... more <p>In this study we used oxygen sensitive optodes, or optical sensor devices, to observe oxygen depletion by soil microbes. Depletion served as a reference for microbial activity along three artificially constructed preferential flow paths consisting of coarse sand in the center surrounded fine sand. Following a flow event with glucose addition, images showed that oxygen depletion is greatest along the boundary between preferential flow paths (coarse sand) and the bulk matrix (fine sand). Oxygen gradients as well as nutrient gradients are commonly attributed to shaping soil bacterial communities, however, these mechanisms have not been studied in the specific soil architecture of preferential flow paths. A separate experiment was performed in which the fine sand matrix was replaced with a sandy soil containing its native microbial community. An addition of glucose and DOM was flowed through the columns containing real soil. Oxygen depletion was again monitored using oxygen sensor foils. To assess changes in the microbial community in time 16S rRNA analysis was performed on soil samples taken from different locations within the chambers. By monitoring the levels of oxygen depletion in time, we are able to gain an understanding of how this dynamic process alters microbial community structure. Additionally, zymography was performed to elucidate the locations where enzyme activity was greatest. By studying the microbial community in time along with oxygen depletion and enzyme activity, we are able to gain insight into structure-function relationships that take place within preferential flow paths. Furthering our understanding of processes taking place within preferential flow paths will allow for better estimation of how these entities function biogeochemically.</p>
<p&amp... more <p>Understanding the mechanisms governing the composition and stability of organo-mineral associations is critical to predicting the dynamics of soil organic matter (SOC) and the related global carbon cycling. Redox-induced biogeochemical transformations are the key processes that control the stabilization of SOC via association with metal oxides in terrestrial environments such as wetlands. Despite its high C content (20-30% of terrestrial C), size-dependent organo-mineral associations and their dynamic changes in the redox-dynamic wetlands are poorly understood. Here we present size distribution, concentration, and composition of organo-mineral associations in pore water samples from a depressional wetland located at the Delmarva Bay in Delaware, USA, as influenced by seasonal fluctuations in water table level. The samples were collected from piezometers installed at multiple depths (50 cm, 100 cm, and 200 cm) and in three zones (upland, transitional, and wetland), respectively. Four size fractions were analyzed: dissolved (<2.3 nm), natural nanoparticle (2.3-100 nm, NNP), fine colloid (100-450 nm), and particulate (450-100 nm). Our results revealed that dissolved, NNP, fine colloid and particulate fractions comprised 47 ± 4%, 37 ± 4%, 8 ± 3% and 8 ± 3% of  the bulk organic C (<1000 nm) concentration, respectively. Relative percentages of respective Al, Mn, and Fe were 47 ± 24%, 30 ± 22%, 50 ± 18% at 2.3-450 nm and 22 ± 16%, 17 ± 12%, 25 ± 19% at 450-1000 nm size fraction. The main finding from this study are 1) dissolved and NNP fractions contain higher amount of C than colloidal and particulate fractions and 2) organo-mineral associations have significant differences in their elemental concentrations among different size fractions within colloidal size range. Additionally, the results clearly indicate that the commonly used operational definition for dissolved organic matter (DOM, <450 nm) significantly overestimates the dissolved phase C concentration by including the NNP and colloidal fractions, which contain mineral-associated C. This has important implications in the estimation of SOC decomposition rate in soils, particularly in redox sensitive wetlands, thus in assessing terrestrial C cycling and the transport of OC as well as the associated elements.</p>