Robert Kremer | University of Missouri Columbia (original) (raw)

Papers by Robert Kremer

Research paper thumbnail of Article Understanding and Enhancing Soil Biological Health: The Solution for Reversing Soil Degradation

Our objective is to provide an optimistic strategy for reversing soil degradation by increasing p... more Our objective is to provide an optimistic strategy for reversing soil degradation by increasing public and private research efforts to understand the role of soil biology, particularly microbiology, on the health of our world's soils. We begin by defining soil quality/soil health (which we consider to be interchangeable terms), characterizing healthy soil resources, and relating the significance of soil health to agroecosystems and their functions. We examine how soil biology influences soil health and how biological properties and processes contribute to sustainability of agriculture and ecosystem services. We continue by examining what can be done to manipulate soil biology to: (i) increase nutrient availability for production of high yielding, high quality crops; (ii) protect crops from pests, pathogens, weeds; and (iii) manage other factors limiting production, provision of ecosystem services, and resilience to stresses like droughts. Next we look to the future by asking what needs to be known about soil biology that is not currently recognized or fully understood and how these needs could be addressed using emerging research tools. We conclude, based on our perceptions of how new knowledge regarding soil biology will help make agriculture more sustainable and productive, by recommending research emphases that should receive first priority through enhanced public and private research in order to reverse the trajectory toward global soil degradation.

Research paper thumbnail of Scanning and transmission electron microscopy of root colonization of morningglory (Ipomoea spp.) seedlings by rhizobacteria

Symbiosis, 2005

Hydroponically-grown ivyleaf morningglory (Ipomoea hederacea) seedlings inoculated with deleterio... more Hydroponically-grown ivyleaf morningglory (Ipomoea hederacea) seedlings inoculated with deleterious rhizobacteria (DRB) were studied to observe colonization of roots using scanning and transmission electron microscopy. The DRB, Bradyrhizobium japonicum isolate GD3, previously isolated as a DRB producing high concentrations of indole-3-acetic acid (IAA), and Pseudomonas putida isolate GD4, were compared with a plant growth promoting rhizobacterium (PGPR), Bacillus megaterium isolate GP4. Scanning electron microscopy revealed that the colonization of isolates GP4 and GD4 were consistently distributed on the surface of roots; however, isolate GD3 was deeply localized into surface furrows of roots. Transmission electron microscopy showed considerable alterations of root cells including vesiculation, partial cell wall degradation, and cytoplasm disorganization. The average population density of isolate GD4 on the root surface was about 10 and 100 times greater than GP4 and GD3, respectiv...

Research paper thumbnail of Consensus on a New Definition for Soil?

CSA News, 2017

U nconsolidated material is not necessarily soil. If such material is without biological input or... more U nconsolidated material is not necessarily soil. If such material is without biological input or modification, such as the presence of at least minimal horizons other than unweathered parent material, it has not traditionally been recognized as soil. Unconsolidated material can hold liquids, gases, etc. and yet is considered to be raw geologic material (not soil) until pedologic alteration becomes evident. Lack of biological material or evidence of biological alteration in some form (past or present) precludes "soil" on extraterrestrial bodies.

Research paper thumbnail of Vegetative Buffer Strips for Reducing Herbicide Transport in Runoff: Effects of Buffer Width, Vegetation, and Season

JAWRA Journal of the American Water Resources Association, 2017

The effectiveness of vegetative buffer strips (VBS) for reducing herbicide transport has not been... more The effectiveness of vegetative buffer strips (VBS) for reducing herbicide transport has not been well documented for runoff prone soils. A multi‐year plot‐scale study was conducted on an eroded claypan soil with the following objectives: (1) assess the effects of buffer width, vegetation, and season on runoff transport of atrazine (ATR), metolachlor (MET), and glyphosate; (2) develop VBS design criteria for herbicides; and (3) compare differences in soil quality among vegetation treatments. Rainfall simulation was used to create uniform antecedent soil water content and to generate runoff. Vegetation treatment and buffer width impacted herbicide loads much more than season. Grass treatments reduced herbicide loads by 19‐28% and sediment loads by 67% compared to the control. Grass treatments increased retention of dissolved‐phase herbicides by both infiltration and adsorption, but adsorption accounted for the greatest proportion of retained herbicide load. This latter finding indica...

Research paper thumbnail of Indications of Associative Nitrogen Fixation in Eastern Gamagrass

Journal of Range Management, 1994

Associative nitrogen-fixation is one mechanism by which phtnts can meet a portion of their nitrog... more Associative nitrogen-fixation is one mechanism by which phtnts can meet a portion of their nitrogen (N) needs in N deficient environments. Eastern gamagrass [ Tripsucum dactyloides (L.) L.] grows under conditions conducive for associative N-fixation. Our objective was to evaluate eastern gamagrass roots for nitrogenase activity and associated N-fixing bacteria, and compare its nitroge nase activity to switchgrass (Panicum virgatum L.). Soil and root samples were collected from unfertilized stands of "PMK-24"eastern gamagrass at 3 locations in northern Missouri and nitrogenase activity measured using the acetylene reduction method. Eastern gamagrass roots supported greater nitrogenase activity when colonized by indigenous bacteria, compared to roots inoculated with Klebsiella pneumoniae or surface sterilized. Eastern gamagrass roots colonized by indigenous bacteria had 17-46 fold greater nitrogenase activity than switchgrass roots. Bacterial composition on eastern gamagrass roots was dominated by fluorescent pseudomonads and Pseudomonas cepacia, with lower populations of other bacteria. Bacterial composition from incubation tubes showing nitrogenase activity was similar to that found on the roots, except that the diazotrophic bacterium Azospirihm brasiliense was isolated from 1 of 3 sites. The potential for associative Nfixation with eastern gamagrass warrants further study and in situ measurement to quantify rates of N fixation.

Research paper thumbnail of The role of bioherbicides in weed management

The bioherbicide approach to weed management involves the inundative use of selected microorganis... more The bioherbicide approach to weed management involves the inundative use of selected microorganisms for attacking specific weeds and controlling their infestations within the same year of application. Ideally, bioherbicides are most effective for weed management in annual cropping systems that are unsuitable for the classical biological control approach, which involve the use of natural enemies requiring more than one year to develop effective, weed suppressive populations. Only a few bioherbicides are successful in field-scale control of weeds while the effectiveness of other candidate bioherbicides has been limited by restricted host-range, elaborate formulation requirements, and lack of persistence in the field. Special situations in which bioherbicides may be most effective include management of weeds that are considered herbicide-resistant, parasitic, and invasive. Based on the current status of bioherbicide use, strategies for widening host ranges, improving formulations for practical use, and improving techniques for enhancement of weed-suppressive activity in conventional and sustainable agricultural systems are needed if bioherbicides are to make significant contributions to nonchemical weed management.

Research paper thumbnail of Biological control of wheat take-all disease: II-Rapid screening for selection of bacteria suppressive to Gaeumannomyces graminis var. tritici in laboratory with greenhouse and field confirmation trials

Biological control of wheat take-all disease: II-Rapid screening for selection of bacteria suppre... more Biological control of wheat take-all disease: II-Rapid screening for selection of bacteria suppressive to Gaeumannomyces graminis var. tritici in laboratory with greenhouse and field confirmation trials. Tunisian Journal of Plant protection 2: 35-46. A quick test tube assay was developed to rapidly screen selected bacterial isolates for their ability to suppress take-all disease of wheat, caused by Gaeumannomyces graminis var. tritici (Ggt). The assay involved the use of test tubes (18 mm in diameter X 95 mm long) in which either vermiculite or soil was infested with Ggt. Seeds of bread wheat (Triticum aestivum) cv. 'Madsen' inoculated with a bacterial isolate were planted in vermiculite or soil containing Ggt growing medium plugs. After 7-10 days, the amount of the take-all symptoms on the roots was determined. Among 23 isolates studied, 3 were selected based on their effectiveness in suppressing the take-all disease symptoms on wheat roots. A greenhouse assay using soils from Tunisia and Missouri with various histories of wheat production and a field trial in Mexico silt loam soil confirmed significant inhibition of take-all symptoms by two bacterial strains: Pseudomonas aureofaciens 6 from Missouri and Bacillus subtilis 177 from Tunisia. Based on results of our screening procedures, these two bacterial strains were selected for their effectiveness as potential biocontrol agents against wheat take-all to use in specific soils.

Research paper thumbnail of ALS-resistantHelianthus annuusinterference inGlycine max

Weed Science, 2000

... Stubbendieck, J., GY Friisoe, and MR Bolick. ... ANDREW A. SCHMIDT, WILLIAM G. JOHNSON, DAVID... more ... Stubbendieck, J., GY Friisoe, and MR Bolick. ... ANDREW A. SCHMIDT, WILLIAM G. JOHNSON, DAVID A. MORTENSEN, ALEX R. MARTIN, ANITA DILLE, DALLAS E. PETERSON, COREY GUZA, JAMES J. KELLS, RYAN D. LINS, CHRIS M. BOERBOOM, CHRISTY L. SPRAGUE ...

Research paper thumbnail of Enhanced suppression of plant growth through production of L-tryptophan-derived compounds by deleterious rhizobacteria

Plant and Soil, 1995

Plant-growth-suppressive activity of deleterious rhizobactena (DRB) may be due to produc~ion of n... more Plant-growth-suppressive activity of deleterious rhizobactena (DRB) may be due to produc~ion of nlctnbolires absorbed through roots. .4uxins produced in high concentrations in the rhizosphere by DRB contribute ro reduce;! root growth. Selected DRB abie to produce excessive amounts of auxin compou!ids for supyrt:ssioii of wccti seedling growth may be effective for biological control of weeds. The objcctivcs io this study were to nsscss :he ability of DRB originating from weed seedlings to synthesize auxins from L-tryptophan (L-TRP), deterrriine eifcc:s of DRB with or w i b o u t L-TRP on seedling root growth, and characterize auxins produced from L-TRP using high performance liquid chrornatography (HPLC). Auxim expressed as indolc-3-acctlc acid iIAA!-equivaicnrs wcre prtiduced by 22.5% o i the DRB tested based on 3 coJorimetric method. Uiider laboratory conilitlons. a DRB isola!e classiiied as EnteroDuner tay!orae with high auxln-producing potential (?I mg I,-' h4-cquivale1:ts) inhibited roor growth of field bindweed (C'onvofvufusun~ensis L.) by 90.5% when combined with lo-' M L-TRP conlpxed w~r h non-meate6 control. Auxin derivatives produced by b:. !a$orae from L-TRP in broth culture after 24 il incubatlt?!? identified by HPLC inc!uded IAA (102 L-I), indole-3-alde!lyae (IALD; 0.4 p g L-' j, and iuciole-3-iactic x i 4 (L A ; 7.5 pg L-I). Results suggest that providixg L-TRP with selected suxin-producing DRR to iucrc:isc phytotos~c activity againsl emerging weed seedliiigs may be a practicai biological control strategy.

Research paper thumbnail of Chemotaxis of deleterious rhizobacteria to velvetleaf (Abutilon theophrasti Medik.) seeds and seedlings

FEMS Microbiology Ecology, 1994

Intact seeds and seed and seedling root exudates of velvetleaf (Abutilon theophrasti Medik.) were... more Intact seeds and seed and seedling root exudates of velvetleaf (Abutilon theophrasti Medik.) were used as chemoattractants in experiments to determine the relative importance of chemotaxis in spermosphere and rhizosphere colonization by selected rhizobacteria. Results for soft-agar, capillary tube and soil chemotaxis assays indicated that selected deleterious rhizobacteria were specifically attracted to seed and seedling root exudates. Several amino acids and sugars detected in exudates were chemoattractants for these rhizobacteria. Using soil-chemotaxis assemblies, migration of rhizobacterial isolates through 2-era distances of soil toward velvetleaf seeds or exudates was detected within 24 h. Isolates were not detected at the same site in soils without seeds or exudates until 72 h after inoculation. These results suggest that attraction of deleterious rhizobacteria toward seeds and seedling roots mediated by exudates (chemotaxis) might be the first step in establishment and subsequent colonization of biological control bacteria on weed seeds and seedling roots in soil.

Research paper thumbnail of Field Evaluation of Selected Rhizobium in an Improved Legume Inoculant1

Agronomy Journal, 1983

Increased grain legume production depends on effective symbiotic dinitrogen fixation through succ... more Increased grain legume production depends on effective symbiotic dinitrogen fixation through successful legume inoculation. Inoculants containing high numbers ≥ l07/g of effective Rhizobium must withstand adverse field conditions. Field studies were performed to determine the effects of selected rhizobia in two different inoculant carriers on nodulation and performance of three grain legumes. The soil at the 1979 site (Vertic Haplaquept) contained = 103 cowpea Rhizobium and = 102 Rhizobium phaseoli per g of dry soil. The soil at the 1980 site (Typic Paleudalf) contained < l02 R. phaseoli per g of dry soil. Selected strains of R. phaseoli and cowpea Rhizobium were incorporated in peat or vegetable oil. Seeds of bean (Phaseolus vulgaris L.), cowpea [Vigna unguiculata (L.) Walp.], and peanut (Arachis hypogaea L.) were inoculated (ca. 108 Rhizobium/seed) and planted. Nodulation, plant growth, and yields were determined in all experiments. Strains of Rhizobium in oil‐base inoculants g...

Research paper thumbnail of Weed Suppression by Deleterious Rhizobacteria is Affected by Formulation and Soil Properties

Communications in Soil Science and Plant Analysis, 2005

Deleterious rhizobacteria (DRB) suppress weed growth in field tests and are considered potential ... more Deleterious rhizobacteria (DRB) suppress weed growth in field tests and are considered potential weed biological control agents. This study compared the relative inhibitory action of the DRB Pseudomonas fluorescens strain G2-11 in different formulations, corn gluten meal (CGM), and semolina flour, toward wheat (Triticum aestivum L.), green foxtail (Setaria viridis (L.) Beauv.), and velvetleaf (Abutilon theophrasti Medik) seeds and seedlings in soil assays. Strain G2-11 successfully established in semolina flour as an inoculum formulation but was incompatible with CGM presumably because of antibacterial factors present. The effect of DRB and plant products on seed germination and plant growth were influenced by soil, with the strongest effects seen in fine sandy loam. Semolina flour alone reduced root growth of all target plants except for velvetleaf in silt loam. Green foxtail seed germination was greatly reduced by strain G2-11. With the exception of wheat seedling growth, strain G2-11 enhanced growth-suppressive qualities of semolina flour. Results suggest that natural plant products such as CGM and semolina flour alone and formulated with

Research paper thumbnail of Seasonal Dynamics of Enzymetic Activities and Functional Diversity in Soils under Different Organic Managements

Soil microbial activity and diversity are affected by organic sources applied to improve soil qua... more Soil microbial activity and diversity are affected by organic sources applied to improve soil quality and fluctuate seasonally. We investigated the effects of municipal compost (MC), poultry litter (PL), and cover crops of spring oats and red clover (RC) on soil enzyme activities, and soil bacterial community-level physiological profiling (CLPP) in a Mexico silt loam in North Central Missouri, USA. Temporal patterns of these parameters were observed by periodic five soil sampling from spring to fall over a two year period. MC increased soil dehydrogenase (DH) activity consistently beginning about three months after MC application; fluorescein diacetate (FDA) hydrolytic activity significantly began to increase by the September of the first year but fluctuated during the following period. DH activity responded more directly to the amount or properties of organic residues in soils while FDA hydrolysis and CLPP were generally influenced by composition of organic sources, and enzyme acti...

Research paper thumbnail of Sensor data fusion for soil health assessment

Geoderma, 2017

Assessment of soil health involves determining how well a soil is performing its biological, chem... more Assessment of soil health involves determining how well a soil is performing its biological, chemical, and physical functions relative to its inherent potential. Due to high cost, labor requirements, and soil disturbance, traditional laboratory analyses cannot provide high resolution soil health data. Therefore, sensor-based approaches are important to facilitate cost-effective, site-specific management for soil health. In the Central Claypan Region of Missouri, USA, visible and near-infrared (VNIR) diffuse reflectance spectroscopy has successfully been used to estimate biological components of soil health as well as Soil Management Assessment Framework (SMAF) scores. In contrast, estimation models for important chemical and physical aspects of soil health have been less successful with VNIR spectroscopy. The primary objective of this study was to apply a sensor fusion approach to estimate soil health indicators and SMAF scores using VNIR spectroscopy in conjunction with soil apparent electrical conductivity (EC a), and penetration resistance measured by cone penetrometer (i.e., cone index, CI). Soil samples were collected from two depths (0-5 and 5-15 cm) at 108 locations within a 10-ha research site encompassing different cropping systems and landscape positions. Soil health measurements and VNIR spectral data were obtained in the laboratory, while CI and EC a data were obtained in situ. Calibration models were developed with partial least squares (PLS) regression and model performance was evaluated using coefficient of determination (R 2) and root mean square error (RMSE). Models integrating EC a and CI with VNIR reflectance data improved estimates of the overall SMAF score (R 2 = 0.78, RMSE = 7.21%) relative to VNIR alone (R 2 = 0.69, RMSE = 8.41%), reducing RMSE by 14%. Improved models were also achieved for estimates of the individual chemical, biological, and physical soil health scores, demonstrating reductions in RMSE of 2.8, 5.4, and 10.0%, respectively. The results of this study illustrate the potential for rapid quantification of soil health by fusing VNIR sensor data with auxiliary data obtained from complementary sensors.

Research paper thumbnail of Glyphosate affects chlorophyll, nodulation and nutrient accumulation of “second generation” glyphosate-resistant soybean (Glycine max L.)

Pesticide Biochemistry and Physiology, 2011

Glyphosate affects chlorophyll, nodulation and nutrient accumulation of ''second generation'' gly... more Glyphosate affects chlorophyll, nodulation and nutrient accumulation of ''second generation'' glyphosate-resistant soybean (Glycine max L.

Research paper thumbnail of Effects of a biological amendment on chemical and biological properties and microbial diversity in soils receiving different organic amendments

Research paper thumbnail of Newly developed technologies for soil and water conservation

Recent discoveries and technological innovations in the field of soil and water conservation can ... more Recent discoveries and technological innovations in the field of soil and water conservation can be traced to the works of our predecessors. In this paper, conservation is defined broadly, to include the quality of water lower in watersheds, and is discussed according to contaminants. Within-field source prevention and reduction practices as well as off-site mitigation practices are described. Examples concerning

Research paper thumbnail of Production and Conservation Outcomes of a Decade-Long Field-Scale Precision Agriculture System

Research paper thumbnail of Management impacts on GHG emissions and yield performance from organic soybean

ABSTRACT Agricultural land has been recognized as a significant source of greenhouse gas (GHG) em... more ABSTRACT Agricultural land has been recognized as a significant source of greenhouse gas (GHG) emissions, however GHG release from soils varies as crop production strategies vary. This study was conducted to determine the effects of tillage, cover crop, and compost rate on the soil release of two GHG, nitrous oxide and carbon dioxide, under an organic soybean cropping system. A corn-soybean-wheat organic cropping system was initiated in 2012 in an organic transition field at the University of Missouri Bradford Research Center using a randomized complete block, split plot design with four replications. Each crop treatment variable included tillage/cover crop for the main plot treatment and compost rate for the split-plot treatment. Tillage/cover crop treatments included tilled without cover crop, tilled with cover crop, and no-till with cover crop. Compost treatments were 0, low, medium, and high rates, based on soil-test phosphorus. GHG were collected in the field and analyzed according to USDA-ARS GRACEnet project protocols. Gas samples were collected at least once a week during the growing season, and several times in succession after significant events such as rain, irrigation, and cultivation. Preliminary results show no significant correlation between GHG and treatment effects in 2012. Soybean yields were highest in the tilled plots without cover crop at 3173 kg/ha, and lowest in the no-till plots without cover crop at 2287 kg/ha. Cover crop had an intermediate level of yield reduction compared to the tilled plots. A medium compost application rate (100 kg P/ha) produced the greatest soybean yield over other compost treatments. Precipitation in 2012 was 33% less than the average of the previous three years, causing overall yield reduction. Excessive heat exacerbated soybean water stress. Cover crops seemed to have suppressed yield as well. However, adjusting compost application rate based on P content appears to benefit adequate nutrition and yields of organically grown soybeans.

Research paper thumbnail of Estimating a Soil Quality Index with VNIR Reflectance Spectroscopy

Soil Science Society of America Journal, 2015

All rights reserved. No part of this periodical may be reproduced or transmitted in any form or b... more All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Permission for printing and for reprinting the material contained herein has been obtained by the publisher. Estimating a Soil Quality Index with VNIR Reflectance Spectroscopy Soil & Water Management & Conservation sensor-based approaches to assessment and quantification of soil quality are important to facilitate cost-effective, site-specific soil management. The objective of this research was to evaluate the ability of visible, near-infrared (VnIR) diffuse reflectance spectroscopy to estimate multiple soil quality indicators (sQIs) and soil Management Assessment framework (sMAf) scores. A total of 234 soil samples from two depths (0-5 and 5-15 cm) were obtained in 2008 from 17 agricultural management systems located in the central claypan Region of Missouri, UsA. The VnIR spectra were obtained on ovendried and field-moist soil, and calibration models were developed with partial least squares (PLs) regression. Models were evaluated using the coefficient of determination (R 2), residual prediction deviation (RPD), and the ratio of prediction error to interquartile range (RPIQ). The most reliable estimation results were achieved using oven-dry soil for organic c, b-glucosidase, total n, the biological sMAf score, the organic c score, and the b-glucosidase score (R 2 ³ 0.76, RPD ³ 2.0, RPIQ ³ 3.2). Using field-moist soils, the most reliable estimation results were achieved for organic c and the organic c score (R 2 ³ 0.80, RPD ³ 2.1, RPIQ ³ 3.6). Incorporating the bulk density score and P score as auxiliary variables with the VnIR spectra improved estimation of the overall sMAf soil quality score for oven-dry soil (R 2 = 0.76, RPD = 2.0, RPIQ = 3.1) and field-moist soil (R 2 = 0.75, RPD = 1.9, RPIQ = 2.8). These results demonstrate the robustness of VnIR estimation of biological sQIs, and illustrate the potential for rapid, in-field quantification of soil quality by fusing VnIR sensors with auxiliary data obtained from complementary sensors or supplemental analyses.

Research paper thumbnail of Article Understanding and Enhancing Soil Biological Health: The Solution for Reversing Soil Degradation

Our objective is to provide an optimistic strategy for reversing soil degradation by increasing p... more Our objective is to provide an optimistic strategy for reversing soil degradation by increasing public and private research efforts to understand the role of soil biology, particularly microbiology, on the health of our world's soils. We begin by defining soil quality/soil health (which we consider to be interchangeable terms), characterizing healthy soil resources, and relating the significance of soil health to agroecosystems and their functions. We examine how soil biology influences soil health and how biological properties and processes contribute to sustainability of agriculture and ecosystem services. We continue by examining what can be done to manipulate soil biology to: (i) increase nutrient availability for production of high yielding, high quality crops; (ii) protect crops from pests, pathogens, weeds; and (iii) manage other factors limiting production, provision of ecosystem services, and resilience to stresses like droughts. Next we look to the future by asking what needs to be known about soil biology that is not currently recognized or fully understood and how these needs could be addressed using emerging research tools. We conclude, based on our perceptions of how new knowledge regarding soil biology will help make agriculture more sustainable and productive, by recommending research emphases that should receive first priority through enhanced public and private research in order to reverse the trajectory toward global soil degradation.

Research paper thumbnail of Scanning and transmission electron microscopy of root colonization of morningglory (Ipomoea spp.) seedlings by rhizobacteria

Symbiosis, 2005

Hydroponically-grown ivyleaf morningglory (Ipomoea hederacea) seedlings inoculated with deleterio... more Hydroponically-grown ivyleaf morningglory (Ipomoea hederacea) seedlings inoculated with deleterious rhizobacteria (DRB) were studied to observe colonization of roots using scanning and transmission electron microscopy. The DRB, Bradyrhizobium japonicum isolate GD3, previously isolated as a DRB producing high concentrations of indole-3-acetic acid (IAA), and Pseudomonas putida isolate GD4, were compared with a plant growth promoting rhizobacterium (PGPR), Bacillus megaterium isolate GP4. Scanning electron microscopy revealed that the colonization of isolates GP4 and GD4 were consistently distributed on the surface of roots; however, isolate GD3 was deeply localized into surface furrows of roots. Transmission electron microscopy showed considerable alterations of root cells including vesiculation, partial cell wall degradation, and cytoplasm disorganization. The average population density of isolate GD4 on the root surface was about 10 and 100 times greater than GP4 and GD3, respectiv...

Research paper thumbnail of Consensus on a New Definition for Soil?

CSA News, 2017

U nconsolidated material is not necessarily soil. If such material is without biological input or... more U nconsolidated material is not necessarily soil. If such material is without biological input or modification, such as the presence of at least minimal horizons other than unweathered parent material, it has not traditionally been recognized as soil. Unconsolidated material can hold liquids, gases, etc. and yet is considered to be raw geologic material (not soil) until pedologic alteration becomes evident. Lack of biological material or evidence of biological alteration in some form (past or present) precludes "soil" on extraterrestrial bodies.

Research paper thumbnail of Vegetative Buffer Strips for Reducing Herbicide Transport in Runoff: Effects of Buffer Width, Vegetation, and Season

JAWRA Journal of the American Water Resources Association, 2017

The effectiveness of vegetative buffer strips (VBS) for reducing herbicide transport has not been... more The effectiveness of vegetative buffer strips (VBS) for reducing herbicide transport has not been well documented for runoff prone soils. A multi‐year plot‐scale study was conducted on an eroded claypan soil with the following objectives: (1) assess the effects of buffer width, vegetation, and season on runoff transport of atrazine (ATR), metolachlor (MET), and glyphosate; (2) develop VBS design criteria for herbicides; and (3) compare differences in soil quality among vegetation treatments. Rainfall simulation was used to create uniform antecedent soil water content and to generate runoff. Vegetation treatment and buffer width impacted herbicide loads much more than season. Grass treatments reduced herbicide loads by 19‐28% and sediment loads by 67% compared to the control. Grass treatments increased retention of dissolved‐phase herbicides by both infiltration and adsorption, but adsorption accounted for the greatest proportion of retained herbicide load. This latter finding indica...

Research paper thumbnail of Indications of Associative Nitrogen Fixation in Eastern Gamagrass

Journal of Range Management, 1994

Associative nitrogen-fixation is one mechanism by which phtnts can meet a portion of their nitrog... more Associative nitrogen-fixation is one mechanism by which phtnts can meet a portion of their nitrogen (N) needs in N deficient environments. Eastern gamagrass [ Tripsucum dactyloides (L.) L.] grows under conditions conducive for associative N-fixation. Our objective was to evaluate eastern gamagrass roots for nitrogenase activity and associated N-fixing bacteria, and compare its nitroge nase activity to switchgrass (Panicum virgatum L.). Soil and root samples were collected from unfertilized stands of "PMK-24"eastern gamagrass at 3 locations in northern Missouri and nitrogenase activity measured using the acetylene reduction method. Eastern gamagrass roots supported greater nitrogenase activity when colonized by indigenous bacteria, compared to roots inoculated with Klebsiella pneumoniae or surface sterilized. Eastern gamagrass roots colonized by indigenous bacteria had 17-46 fold greater nitrogenase activity than switchgrass roots. Bacterial composition on eastern gamagrass roots was dominated by fluorescent pseudomonads and Pseudomonas cepacia, with lower populations of other bacteria. Bacterial composition from incubation tubes showing nitrogenase activity was similar to that found on the roots, except that the diazotrophic bacterium Azospirihm brasiliense was isolated from 1 of 3 sites. The potential for associative Nfixation with eastern gamagrass warrants further study and in situ measurement to quantify rates of N fixation.

Research paper thumbnail of The role of bioherbicides in weed management

The bioherbicide approach to weed management involves the inundative use of selected microorganis... more The bioherbicide approach to weed management involves the inundative use of selected microorganisms for attacking specific weeds and controlling their infestations within the same year of application. Ideally, bioherbicides are most effective for weed management in annual cropping systems that are unsuitable for the classical biological control approach, which involve the use of natural enemies requiring more than one year to develop effective, weed suppressive populations. Only a few bioherbicides are successful in field-scale control of weeds while the effectiveness of other candidate bioherbicides has been limited by restricted host-range, elaborate formulation requirements, and lack of persistence in the field. Special situations in which bioherbicides may be most effective include management of weeds that are considered herbicide-resistant, parasitic, and invasive. Based on the current status of bioherbicide use, strategies for widening host ranges, improving formulations for practical use, and improving techniques for enhancement of weed-suppressive activity in conventional and sustainable agricultural systems are needed if bioherbicides are to make significant contributions to nonchemical weed management.

Research paper thumbnail of Biological control of wheat take-all disease: II-Rapid screening for selection of bacteria suppressive to Gaeumannomyces graminis var. tritici in laboratory with greenhouse and field confirmation trials

Biological control of wheat take-all disease: II-Rapid screening for selection of bacteria suppre... more Biological control of wheat take-all disease: II-Rapid screening for selection of bacteria suppressive to Gaeumannomyces graminis var. tritici in laboratory with greenhouse and field confirmation trials. Tunisian Journal of Plant protection 2: 35-46. A quick test tube assay was developed to rapidly screen selected bacterial isolates for their ability to suppress take-all disease of wheat, caused by Gaeumannomyces graminis var. tritici (Ggt). The assay involved the use of test tubes (18 mm in diameter X 95 mm long) in which either vermiculite or soil was infested with Ggt. Seeds of bread wheat (Triticum aestivum) cv. 'Madsen' inoculated with a bacterial isolate were planted in vermiculite or soil containing Ggt growing medium plugs. After 7-10 days, the amount of the take-all symptoms on the roots was determined. Among 23 isolates studied, 3 were selected based on their effectiveness in suppressing the take-all disease symptoms on wheat roots. A greenhouse assay using soils from Tunisia and Missouri with various histories of wheat production and a field trial in Mexico silt loam soil confirmed significant inhibition of take-all symptoms by two bacterial strains: Pseudomonas aureofaciens 6 from Missouri and Bacillus subtilis 177 from Tunisia. Based on results of our screening procedures, these two bacterial strains were selected for their effectiveness as potential biocontrol agents against wheat take-all to use in specific soils.

Research paper thumbnail of ALS-resistantHelianthus annuusinterference inGlycine max

Weed Science, 2000

... Stubbendieck, J., GY Friisoe, and MR Bolick. ... ANDREW A. SCHMIDT, WILLIAM G. JOHNSON, DAVID... more ... Stubbendieck, J., GY Friisoe, and MR Bolick. ... ANDREW A. SCHMIDT, WILLIAM G. JOHNSON, DAVID A. MORTENSEN, ALEX R. MARTIN, ANITA DILLE, DALLAS E. PETERSON, COREY GUZA, JAMES J. KELLS, RYAN D. LINS, CHRIS M. BOERBOOM, CHRISTY L. SPRAGUE ...

Research paper thumbnail of Enhanced suppression of plant growth through production of L-tryptophan-derived compounds by deleterious rhizobacteria

Plant and Soil, 1995

Plant-growth-suppressive activity of deleterious rhizobactena (DRB) may be due to produc~ion of n... more Plant-growth-suppressive activity of deleterious rhizobactena (DRB) may be due to produc~ion of nlctnbolires absorbed through roots. .4uxins produced in high concentrations in the rhizosphere by DRB contribute ro reduce;! root growth. Selected DRB abie to produce excessive amounts of auxin compou!ids for supyrt:ssioii of wccti seedling growth may be effective for biological control of weeds. The objcctivcs io this study were to nsscss :he ability of DRB originating from weed seedlings to synthesize auxins from L-tryptophan (L-TRP), deterrriine eifcc:s of DRB with or w i b o u t L-TRP on seedling root growth, and characterize auxins produced from L-TRP using high performance liquid chrornatography (HPLC). Auxim expressed as indolc-3-acctlc acid iIAA!-equivaicnrs wcre prtiduced by 22.5% o i the DRB tested based on 3 coJorimetric method. Uiider laboratory conilitlons. a DRB isola!e classiiied as EnteroDuner tay!orae with high auxln-producing potential (?I mg I,-' h4-cquivale1:ts) inhibited roor growth of field bindweed (C'onvofvufusun~ensis L.) by 90.5% when combined with lo-' M L-TRP conlpxed w~r h non-meate6 control. Auxin derivatives produced by b:. !a$orae from L-TRP in broth culture after 24 il incubatlt?!? identified by HPLC inc!uded IAA (102 L-I), indole-3-alde!lyae (IALD; 0.4 p g L-' j, and iuciole-3-iactic x i 4 (L A ; 7.5 pg L-I). Results suggest that providixg L-TRP with selected suxin-producing DRR to iucrc:isc phytotos~c activity againsl emerging weed seedliiigs may be a practicai biological control strategy.

Research paper thumbnail of Chemotaxis of deleterious rhizobacteria to velvetleaf (Abutilon theophrasti Medik.) seeds and seedlings

FEMS Microbiology Ecology, 1994

Intact seeds and seed and seedling root exudates of velvetleaf (Abutilon theophrasti Medik.) were... more Intact seeds and seed and seedling root exudates of velvetleaf (Abutilon theophrasti Medik.) were used as chemoattractants in experiments to determine the relative importance of chemotaxis in spermosphere and rhizosphere colonization by selected rhizobacteria. Results for soft-agar, capillary tube and soil chemotaxis assays indicated that selected deleterious rhizobacteria were specifically attracted to seed and seedling root exudates. Several amino acids and sugars detected in exudates were chemoattractants for these rhizobacteria. Using soil-chemotaxis assemblies, migration of rhizobacterial isolates through 2-era distances of soil toward velvetleaf seeds or exudates was detected within 24 h. Isolates were not detected at the same site in soils without seeds or exudates until 72 h after inoculation. These results suggest that attraction of deleterious rhizobacteria toward seeds and seedling roots mediated by exudates (chemotaxis) might be the first step in establishment and subsequent colonization of biological control bacteria on weed seeds and seedling roots in soil.

Research paper thumbnail of Field Evaluation of Selected Rhizobium in an Improved Legume Inoculant1

Agronomy Journal, 1983

Increased grain legume production depends on effective symbiotic dinitrogen fixation through succ... more Increased grain legume production depends on effective symbiotic dinitrogen fixation through successful legume inoculation. Inoculants containing high numbers ≥ l07/g of effective Rhizobium must withstand adverse field conditions. Field studies were performed to determine the effects of selected rhizobia in two different inoculant carriers on nodulation and performance of three grain legumes. The soil at the 1979 site (Vertic Haplaquept) contained = 103 cowpea Rhizobium and = 102 Rhizobium phaseoli per g of dry soil. The soil at the 1980 site (Typic Paleudalf) contained < l02 R. phaseoli per g of dry soil. Selected strains of R. phaseoli and cowpea Rhizobium were incorporated in peat or vegetable oil. Seeds of bean (Phaseolus vulgaris L.), cowpea [Vigna unguiculata (L.) Walp.], and peanut (Arachis hypogaea L.) were inoculated (ca. 108 Rhizobium/seed) and planted. Nodulation, plant growth, and yields were determined in all experiments. Strains of Rhizobium in oil‐base inoculants g...

Research paper thumbnail of Weed Suppression by Deleterious Rhizobacteria is Affected by Formulation and Soil Properties

Communications in Soil Science and Plant Analysis, 2005

Deleterious rhizobacteria (DRB) suppress weed growth in field tests and are considered potential ... more Deleterious rhizobacteria (DRB) suppress weed growth in field tests and are considered potential weed biological control agents. This study compared the relative inhibitory action of the DRB Pseudomonas fluorescens strain G2-11 in different formulations, corn gluten meal (CGM), and semolina flour, toward wheat (Triticum aestivum L.), green foxtail (Setaria viridis (L.) Beauv.), and velvetleaf (Abutilon theophrasti Medik) seeds and seedlings in soil assays. Strain G2-11 successfully established in semolina flour as an inoculum formulation but was incompatible with CGM presumably because of antibacterial factors present. The effect of DRB and plant products on seed germination and plant growth were influenced by soil, with the strongest effects seen in fine sandy loam. Semolina flour alone reduced root growth of all target plants except for velvetleaf in silt loam. Green foxtail seed germination was greatly reduced by strain G2-11. With the exception of wheat seedling growth, strain G2-11 enhanced growth-suppressive qualities of semolina flour. Results suggest that natural plant products such as CGM and semolina flour alone and formulated with

Research paper thumbnail of Seasonal Dynamics of Enzymetic Activities and Functional Diversity in Soils under Different Organic Managements

Soil microbial activity and diversity are affected by organic sources applied to improve soil qua... more Soil microbial activity and diversity are affected by organic sources applied to improve soil quality and fluctuate seasonally. We investigated the effects of municipal compost (MC), poultry litter (PL), and cover crops of spring oats and red clover (RC) on soil enzyme activities, and soil bacterial community-level physiological profiling (CLPP) in a Mexico silt loam in North Central Missouri, USA. Temporal patterns of these parameters were observed by periodic five soil sampling from spring to fall over a two year period. MC increased soil dehydrogenase (DH) activity consistently beginning about three months after MC application; fluorescein diacetate (FDA) hydrolytic activity significantly began to increase by the September of the first year but fluctuated during the following period. DH activity responded more directly to the amount or properties of organic residues in soils while FDA hydrolysis and CLPP were generally influenced by composition of organic sources, and enzyme acti...

Research paper thumbnail of Sensor data fusion for soil health assessment

Geoderma, 2017

Assessment of soil health involves determining how well a soil is performing its biological, chem... more Assessment of soil health involves determining how well a soil is performing its biological, chemical, and physical functions relative to its inherent potential. Due to high cost, labor requirements, and soil disturbance, traditional laboratory analyses cannot provide high resolution soil health data. Therefore, sensor-based approaches are important to facilitate cost-effective, site-specific management for soil health. In the Central Claypan Region of Missouri, USA, visible and near-infrared (VNIR) diffuse reflectance spectroscopy has successfully been used to estimate biological components of soil health as well as Soil Management Assessment Framework (SMAF) scores. In contrast, estimation models for important chemical and physical aspects of soil health have been less successful with VNIR spectroscopy. The primary objective of this study was to apply a sensor fusion approach to estimate soil health indicators and SMAF scores using VNIR spectroscopy in conjunction with soil apparent electrical conductivity (EC a), and penetration resistance measured by cone penetrometer (i.e., cone index, CI). Soil samples were collected from two depths (0-5 and 5-15 cm) at 108 locations within a 10-ha research site encompassing different cropping systems and landscape positions. Soil health measurements and VNIR spectral data were obtained in the laboratory, while CI and EC a data were obtained in situ. Calibration models were developed with partial least squares (PLS) regression and model performance was evaluated using coefficient of determination (R 2) and root mean square error (RMSE). Models integrating EC a and CI with VNIR reflectance data improved estimates of the overall SMAF score (R 2 = 0.78, RMSE = 7.21%) relative to VNIR alone (R 2 = 0.69, RMSE = 8.41%), reducing RMSE by 14%. Improved models were also achieved for estimates of the individual chemical, biological, and physical soil health scores, demonstrating reductions in RMSE of 2.8, 5.4, and 10.0%, respectively. The results of this study illustrate the potential for rapid quantification of soil health by fusing VNIR sensor data with auxiliary data obtained from complementary sensors.

Research paper thumbnail of Glyphosate affects chlorophyll, nodulation and nutrient accumulation of “second generation” glyphosate-resistant soybean (Glycine max L.)

Pesticide Biochemistry and Physiology, 2011

Glyphosate affects chlorophyll, nodulation and nutrient accumulation of ''second generation'' gly... more Glyphosate affects chlorophyll, nodulation and nutrient accumulation of ''second generation'' glyphosate-resistant soybean (Glycine max L.

Research paper thumbnail of Effects of a biological amendment on chemical and biological properties and microbial diversity in soils receiving different organic amendments

Research paper thumbnail of Newly developed technologies for soil and water conservation

Recent discoveries and technological innovations in the field of soil and water conservation can ... more Recent discoveries and technological innovations in the field of soil and water conservation can be traced to the works of our predecessors. In this paper, conservation is defined broadly, to include the quality of water lower in watersheds, and is discussed according to contaminants. Within-field source prevention and reduction practices as well as off-site mitigation practices are described. Examples concerning

Research paper thumbnail of Production and Conservation Outcomes of a Decade-Long Field-Scale Precision Agriculture System

Research paper thumbnail of Management impacts on GHG emissions and yield performance from organic soybean

ABSTRACT Agricultural land has been recognized as a significant source of greenhouse gas (GHG) em... more ABSTRACT Agricultural land has been recognized as a significant source of greenhouse gas (GHG) emissions, however GHG release from soils varies as crop production strategies vary. This study was conducted to determine the effects of tillage, cover crop, and compost rate on the soil release of two GHG, nitrous oxide and carbon dioxide, under an organic soybean cropping system. A corn-soybean-wheat organic cropping system was initiated in 2012 in an organic transition field at the University of Missouri Bradford Research Center using a randomized complete block, split plot design with four replications. Each crop treatment variable included tillage/cover crop for the main plot treatment and compost rate for the split-plot treatment. Tillage/cover crop treatments included tilled without cover crop, tilled with cover crop, and no-till with cover crop. Compost treatments were 0, low, medium, and high rates, based on soil-test phosphorus. GHG were collected in the field and analyzed according to USDA-ARS GRACEnet project protocols. Gas samples were collected at least once a week during the growing season, and several times in succession after significant events such as rain, irrigation, and cultivation. Preliminary results show no significant correlation between GHG and treatment effects in 2012. Soybean yields were highest in the tilled plots without cover crop at 3173 kg/ha, and lowest in the no-till plots without cover crop at 2287 kg/ha. Cover crop had an intermediate level of yield reduction compared to the tilled plots. A medium compost application rate (100 kg P/ha) produced the greatest soybean yield over other compost treatments. Precipitation in 2012 was 33% less than the average of the previous three years, causing overall yield reduction. Excessive heat exacerbated soybean water stress. Cover crops seemed to have suppressed yield as well. However, adjusting compost application rate based on P content appears to benefit adequate nutrition and yields of organically grown soybeans.

Research paper thumbnail of Estimating a Soil Quality Index with VNIR Reflectance Spectroscopy

Soil Science Society of America Journal, 2015

All rights reserved. No part of this periodical may be reproduced or transmitted in any form or b... more All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Permission for printing and for reprinting the material contained herein has been obtained by the publisher. Estimating a Soil Quality Index with VNIR Reflectance Spectroscopy Soil & Water Management & Conservation sensor-based approaches to assessment and quantification of soil quality are important to facilitate cost-effective, site-specific soil management. The objective of this research was to evaluate the ability of visible, near-infrared (VnIR) diffuse reflectance spectroscopy to estimate multiple soil quality indicators (sQIs) and soil Management Assessment framework (sMAf) scores. A total of 234 soil samples from two depths (0-5 and 5-15 cm) were obtained in 2008 from 17 agricultural management systems located in the central claypan Region of Missouri, UsA. The VnIR spectra were obtained on ovendried and field-moist soil, and calibration models were developed with partial least squares (PLs) regression. Models were evaluated using the coefficient of determination (R 2), residual prediction deviation (RPD), and the ratio of prediction error to interquartile range (RPIQ). The most reliable estimation results were achieved using oven-dry soil for organic c, b-glucosidase, total n, the biological sMAf score, the organic c score, and the b-glucosidase score (R 2 ³ 0.76, RPD ³ 2.0, RPIQ ³ 3.2). Using field-moist soils, the most reliable estimation results were achieved for organic c and the organic c score (R 2 ³ 0.80, RPD ³ 2.1, RPIQ ³ 3.6). Incorporating the bulk density score and P score as auxiliary variables with the VnIR spectra improved estimation of the overall sMAf soil quality score for oven-dry soil (R 2 = 0.76, RPD = 2.0, RPIQ = 3.1) and field-moist soil (R 2 = 0.75, RPD = 1.9, RPIQ = 2.8). These results demonstrate the robustness of VnIR estimation of biological sQIs, and illustrate the potential for rapid, in-field quantification of soil quality by fusing VnIR sensors with auxiliary data obtained from complementary sensors or supplemental analyses.