@article{tarkalson_mikkelsen_2007, title={Phosphorus losses in runoff after application of litter from broilers fed high-available phosphorus corn feed}, volume={38}, ISSN={["1532-2416"]}, DOI={10.1080/00103620701435571}, abstractNote={Abstract Recent efforts to reduce phosphorus (P) content of corn grain fed to poultry have led to the development of low‐phytic‐acid corn. Research is needed to evaluate the environmental impact of the application to cropland of manure from animals fed low‐phytic‐acid corn. The purpose of this research was to determine P losses in runoff from a bare Piedmont soil (cecil clay loam; clayey, kaolinitic, thermic, Typic Kanhapludult) in the southeastern United States receiving surface applications of broiler litter from birds fed a low‐phytic‐acid corn (HAP broiler litter). The HAP litter was applied at rates of 0, 8, 16, 33, 49, 66, and 82 kg P ha−1. Simulated rainfall was applied at a rate of 7.6 cm hr−1 on the same day the litter sources were applied to the plots. Runoff volumes were measured, and samples were collected at 5‐min intervals for 30 min and analyzed for reactive P (RP), algal‐available P (AAP), and total P (TP). Flow‐weighted concentrations and mass losses of P increased linearly with litter application rate (r2 values=0.99). Flow‐weighted concentrations of RP in runoff increased from 2.2 to 15.4 mg RP L−1, and mass loss of TP in runoff ranged from 1.3 to 7.3 kg P ha−1 over all application rates based on linear regression. Runoff volume losses were 47% greater after litter applications compare to the 0 application rate treatment. Reduced infiltration resulting from litter particles blocking pores in the soil surface is likely the reason for the increased runoff volumes.}, number={13-14}, journal={COMMUNICATIONS IN SOIL SCIENCE AND PLANT ANALYSIS}, author={Tarkalson, David D. and Mikkelsen, Robert L.}, year={2007}, pages={1805–1814} }
 @article{nelson_mikkelsen_2006, title={Polyethersulfone membrane filters for sampling soil water from in situ soils and intact soil columns for phosphate analysis}, volume={37}, ISSN={["1532-2416"]}, DOI={10.1080/00103620500440236}, abstractNote={Abstract Porous plates or cups are commonly used to collect soil solution samples in field studies or from intact soil columns. Some commonly used materials for porous plates may adsorb soil solution constituents such as phosphorus (P). An alternative to using a porous plate is to use a membrane filter with a known pore size and bubble point. The objective of this study was to evaluate the utility of polyethersulfone membranes (pore size 0.45 µm and bubble point >200 kPa) to extract soil solution from in situ soils and intact soil columns for phosphate analysis. In situ soil solution samplers were constructed from modified reusable polysulfone membrane filter holders equipped with polyethersulfone membranes (47 mm diameter). A −10 kPa vacuum was maintained in the samplers, which enabled soil solution collection at soil water potentials of 0 to −4 kPa in loamy sand, 0 to −10 kPa in sandy loam, and 0 to −12 kPa in sandy clay loam soils. In a laboratory study, soil solution samplers continued to hold a vacuum to −77 kPa soil water potential. Soil solution samplers were further evaluated in a field study at 45‐, 90‐, and 135‐cm depths in two soils. Samplers operated with relatively few difficulties for the first 12 months of field evaluation. Membranes apparently dried during periods of low soil water potential but increases in soil moisture were sufficient to rewet the membrane. Sampler failures in the field increased during 13–18 months because aged vacuum tubing and root interferences with samplers at 45 cm. Improvements in sampler design may improve the durability for implementation in long‐term field experiments. Membrane filters worked near flawlessly to maintain unsaturated conditions in intact soil columns. The filter units facilitated easy collection of soil water from the intact soil columns without altering the chemical composition of the percolate.}, number={3-4}, journal={COMMUNICATIONS IN SOIL SCIENCE AND PLANT ANALYSIS}, author={Nelson, NO and Mikkelsen, RL}, year={2006}, pages={377–388} }
 @article{nelson_mikkelsen_2005, title={Balancing the phosphorus budget of a swine farm: A case study}, volume={34}, journal={Journal of Natural Resources and Life Sciences Education}, author={Nelson, N. O. and Mikkelsen, R. L.}, year={2005}, pages={90–95} }
 @article{mikkelsen_bruulsema_2005, title={Fertilizer use for horticultural crops in the US during the 20th century}, volume={15}, number={1}, journal={HortTechnology}, author={Mikkelsen, R. L. and Bruulsema, T. W.}, year={2005}, pages={24–30} }
 @article{nelson_parsons_mikkelsen_2005, title={Field-scale evaluation of phosphorus leaching in acid sandy soils receiving swine waste}, volume={34}, ISSN={["1537-2537"]}, DOI={10.2134/jeq2004.0445}, abstractNote={ABSTRACT}, number={6}, journal={JOURNAL OF ENVIRONMENTAL QUALITY}, author={Nelson, NO and Parsons, JE and Mikkelsen, RL}, year={2005}, pages={2024–2035} }
 @article{moore_israel_mikkelsen_2005, title={Nitrogen availability of anaerobic swine lagoon sludge: sludge source effects}, volume={96}, ISSN={["1873-2976"]}, DOI={10.1016/j.biortech.2004.04.013}, abstractNote={Increased numbers of swine producers will be removing sludge from their anaerobic waste treatment lagoons in the next few years, due to sludge exceeding designed storage capacity. Information on availability of nitrogen (N) in the sludge is needed to improve application recommendations for crops. The objective of this study was to investigate possible effects of different companies and types of swine operations on the availability of N in sludge from their associated lagoons. A laboratory incubation study was conducted to quantify the availability of N (i.e. initial inorganic N plus the potentially mineralizable organic N) in the sludge. Nine sludge sources from lagoons of sow, nursery and finishing operations of three different swine companies were mixed with a loamy sand soil (200 mg total Kjeldahl N kg−1 soil) and incubated at a water content of 0.19 g. water g−1 dry soil and 25 ± 2 °C for 12 weeks. Samples were taken at eight times over the 12-week period and analyzed for inorganic N (i.e. NH4–N and NO3–N) to determine mineralization of organic N in the sludge. Company and type of swine operation had no significant effects (P<0.05) on the pattern of inorganic N accumulation over time. Thus, inorganic N accumulation from all sludge sources was fit to a first order equation [Nt=Ni+No(1−e−kt)]. This relationship indicated that of the 200 mg of total sludge N added per kg soil, 23.5% was in the form of potentially mineralizable organic N (No) and 17.5% was in the form of inorganic N (Ni). The sum of these two pools (41%) represents an estimate of the proportion of total N in the applied sludge in plant available form after the 12 week incubation. While plant N availability coefficients were not measured in this study, the lack of significant company or type of swine operation effects on sludge N mineralization suggests that use of the same plant N availability coefficient for sludge from different types of lagoons is justifiable. The validity of this interpretation depends on the assumption that variation in other components of different sludge sources such as Cu and Zn does not differentially alter N uptake by the receiver crops.}, number={3}, journal={BIORESOURCE TECHNOLOGY}, author={Moore, AD and Israel, DW and Mikkelsen, RL}, year={2005}, month={Feb}, pages={323–329} }
 @article{moore_mikkelsen_israel_2004, title={Nitrogen mineralization of anaerobic swine lagoon sludge as influenced by seasonal temperatures}, volume={35}, ISSN={["1532-2416"]}, DOI={10.1081/CSS-120030575}, abstractNote={Abstract As anaerobic swine lagoons approach maximum sludge storage capacity, producers must periodically remove sludge and apply it to nearby fields. Information regarding the availability of nitrogen (N) in sludge as a nutrient source applied at different seasons of the year could improve crop-use efficiency. A 12-month laboratory study was conducted to quantify the effects of seasonal temperatures on mineralization of N in lagoon sludge. Sludge was mixed with a Coastal Plain soil (Arenic Kandiudult) and incubated for one year at weekly fluctuating temperatures based on Winter, Spring, Summer, and Fall application dates, ranging from a Winter low temperature of 9°C to a Summer maximum temperature of 30°C. Samples were analyzed monthly for NO3-N and NH4-N in 1.0 M KCl extracts of sludge amended soil. Sludge N availability (sum of NO3-N plus NH4-N concentration in 1.0 M KCl extract) was fit to a nonlinear regression model for a first-order reaction. Net N mineralization rate constants (k) derived from these models for the initial season of application increased in the order Fall (0.07) < Winter (0.075) < Spring (0.22) < Summer (0.36). While initial rates of net N mineralization differed, N availability predicted from first order equations was similar for all temperature regimes after one year of incubation and averaged 74% of the total N applied. Forty-two to 53% of the organic N in the sludge was mineralized during the one-year incubation.}, number={7-8}, journal={COMMUNICATIONS IN SOIL SCIENCE AND PLANT ANALYSIS}, author={Moore, AD and Mikkelsen, RL and Israel, DW}, year={2004}, month={Apr}, pages={991–1005} }
 @article{tarkalson_mikkelsen_2004, title={Runoff phosphorus losses as related to phosphorus source, application method, and application rate on a piedmont soil}, volume={33}, ISSN={["0047-2425"]}, DOI={10.2134/jeq2004.1424}, abstractNote={ABSTRACT}, number={4}, journal={JOURNAL OF ENVIRONMENTAL QUALITY}, author={Tarkalson, DD and Mikkelsen, RL}, year={2004}, pages={1424–1430} }
 @article{tarkalson_mikkelsen_2004, title={Runoff phosphorus losses as related to soil test phosphorus and degree of phosphorus saturation on piedmont soils under conventional and no-tillage}, volume={35}, ISSN={["0010-3624"]}, DOI={10.1081/LCSS-200036527}, abstractNote={Abstract Elevated soil phosphorus (P) concentrations on agricultural land from the application of P in fertilizers and animal manures have increased the potential for excessive P losses in runoff to nutrient-sensitive waters. This study was conducted to determine P losses in runoff from agricultural land in the Piedmont region of the southeastern U.S. with varying soil P levels resulting from past applications of broiler litter and inorganic P fertilizers. The correlations between soil P content and P in runoff can be used to validate and develop P loss-assessment tools for Piedmont soils of the southeastern US. Rainfall simulation at rates of 6.35 cm hr−1 were utilized to collect runoff samples from cropland under conventional tillage (CT) and no tillage (NT) with a range of initial P concentrations. Runoff samples were collected at 5-min intervals for 30 min and analyzed for reactive P (RP), algal-available P (AAP), and total P (TP). Concentration of RP in runoff from CT and NT plots was positively correlated with Mehlich-3 extractable P (M3 STP) (r 2 = 0.70 and 0.67, respectively) and oxalate extractable degree of P saturation (DPS) (r 2 = 0.62 and 0.57, respectively). A Mehlich-3 extractable P concentration of 294 mg P kg−1 and a DPS of 65% corresponded to 1 mg RP L−1 in runoff from NT plots. There was a significant linear relationship between M3 STP concentration and DPS on CT and NT plots. Results of this study indicate that both M3 STP concentration and DPS can be used to help predict P losses from a typical Piedmont soil managed with CT and NT cultivation. Overall, these soil tests predicted P concentration in runoff more effectively than P mass losses in runoff.}, number={19-20}, journal={COMMUNICATIONS IN SOIL SCIENCE AND PLANT ANALYSIS}, author={Tarkalson, DD and Mikkelsen, RL}, year={2004}, pages={2987–3007} }
 @article{tarkalson_mikkelsen_2003, title={A phosphorus budget of a poultry farm and a dairy farm in the southeastern US, and the potential impacts of diet alterations}, volume={66}, ISSN={["1385-1314"]}, DOI={10.1023/A:1024435909139}, number={3}, journal={NUTRIENT CYCLING IN AGROECOSYSTEMS}, author={Tarkalson, DD and Mikkelsen, RL}, year={2003}, month={Jul}, pages={295–303} }
 @article{leytem_mikkelsen_2003, title={Separation of soil organic phosphorus compounds using reverse-phase ion-pair chromatography}, volume={34}, ISSN={["1532-2416"]}, DOI={10.1081/CSS-120020452}, abstractNote={Methods were developed for the extraction and separation of soil organic phosphorus compounds using reverse-phase ion-pair chromatography (RP-ICP). Nucleotides (ATP, ADP, and AMP) were separated using a mobile phase of 15 mM TBAHS, 15 mM KH2PO4, and 7% acetonitrile. Inositol hexakisphosphate was separated using a mobile phase composition of 0.05 M formic acid:methanol (49:51 v/v) and 1.5 mL/100 mL of TBAOH. Extraction procedures were developed for the nucleotides which would be compatible with the RP-ICP system developed for their separation.}, number={9-10}, journal={COMMUNICATIONS IN SOIL SCIENCE AND PLANT ANALYSIS}, author={Leytem, AB and Mikkelsen, RL}, year={2003}, pages={1393–1406} }
 @article{nelson_mikkelsen_hesterberg_2003, title={Struvite precipitation in anaerobic swine lagoon liquid: effect of pH and Mg : P ratio and determination of rate constant}, volume={89}, ISSN={["0960-8524"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0038182035&partnerID=MN8TOARS}, DOI={10.1016/S0960-8524(03)00076-2}, abstractNote={Because of increased concern about surface water eutrophication from nutrient-enriched agricultural runoff, many swine producers are encouraged to decrease application rates of waste-based P. Precipitation and subsequent removal of magnesium ammonium phosphate (MgNH(4)PO(4) x 6H(2)O), commonly known as struvite, is a promising mechanism for N and P removal from anaerobic swine lagoon effluent. The objectives of this research were to (i) quantify the effects of adjusting pH and Mg:P ratio on struvite precipitation and (ii) determine the rate constant pH effect for struvite precipitation in anaerobic swine lagoon liquid. Concentrations of PO(4)-P in liquid from two anaerobic swine lagoons were determined after 24 h of equilibration for a pH range of 7.5-9.5 and Mg:P ratios between 1:1 and 1.6:1. Struvite formation reduced the PO(4)-P concentration in the effluents to as low as 2 mgl(-1). Minimum concentrations of PO(4)-P occurred between pH 8.9 and 9.25 at all Mg:P ratios. Struvite precipitation decreased PO(4)-P concentrations by 85% within 20 min at pH 9.0 for an initial Mg:P ratio of 1.2:1. The rate of PO(4)-P decrease was described by a first-order kinetic model, with rate constants of 3.7, 7.9, and 12.3 h(-1) at pH 8.4, 8.7 and 9.0 respectively. Our results indicate that induced struvite formation is a technically feasible method to remove N and P from swine lagoon liquid and it may allow swine producers to recover nutrients for off-farm sale.}, number={3}, journal={BIORESOURCE TECHNOLOGY}, author={Nelson, NO and Mikkelsen, RL and Hesterberg, DL}, year={2003}, month={Sep}, pages={229–236} }
 @article{mikkelsen_2003, title={Using tobacco by-products as a nitrogen source for container-grown houseplants}, volume={26}, ISSN={["0190-4167"]}, DOI={10.1081/PLN-120022383}, abstractNote={Abstract There is continuing interest in using various agricultural by‐products as organic nutrient sources for plants. This experiment was designed to evaluate the use of a by‐product from the tobacco (Nicotiana tobacum L.) processing industry as a nutrient source for commonly grown houseplants. A 8‐week laboratory experiment was conducted to measure nitrogen (N) mineralization from pelletized and powder mixtures of tobacco by‐product combined with dried blood and bone meal. The mixtures were added to a fresh field soil, a peat‐based medium, or the peat‐based medium that had been sterilized in an autoclave. The N mineralization rate was in the order of soil > peat medium > sterilized peat medium. Mineralization was more rapid from the powdered formulation of the by‐product than from the pelletized form. In a 14‐week greenhouse experiment, ten common houseplants were fertilized with 0, 150, 300, or 900 mg N/pot from pelletized by‐product, Osmocote (14% N, 6% P, and 12% K), a resin‐coated controlled‐release (3 months) fertilizer, or NH4NO3. The species examined were Aglonema commutatum, Chlorophytum comosum, Diffenbachia amoena, Dracena deremensis, Ficus benjamina, Nephrolepsis exaltata, Philodendron scandens oxycardium, Saintpaulia ionantha, Schefflera actinophylla, Tradescantia fluminensis. At a given N application rate, Osmocote and NH4NO3 more effectively increased tissue N concentrations than did the tobacco by‐product. Therefore, more by‐product is required than inorganic fertilizer to achieve a given N concentration in the plant. At high rates of by‐product application, excessive salinity may become a concern for salt‐sensitive plants.}, number={8}, journal={JOURNAL OF PLANT NUTRITION}, author={Mikkelsen, RL}, year={2003}, pages={1697–1708} }
 @article{crouse_sierzputowska-gracz_mikkelsen_wollum_2002, title={Monitoring phosphorus mineralization from poultry manure using phosphatase assays and phosphorus-31 nuclear magnetic resonance spectroscopy}, volume={33}, ISSN={["0010-3624"]}, DOI={10.1081/CSS-120003882}, abstractNote={Phosphatase enzymes are responsible for mineralization of organic-phosphorus (P) compounds in soil where they hydrolyze the organic phosphate esters to inorganic phosphate. One way to monitor the mineralization process in soils receiving poultry manure is by assessing the activity of phosphatase in a soil amended with poultry manure relative to a soil that is not amended. In a laboratory incubation, soil phosphomonoesterase activity and soil phosphodiesterase activity were measured 0, 1, 2, 4, 8, 12, 16, and 20 weeks after soil incorporation of poultry litter. Two soils, both Fine-loamy siliceous, thermic Typic Kandiudults, were used in the study. Both soils differed in their previous management. The first soil was from a conventionally tilled field that received annual poultry litter applications for 18 consecutive years. The second soil was from an adjacent recently cleared woodland that had no history of manure application. In the previously non-manured soil, soil phosphodiesterase activity following poultry litter addition increased from 4 to 66 μg p-nitrophenol g soil−1 hour−1 by the second week. However, in the same soil, after 8 weeks, phosphodiesterase activity resulting from poultry litter applications was not evident. There was a net increase in phosphomonoesterase activity from week 0 to 20 in the previously manured and previously non-manured soils that were amended with poultry litter. A simultaneous study was conducted to measure the relative concentration of organic P forms during the mineralization process using 31P nuclear magnetic resonance. Subsamples from the poultry manure-amended soil were extracted with 0.25 M NaOH+0.05 M EDTA following 0, 1, 2, 4, 8, 12, 16, and 20 weeks after manure addition and incorporation. The concentration of organic P compounds decreased from the time of poultry litter incorporation until week 20 whereas orthophosphate concentration increased during this period.}, number={7-8}, journal={COMMUNICATIONS IN SOIL SCIENCE AND PLANT ANALYSIS}, author={Crouse, DA and Sierzputowska-Gracz, H and Mikkelsen, RL and Wollum, AG}, year={2002}, pages={1205–1217} }
 @article{leytem_mikkelsen_gilliam_2002, title={Sorption of organic phosphorus compounds in Atlantic coastal plain soils}, volume={167}, DOI={10.1097/01.ss0000034854.98442.39}, number={10}, journal={Soil Science}, author={Leytem, A. B. and Mikkelsen, R. L. and Gilliam, J. W.}, year={2002}, pages={652–658} }
 @article{byers_mikkelsen_cox_2001, title={Greenhouse evaluation of four boron fertilizer materials}, volume={24}, ISSN={["1532-4087"]}, DOI={10.1081/PLN-100103665}, abstractNote={Management of boron (B) in soils can be difficult since a narrow range exists between plant deficiency and toxicity. A greenhouse study was conducted to evaluate the effectiveness of four soil-applied B fertilizers varying in solubility (Granubor, Hydroboracite, Ulexite, and Colemanite) in supplying B to alfalfa (Medicago sativa L.). Boron was incorporated at rates of 0, 1, or 2 mg B kg−1 into Norfolk (fine-loamy, kaolinitic, thermic, Typic Kandiudults) or a Cecil (fine, kaolinitic, thermic Typic Kanhapludults) soil and planted with alfalfa. After establishment, shoots were harvested four times at approximately five-week intervals and analyzed for dry matter and B. Following the last harvest, soil samples were taken and analyzed for Mehlich-1 extractable B. There was no effect of fertilizer material, application rate, or their interaction on the dry weight of alfalfa. Boron concentrations in alfalfa did not significantly decline with each successive cutting, indicating that a sufficient amount was applied for the duration of the study. In the first cutting, plants grown with Granubor and Ulexite had higher concentrations of B than those with Hydroboracite, which was in turn higher than Colemanite, reflecting differences in solubility. However, by the third and fourth cuttings, there were no significant differences in tissue B concentrations among the four fertilizer sources. This indicates that given adequate time, even less-soluble fertilizer sources may provide sufficient B to growing plants.}, number={4-5}, journal={JOURNAL OF PLANT NUTRITION}, author={Byers, DE and Mikkelsen, RL and Cox, FR}, year={2001}, pages={717–725} }
 @article{israel_mikkelsen_2001, title={Soybean as a receiver crop for nitrogen in swine lagoon effluent}, volume={166}, ISSN={["1538-9243"]}, DOI={10.1097/00010694-200107000-00003}, abstractNote={Soybean (Glycine max L. Merr.) has been approved by the Natural Resource Conservation Service as a receiver crop for N in swine lagoon effluent applied to spray fields. However, its efficacy as a N receiver crop depends on the sensitivity of symbiotic N2 fixation to inhibition by N in the applied effluent. The objectives of this study were to use a 15N natural abundance method to (i) assess the degree of inhibition of symbiotic N2 fixation in soybean by applied effluent N and (ii) determine the quantity of effluent N removed from the soil in harvested seed of nodulating soybean. Two field experiments were conducted to evaluate seed yield; seed N accumulation and whole shoot N accumulation of nodulating and nonnodulating soybean cultivars supplied a range of N levels as either lagoon effluent or ammonium nitrate. Measurement of 15N natural abundances indicated that, on average, 27% of the N in seed of nodulating cultivars supplied 200 kg of plant-available N (PAN)/ha as swine lagoon effluent was derived from symbiotic N2 fixation. While this effluent N rate did not inhibit N2 fixation completely, seed N recovery of 100 kg effluent N/ha (1997 trial) and 64 kg effluent N/ha (1998 trial) was not different between the nodulating and nonnodulating cultivars. Similar recovery of effluent N in nodulating and nonnodulating cultivars, even though inhibition of N2 fixation by the nodulating cultivar was incomplete, resulted from the nodulating cultivars having higher yields and harvest indices than the nonnodulating cultivar. Subtraction of seed N at maturity from whole shoot N at the R6.5 growth stage (between full seed stage and physiological maturity) was used to estimate crop N returned to the soil. This estimate indicated that nodulating and nonnodulating cultivars returned similar amounts of N to the soil. Our results show that nodulating soybeans can recover as much applied effluent N in seed as a 6.3 Mg/ha (100 bu/ac) corn crop.}, number={7}, journal={SOIL SCIENCE}, author={Israel, DW and Mikkelsen, RL}, year={2001}, month={Jul}, pages={453–464} }
 @inbook{mikkelsen_2000, title={Beneficial use of swine by-products: Opportunities for the future source}, DOI={10.2136/sssabookser6.c16}, abstractNote={The U.S. pork industry, like many other agricultural enterprises, is undergoing tremendous restructuring as production moves towards a greater degree of integration and specialization. Economic efficiencies related to the size of production facilities have led to a rapid centralization of the swine production industry that is still underway. For centuries, the productivity of crops and grasslands has relied upon nutrient inputs from organic materials and animal manures. Therefore the historic value of swine manure has been primarily as a source of nutrients for crop production. During the anaerobic decomposition of swine manure, natural microbial processes result in production of methane (biogas). There is considerable potential for energy production from farm manures as a result of anaerobic digestion when organic matter decomposition is managed for this purpose. One option for treatment of swine manure is compost production. Composting swine solids involves thermophilic processing and decomposition by aerobic microorganisms to produce a relatively stable organic material.}, booktitle={Land application of agricultural, industrial, and municipal by-products}, publisher={Madison, Wis.: Soil Science Society of America}, author={Mikkelsen, R. L.}, editor={J. F. Power and Dick, W. P.Editors}, year={2000}, pages={451–480} }
 @article{kraus_mikkelsen_warren_2000, title={Container substrate temperatures affect mineralization of composts}, volume={35}, number={1}, journal={HortScience}, author={Kraus, H. T. and Mikkelsen, R. L. and Warren, S. L.}, year={2000}, pages={16–18} }
 @inproceedings{hernandez_cobb_mikkelsen_2000, title={Nitrogen loss and transformations in croplands receiving applications of swine lagoon effluent}, number={2000}, booktitle={Animal, agriculture and food processing waste: 8th Symposium}, publisher={St. Joseph, Michigan: American Society of Agricultural Engineers}, author={Hernandez, J. A. and Cobb, C. R. and Mikkelsen, R. L.}, year={2000}, pages={588–596} }
 @article{mikkelsen_2000, title={Nutrient management for organic farming: A case study}, volume={29}, number={2000}, journal={Journal of Natural Resources and Life Sciences Education}, author={Mikkelsen, R. L.}, year={2000}, pages={88–92} }
 @article{crouse_sierzputowska-gracz_mikkelsen_2000, title={Optimization of sample pH and temperature for phosphorus-31 nuclear magnetic resonance spectroscopy of poultry manure extracts}, volume={31}, ISSN={["0010-3624"]}, DOI={10.1080/00103620009370432}, abstractNote={Abstract Organic phosphorus (P) compounds can be characterized using nuclear magnetic resonance (NMR) spectroscopy provided conditions are suitable for detecting the NMR signal. The objective of the research was to optimize pH and temperature conditions for turkey manure extracts prior to analysis of organic P compounds using NMR. Samples of turkey manure were extracted with 0.25 MNaOH + 0.05 MEDTA. The extracts were lyophilized and resolubilized in distilled H2O before analysis on a General Electric GN500 NMR spectrometer. Initial 31P NMR experiments were run to determine the optimal instrumental parameters for 31P studies. Samples were titrated to seventeen pH values ranging from 4.0 to 13.2. Samples adjusted to pH 10.0 had the greatest spectral resolution. A seven‐by‐three factorial experiment was used to investigate the effect of seven temperatures (5,10,20,30,40,50, and 60°C) on three separate samples at pH 6.5,9.0, or 10.0. Spectra resolution was greatest at pH 10.0 and 20°C.}, number={1-2}, journal={COMMUNICATIONS IN SOIL SCIENCE AND PLANT ANALYSIS}, author={Crouse, DA and Sierzputowska-Gracz, H and Mikkelsen, RL}, year={2000}, pages={229–240} }
 @article{jenkins_crouse_mikkelsen_heiniger_2000, title={Spatial variability of phosphorus retention capacities for various fields}, journal={Proceedings of the 5th International conference on precision agriculture, Bloomington, Minnesota, USA, 16-19 July, 2000}, publisher={Madison, WI : Precision Agriculture Center, University of Minnesota, ASA-CSSA-SSSA}, author={Jenkins, J. R. and Crouse, D. A. and Mikkelsen, R. L. and Heiniger, R. W.}, year={2000}, pages={1} }
 @inproceedings{robert_crouse_mikkelsen_heiniger_robarge_2000, title={Spatial variability of soil pH, phosphorus, copper and zinc in fields receiving long-term applications of animal manure}, number={2000}, booktitle={Animal, agriculture and food processing waste: 8th Symposium: American Society of Agriculture Engineers, 2000}, publisher={St. Joseph, Michigan: American Society of Agricultural Engineers}, author={Robert, B. and Crouse, D.A. and Mikkelsen, R.L. and Heiniger, R. and Robarge, W.}, year={2000}, pages={597–601} }
 @inproceedings{nelson_mikkelsen_hesterberg_2000, title={Struvite formation to remove phosphorus from anaerobic swine lagoon effluent}, number={2000}, booktitle={Animal, agriculture and food processing waste: 8th Symposium: American Society of Agriculture Engineers, 2000}, publisher={St. Joseph, Michigan: American Society of Agricultural Engineers}, author={Nelson, N. O. and Mikkelsen, R. L. and Hesterberg, D. L.}, year={2000}, pages={18–26} }
 @article{mcbride_mikkelsen_barker_2000, title={The role of low molecular weight organic acids from decomposing rye in inhibiting root-knot nematode populations in soil}, volume={15}, ISSN={["1873-0272"]}, DOI={10.1016/S0929-1393(00)00062-7}, abstractNote={Organic soil amendments have been employed as an alternative to or in combination with, chemical nematicides and cultural practices to control plant-parasitic nematodes. Rye (Secale cereale L.) has been shown to be effective in minimizing the damage caused by root-knot nematodes (Meloidogyne incognita (Kofoid and White) Chitwood) when grown as a cover crop and then incorporated into the soil prior to planting. It has been suggested that the release of low molecular weight organic acids during the decomposition of rye is the cause of the nematicidal effects. This study was conducted to quantify the concentration and persistence of formic, acetic, propionic, butyric, and valeric acids in soil solution following the incorporation of fresh rye foliage. Formic and acetic acids were detected by means of ion exclusion chromatography, primarily in the first 24 h following addition of rye, and at concentrations <450 μmol/l. The effect of the rye treatment on the root-knot nematode population was determined by growing tomato plants (Lycopersicon esculentum Mill.) in the rye-amended soil and assessing the nematode damage to the root systems. Despite the low concentrations of organic acids detected, the rye treatment resulted in a significant suppression of root-knot nematode activity. To determine the fate of these acids in soil, an addition of each acid was made to a field soil resulting in a soil water concentration of 1500 μmol/l for each acid. Soil solution samples were collected every 2 h for 10 h and analyzed for the five added organic acids by means of ion exclusion chromatography. The concentration of all acids declined by 54–97% over the 10 h incubation. Although low molecular weight organic acids may be one of many factors that contribute to restriction in root-knot nematode damage, these acids do not appear to be solely responsible for the nematicidal effect of the rye.}, number={3}, journal={APPLIED SOIL ECOLOGY}, author={McBride, RG and Mikkelsen, RL and Barker, KR}, year={2000}, month={Nov}, pages={243–251} }
 @article{mcbride_mikkelsen_barker_1999, title={A comparison of three methods for determining root-knot nematode infection of cotton roots}, volume={29}, number={2}, journal={Nematropica}, author={McBride, R. G. and Mikkelsen, R. L. and Barker, K. R.}, year={1999}, pages={147–151} }
 @article{pierce_warren_mikkelsen_linker_1999, title={Effects of soil calcium and pH on seed germination and subsequent growth of large crabgrass (Digitaria sanguinalis)}, volume={13}, ISSN={["0890-037X"]}, DOI={10.1017/s0890037x00041968}, abstractNote={Large crabgrass is a problem weed in horticultural crops, particularly in turfgrass in the southeastern United States. If growth of large crabgrass could be suppressed via soil pH or calcium levels, control of this weed in turfgrass might be improved while minimizing herbicide usage. To determine the effect of soil calcium and pH on germination and growth of large crabgrass, seeds were sown in a loamy sand soil amended with calcium carbonate (CaCO3) or magnesium carbonate (MgCO3) that established a range of soil pH from 4.8 to 7.8. Seeds were also sown in soil amended similarly with calcium sulfate (CaSO4), which does not affect pH, that established a range of exchangeable Ca levels corresponding to the Ca range in CaCO3from pH 4.8 to 7.8. Seed germination of large crabgrass was unaffected by pH when soil was amended with CaCO3, whereas seed germination decreased with increasing pH when soil was amended with MgCO3. Crabgrass germination was not affected by Ca (CaSO4) independent of pH changes. Increasing soil pH reduced shoot and root dry weights of seedlings regardless of material used to raise pH. Maximum shoot dry weights occurred at pH 4.8 in the unamended soil, whereas maximum root dry weights occurred at ranges from pH 5.8 to 6.3 for CaCO3and pH 5.3 to 5.8 for MgCO3. Shoot and root dry weights were not affected by Ca when soil was amended with CaSO4. By raising soil pH levels, the growth of large crabgrass and its ability to compete with turfgrass may be reduced. Raising exchangeable Ca does not appear to be an effective management tool for control of this weed species.}, number={2}, journal={WEED TECHNOLOGY}, author={Pierce, GL and Warren, SL and Mikkelsen, RL and Linker, HM}, year={1999}, pages={421–424} }
 @article{duffera_robarge_mikkelsen_1999, title={Estimating the availability of nutrients from processed swine lagoon solids through incubation studies}, volume={70}, ISSN={["0960-8524"]}, DOI={10.1016/S0960-8524(99)00039-5}, abstractNote={Potential environmental hazards from the excess accumulation of swine (Sus scrofa domesticus) manure in eastern North Carolina and new state guidelines on treatment alternatives have necessitated the reevaluation of best management practices for disposal of swine waste (manure and effluent) as a fertilizer source on local crop land. Creation of a value-added product is one viable means of utilizing and economically redistributing the nutrients in swine manure. Incubation studies using four agricultural soils from eastern North Carolina were conducted with pelletized processed swine lagoon solids (PSLS) (1.7% N, 2.5% P, 0.12% Cu and 0.18% Zn) composed of dewatered swine lagoon sludge plus rock flour. The PSLS was added at three application rates (0, 200, 400 mg N kg−1 soil) and incubated for 16 weeks at 25°C. The soil was sampled at 0, 1, 2, 4, 8, 12, and 16 weeks and analyzed for NO3–N, NH4–N and Mehlich III-extractable P, Zn, and Cu. High concentrations of NH4–N and low concentrations of NO3–N were present in the soils shortly after addition of PSLS. After the second week, extractable NH4–N dropped to <4 mg kg−1, while the soil concentration of NO3–N increased rapidly. The amount of NO3–N generated reached 90% of its final value after the fourth week. Across the four soils, 24–35% of the added N, 15–50% of the added P, 20–50% of the added Zn and 15–20% of the added Cu was extractable after 8 weeks. The PSLS is an excellent source of P, but may require additional N if used as a fertilizer source for most row crops.}, number={3}, journal={BIORESOURCE TECHNOLOGY}, author={Duffera, M and Robarge, WP and Mikkelsen, RL}, year={1999}, month={Dec}, pages={261–268} }
 @article{duffera_robarge_mikkelsen_1999, title={Greenhouse evaluation of processed swine lagoon solids as a fertilizer source}, volume={22}, ISSN={["0190-4167"]}, DOI={10.1080/01904169909365748}, abstractNote={Abstract The highly concentrated nature of the swine (Sus scrofa domesticus) production industry in the Coastal Plain region of North Carolina, along with economic constraints that discourage transport of the swine effluent more than a few kilometers from the site of production, result in frequent and repeated application of swine effluent to the same agricultural fields or pastures. Creation of value‐added products and marketing as a fertilizer is an alternative means of redistributing nutrients that are concentrated regionally. Fertilizer equivalency greenhouse studies were conducted to evaluate the potential for processed swine lagoon solids (PSLS) formulated from dewatered swine lagoon solids and rock flour to serve as a fertilizer source for agricultural crops. Sweet corn (Zea mays L.), sorghum (Sorghum bicolor L.), and field bean (Phaseolus vulgaris L.) were grown for six weeks, and common bermudagrass (Cynodon dactylon L. Pers.) was grown for 18 weeks on a Norfolk sandy loam (fine‐loamy, Kaolinitic...}, number={11}, journal={JOURNAL OF PLANT NUTRITION}, author={Duffera, M and Robarge, WP and Mikkelsen, RL}, year={1999}, pages={1701–1715} }
 @article{groundwater nitrate depletion in a swine lagoon effluent-irrigated pasture and adjacent riparian zone_1999, volume={54}, number={4}, journal={Journal of Soil & Water Conservation}, year={1999}, pages={651–656} }
 @inproceedings{gilliam_parsons_mikkelsen_1999, title={Nitrogen dynamics and buffer zones}, number={1999}, booktitle={Buffer zones: Their processes and potential in water protection: The proceedings of the International Conference on Buffer Zones}, author={Gilliam, J. W. and Parsons, J. E. and Mikkelsen, R. L.}, year={1999}, pages={54–61} }
 @article{mcbride_mikkelsen_barker_1999, title={Survival and infection of root-knot nematodes added to soil amended with rye at different stages of decomposition and cropped with cotton}, volume={13}, ISSN={["0929-1393"]}, DOI={10.1016/S0929-1393(99)00041-4}, abstractNote={Abstract The incorporation of a rye ( Secale cereale L.) cover crop into the soil prior to planting cotton ( Gossypium hirsutum L.) has been shown to restrict damage caused by root-knot nematodes ( Meloidogyne incognita (Kofoid and White) Chitwood). A greenhouse study was conducted to determine the duration of the effectiveness of rye decomposition in controlling root-knot nematode damage in relation to the time between rye incorporation and cotton planting. Fresh, chopped-rye foliage was mixed into pots of soil and root-knot nematode eggs were added to the rye + soil mixture or a non-amended soil at 0, 1, 3, 5, 7, 9, 11, 13, 15, 17, 19, and 21 days following rye incorporation. This resulted in a sequence of pots containing nematode eggs exposed to rye at different stages of decomposition. Cotton plants were transplanted into the pots after the addition of nematode eggs and assessed for damage after 28 days of exposure. Although the effectiveness of the rye treatment declined over the 21 days of the incubation, the root-knot nematode populations were significantly reduced by the rye treatment for all planting dates. This suggests that it is not necessary to plant cotton immediately after plowing in a rye cover crop, thereby providing some flexibility in the cotton planting date, minimizing any associated phytotoxicity to the young cotton plants.}, number={3}, journal={APPLIED SOIL ECOLOGY}, author={McBride, RG and Mikkelsen, RL and Barker, KR}, year={1999}, month={Dec}, pages={231–235} }
 @article{williams_grimes_mikkelsen_1999, title={The use of poultry litter as Co-substrate and source of inorganic nutrients and microorganisms for the ex situ biodegradation of petroleum compounds}, volume={78}, ISSN={["0032-5791"]}, DOI={10.1093/ps/78.7.956}, abstractNote={The purpose of this investigation was to determine the feasibility of utilizing poultry litter as a source of microorganisms, C co-substrate, N, and P to enhance the biodegradation of petroleum compounds in contaminated soil. An initial laboratory-scale study utilized soil contaminated with approximately 3,000 mg/kg (ppm) total petroleum hydrocarbons (TPHC) as diesel fuel. Biotreatment units, each containing 10 L of contaminated soil, were supplemented (0, 1, 10, and 20%, total weight basis) with broiler litter containing 3.65% N and 1.89% P. Petroleum-degrading microorganisms previously enriched from broiler and turkey litter were also inoculated into the litter-treated units. A significant first order rate of TPHC biodegradation was measured for all treatment units containing broiler litter (P < 0.05). Based on these results, a subsequent study was conducted at the site of a commercial facility permitted to treat soil (ex situ) contaminated with hazardous compounds. Soil treatment plots, each containing approximately 1 ton of soil contaminated with approximately 1,200 to 1,600 mg/kg diesel fuel were established. Each plot was replicated four times and the experiment was conducted for 35 d. Treatments were as follows: control, soil only; soil + commercial blend of bioremediation nutrients; soil + commercial fertilizer; soil + poultry litter (1% by volume); soil + poultry litter (10% by volume); soil + pelleted poultry litter (10% by volume). The results showed that the remediation of soil contaminated with petroleum compounds is significantly (P < 0.05) enhanced when supplemented with poultry litter (pelleted or nonpelleted) in concentrations of 10% soil volume. These results demonstrate the potential for a specialized market for the use of poultry litter.}, number={7}, journal={POULTRY SCIENCE}, author={Williams, CM and Grimes, JL and Mikkelsen, RL}, year={1999}, month={Jul}, pages={956–964} }
 @inproceedings{parsons_gilliam_mikkelsen_1998, title={Stream water level control to enhance riparian buffer effectiveness removing nitrate-nitrogen}, booktitle={Drainage in the 21st century: Food production and the environment: Proceedings of the seventh International Drainage Symposium}, publisher={St. Joseph, Michigan: American Society of Agricultural Engineers}, author={Parsons, J. E. and Gilliam, J. W. and Mikkelsen, R. L.}, year={1998}, pages={551–558} }
 @misc{mikkelsen_1997, title={Agricultural and environmental issues in the management of swine waste}, volume={668}, ISBN={["0-8412-3514-7"]}, ISSN={["0097-6156"]}, DOI={10.1021/bk-1997-0668.ch008}, abstractNote={The concentrated and regionalized nature of the U.S. swine industry results in large quantities of animal waste being produced in a relatively small area. Although animal wastes can be used for a variety of purposes (e.g. animal feed, biogas generation, and composting) their primary use has been as a source of plant nutrients for crop production. Since the concentration of essential plant nutrients is generally low in manures compared with inorganic fertilizers, there is often little incentive to recover the full agricultural value from these materials. Waste is commonly stored in pits or in lagoons prior to application, depending on the type of production system. Manure management practices may have significant impacts on surface water, groundwater, and atmospheric emissions. When swine manure is applied to crop land for extended periods of time, an accumulation of nutrients can occur in excess of the plants nutritional requirement.}, journal={AGRICULTURAL USES OF BY-PRODUCTS AND WASTES}, author={Mikkelsen, RL}, year={1997}, pages={110–119} }
 @article{mikkelsen_1997, title={Providing students with an international exposure to soil fertility}, volume={26}, number={1}, journal={Journal of Natural Resources and Life Sciences Education}, author={Mikkelsen, R. L.}, year={1997}, pages={69–70} }
 @article{mikkelsen_1995, title={USING HYDROPHILIC POLYMERS TO IMPROVE UPTAKE OF MANGANESE FERTILIZERS BY SOYBEANS}, volume={41}, ISSN={["0167-1731"]}, DOI={10.1007/BF00750749}, number={2}, journal={FERTILIZER RESEARCH}, author={MIKKELSEN, RL}, year={1995}, pages={87–92} }
 @article{mikkelsen_behel_williams_1993, title={ADDITION OF GEL-FORMING HYDROPHILIC POLYMERS TO NITROGEN-FERTILIZER SOLUTIONS}, volume={36}, ISSN={["0167-1731"]}, DOI={10.1007/BF00749948}, number={1}, journal={FERTILIZER RESEARCH}, author={MIKKELSEN, RL and BEHEL, AD and WILLIAMS, HM}, year={1993}, pages={55–61} }