@article{matthieu_bowman_thapa_cassel_rufty_2011, title={Turfgrass Root Response to Subsurface Soil Compaction}, volume={42}, ISSN={["1532-2416"]}, DOI={10.1080/00103624.2011.622826}, abstractNote={Soil compaction prevents turfgrass roots from growing deep into the soil and may limit access to water and nutrients. The objective of this study was to characterize the ability of turfgrass roots to penetrate a compacted subsurface layer. Seven turfgrasses were grown in soil columns. Each column was divided into three sections with the top and bottom packed to a bulk density of 1.6 g cm−3, and the middle (treatment) layer packed to 1.6, 1.7, 1.8, 1.9, or 2.0 g cm−3. Subsurface compaction reduced root mass for two of the species, and inhibited deep root growth in all seven species, with the greatest reduction occurring between 1.7 and 1.8 g cm−3. There appears to be little difference between species in ability to penetrate compacted soils, suggesting that soil preparation and routine management practices, rather than grass selection, is the more viable way to handle soil compaction problems in turf.}, number={22}, journal={COMMUNICATIONS IN SOIL SCIENCE AND PLANT ANALYSIS}, author={Matthieu, Donald E. and Bowman, Daniel C. and Thapa, Bir B. and Cassel, D. Keith and Rufty, Thomas W.}, year={2011}, pages={2813–2823} }
 @article{arya_bowman_thapa_cassel_2008, title={Scaling soil water characteristics of golf course and athletic field sands from particle-size distribution}, volume={72}, ISSN={["0361-5995"]}, DOI={10.2136/sssaj2006.0232}, abstractNote={The soil water characteristic (SWC) of sands is an important hydraulic parameter in designing golf courses and athletic fields. A modified version of the Arya–Paris model of the soil water characteristic was adapted to 14 golf course media that contained no to minor amounts of clay and silt. In this model, the particle‐size distribution curve is divided into a number of fractions and the natural pore length, Li(n), is scaled using the diameter of spherical particles as the length unit. The scaled pore length is given by 2Ri, where ni is the number of spherical particles in the ith fraction, 2Ri is the particle diameter, and αi is the scaling parameter, which is calculated using the relationship log= a + blogni Although the model adapted well, there were concerns about the sensitivity of predicted SWCs to uncertainties in parameters a and b Consequently, we developed and evaluated a procedure to predict Li(n) directly from straight pore lengths, Li(c) in counterpart cubic close‐packed assemblages of spherical particles, using the relationship logLi(n) = c + dlogLi(c) Predicted pressure heads using both procedures were similar with best‐fit parameters. When uncertainties were imposed on Parameters a, b and c, d, however, SWCs using the latter procedure showed far less sensitivity, as measured by the root mean square residuals (RMSRs). In addition, for sand materials grouped together on the basis of similarity in particle‐size distribution and bulk density, replacing individual best‐fit parameters by the group mean parameters did not have significant effects on predicted pressure heads.}, number={1}, journal={SOIL SCIENCE SOCIETY OF AMERICA JOURNAL}, author={Arya, Lalit A. and Bowman, Daniel C. and Thapa, Bir B. and Cassel, D. Keith}, year={2008}, pages={25–32} }
 @article{hong_white_weisz_gumpertz_duffera_cassel_2007, title={Groundwater nitrate spatial and temporal patterns and correlations: Influence of natural controls and nitrogen management}, volume={6}, ISSN={["1539-1663"]}, DOI={10.2136/vzj2006.0065}, abstractNote={To use shallow groundwater NO3–N concentration as an indicator of groundwater quality requires understanding its patterns, correlations, and controls across space and time. Within a study comparing variable‐rate and uniform N management, our objectives were to determine groundwater NO3–N patterns and correlations at various spatial and temporal scales and their association with natural controls and N management. Experiments in a random, complete block design were conducted in a 2‐yr crop rotation in North Carolina that included one variable‐rate and two uniform N management treatments to wheat (Triticum aestivumL.) and corn (Zea maysL.). We measured groundwater NO3–N and depth every 2 wk at 60 well nests, sampling the 0.9‐ to 3.7‐m depth. Field‐mean NO3–N varied with time from 5.5 to 15.3 mg NO3–N L−1These variations were correlated primarily with concurrent changes in water table elevation and depth. Mean NO3–N exhibited two preferred states: high when the water table was shallow and low when the water table was deep. Temporal NO3–N fluctuations greatly exceeded treatment effects. Treatments appeared to affect NO3–N temporal covariance structure. Groundwater NO3–N spatial patterns and correlations were associated mostly with saturated hydraulic conductivity and water table fluctuations and appeared influenced by subsurface lateral flow. When treatment effects became consistently significant later in the study, they overrode natural controls, and NO3–N was spatially uncorrelated or exhibited shorter spatial correlation ranges and patterns associated predominantly with treatments.}, number={1}, journal={VADOSE ZONE JOURNAL}, publisher={Soil Science Society of America}, author={Hong, Nan and White, Jeffrey G. and Weisz, Randy and Gumpertz, Marcia L. and Duffera, Miressa G. and Cassel, D. Keith}, year={2007}, month={Feb}, pages={53–66} }
 @article{grace_skaggs_cassel_2007, title={Influence of thinning loblolly pine (Pinus taeda L.) on hydraulic properties of an organic soil}, volume={50}, DOI={10.13031/2013.22640}, abstractNote={The impact of forest operations on soil properties has been a concern in forest management over the past 30 years. The objective of this study was to evaluate the impact of forest thinning operations on soil hydraulic properties of a shallow organic (Belhaven series) soil in the Tidewater region of North Carolina. Soil physical properties were evaluated in a nested design by collecting soil cores from an unthinned control and following a 40 ha fifth-row thinning with selection performed on a 14-year-old loblolly pine plantation in April 2001. Thinning decreased saturated hydraulic conductivity and drained volumes for a given water table depth; however, changes in bulk density were not detected. Saturated hydraulic conductivity determined by the constant head method before thinning was 100 cm h-1. Thinning resulted in a 3-fold decrease (from 100 to 32 cm h-1) in saturated hydraulic conductivity. The thinned watershed had less drainage at low pressures and greater retained water contents under increased soil water tensions in comparison with the control. Drained volume on the thinned watershed for a water table depth of 200 cm under drained to equilibrium conditions was reduced by 60% in comparison to drained volume for the control watershed. The reductions in ksat, drained volumes, and drainable porosity will likely result in shallower water tables and increased runoff for the thinned watershed.}, number={2}, journal={Transactions of the ASABE}, author={Grace, J. M. and Skaggs, R. W. and Cassel, D. K.}, year={2007}, pages={517–522} }
 @article{hong_white_weisz_crozier_gumpertz_cassel_2006, title={Remote Sensing-Informed Variable-Rate Nitrogen Management of Wheat and Corn}, volume={98}, ISSN={["1435-0645"]}, DOI={10.2134/agronj2005.0154}, abstractNote={In‐season, site‐specific, variable‐rate (SS) N management based on remote sensing (RS) may reduce N losses to groundwater while maintaining or increasing yield and N fertilizer‐use efficiency. We compared in‐season, RS‐informed N management applied on a uniform, field‐average (FA) or SS basis with the current uniform best management practice (BMP) based on “Realistic Yield Expectations” (RYE) in a typical 2‐yr southeastern U.S. coastal plain rotation: winter wheat (Triticum aestivum L.)–double‐crop soybean [Glycine max (L.) Merr.]–corn (Zea mays L.). Compared with the RYE‐based BMP, RS‐informed SS management achieved: (i) a maximum of 2.3 mg L−1 less groundwater NO3–N after 2001 wheat due to 39 kg ha−1 less fertilizer N and a 25% greater harvest N ratio (N in grain or forage/total N applied); (ii) 370 kg ha−1 more 2002 corn grain with 32 kg ha−1 greater N applied, similar harvest N ratio, and 37 kg ha−1 greater surplus N; (iii) 670 kg ha−1 more 2003 wheat grain associated with 14 kg ha−1 greater fertilizer N, 27% greater harvest N ratio, and 9 kg ha−1 less surplus N. Excepting one corn FA treatment that received excessive N, RS‐informed management produced equal or greater economic returns to N than RYE, and less surplus N for wheat. Treatments produced enduring effects on groundwater [NO3–N] consistent with agronomic results, but small relative to temporal [NO3–N] fluctuations that were positively correlated with water table elevation. To assess N management in leaching‐prone soils, frequent, periodic groundwater monitoring during and after the cropping season appears essential.}, number={2}, journal={Agronomy Journal}, publisher={American Society of Agronomy}, author={Hong, N. and White, J.G. and Weisz, R. and Crozier, C.R. and Gumpertz, M.L. and Cassel, D.K.}, year={2006}, pages={327–338} }
 @article{grace_skaggs_cassel_2006, title={Soil physical changes associated with forest harvesting operations on an organic soil}, volume={70}, ISSN={["1435-0661"]}, DOI={10.2136/sssaj2005.0154}, abstractNote={The influence of forest operations on forest soil and water continues to be an issue of concern in forest management. Research has focused on evaluating forest operation effects on numerous soil and water quality indicators. However, poorly drained forested watersheds with organic soil surface horizons have not been extensively investigated. A study was initiated in the Tidewater region of North Carolina to gain a better understanding of the impact of harvesting operations on poorly drained organic soils. Soils on the study site, having >80% organic matter (OM) content to a depth of 60 cm below the soil surface, were classified as shallow organic soils. Soil physical properties were examined by collecting soil cores from control and treatment watersheds in a nested design. Compaction caused by the harvest operation increased bulk density (Db) from 0.22 to 0.27 g cm−3, decreased saturated hydraulic conductivity (ksat) from 397 to 82 cm h−1, and decreased the drained volume for a given water table depth. However, Db following the harvest remained low at 0.27 g cm−3 The drained volume at equilibrium following the lowering of the water table from the soil surface to a depth of 200 cm was reduced by 10% from that of control watershed as a result of harvesting.}, number={2}, journal={SOIL SCIENCE SOCIETY OF AMERICA JOURNAL}, author={Grace, JM and Skaggs, RW and Cassel, DK}, year={2006}, pages={503–509} }
 @article{nelson_oh_cassel_2004, title={Changes in physical properties of coir dust substrates during crop production}, ISBN={["90-6605-537-5"]}, ISSN={["2406-6168"]}, DOI={10.17660/actahortic.2004.644.35}, number={644}, journal={PROCEEDINGS OF THE INTERNATIONAL SYMPOSIUM ON GROWING MEDIA & HYDROPONICS}, author={Nelson, PV and Oh, YM and Cassel, DK}, year={2004}, pages={261–268} }
 @article{bigelow_bowman_cassel_2004, title={Physical properties of three sand size classes amended with inorganic materials or sphagnum peat moss for putting green rootzones}, volume={44}, ISSN={["0011-183X"]}, DOI={10.2135/cropsci2004.0900}, abstractNote={Modern putting green rootzones are typically constructed using sands to avoid compaction and facilitate rapid drainage. Sands are often amended with organic matter (OM) such as sphagnum peat moss (SP) to increase moisture holding capacity. However, OM decomposition into finely divided material may negatively affect long-term soil physical properties. Inorganic amendments (IAs) having high water retention may be more suitable because of their resistance to biodegradation. A laboratory study determined the physical properties [bulk density, saturated hydraulic conductivity (Ksat), water retention, and pore size distribution] of three USDA sand size classes (fine, medium, and coarse) with and without amendment. Amendments used were calcined clay, vitrified clay, extruded diatomaceous earth, a processed zeolite, and SP. Amendments were tested at two incorporation rates (10 and 20% v/v), and in situ in 30-cm-deep rootzones at two incorporation depths (15 and 30 cm). Bulk density decreased, total porosity increased, and Ksat declined with amendment rate, but varied considerably depending on amendment, sand size, and incorporation depth. The Ksat was high for all mixtures, averaging 250 cm h−1, probably because of the very uniform sands. On the basis of standard pressure plate methods, IAs increased total water holding capacity (WHC) of all three sands but did not increase available water. However, a unique bioassay for available water indicated that porous IAs may contain appreciably more available water than measured by the pressure plate technique. Although the IAs significantly altered the physical properties of the three sands, they were not as effective as SP at improving water retention in coarse-textured, drought-prone sands.}, number={3}, journal={CROP SCIENCE}, author={Bigelow, CA and Bowman, DC and Cassel, DK}, year={2004}, pages={900–907} }
 @article{letey_sojka_upchurch_cassel_olson_payne_petrie_price_reginato_scott_et al._2003, title={Deficiencies in the soil quality concept and its application}, volume={58}, number={4}, journal={Journal of Soil & Water Conservation}, author={Letey, J. and Sojka, R. E. and Upchurch, D. R. and Cassel, D. K. and Olson, K. R. and Payne, W. A. and Petrie, S. E. and Price, G. H. and Reginato, R. J. and Scott, H. D. and et al.}, year={2003}, pages={180–187} }
 @article{lee_bowman_cassel_peacock_rufty_2003, title={Soil inorganic nitrogen under fertilized bermudagrass turf}, volume={43}, DOI={10.2135/cropsci2003.2470}, abstractNote={Managed turfgrass acreage in the southeastern USA is steadily increasing. There is public concern that fertilization of turfgrass systems, particularly additions of N on golf courses, might be adversely affecting groundwater quality due to nitrate leaching. This study was conducted to measure soil nitrate levels in situ under continuously managed bermudagrass (Cynodon spp.) and to evaluate influences from fertilization and mineralization. Two experimental sites were established on 50‐ and 75‐yr‐old golf course fairways in the Neuse and Cape Fear River basins in eastern North Carolina. Soil sampling was done seasonally. Results indicate that nitrate‐N levels were consistently low (1 to 4 mg kg−1 soil) and similar to adjacent natural areas throughout the 120‐cm sampling depths during the 2‐yr experiment at both sites. Levels were relatively uniform with depth and across several landscape positions. The soil nitrate levels under fertilized fairways were similar to those in adjacent nonfertilized natural areas, indicating minimal influence from turf management practices. From laboratory mineralization studies and soil temperature data, it was estimated that 60 to 154 kg N ha−1 would be released from organic N pools during the bermudagrass growing season (May to October). Because of similar temperature responses, it appeared that N release from mineralization would be synchronized with bermudagrass growth. Substantial bermudagrass growth in nonfertilized plots provided direct evidence that mineralization was a significant contributor to turf nutrition. There was no evidence that N fertilization or the ecology of the bermudagrass system posed inherent risks to water quality and the environment.}, number={1}, journal={Crop Science}, author={Lee, D. J. and Bowman, D. C. and Cassel, D. K. and Peacock, C. H. and Rufty, T. W.}, year={2003}, pages={247–257} }
 @article{cassel_afyuni_robarge_2002, title={Manganese distribution and patterns of soil wetting and depletion in a Piedmont hillslope}, volume={66}, DOI={10.2136/sssaj2002.9390}, abstractNote={The distribution of Mn in soils across the landscape is a function of mineralogy, topography, vegetation, and soil properties that control soil water movement and solute transport. We hypothesized (i) that current landscape properties and processes would explain the observed distribution of acid‐extractable soil Mn in a cropped hillslope in the Carolina Slate Belt of the southern Piedmont, and (ii) that the current spatial patterns of soil water movement would be related to the observed Mn distribution. Soil samples were collected in 10‐cm increments to the 1‐m depth at 5‐m intervals along 110‐m‐long Transect AB and at 10‐m intervals along 80‐m‐long Transect CD. The air‐dried samples were analyzed for acid‐extractable (1 M HCl) Mn. Soil water content (θ) along the transects was periodically monitored by neutron attenuation to the 120‐cm depth. Duplicate banks of tensiometers were installed at depths of 30, 45, and 60 cm at these locations. The concentration of acid‐extractable soil Mn was greatest in the footslope (FS), exceeding values >500 and 600 mg kg−1 soil for Transects AB and CD, respectively. For a wet period in July 1989, θ along Transect AB varied from 0.40 m3 m−3 for the FS to 0.50 m3 m−3 at the summit and was significantly correlated with clay content. Increases in water content of a dry soil after rainfall of 80 mm in July 1989 were similar at all landscape positions, but further increases following additional rainfall were less for the FS, indicating that soil at the FS was already near saturation. The slightly coarser‐textured FS consistently had the lowest water contents. Tensiometric and lateral Br transport data for this site, coupled with the water content measurements, indicate that subsurface flow of water and dissolved Mn from higher to lower elevations on the hillslopes is occurring.}, number={3}, journal={Soil Science Society of America Journal}, author={Cassel, D. K. and Afyuni, M. M. and Robarge, W. P.}, year={2002}, pages={939–947} }
 @article{thapa_cassel_garrity_2001, title={Animal powered tillage translocated soil affects nutrient dynamics and soil properties at Claveria, Philippines}, volume={56}, number={1}, journal={Journal of Soil & Water Conservation}, author={Thapa, B. B. and Cassel, D. K. and Garrity, D. P.}, year={2001}, pages={14–21} }
 @article{bigelow_bowman_cassel_rufty_2001, title={Creeping bentgrass response to inorganic soil amendments and mechanically induced subsurface drainage and aeration}, volume={41}, ISSN={["0011-183X"]}, DOI={10.2135/cropsci2001.413797x}, abstractNote={Creeping bentgrass (Agrostis stolonifera var. palustris Huds. Farw.) golf greens often decline under the hot, humid summer conditions of the southeastern USA. Factors associated with this decline may be poor soil aeration, excessive soil wetness, high temperatures, and turfgrass diseases. A field study evaluated a mechanical forced air system for its ability to modify the soil water content and oxygen (O2) status of newly constructed sand‐based rootzones, and its effects on turfgrass quality (TQ) and seasonal bentgrass rooting. Three drainage situations were studied: gravity drainage (control treatment) and gravity drainage supplemented by two mechanically induced drainage treatments, water evacuation (WE) or WE followed by air‐injection (AI). In addition, the effects of peat moss and several inorganic soil amendments on bentgrass establishment and growth were studied. Compared with gravity drainage, WE significantly decreased water contents (0.01–0.05 m3 m−3) averaged across the 0‐ to 27‐cm depth, with the greatest change occurring near the bottom of the rooting media. Seasonal fluctuations in soil O2 and CO2 concentrations were observed, but O2 remained high, 0.19 m3 m−3, and CO2 was low, <0.01 m3 m−3, regardless of drainage treatment. Drainage treatments had no effect on TQ or root mass density (RMD). However, both TQ and RMD increased from 1998 to 1999, possibly becaue of greater turfgrass density. Amendments had significant effects on establishment and TQ in the following order: peat moss > Ecolite = Profile > Greenschoice ≥ unamended sand. This response was probably due to improved water and nutrient retention of the amended rootzones. Although the forced air–vacuum technology provided little benefit in these newly constructed greens, it may be useful on mature putting greens that suffer from poor soil aeration or drainage.}, number={3}, journal={CROP SCIENCE}, author={Bigelow, CA and Bowman, DC and Cassel, DK and Rufty, TW}, year={2001}, pages={797–805} }
 @article{strock_cassel_2001, title={Developing and testing a system for studying unsaturated solute transport on undisturbed soil blocks}, volume={56}, number={2}, journal={Journal of Soil & Water Conservation}, author={Strock, J. S. and Cassel, D. K.}, year={2001}, pages={112–119} }
 @article{hartwiger_peacock_dipaola_cassel_2001, title={Impact of light-weight rolling on putting green performance}, volume={41}, ISSN={["0011-183X"]}, DOI={10.2135/cropsci2001.4141179x}, abstractNote={The introduction of light‐weight rollers has contributed to the reconsideration of the practice of rolling golf putting greens. Studies were conducted in 1993 and 1994 to determine the effects of rolling on soil bulk density, putting green speed, turf quality, root mass, and thatch mass. Experimental ‘Penncross’ creeping bentgrass (Agrostis stolonifera L.) putting greens built on a United States Golf Association (USGA) specification root zone and on a Cecil gravelly sandy loam (Typic Hapludult clayey, kaolinitic, thermic) (native soil) root zone were mowed daily and subjected to four rates of rolling (0, 1, 4, or 7 times per week) with a light‐weight roller for a 10‐wk period. Soil bulk density did not change for any rolling frequency on the USGA green. Rolling rates of four and seven times per week increased bulk density on the native soil green by 4 and 3% in the first year while no changes were detected in the second year. Turf quality was diminished for rolling rates of four and seven times per week. Ball roll increased as the rate of rolling increased. Rolling rate did not alter root mass. Thatch levels were not affected by rolling frequency on the USGA green. On the native soil green, four and seven rolling treatments per week resulted in thatch levels 12 and 11% higher than the control. Rolling once per week appears to offer increased green speed without any deleterious turf effects.}, number={4}, journal={CROP SCIENCE}, author={Hartwiger, CE and Peacock, CH and DiPaola, JM and Cassel, DK}, year={2001}, pages={1179–1184} }
 @article{bigelow_bowman_cassel_2001, title={Nitrogen leaching in sand-based rootzones amended with inorganic soil amendments and sphagnum peat}, volume={126}, number={1}, journal={Journal of the American Society for Horticultural Science}, author={Bigelow, C. A. and Bowman, D. C. and Cassel, D. K.}, year={2001}, pages={151–156} }
 @article{strock_cassel_gumpertz_2001, title={Spatial variability of water and bromide transport through variably saturated soil blocks}, volume={65}, ISSN={["1435-0661"]}, DOI={10.2136/sssaj2001.1607}, abstractNote={Water and solute transport pathways through soil are very complex. Soil properties affecting solute transport vary spatially and temporally within a soil profile and across landscape positions. The objective of this laboratory study was to evaluate water and bromide (Br) transport through 38‐ by 38‐ by 60‐cm‐deep undisturbed blocks of Cecil soil (Clayey, kaolinitic, thermic Typic Kanhapludults) collected from three contrasting landscape positions (interfluve, linear slope, and foot slope) in the Piedmont region of North Carolina. Two replicate soil blocks from each position were placed on a grid lysimeter‐plate effluent collection system which facilitated collection of the effluent from 81 discrete cells under −2.5 kPa pressure. Each block was equilibrated for 5 d with a once daily application of 3.5 L of 0.005 M CaSO4 solution by a water drop applicator at a rate of 14 mm h−1 Four‐hundred mL of KBr solution (4000 g Br m−2) was uniformly sprayed onto the soil surface. Thereafter, 3.5 L of 0.005 M CaSO4 solution was applied daily for the duration of each experiment (19–33 d). Effluent volume and Br concentration in the effluent were measured daily for each of the 81 4 by 4‐cm cells. Cumulative water outflow and Br distribution plots, spatial distribution of cumulative effluent percent, frequency plots, and Br breakthrough curves (BTCs) showed that differences in preferential flow of water and Br occurred for soil blocks from different landscape positions. Differences in preferential flow of water and Br were attributed to soil horizon thickness, soil texture and structure, macroporosity, and slope gradient. Preferential flow of water and Br under variably saturated conditions was found to be highly variable within a given soil profile and that differences in the distribution and magnitude of preferential flow occurred across topographic positions.}, number={6}, journal={SOIL SCIENCE SOCIETY OF AMERICA JOURNAL}, author={Strock, JS and Cassel, DK and Gumpertz, ML}, year={2001}, pages={1607–1617} }
 @article{bigelow_bowman_cassel_2001, title={Water retention of sand-based putting green mixtures as affected by the presence of gravel sub-layers}, volume={9}, journal={International Turfgrass Society Research Journal}, author={Bigelow, C. A. and Bowman, D. C. and Cassel, D. K.}, year={2001}, pages={479} }
 @article{cassel_wendroth_nielsen_2000, title={Assessing spatial variability in an agricultural experiment station field: Opportunities arising from spatial dependence}, volume={92}, ISSN={["1435-0645"]}, DOI={10.2134/agronj2000.924706x}, abstractNote={Spatio‐temporal field soil and crop processes are important for site‐specific farming. The objectives of this study were to spatially evaluate selected soil physical and chemical properties and their relationship to wheat (Triticum aestivum L.) yield, and to discuss stochastic approaches to help identify processes underlying yield variability in heterogeneous field sites. Modified grid sampling included 330 sites including a primary transect. Soil properties measured for the Ap, E if present, and upper B horizons at each site included pH, P, Zn, Cu, exchangeable cations, percentage base saturation, cation exchange capacity, bulk density, soil water contents at −10, −33, and −1500 kPa, texture, and humic matter content. Wheat grain and straw were hand‐harvested on 1‐ by 2‐m plots centered on each site. Soil water content on the primary transect was determined by neutron attenuation on nine dates. Field and primary transect means and semivariograms for a given soil or plant parameter were similar. The range of spatial dependence or autocorrelation of soil parameters ranged from 10 m for Ap horizon depth to 100 m for −1500 kPa water content of the Ap. Base saturation and available water storage capacity were cross‐correlated with grain yield to a distance of ±15 and 12.5 m, respectively. State‐space analysis was used to develop a grain yield model using these two variables. Spearman rank correlation of the soil water content data suggests that the temporal stability of soil water storage is less for shallow than for deeper soil layers.}, number={4}, journal={AGRONOMY JOURNAL}, author={Cassel, DK and Wendroth, O and Nielsen, DR}, year={2000}, pages={706–714} }
 @article{thapa_garrity_cassel_mercado_2000, title={Contour grass strips and tillage affect corn production on Philippine steepland oxisols}, volume={92}, ISSN={["1435-0645"]}, DOI={10.1007/s100870050012}, number={1}, journal={AGRONOMY JOURNAL}, author={Thapa, BB and Garrity, DP and Cassel, DK and Mercado, AR}, year={2000}, pages={98–105} }
 @article{thapa_cassel_garrity_1999, title={Assessment of tillage erosion rates on steepland Oxisols in the humid tropics using granite rocks}, volume={51}, ISSN={["1879-3444"]}, DOI={10.1016/s0167-1987(99)00040-9}, abstractNote={Soil translocation by tillage may be an important factor in land degradation in the humid tropics. The objective of this study was to evaluate tillage-induced soil translocation on an Oxisol with 25% and 36% slopes in Claveria, Philippines for three tillage systems: contour moldboard plowing (CMP), moldboard plowing up and downslope (UMP), and contour ridge tillage (CRT). Small rocks 3–4 cm in “diameter” were used as soil movement detection units (SMDU). The SMDUs were placed at 10 cm intervals in a narrow 5-cm-deep trench near the upper boundary of each plot, the position of each rock recorded, and the trench backfilled. Five tillage operations used to produce one corn crop were performed during a one month period: two moldboard plowing operations for land preparation (except for CRT), one moldboard plowing for corn planting, and two inter-culture (inter-row cultivation) operations. After these operations, over 95% of the SMDU were recovered manually and their exact locations recorded. Mean annual soil flux for the 25% slope was 365 and 306 kg m−1 y−1 for UMP and CMP, respectively. For the 36% slope, comparable values were 481 and 478 kg m−1 y−1. Estimated tillage erosion rates for the 25% slope were 456 and 382 Mg ha−1 y−1 for UMP and CMP, respectively, and increased to 601 and 598 Mg ha−1 y−1, respectively, for the 36% slope. The mean displacement distance, mean annual soil flux, and mean annual tillage-induced soil loss for both slopes were reduced by approximately 70% using CRT compared to CMP and UMP.}, number={3-4}, journal={SOIL & TILLAGE RESEARCH}, author={Thapa, BB and Cassel, DK and Garrity, DP}, year={1999}, month={Aug}, pages={233–243} }
 @article{olson_cassel_1999, title={Bromide leaching on a Piedmont toposequence}, volume={63}, ISSN={["0361-5995"]}, DOI={10.2136/sssaj1999.6351319x}, abstractNote={Solute leaching on the field‐scale is a poorly understood, complex process affected by local soil variation and landscape position. We hypothesized that Br ion leaching is a function of landscape position in a well‐structured, clayey soil on a Piedmont toposequence that had been in pasture for the previous 30 yr. Dry KBr, mixed with sand at a ratio of 12 g sand to 1 g KBr, was surface‐applied at a rate of 314 kg Br ha−1 on 24 May 1994 along two transects and allowed to move into the soil under natural rainfall conditions. Soil cores 0.90‐ and 2.00‐m‐long were taken 13 June and 20 Dec. 1994, respectively (corresponding to 20 and 210 d after Br application and 15 and 63 cm rain, respectively). The cores were subdivided into increments 10 or 15 cm, oven dried, and analyzed for Br. Centers of Br mass at both sampling times were significantly deeper in the footslope position (31 and 82 cm for June and December, respectively) compared with the shoulder and linear slope positions combined (25 and 70 cm for June and December, respectively), which was possibly due to lower clay contents (44 vs. 50% clay) and lower water retention (37 vs. 43 cm in the top meter in December) for the footslope vs. the linear and shoulder slopes combined, respectively. Predicted leaching depths were calculated from measured soil water content profiles and were positively correlated with observed depths to the center of Br mass for the Dec. 20 sampling (r2 = 0.35, P < 0.007). Anion leaching may be partially controlled by landscape position, and soils susceptible to initial rapid leaching may not necessarily be susceptible to sustained rapid leaching throughout the year.}, number={5}, journal={SOIL SCIENCE SOCIETY OF AMERICA JOURNAL}, author={Olson, GL and Cassel, DK}, year={1999}, pages={1319–1326} }
 @article{thapa_cassel_garrity_1999, title={Ridge tillage and contour natural grass barrier strips reduce tillage erosion}, volume={51}, DOI={10.1016/s0167-1987(99)00047-1}, abstractNote={Large amounts of soil are eroded annually from tilled, hilly upland soils in the humid tropics. Awareness has been increasing that much of this erosion may be due to tillage operations rather than water-induced soil movement. This field study estimated soil translocation and tillage erosion for four tillage systems on Oxisols with slope gradients of 16–22% at Claveria, Misamis Oriental, Philippines. Soil movement was estimated using `soil movement tracers' (SMT) which consisted of painted 12-mm hexagonal steel nuts. The SMT were buried in three replicate plots of the following tillage treatments: (1) contour moldboard plowing in the open field (MP-open); (2) contour ridge tillage in the open field (RT-open); (3) contour moldboard plowing plus contour natural grass barrier strips (MP-strip); and (4) contour natural grass barrier strips plus ridge tillage (RT-strip). Two hundred SMT were placed at the 5-cm depth at 5-cm spacings on 10 rows and 20 columns in two microplots within each plot. The microplots were oriented with the boundaries running downslope and along the contour of each 8-m-wide × 38-m-long (downslope) tillage plot. After tilling the land for four successive corn (Zea mays L.) crops (20 tillage operations), the SMT were manually excavated and their positions recorded. Recovery of SMT ranged from 82% to 85%. Displacement of SMT was directly related to slope length, percent slope, and tillage method. Mean displacement distance of SMT during the four corn growing seasons was 3.3 m for MP-open, 1.8 m for RT-open, 1.5 m for the RT-strip, and 2.2 m for MP-strip. Based on tillage operations associated with two corn crops per year, mean annual soil flux was estimated to be 241, 131, 158 and 112 kg m−1 for MP-open, RT-open MP-strip, and RT-strip, respectively. Compared to the mean annual soil loss for MP-open of 63 Mg ha−1, soil loss was reduced by 30%, 45%, and 53% for the MP-strip, RT-open, and RT-strip systems, respectively. Both ridge tillage and natural grass barrier strips reduced soil displacement, soil translocation flux, and tillage erosion rates.}, number={3-4}, journal={Soil & Tillage Research}, author={Thapa, B. B. and Cassel, D. K. and Garrity, D. P.}, year={1999}, pages={341–356} }
 @article{bigelow_cassel_bowman_1999, title={Soil amendments: reduce nitrate leaching}, volume={8}, number={9}, journal={Turf Grass Trends}, author={Bigelow, C. A. and Cassel, D. K. and Bowman, D. C.}, year={1999}, pages={11} }
 @article{agus_garrity_cassel_1999, title={Soil fertility in contour hedgerow systems on sloping oxisols in Mindanao, Philippines}, volume={50}, ISSN={["1879-3444"]}, DOI={10.1016/S0167-1987(99)00005-7}, abstractNote={Although contour hedgerows are widely advocated to sustain food crop production in cereal-based farming systems in the tropics, little is known about the nutrient dynamics of these systems or the spatial gradients in soil fertility that may develop in the terraces that evolve behind the vegetative barriers. We studied the effects on soil chemical properties of four contour hedgerow systems: double rows of a tree legume Gliricidia sepium (Jacq.) (G); a row of G. sepium and a row of a native pasture grass Paspalum conjugatum (GPas); a row of G. sepium and a row of a productive fodder grass Penisetum purpureum (napier grass) (GPen); and a double row of P. purpureum (Pen). An open-field control (C) without hedgerows was included. The research was conducted in Mindanao, the Philippines on two Oxisols (Ferralsols) with slopes ranging from 20% to 30%; average alley width was 4.7 m and the average hedgerow width was 0.8 m. The prunings of Gliricidia were mulched on the alley (food-crop planting) area, the clippings of Penisetum were removed from the plots, and no pruning was done for Paspalum. Crop residues were distributed uniformly on the alley area as mulch. Each of the two crops in the rotation, rice (Oryza sativa L.) and corn (Zea mays L.), received 20 kg ha−1 each of P and K and 60 kg ha−1 of N. After 4 years of experimentation exchangeable Mg was about 40% lower in the Pen treatment compared to that in the C treatment. There was a tendency for the Pen treatment to have the lowest exchangeable K, Ca, and Mg and Bray-2 extractable P. Exchangeable Ca and Bray-2 P increased while exchangeable Al decreased linearly with a decrease in soil elevation in the alleyways in the hedgerow treatments, although these gradients were not always significant at the p = 0.05 level. Exchangeable K decreased linearly with the decrease in the soil elevation in the Pen treatment (p = 0.12). The use of Penisetum grass as hedgerow crop and at the same time for supplying fodder, mined the soil nutrients indicating that the system is unsustainable unless accompanied by fertilization or manuring.}, number={2}, journal={SOIL & TILLAGE RESEARCH}, author={Agus, F and Garrity, DP and Cassel, DK}, year={1999}, month={Mar}, pages={159–167} }
 @article{horowitz_cassel_lopez_1999, title={Soil physical and chemical properties under continuous maize and a maize-mucuna rotation on hillsides in Honduras}, volume={76}, number={3}, journal={Tropical Agriculture}, author={Horowitz, A. J. and Cassel, D. K. and Lopez, M. J.}, year={1999}, pages={164–170} }
 @article{jipp_nepstad_cassel_de carvalho_1998, title={Deep soil moisture storage and transpiration in forests and pastures of seasonally-dry amazonia}, volume={39}, ISSN={["1573-1480"]}, DOI={10.1023/A:1005308930871}, number={2-3}, journal={CLIMATIC CHANGE}, author={Jipp, PH and Nepstad, DC and Cassel, DK and De Carvalho, CR}, year={1998}, month={Jul}, pages={395–412} }
 @article{agus_cassel_garrity_1998, title={Division S-7 - Forest & range soils - Bromide transport under contour hedgerow systems in sloping oxisols}, volume={62}, ISSN={["1435-0661"]}, DOI={10.2136/sssaj1998.03615995006200040027x}, abstractNote={Abstract}, number={4}, journal={SOIL SCIENCE SOCIETY OF AMERICA JOURNAL}, author={Agus, F and Cassel, DK and Garrity, DP}, year={1998}, pages={1042–1048} }
 @article{przepiora_hesterberg_parsons_gilliam_cassel_faircloth_1998, title={Field evaluation of calcium sulfate as a chemical flocculant for sedimentation basins}, volume={27}, ISSN={["0047-2425"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0032076630&partnerID=MN8TOARS}, DOI={10.2134/jeq1998.00472425002700030026x}, abstractNote={Abstract}, number={3}, journal={JOURNAL OF ENVIRONMENTAL QUALITY}, author={Przepiora, A and Hesterberg, D and Parsons, JE and Gilliam, JW and Cassel, DK and Faircloth, W}, year={1998}, pages={669–678} }
 @article{stolf_cassel_king_reichardt_1998, title={Measuring mechanical impedance in clayey gravelly soils}, volume={22}, DOI={10.1590/s0100-06831998000200003}, abstractNote={Mechanical impedance of clayey and gravelly soils is often needed to interpret experimental results from tillage and other field experiments. Its measurement is difficult with manual and hydraulic penetrometers, which often bend or break in such soils. The purpose of this study was to evaluate the feasibility of a hand-operated "Stolf" impact penetrometer to measure mechanical impedance (soil resistance). The research was conducted in Raleigh, North Carolina, USA (35º 45'N, 78º 42'W, elevation 75 m). Corn was planted on April 19, 1991. Penetrometer measurements were taken on May 10, 1991, in 5 cm intervals to 60 cm at 33 locations on a transect perpendicular to the corn rows in each of four tillage treatments. The data permitted three-dimensional displays showing how mechanical impedance changed with depth and distance along the transect. The impact penetrometer proved to be a useful tool to collect quantitative mechanical impedance data on "hard" clayey and/or gravelly soils which previously were difficult to reliably quantify.}, number={1998}, journal={Revista Brasileira De Ciencia Do Solo}, author={Stolf, R. and Cassel, D. K. and King, L. D. and Reichardt, K.}, year={1998}, pages={189–196} }
 @article{keller_weber_cassel_wollum_miller_1998, title={Temporal distribution of C-14 in soil water from field lysimeters treated with C-14-metolachlor}, volume={163}, ISSN={["1538-9243"]}, DOI={10.1097/00010694-199811000-00004}, abstractNote={In a previous study utilizing fallow field lysimeters of an undisturbed, loamy sand soil treated with 14 C-metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl) acetamide], 2 to 5% of the applied 14 C was mobile to soil depths of 56 to 96 cm. The objective of this 120-day study was to determine the temporal distribution of 14 C-metolachlor and/or metabolite(s) in soil water from similar field lysimeters and their possible contribution to groundwater contamination. Undisturbed soil column field lysimeters (20.3-cm i.d. × 101-cm long; 16 gauge steel) were driven into a conventionally tilled Dothan loamy sand (fine-loamy, siliceous, thermic Plinthic Kandiudult) and treated with 14 C-metolachlor and tritiated water ( 3 H 2 O) and subjected to natural rainfall or irrigation. Percent recovery of metolachlor and/or metabolite(s) in the soil, as based on 14 C measurement, was 62% at 30 days, 63% at 60 days, 51% at 90 days, and 49% at 120 days. Recovery of 3 H 2 O was 36, 24, 6 and 0.25% of the applied for the same time periods. By 30 and 60 days after application (DAA), 3 H 2 O had distributed symmetrically in the soil profile, whereas, a large percentage of the 14 C was retained in the upper 24 cm. No 14 C and <1% of the applied 3 H 2 O was recovered in leachate the first 30 days. Cumulative recovery of 14 C in leachate was <1% of that applied at 60 days, 3% at 90 days, and 7% at 120 days. Cumulative recovery of 3 H 2 O in leachate for the same time periods was 22, 39, and 39% of that applied. The symmetrical breakthrough curve for 3 H 2 O indicated no preferential flow or immobile water, whereas the breakthrough curve for 14 C was asymmetrical as a result of the sorption-desorption processes. Peak concentrations of 14 C and 3 H 2 O in the leachate occurred at 94 and 63 DAA, respectively. The sorptive tendencies of both radiolabeled species distinguished the magnitude of movement, with 3 H 2 O much more mobile than 14 C-metolachlor and/or metabolite(s). Assuming that all 14 C in leachate was parent, average metolachlor concentrations in leachate were less than the National Health Advisory level, which may indicate that metolachlor should be considered a low risk chemical because of its potential to contaminate groundwater in soils with low organic matter and high clay content in the subsoil.}, number={11}, journal={SOIL SCIENCE}, author={Keller, KE and Weber, JB and Cassel, DK and Wollum, AG and Miller, CT}, year={1998}, month={Nov}, pages={872–882} }
 @article{przepiora_hesterberg_parsons_gilliam_cassel_faircloth_1997, title={Calcium sulfate as a flocculant to reduce sedimentation basin water turbidity}, volume={26}, ISSN={["0047-2425"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0031278959&partnerID=MN8TOARS}, DOI={10.2134/jeq1997.00472425002600060021x}, abstractNote={Abstract}, number={6}, journal={JOURNAL OF ENVIRONMENTAL QUALITY}, author={Przepiora, A and Hesterberg, D and Parsons, JE and Gilliam, JW and Cassel, DK and Faircloth, W}, year={1997}, pages={1605–1611} }
 @article{agus_cassel_garrity_1997, title={Soil-water and soil physical properties under contour hedgerow systems on sloping oxisols}, volume={40}, ISSN={["1879-3444"]}, DOI={10.1016/S0167-1987(96)01069-0}, abstractNote={Hedgerows planted along the contour on steep lands in the humid tropics reduce soil erosion and build terraces over time. The objectives of this study in two Hapludoxes in the Philippines were to evaluate changes after 4 years in soil properties and soil water relations on transects perpendicular to the cropped alleys between four grass and tree hedgerow systems and a control. Hedgerow plants included Gliricidia sepium, Paspalum conjugatum, and Penisetum purpureum. Soil properties evaluated as a function of position in the alley (upper, middle, or lower elevation in an alley) included bulk density, mechanical impedance, soil water transmissivity, water retention, soil water pressure, and soil water content. In general, soil properties were not affected by hedgerow system, but were affected by position in the alley. Nearness to the hedgerow, but not hedgerow species, affected soil water distribution (P = 0.05). Plant available water at the 10–15 cm depth was 0.16 m3 m−3, 0.13 m3 m−3, and 0.08 m3 m−3 for the lower, middle, and upper alley position, respectively. Water transmissivity decreased from 0.49 mm s−1 in the lower alley to 0.12 mm s−1 in the upper alley. The lower soil water contents and soil water pressures in and near the hedgerows confirmed competition for water between the hedgerow species and the food crop in the alley, a condition that is expected to suppress food crop production.}, number={3-4}, journal={SOIL & TILLAGE RESEARCH}, author={Agus, F and Cassel, DK and Garrity, DP}, year={1997}, month={Jan}, pages={185–199} }
 @article{cassel_wagger_1996, title={Residue management for irrigated maize grain and silage production}, volume={39}, ISSN={["0167-1987"]}, DOI={10.1016/S0167-1987(96)01037-9}, abstractNote={Certain farming systems limit the opportunity to leave crop residue on the soil surface which could conserve soil and water. The objectives of this study were to determine the effects of residue management, tillage, and irrigation regime on maize (Zea Mays L.) grain and silage yields and selected soil properties. The soil type was a Hiwassee clay loam (Rhodic Kanhapludults) and is representative of soils in the southern Piedmont region (USA). Two tillage treatments (no-tillage (NT) and conventional chisel plow/disk (CT)), in factorial combination with three sprinkler irrigation levels (none, full, and limited), were evaluated in 1988 and 1989. Each tillage/irrigation treatment was split to simulate maize stover removal (silage system) or maize stover left in place (grain system). Grain and silage yields for the 2 year period averaged 13% and 17% greater, respectively, for NT compared with CT. Residue removal decreased silage yield in 1989 from 18.9 to 17.5 Mg ha−1. Total and irrigation water use efficiencies were slightly greater in NT plots when residue remained on the soil surface. In general, both sorptivity and cumulative infiltration were greater for CT compared with NT. These same parameters were at least 200% greater in the non-trafficked interrow compared with the trafficked interrow position. Residual nitrate concentrations in the soil profile were less under NT compared with CT, reflecting the higher maize yields because of improved water availability under NT. While only small differences in yields and water use efficiencies were affected by residue management, the differences likely will increase with time under these management systems.}, number={1-2}, journal={SOIL & TILLAGE RESEARCH}, author={Cassel, DK and Wagger, MG}, year={1996}, month={Nov}, pages={101–114} }
 @article{cassel_kachanoski_topp_1994, title={PRACTICAL CONSIDERATIONS FOR USING A TDR CABLE TESTER}, volume={7}, ISSN={["0933-3630"]}, DOI={10.1016/0933-3630(94)90013-2}, abstractNote={Time domain reflectometry (TDR) technology can be used to measure soil water content, but due to an incomplete understanding of this technology, some scientists are still reluctant to adopt it. The objectives of this paper are to discuss the basic principles of TDR to measure soil water content, to present the equations to convert TDR screen readings to soil water content values, and to describe a custom built TDR system. Commercial cable testers operate under the assumption the dielectric constant of the medium is known. For soils applications the dielectric constant varies with soil water content and is unknown. The equations which govern the TDR technology presented in logical order allow the user to understand the relationships between wave velocity, dielectric constant, and soil water content. The custom-built TDR system described here uses a commercially available cable tester; a balun transformer; shielded, two-wire transmission cable; and wave guides constructed from stainless steel welding rod. Several of these systems have been successfully used for six years.}, number={2}, journal={SOIL TECHNOLOGY}, author={CASSEL, DK and KACHANOSKI, RG and TOPP, GC}, year={1994}, month={Jun}, pages={113–126} }
 @article{cassel_elrick_1992, title={Using the software package 'MathCAD' as a tool to teach soil physics}, volume={21}, number={1}, journal={Journal of Natural Resources and Life Sciences Education}, author={Cassel, D. K. and Elrick, D. E.}, year={1992}, pages={74} }
 @article{cassel_nelson_1985, title={SPATIAL AND TEMPORAL VARIABILITY OF SOIL PHYSICAL-PROPERTIES OF NORFOLK LOAMY SAND AS AFFECTED BY TILLAGE}, volume={5}, ISSN={["1879-3444"]}, DOI={10.1016/S0167-1987(85)80013-1}, abstractNote={Physical properties of field soil vary both spatially and temporally. Because so little information is available concerning the changes in magnitude of soil physical properties as functions of soil depth, distance normal to a crop row, and time, they have largely been ignored in model development. The purpose of this study was to evaluate quantitatively the spatial and temporal variability imposed by several tillage operations on several soil physical properties. Three tillage treatments, replicated 4 times in a randomized complete block design, were (1) conventionally-disked 3 times before planting, (2) full width strip chisel plowed to a 27-cm depth, and (3) in-row-subsoiled plus bedding. Soil physical properties measured were cone index (CI), weight percentage water (Pw), bulk density (Db), soil water characteristic curve, saturated hydraulic conductivity (Ksat) and soil settling. These properties were measured 3 times: immediately after planting soybeans (Glycine max (L.) Merr.) on 16 May; on 3 June; on 8 July 1977. Soil properties were measured at the 0–14, 14–28, and 28–41-cm soil depths at 3 positions relative to the row i.e., in the row, in the trafficked interrow, and in the non-trafficked interrow. Significant differences due to tillage treatment were found for Db, CI, and the soil water characteristic. The greatest spatial variation occurred in the 0–14-cm depth and decreased with depth. Significant differences for most variables were also found for the tillage by depth and tillage by position interactions. All properties exhibited significant temporal variation.}, number={1}, journal={SOIL & TILLAGE RESEARCH}, author={CASSEL, DK and NELSON, LA}, year={1985}, pages={5–17} }
 @article{cassel_1980, title={EFFECTS OF PLOWING DEPTH AND DEEP INCORPORATION OF LIME AND PHOSPHORUS UPON PHYSICAL AND CHEMICAL-PROPERTIES OF 2 COASTAL-PLAIN SOILS AFTER 15 YEARS}, volume={44}, ISSN={["1435-0661"]}, DOI={10.2136/sssaj1980.03615995004400010020x}, abstractNote={Selected soil properties were evaluated 15 years after installing various depth-of-plowing treatments on two Atlantic Coastal Plain soils which initially had tillage-induced pans and low subsoil pH. In 1960, Norfolk sandy loam was plowed to depths of 18, 38, and 56 cm, and Wakulla loamy sand was plowed to depths of 18 and 56 cm. Prior to and during the plowing operation, specified amounts of dolomitic limestone and phosphorus were applied. In 1975, the following variables were measured for each depth-of-plowing treatment as a function of depth: bulk density; texture; 1/3- and 15-bar water contents; available water; cone index; modulus of rupture; pH; extractable P, K, Na, Ca, and Mg; percent organic matter; and acidity. In addition, the soil water characteristic, in situ unsaturated hydraulic conductivity [K(θ)], and infiltration rate were measured on 3.6 m2 plots for each treatment. Soil strength increased and infiltration rate decreased as plowing depth increased, creating physical conditions more unfavorable for root growth. Incorporation of P and lime by deep plowing increased the levels of P, Mg, and Ca in the 18- to 38- and 38- to 51-cm depths making chemical conditions more favorable for rooting. Deep plowing increased K(θ) at the 0- to 18- and 18- to 38-cm depths at higher soil water pressures primarily due to higher volumetric soil water contents which resulted from higher bulk densities and finer textured material in the soil matrix.}, number={1}, journal={SOIL SCIENCE SOCIETY OF AMERICA JOURNAL}, author={CASSEL, DK}, year={1980}, pages={89–95} }
 @article{cassel_nelson_1979, title={VARIABILITY OF MECHANICAL IMPEDANCE IN A TILLED ONE HECTARE FIELD OF NORFOLK SANDY LOAM}, volume={43}, ISSN={["0361-5995"]}, DOI={10.2136/sssaj1979.03615995004300030006x}, abstractNote={Abstract}, number={3}, journal={SOIL SCIENCE SOCIETY OF AMERICA JOURNAL}, author={CASSEL, DK and NELSON, LA}, year={1979}, pages={450–455} }