@article{mueller_barbercheck_bell_brownie_creamer_hitt_hu_king_linker_louws_et al._2002, title={Development and implementation of a long-term agricultural systems study: Challenges and opportunities}, volume={12}, number={3}, journal={HortTechnology}, author={Mueller, J. P. and Barbercheck, M. E. and Bell, M. and Brownie, C. and Creamer, N. G. and Hitt, A. and Hu, S. and King, L. and Linker, H. M. and Louws, F. J. and et al.}, year={2002}, pages={362–368} }
 @article{blum_king_brownie_2002, title={Effects of wheat residues on dicotyledonous weed emergence in a simulated no-till system}, volume={9}, number={2}, journal={Allelopathy Journal}, author={Blum, U. and King, L. D. and Brownie, C.}, year={2002}, pages={159–176} }
 @article{muriuki_king_volk_2001, title={Nitrogen-15 recovery in soil incubated with potassium nitrate and clover residues}, volume={65}, ISSN={["0361-5995"]}, DOI={10.2136/sssaj2001.6551430x}, abstractNote={In the southeastern USA, legumes are used as green manure to meet crop N requirements of a following crop, but recovery is usually lower than from conventional fertilizers. We conducted a laboratory study for 26 wk under aerobic conditions to monitor recovery of 15N‐labeled KNO3 (fertilizer) and crimson clover (Trifolium incarnatum L.) residues (clover) in organic, inorganic, and microbial biomass N pools. Volatilization of NH3 from decomposing clover residues was monitored for 12 wk. Three hundred–gram samples of a Typic Kanhapludult soil were amended with N (0.051 mg N kg−1 dry soil in fertilizer and 0.049 mg N kg−1 dry soil in clover). A control with no N was also included. Although inorganic N (NH4, NO2, and NO3) accumulated throughout (fertilizer > clover > control), the rate of accumulation did not differ among treatments. Organic and microbial biomass N concentration did not differ among treatments, but applied N recovery in microbial biomass was greater in clover than fertilizer (P < 0.05) throughout. Ammonia volatilized was negligible. After 26 wk, applied N recovered in soil inorganic N was 66% for fertilizer and 40% for clover; in soil organic N, 18% for fertilizer and 50% for clover; and in microbial biomass N, 0.75% for fertilizer and 1.5% for clover. Applied N presumed denitrified was 16% in fertilizer and 10% in clover. We concluded that clover green manure can meet the N requirements of a following crop from the time of emergence in the southeastern USA.}, number={5}, journal={SOIL SCIENCE SOCIETY OF AMERICA JOURNAL}, author={Muriuki, AW and King, LD and Volk, RJ}, year={2001}, pages={1430–1436} }
 @article{white_sheffield_washburn_king_green_2001, title={Spatial and time distribution of dairy cattle excreta in an intensive pasture system}, volume={30}, ISSN={["0047-2425"]}, DOI={10.2134/jeq2001.2180}, abstractNote={ABSTRACTThis study determined distribution of feces and urine from 36 lactating dairy cattle (Bos taurus) managed in a rotationally grazed 0.74‐ha endophyte‐free tall fescue (Festuca arundinacea Schreb.)–white clover (Trifolium repens L.) pasture. Cows were observed for 24 h five times from July 1997 to April 1998, and for 13.5 h in September 1997. During each 24‐h observation period, the first grazing period (12 h) used 54% of the paddock and the second grazing period (8 h) used the entire paddock. Times and locations of all defecations and urinations from a subgroup of eight cows, observed while in the pasture, feed area, milking parlor, or in transit were recorded during the observation periods listed above and another time in May 1997. On pasture, all defecations and urinations were surveyed and mapped for all 36 cows. Feces and urine from six observation periods covered an estimated 10% of the paddock area in one year. Within 30 m of the water tank, concentrations of feces and urine from three warm‐season observations were significantly greater than concentrations during three cool‐season observations. Percentages of defecations and urinations on the pasture, feeding, and milking areas were highly correlated (r > 0.90) with time spent in those areas. Pasture‐based systems could reduce manure handling and storage requirements proportional to the time cattle are on pastures. Manure on the pasture was evenly distributed, except around the water tank during warm‐weather grazings. Results indicate that pasture‐based dairy systems may require smaller, less‐expensive manure management systems compared with confinement dairy farms.}, number={6}, journal={JOURNAL OF ENVIRONMENTAL QUALITY}, author={White, SL and Sheffield, RE and Washburn, SP and King, LD and Green, JT}, year={2001}, pages={2180–2187} }
 @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{king_hoag_1998, title={Reduced chemical input cropping systems in the southeastern United States. III, Economic analysis}, volume={13}, DOI={10.1017/s088918930000758x}, abstractNote={AbstractThis study evaluated the profitability of several cropping systems during a 10-year period of an experiment comparing rotations and levels of purchased inputs. Continuous corn or sorghum, corn/wheat-soybean (2-year), and corn/wheat-soybean/corn/clover hay (4-year) were managed with recommended fertilizer and pesticide rates and no-till planting (C) or with N from legumes, conventional tillage, and cultivation for weed control (L). Medium input management (M: medium rate of N and banded herbicides) was included during years 5 through 10. Generally, corn was the least profitable crop, regardless of input level or type of rotation. Rotating crops improved profit more than did adding inputs to continuous corn. With L, average annual profit was: continuous corn, -$64/ha; 2-year rotation, $135/ha; and 4-year rotation, $158/ha. With C, the 2-year rotation increased profit to $165/ha from -$119/ha with continuous corn. The increased profit with rotations was due to greater profits from wheat, soybean, and hay offsetting low or negative profit from corn. Sorghum (grown only in monoculture) was more profitable with L ($34/ha) than with C (-$20/ha). During the 6 years when all input levels were compared, the order of average profit was M>L>C with continuous corn. Generally, profit was not increased by M compared with L in the 2-and 4-year rotations. With L, the cost of weed control was 20% of that for C with corn and 44% with soybean. Cost of N from fertilizer was $0.66/kg, but cost of N from crimson clover (seed and planting costs) averaged $0.92/kg when clover was drilled, $1.27/kg when aerially seeded, and $0.16/kg when naturally reseeded.}, number={1}, journal={American Journal of Alternative Agriculture}, author={King, L. D. and Hoag, D.}, year={1998}, pages={12–27} }
 @article{crozier_king_volk_1998, title={Tracing nitrogen movement in corn production systems in the North Carolina Piedmont: A nitrogen-15 study}, volume={90}, ISSN={["0002-1962"]}, DOI={10.2134/agronj1998.00021962009000020009x}, abstractNote={AbstractLegume cover crops have been studied in the southeastern USA, but there have been no 15N tracer studies comparing movement of legume N and fertilizer N for this region. Our study used l5N‐enriched crimson clover (Trifolium incarnatum L.) (135 kg N ha−1) and either 15NH4NO3 or NH154NO3 (70 kg total N ha−1) to quantify N movement through soil inorganic and organic N pools and into corn (Zea mays L.). Clover N mineralized rapidly, with 45% of the initially applied N detectable as inorganic N at 18 d following incorporation. Rapid nitrification of enriched NH+4 occurred, but, since the soil NO‐3 pool was larger in this treatment than in the enriched NO‐3 treatment (presumably due to chance), the relative enrichment of the soil NO‐3 pool was less than with the application of enriched NO‐3. At anthesis, 25% of the N in corn had been derived from the NO‐3 source, while only 11% had been derived from the NH+4 source (P < 0.05). At physiological maturity in 1990, the first growing season, 38 to 44% of each enriched source could be accounted for. By physiological maturity in 1991, 60% of the clover source but only 28 to 36% of the fertilizer sources could be accounted for. This study demonstrates the substantial amounts of endogenous soil N mineralization, inorganic N immobilization, and legume N persistence in these cropping systems.}, number={2}, journal={AGRONOMY JOURNAL}, author={Crozier, CR and King, LD and Volk, RJ}, year={1998}, pages={171–177} }
 @article{blum_king_gerig_lehman_worsham_1997, title={Effects of clover and small grain cover crops and tillage techniques on seedling emergence of dicotyledonous weed species}, volume={12}, DOI={10.1017/s0889189300007487}, abstractNote={AbstractWe monitored emergence of morning-glory, pigweed, and prickly sida from seeded populations in no-till plots with no debris (reference plots) or with crimson clover, subterranean clover, rye, or wheat debris. Cover crops were either desiccated by glyphosate or mowed and tilled into the soil. Debris levels, soil temperature, moisture, pH, nitrate, total phenolic acid and compaction were monitored during May to August in both 1992 and 1993. Seedling emergence for all three weed species ranged from <1 to 16% of seeds sown. Surface debris treatments delayed weed seedling emergence compared with the reference plots. Rye and wheat debris consistently suppressed weed emergence; in contrast, the effects of clover debris on weed emergence ranged from suppression to stimulation. Gfyphosate application resulted in a longer delay and greater suppression of seedling emergence in May than in April. In 1993, plots in which living biomass was tilled into the soil were also included and monitored. Weed seedling emergence was stimulated when living biomass was incorporated into the soil. Covariate, correlation and principle component analyses did not identify significant relationships between weed seedling emergence and soil physical and chemical characteristics (e.g., total phenolic acid, nitrate, moisture, temperature). We hypothesize that the observed initial delay of the weed seedling emergence for all three species was likely due to low initial soil moisture. The subsequent rapid recovery of seedling emergence of morning-glory and pigweed but notprickfy sida in the clover compared with the small grain debris plots was likely due to variation in soil allelopathic agents or nitrate-N levels. The stimulation of weed seedling emergence when living biomass was incorporated into the soil was likely caused by an increase in “safe” germination sites coupled with the absence of a zone of inhibition resulting from tillage.}, number={4}, journal={American Journal of Alternative Agriculture}, author={Blum, Udo and King, L. D. and Gerig, T. M. and Lehman, M. E. and Worsham, A. D.}, year={1997}, pages={146–161} }
 @article{miner_gutierrez_king_1997, title={Soil factors affecting plant concentrations of cadmium, copper, and zinc on sludge-amended soils}, volume={26}, ISSN={["0047-2425"]}, DOI={10.2134/jeq1997.00472425002600040009x}, abstractNote={Establishment of maximum cumulative metal loading rates of sludge require metals in soils be related to metal concentrations in plants grown on those soils. The relationship between plant concentrations of Cd, Cu, and Zn and soil properties on sites of long-term municipal sludge application were evaluated. Swiss chard (Beta vulgaris L.) and lettuce (Lactuca sativa L.) were planted on five fields (Typic Hapludults) with known sludge disposal history. After harvest, tobacco (Nicotina tabacum L.) following swiss chard and peanut (Arachis hypogea L.) following lettuce were planted in the same plots. Extractable Cd, Cu, and Zn (Mehlich-3, 0.05 M DTPA, 0.05 M EDTA), clay, humic matter, organic C, and pH were determined on a composite 20-cm depth soil sample and Mehlich-3 extractable metals were determined by 15-cm increments on a 60-cm depth sample from each plot. Tissue concentrations of Cd, Cu, and Zn were measured near harvest maturity (swiss chard and lettuce) or shortly after anthesis (tobacco and peanut). Simple linear regressions were poor between plant metal concentration and soil-extractable metal for all extractants. Inclusion of soil properties in the best-fit multivariate regression models improved the relationship for metal concentration in plants. Values for R 2 ranged from 0.30 to 0.96 with the poorest correlations obtained for Cu in lettuce and peanut. Best-fit models for all other crop-extractant-metal combinations had R 2 > 0.83. Metals extracted by the three extractants were correlated with each other so their inclusion in models describing plant concentrations of heavy metal in this study gave similar results.}, number={4}, journal={JOURNAL OF ENVIRONMENTAL QUALITY}, author={Miner, GS and Gutierrez, R and King, LD}, year={1997}, pages={989–994} }
 @article{king_1994, title={Reduced chemical input cropping systems in the southeastern United States. II. Effects of moderate rates of N fertilizer and herbicides, tillage, and delayed cover plow-down on crop yields}, volume={9}, DOI={10.1017/s0889189300005920}, abstractNote={AbstractIn a previous study of reduced chemical cropping systems (N from legumes; chisel plow and disk tillage; cultivation for weed control) in the southeastern U.S., corn and wheat yields were less than half those obtained with recommended practices. The following practices were studied as possible ways to improve yields in the reduced chemical systems: 1) conventional tillage (chisel plowing and disking), inorganic Nat 70 or 140 kg/ha, and either cultivation or herbicides; 2) early versus late plow-down of clover green manures; 3) supplemental inorganic N fertilizer on corn and wheat in rotations relying on clover green manures for N; and 4) nicosulfuron herbicide banded on corn.Yield of soybean in the rotations was not affected by any of these practices. With herbicides and fertilizer N at 140 kg/ha, continuous corn yields with no-till and conventional tillage were equal in 1990 and 1992, but no-till yield was 30% higher in 1991. When cultivation was used for weed control in the conventional tillage treatment, corn yield was similar to that of no-till with herbicide in the one year when rain was plentiful (yield 6000 kg/ha). However, in 2 of 4 dry years, yields (<2600 kg/ha) were higher with no-till. Clover biomass consistently increased by between 700 and 3500 kg/ha when plow-down was delayed from mid-April to early or mid-May (13 to 26 days). However, biomass N content increased significantly (by between 35 and 90 kg/ha) in only 2 of 5 years. Corn yields were affected in only 2 of 12 possible comparisons. In these cases, delayed clover plow-down reduced yield by about 50%. Supplementing corn with 45 kg N/ha and banding nicosulfuron increased yields, but only to between 62 and 84% of yields with recommended practices. Supplementing wheat with 45 kg N/ha increased yields by half, but only to between 40 and 60% of the yields with 90 kg N/ha.}, number={4}, journal={American Journal of Alternative Agriculture}, author={King, L. D.}, year={1994}, pages={162} }
 @article{king_buchanan_1993, title={Reduced chemical input cropping systems in the southeastern United States. I. Effect of rotations, green manure crops and nitrogen fertilizer on crop yields}, volume={8}, DOI={10.1017/s0889189300004999}, abstractNote={AbstractInterest in reducing purchased chemical inputs to reduce production costs and avoid possible environmental damage prompted this 7-year study. Two management systems, current management practices (CMP) and reduced chemical inputs (RCI), were evaluated for four crop sequences from 1985 through 1992: continuous grain sorghum; continuous corn; a 2-year rotation of corn and double-cropped winter wheat and soybean; and a 4-year rotation of corn, winter wheat/soybean, corn, and red clover hay (changed in 1989 to a 3-year rotation of corn, red clover hay, and wheat/soybean). No-till planting and recommended rates of fertilizer and pesticides were used in the CMP system. In the RCI system, N was supplied by a crimson clover green manure crop or the red clover in the rotation. Weed control was by chisel plowing, disking, and cultivation.Crimson clover top growth accumulated from 70 to 180 kgN/ha, red clover from 77 to 130 kg N/ha. Rotating crops increased corn yield with CMP but not with RCI. lndry years, corn yields were low (less than 3000 kg/ha), corn did not respond to fertilizer N, and yields generally were higher with CMP than with RCI. With adequate rain, yield of all RCI treatments were the same as yield in CMP continuous corn receiving no fertilizer N. Johnsongrass competition was the main reason for low yields in the RCI treatments. Soybean yields were higher with CMP in 4 years and higher with RCI one year. Wheat and grain sorghum yields were higher with CMP than with RCI. A dramatic decline in johnsongrass in sorghum was noted in 1989, and several plots remained relatively free of johnsongrass through 1992.Management decisions made during the experiment included the degree of input reduction in RCI; whether to either end or modify unproductive treatments; whether to use newly available varieties and pesticides; whether to suspend the experiment to eliminate johnsongrass; and how to add new treatments while retaining the original treatments.}, number={2}, journal={American Journal of Alternative Agriculture}, author={King, L. D. and Buchanan, M.}, year={1993}, pages={58} }
 @article{king_hajjar_1990, title={THE RESIDUAL EFFECT OF SEWAGE-SLUDGE ON HEAVY-METAL CONTENT OF TOBACCO AND PEANUT}, volume={19}, ISSN={["1537-2537"]}, DOI={10.2134/jeq1990.00472425001900040018x}, abstractNote={AbstractSewage sludge normally would not be applied on land where peanut (Arachis hypogaea L.) or tobacco (Nicotiana tabacum L.) are being grown because of possible contamination of peanut with pathogens and increased Cd concentration in tobacco. These crops, however, might be grown in rotation with other crops to which sludge had been applied. The residual effect of sewage sludge on metal concentrations in tobacco and peanut was evaluated in a greenhouse pot experiment with a Typic Hapludult soil from a field that received aerobically digested municipal sewage sludge at 0, 9, 18, and 27 Mg ha−yr−1 for 3 yr. Cumulative amount of metals applied at the 27‐Mg rate were (kg ha−1) 1.8 Cd, 39 Cu, 48 Cr, 9 Ni, 30 Pb, and 84 Zn. Sulfuric acid or Ca(OH)2 was used to effect three soil pH regimes: 5.2, 5.8, and 6.4 (median value within each regime). Tobacco (‘Speight G‐28’) was grown to flowering and peanut (NC 7) was grown to maturity. At the termination of the experiment, soils were extracted with diethylenetriaminepentaacetic acid (DTPA) and Mehlich 3 extractant (M3) for metal analysis. Tobacco dry weight (averaged over pH) increased from 66 g pot−1 with no sludge to 94 g pot−1 at the highest sludge rate. Peanut kernel yield (averaged over pH) was depressed at the highest rate (35 g pot−1) as compared to the lower rates (mean of 48 g pot−1). At low pH peanut top growth was depressed by sludge (probably a result of Zn toxicity) and no kernels were formed at the medium and high rates. Sludge rates and soil pH had little effect on concentration of Cr and Pb in tobacco or peanut. Concentration of Cd, Ni, and Zn in tobacco and in peanut top growth decreased as soil pH increased to 5.8 to 6.0 but no decrease was noted at higher pH. Sludge rate effect was significant at low pH but diminished as pH increased. Concentration of Cd, Ni, and Zn declined but Cu concentration increased with increasing height of leaf on the tobacco stalk. Results of stepwise multiple regression using linear and quadratic forms of cumulative sludge rate, soil pH, and DTPA‐extractable metals and pH × rate and pH × DTPA‐extractable metals interactions as independent variables and metal concentration in the lower tobacco leaves or in peanut tops as dependent variables suggested DTPA would predict tissue metal concentrations better than would M3.}, number={4}, journal={JOURNAL OF ENVIRONMENTAL QUALITY}, author={KING, LD and HAJJAR, LM}, year={1990}, pages={738–748} }
 @article{king_dunlop_1982, title={APPLICATION OF SEWAGE-SLUDGE TO SOILS HIGH IN ORGANIC-MATTER}, volume={11}, ISSN={["0047-2425"]}, DOI={10.2134/jeq1982.00472425001100040011x}, abstractNote={AbstractIn a greenhouse study corn (Zea mays L.) was grown in four soils (1.4, 19, 38, and 72% organic matter) that received sewage sludge from Philadelphia, Pa., (PS) at rates to supply 0, 2, 4, and 8 kg Cd/ha. Corn and soybeans (Glycine max. L.) were grown in 1.4 and 19% organic matter (OM) soils that received sewage sludge from Wilmington, N.C., (WS) at rates to supply 0, 2, 4, and 6 kg Cd/ha. The pH of the 1.4% OM soil was adjusted to 6.5 with CaCO3. The higher OM‐content soils received recommended rates of CaCO3 to increase the pH to 5.0–5.5, the desired range for crop production on these soils. Actual resulting pH values were 5.5, 4.9, and 4.6 for the 19, 38, and 72% OM soils respectively.Corn yields were depressed by PS but enhanced by WS. Soybean yield was enhanced by WS on the 19% OM soil but depressed on the 1.4% OM soils. Both sludges caused increases in concentrations of Cd, Cu, and Zn in the plant tissue, but concentrations were not high enough to be responsible for the observed yield depressions. The PS was more effective in raising Cd and Zn concentrations in plant tissues than was WS. The type of soil had a varying effect on metal concentrations in the plants. The expected reduction in heavy metal uptake with higher soil OM content was confounded by the low pH of the soils with high OM content. The large quantity of OM added via WS masked the effect of soil OM.Since the bulk densities of the soils varied from 0.45 to 1.35 g/cm3, regression equations describing Cd concentration in corn stover as a function of OM and cation exchange capacity (CEC) were more precise when OM and CEC were expressed on a volume basis and when OM was determined by a procedure designed to estimate humus rather than total oxidizable OM.}, number={4}, journal={JOURNAL OF ENVIRONMENTAL QUALITY}, author={KING, LD and DUNLOP, WR}, year={1982}, pages={608–616} }
 @article{king_1982, title={LAND APPLICATION OF UNTREATED INDUSTRIAL-WASTE WATER}, volume={11}, ISSN={["0047-2425"]}, DOI={10.2134/jeq1982.00472425001100040016x}, abstractNote={AbstractExcessive pretreatment of waste water prior to land application unduly increases the cost and energy requirement of land treatment systems. This study was conducted to determine if untreated industrial waste water can be applied to soil without adversely affecting crop growth and soil properties or posing a ground‐water pollution hazard.Untreated (UW) and treated (TW) waste water were diverted from the treatment plant at a fiberboard mill and spray‐irrigated on fescue‐grass (Festuca arundinacea Schreb) on Cecil soil (clayey kaolinitic, thermic Typic Hapludult) at 1.4 cm/week. After 2 years the treatments were changed to 1.5, 2.0, and 3.0 cm UW/week and continued for 2 more years.Grass yields with UW and TW were equal to or greater than yields with inorganic fertilizer and no irrigation (control treatment). Recovery of waste‐water‐applied N via crop harvest ranged from 20 to 30%. Analysis of washed and unwashed grass samples showed that increased Mn concentrations were due to waste‐water solids adhering to the sample, rather than to increased Mn uptake. Concentrations of Ni, Pb, and Cr of unwashed samples were increased slightly but were far below concentrations toxic to livestock.Soil nitrate concentrations resulting from UW applications were generally not significantly different from concentration in the control treatment except when UW contained appreciable quantities of inorganic N. There was evidence that denitrification was a significant N sink.Waste‐water irrigation increased concentrations of soil P, K, and Ca and increased soil pH to 7.4–7.8. Sodium accumulated in the subsoil to an exchangeable‐Na percentage of 10.Results of the study showed that extensive pretreatment was not necessary prior to irrigation with the waste water.}, number={4}, journal={JOURNAL OF ENVIRONMENTAL QUALITY}, author={KING, LD}, year={1982}, pages={638–644} }