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Background The American Council of Graduate Medical Education (ACGME) guidelines for scholarly activities by family medicine residents require at least one activity per resident and encourage conference presentations. Meeting these guidelines has traditionally been challenging due to a multitude of factors from lack of time to limited administrative support. Studies have shown that resident participation in research was associated with higher levels of satisfaction with training. We aimed to develop and evaluate the effectiveness of a dedicated research curriculum in achieving ACGME goals for our residents. Methods We performed a need assessment that identified strengths and obstacles related to research which then guided the actions taken to build the curriculum. Revised curricular elements included a research focused lecture series, a restructured journal club, financial support for presentations and project expenses, a specific timeline for project completion, and the development of a regional research day involving multiple family medicine programs. Dedicated research time was built into the resident schedule and presentations at local, regional and national conferences were encouraged and supported. Results Following implementation of the curriculum there was a marked increase in the number of scholarly projects performed by residents. Prior to implementation there had only been one presentation at a national conference in the previous five years. This increased to an average of four presentations per year in the following five year period. On a regional scale, the initial success of the local research day led to a continued expansion and now includes six family medicine programs. Conclusion Implementation of a dedicated multifaceted research curriculum significantly increased the participation of our residents in scholarly activities and led to a near five-fold increase in presentations at regional and national levels. Additionally, resident satisfaction in scholarly activities increased and a far greater number of graduating residents went on to complete fellowships.

Background Despite well-established negative consequences, high rates of substance use and related disorders continue to be reported. Physicians in training are not immune from this, or the associated risks to their health and careers, while impaired physicians are a threat to patient safety. Objective We surveyed family medicine residency programs' practices relating to drug testing of medical students and incoming residents. The survey asked about the extent to which residency programs are confronted with trainees testing positive for prohibited substances, and how they respond. Methods The survey was sent to the directors of family medicine residency programs. A total of 205 directors (47.2%) completed the survey. Results A majority of the responding programs required drug testing for incoming residents (143, 68.9%). Most programs did not require testing of medical students (161, 81.7%). Few programs reported positive drug tests among incoming residents (9, 6.5%), and there was only 1 reported instance of a positive result among medical students (1, 3.3%). Respondents reported a range of responses to positive results, with few reporting that they would keep open training spots or offer supportive services for a medical student who tested positive. Conclusions Changing laws legalizing certain drugs may require corresponding changes in the focus on drug testing and associated issues in medical training; however, many residency program directors were not aware of their institution's current policies. Programs will need to reexamine drug testing policies as new generations of physicians, growing up under altered legal circumstances concerning drug use, progress to clinical training.

This study examined two guidelines for preparing hydroponic solutions to ensure adequate iron (Fe) for Poaceae plants: (1) not to add chelator in excess of Fe concentrations and (2) to use only weaker forms of Fe(III) chelators. Barley was grown in low-Fe solutions for 9 d and transferred to 59Fe-spiked nutrient solutions at pH 8.1 containing ligand:Fe μ M concentrations of 30:10, 200:10, and 500:10 for 6 h assays. Shoot 59Fe increased with increasing citrate or N,N-bis(carbozymethyl)glycine (NTA). Shoot 59Fe was higher from treatment with citrate than with corresponding NTA treatments despite the ligands' similar Fe(III) binding affinity. Soluble Fe was higher from the citrate than the NTA solutions at the two highest chelator concentrations (P < 0.05). Citrate maintained higher soluble Fe levels and provided more Fe to barley than did NTA. Results of the second experiment found adequate Fe in barley when grown in equimolar HBED:Fe treatments (HBED is the strongest Fe(III) synthetic chelator). R...

The free-ion model (FIM) describes iron (Fe) uptake by barley [Hordeum vulgare(L.) ‘Grammett’] as being controlled by the activity of the buffered, free, uncomplexed Fe3 + in solution. Chelators' effect on Fe uptake by barley was evaluated and the rate of exchange of Fe between chelators was examined. Barley was grown for two weeks in a low-Fe nutrient solution and transferred to solutions varying in Fe and chelators for 6 h assays. Shoot 59Fe was higher in barley grown in citrate (7743 and 1928 59Fe Bq g− 1) than in NTA (3220 and 1113 59Fe Bq g− 1; P = 0.045) despite similar free-Fe3 + activities. A comparison of Fe uptake by barley from solutions with pFe3 + activities of 17.1 and 24.6 showed < 5% was from indiscriminate apoplastic-flow uptake (3250 59Fe Bq g− 1 vs. 160 59Fe Bq g− 1). Using nutrient solutions from the barley studies but without plants, Fe exchange between chelators and a simulant for the barley phytosiderophore occurred within hours (for NTA and citrate), or days (EDTA and HEDT...

Soils of different geographic regions affect efficiencies of individual soil-test extractants. Recent effort on nutrient-management programs across the United States has promoted establishment of conversion equations between different soil-test extractants for evaluating nutrients in similar soils. This study was carried out to compare soil-extractable phosphorus (P) by strong Bray (Bray 2), potassium (K), calcium (Ca), magnesium (Mg), sodium (Na) by 1 M ammonium acetate (pH 7.0), and zinc (Zn), copper (Cu), manganese (Mn), iron (Fe) by DTPA-TEA at pH 7.3 with those extracted by Mehlich 3 on 317 soil samples collected from all parishes of Louisiana. Mehlich 3-extractable P correlated (R 2 = 0.709, P > 0.01) with that extracted by Bray 2 but was, on average, about half of that by Bray 2. Soils with pH > 6.5 or with finer textures tended to yield larger differences between the two extractants for P. Mehlich 3 extractable cations were highly correlated with those of ammonium acetate (R 2 ≥ 0.923, P ...

Nitrogen fertilization is a required production practice for cotton (Gossypium hirsutum L.) with risks arising from under- and over-fertilization. Tissue testing for diagnosing N deficiencies in crops can use leaf blades and the total N concentration, but this practice has not been rigorously examined in cotton. The primary objective of these experiments was to determine the leaf-N concentration of the uppermost, fully mature leaf blade below which yield loss could be expected. Nitrogen-rate field experiments were conducted at 12 research station and farm sites in the Midsouth USA in Louisiana, Arkansas, Mississippi, and Alabama in 1996 and 1997. Leaf-blade total N concentrations associated with yield loss were 43% N at early bloom (R 2 = 0.50) and 4.1% N at mid-bloom (3 wk after early bloom, R 2 = 0.32). The likelihood of applying N when not needed could be reduced by lowering the early bloom critical value to 3.9%. Only 4% of all samples sufficient in N would have been incorrectly diagnosed N deficient at that critical value, but 44% of all deficient samples would have been misidentified as N sufficient. Reduced yields due to over application of N were evident in some samples with leaf N between 4.6 and 4.8% at early bloom These concentrations were also common for N-sufficient plants, making accurate diagnoses of the over application of N unlikely. Our leaf-N critical values probably differ from previously established values because earlier values were derived via survey techniques and because faster fruiting cultivars may require higher leaf N.

Chelator-buffered hydroponic solutions provide low and buffered free-metal concentrations and allow the easy calculation of nutrient species expected in these solutions. Some researchers suspect that the solutions allow plant uptake of chelates and that this uptake explains the failure of the free-ion activity model using these solutions. To determine the amount and method of chelate uptake, swiss chard was grown in solution culture in growth chambers for about three wks and then transferred to solutions containing 14C-EDTA, 14C-citrate, or 14C-L-histidine for a 21-hour assay. Much higher root and shoot 14C were found from treatments containing metabolites histidine (2706 097 shoot Bq 14C) or citrate (2241 953 shoot Bq 14C) than EDTA (280 110 shoot Bq 14C). Passive transpirational flow could explain all of the EDTA uptake, but active uptake would be required to explain most of the citrate and histidine uptake even assuming some adsorption of ligand bound to roots. Swiss chard grown in solutions with the same total EDTA concentrations, but different amounts of Fe bound to EDTA, had ≥3-fold differences in root and shoot 14C concentrations. In a second experiment, swiss chard roots removed more EDTA from solutions containing mostly M-EDTA0 than M-EDTA1- or M-EDTA2- (288 140, 245 051, and 192 559 Bq 14C, respectively) suggesting plant selectivity for EDTA and a non-apoplastic route of uptake or an effect resulting from root cell-wall adsorption. Results indicated buffering of metals by ligands allowed some ligand uptake with much more uptake occurring with metabolites citrate and histidine than EDTA. A passive or indiscriminate form of uptake does not appear to explain all EDTA uptake with a selectivity by swiss chard for M-EDTA complexes of lower charge.

No boron (B) deficiencies have been reported for rice (Oryza sativa L.) grown in the United States and, when occurring elsewhere, reports often lack details of deficiency symptoms and leaf-B critical values. An experiment was conducted to determine the effect of B and lime on yield, pollen viability, and to determine diagnostic symptoms of B deficiency in rice. Rice cv. “Bengal” was grown in the greenhouse on a soil acquired from a rice farm from SW Louisiana in the United States, a Caddo silt loam (Caddo sl) (Typic Glossaqualf, fine-silty, siliceous, thermic), treated with 0.44 mg B kg−1 (+B) or no B (−B). Split plots were limed at rates of (i) none; (ii) 224 mg kg−1 CaO+40.3 mg kg−1 MgO; and (iii) 673 mg kg−1 CaO+121 mg kg−1 MgO. Rice was also grown in −B and +B potting media and in −B sand culture using nutrient solution identical to that used in other studies of ours. Rough-rice yields from the +B Caddo sl treatment was 11% higher than from the −B treatment (29.3 vs. 26.3 g pot−1; P=0.02). Th...

Pearl millet [Pennisetum glaucum (R) Br.] is a promising alternative grain crop for the Southeast and mid-South regions of the USA, but additional N fertility information is needed to optimize its production. Identification of a critical tissue N level at early growth stages is necessary to determine the need for subsequent applications of N. Field experiments were conducted to determine the response of hybrid 'HGM 100' grain yield, protein yield, and shoot N concentration to N application rate and to determine the relationship of grain yield and protein yield with shoot N concentration at different growth stages. Grain yield response to N fertilizer applications from 0 to 168 kg ha -1 , in 34-kg increments, varied among five field environments ranging from sandy loam to silty clay loam soils and resulted in a moderately low correlation (r 2 = 0.36). Relative total protein yield was more consistent (r 2 = 0.67). Tissue N concentration of shoots harvested 44 ± 4 d after seeding [early boot(EB)] was related to relative grain yield (r 2 = 0.65). A critical N concentration of 31 kg -1 dry matter (dm), determined by regression and old Cate-Nelson procedures, resulted in optimum grain yield. On a per hectare basis, total relative protein yield also correlated moderately high with shoot tissue N concentration at EB (r 2 = 0.70). The use of Cate-Nelson procedures determined a critical N concentration in shoot tissue at EB of 32 g kg -1 dm. Determination of a critical N level at an earlier growth stage resulted in low correlations with yield parameters. On the basis of critical values at the EB stage, N amendments could possibly be applied in time to enhance some yield components, although the effective application window is narrow.

Microwave‐oven digestion of plant materials for the determination of plant‐nutrient concentrations is an aggressive and effective dissolution procedure. Commercial ovens are expensive, however, and ovens designed for home use may provide an inexpensive alternative. We evaluated three microwave ovens: Panasonic NN5510, Sharp Carousel II, and a commercial unit CEM MDS‐2000; and two Teflon vessels: Savillex 571R2 and CEM 327011 for their ability to digest batches of six or twelve plant samples and to compare their analyses with those from conventional block‐heater digestions. For the microwave‐oven digestions, we placed in each vessel 0.1 g National Institute of Standards and Technology (NIST) standard reference material (SRM) 1547 peach leaves, 1.0 mL conc. HNO3, and 0.6 mL 30% w/v H2O2. The digestates were stirred, soaked for 15 min., heated in a rotating carousel as described below, cooled 15 min, added 8.4 mL deionized‐distilled water to make 10 mL volume, filtered, and analyzed with ICP‐AES. Th...

Nitrogen (N) is applied to golf course fairways at rates similar to that applied to corn. This appears excessive since N fertilization of corn is approximately equal to the amount of N removed at h...

A survey ofthe nutrient status ofthe citrus groves of Louisiana was conducted to determine the extent of possible deficient or toxic areas of the region and to help determine the accuracy of critical values developed in the major citrus-growing regions of the world and their relevance to a region where critical values had not been developed. The nutrient status of 29 orchards of Washington navel orange (Citrus sinensis) and satsuma mandarin (Citrus unshiu) trees on P. trifoliate rootstock representing 90% of the citrus region in Louisiana were determined using critical values from the literature. Twenty percent of survey samples ranked excessively high in chloride indicating possible toxicity from recent salt-water intrusion. Chloride contents were higher in groves closer to the Gulf of Mexico. More than 60% of the leaf samples analyzed were diagnosed as having very low concentrations of zinc (Zn) and manganese (Mn). Soil tests of surface soils to a 15-cm depth did not prove useful in predicting Zn and Mn nutrition oftrees, as all soil samples had medium or high levels of DTPA-extractable Zn and Mn. Phosphorus (P) and potassium (K) were low in more than 20% of the leaf samples and high in less than 5% of the samples. Calcium (Ca) in the young leaves was low or very low in 95% of the samples, but no samples from older leaves were low or very low in Ca. These results indicate possible transient effects, errors in the critical values used, or environmental conditions that inhibit Ca uptake.

Whether a tropical soil should be limed or not for a particular crop is strongly dependent on the levels of soil aluminum (Al) which can be determined with soil tests. Soil pH is used to predict whether lime is needed in less‐weathered soils, although some evidence indicates a soil Al test would be more accurate. The objectives of this study were to determine and to compare the accuracies of four soil tests to separate soils requiring lime from those that do not, and to determine the cause of acid‐soil injury to soybean [Glycine max (L.) Merr.]. Soybean was grown in the greenhouse on four surface soils representing the major land resource areas of Louisiana and were amended with eight rates of lime, yields determined, and soils analyzed for soil pH, extractable Al, CaCl2‐extractable Al, CaCl2‐extractable manganese (Mn), and Al saturation. Acid‐soil injury in soybean grown on the Litro clay and Stough fsl was probably caused by soil‐Al effects while low soil calcium (Ca) and high soil Mn was likel...

Plant nutrient deficiencies may be diagnosed with DRIS (diagnosis and recommendation integrated system) or critical nutrient level (CNL) procedures. While extensive efforts have been made to improve diagnoses by DRIS and M-DRIS, little has been done to refine CNL diagnoses for soybean [Glycine max (L.) Merr.]. In this study, we compare diagnoses made by M-DRIS with those from CNL and modify these procedures to improve their diagnostic accuracy. Two databases of R2 (full bloom) soybean leaf nutrient concentrations from 828 field observations of known K, Mn, Zn, or P deficiencies or sufficiencies were used for comparing the procedures. We optimized critical nutrient levels (modified CNL) using the same cases from a database that was used earlier to improve M-DRIS. Using this optimization database, the M-DRIS and modified-CNL procedures had ≤13 misdiagnoses each of K nutrient status compared to 81 by unmodified CNL. M-DRIS was more accurate than the two CNL procedures in diagnosing P deficiencies from cases in the optimized and independent data sets. Unmodified CNL produced 18 misdiagnoses for Zn status from cases in the independent data set, versus >27 for M-DRIS or modified CNL. Generally, M-DRIS was the same or more accurate than CNL methods in diagnosing nutrient status. We recommend CNL concentrations for R2 stage soybean of 3.1 g P kg -1 , 15.1 g K kg -1 , 17 mg Mn kg -1 , and 21 mg Zn kg -1 . For M-DRIS, we recommend critical index values of zero for K and Mn, 18 for P, and -19 for Zn.

The shoots of primary Se-accumulating plant species can accrue Se to several thousand micrograms per gram of dry weight, even when growing in gypsiferous soils, yet no detailed studies of the mutual antagonism between SeO4 and SO4 during plant uptake have been conducted with these species. In a comparative study, we grew a nonaccumulator (alfalfa, [Medicago sativa L.]) and a primary Se accumulator [Astragalus bisulcatus (Hook.) A. Gray] in identical nutrient solutions with varied SeO4 (2-80 and SO4 (0.5-15.5 mM) concentrations for 21 (alfalfa) or 32 to 35 d (A. bisulcatus). Shoot S concentrations in alfalfa were increased by increases in solution SeO4, but only when shoot Se was above 20 g, suggesting that SeO4induced stimulation of S uptake may be a result of incipient Se toxicity. Similar stimulations of S uptake were less apparent in A. bisulcatus. Alfalfa shoot Se concentrations ranged from 4 to 154 g, while the same treatments resulted in shoot levels of 175 to 1200 g 1 in A. bisulcatus. Uptake of SeO4 by alfalfa was profoundly inhibited by increases in solution SO4, while Se uptake by A. bisulcatus was much less, although still significantly, affected. Comparison of molar Se/S ratios in plants and nutrient solutions indicated discrimination against Se by alfalfa, but preferential accumulation of Se by A. bisulcatus. A reevaluation of previously published results was in general agreement with our findings, and suggested that primary Se accumulators have a unique ability to accumulate SeO4 in the face of competition from SO4. These species could thus prove useful in efforts to remediate Se-contaminated soils or sediments that are also enriched in SO4. Overall plant discrimination between SeO4 and SO4 may be related to (i) discrimination between the two analogues during initial absorption, or (ii) differential retranslocation of these elements to the root with subsequent afflux to the external solution. View complete article To view this complete article, insert Disc 5 then click button8

Chaney and Coulombe introduced an effective method to screen dicot genotypes for resistance to bicarbonate‐induced Fe‐deficiency chlorosis. Their method used low levels of FeEDDHA in a nutrient solution with high levels of Ca and Mg salts to mimic the soil solution of problem soils in Iowa and Minnesota. The combination of low Fe supply and high NaHCO3 induced Fe‐stress. Only chlorosis‐resistant soybean and bean cultivars were able to de‐repress their Fe‐stress‐response enough to obtain adequate Fe and remain green. Susceptible genotypes became severely chlorotic. Although Fehr and Cianzio et al. found the method reliable, commercial breeders had poorer reproducibility. As more highly improved Fe‐chlorosis resistance soybean genotypes were developed, lower FeEDDHA and/or higher bicarbonate were required in the screening solutions. With these very low FeEDDHA levels (1.5–2 μM), small amounts of soil or dust contamination of the solutions could markedly shift the screening results. With the develop...

In an effort to expand the data base concerning heavy metal concentrations in Maryland tobacco and to acquire information on the nutritional status for Cu, 402 samples of cured tobacco collected on farms over the period 1980 to 1983 were analyzed for their Zn, Mn, Pb, Ni, and Cd contents, and the Cu contents were examined in 198 samples from 1982 and 1983. Mean concentrations for individual metals in mg/kg were: Zn (43.6), Cu (7.6), Mn (192), Pb (1.92), Ni (1.20), and Cd (2.26). Approximately 5% of the samples contained Zn, Cu, Ni, Pb, or Cd concentrations higher than expected for these elements in Maryland tobacco. Some 25% of the samples contained Mn levels within the range 332–2400 mg/kg which were likely caused by low soil pH conditions. A total of 5% of the cured samples were borderline deficient in Zn (≤18 mg/kg), and 27% were considered deficient in Cu (≤5.2 mg/kg). Problems associated with inadequate liming programs and the use of croplands for municipal waste disposal were discussed.

The purpose of the research was to develop mathematical relationships which utilize soil test information to estimate the concentration of heavy metals (Zn, Cu, Mn, Ni and Cd) in tobacco grown in sludge‐amended soils. Regression analyses were performed on plant and soil metal concentration results obtained from investigations conducted in Maryland involving two sites amended with municipal sludge materials at several rates 12 and 8 years earlier, respectively. Soil test information consisted of pH, total and extractable metals utilizing three extractants (DTPA pH 7.3, Mehlich 1 and 3). Mathematical relationships were developed using linear regression, stepwise multiple regression, and General Linear Model (GLM) analysis procedures available through SAS. R2 values for Zn, Cu, Mn, Ni and Cd ranged from 0.65 to 0.95 depending on the extractant; however, equations for Fe and Pb were not presented because of low R2 (

The purposes for this research were: to examine the long‐term residual effects of farmland applications of municipal sludges from four treatment technologies on the total and extractable Zn, Cu, Mn, Fe, Pb, Ni and Cd concentrations in Coastal Plain soils; to investigate the effects of sludge sources and rates on the effectiveness of soil extractants to remove the various metals; and to determine correlation coefficients for soil extractable versus plant accumulation in tobacco. The extractants evaluated were Mehlich 1 and 3, and DTPA‐pH 7.3. Composite Ap horizon soil samples and tobacco leaf samples were obtained in 1984 from research plots at two sites in Maryland that were established in 1972 and 1976, respectively, using sludge materials from three wastewater treatment facilities in the Washington, D.C. metropolitan region. Similar application rates were used at both sites. A wide range in soil pH values was found among treatments at each site. Significant (p ≤ 0.05) increases were observed in...

(...) To determine the long-term changes in forms of Cd added to a soil, Cd and other heavy metals were extracted with several solutions from a Christiana fine sandy loam (Typic Paleudult; clayey, kaolinitic, mesic) Ap horizon 8 or 9 yr after application of sewage sludge or CdCl 2 . Cadmium was applied at the rate of 21 kg ha −1 either as a component of sewage sludge or as CdCl 2 in 1978 and 1979, respectively. (...)

The form in which a micronutrient is found in the rhizosphere affects its availability to plants. We compared the availability to barley of the free hydrated cation form of Fe3+, Cu2+, Zn2+, and Mn2+ versus their total metal concentrations (free ion plus complexes) in chelator-buffered solutions. Free metal ion activities were estimated using the chemical equilibrium program GEOCHEM-PC with the corrected database. In experiment 1, barley was grown in nutrient solutions with different Fe3+ activities using chelators to control Fe levels. Chlorosis occurred at Fe3+ activities of 10−18 and 10−19M for barley grown in HEDTA and EDTA solutions, respectively. In experiment 2, barley was grown in nutrient solutions with the same calculated Fe3+ activity and the same chelator, but different total Fe concentrations. Leaf, root and shoot Fe concentrations were higher from CDTA buffered solutions which had the higher total Fe concentration indicating the importance of the total Fe concentration on Fe uptake. Results from treatments using EDTA or HEDTA, with one exception, were similar to the results from the CDTA treatment. This suggests differences in critical Fe3+ activities found in experiment 1 were due to differences in the total Fe concentration and not errors in chelate formation constants used to estimate the critical activities. Results for Cu, Zn, and Mn were similar to Fe; despite solutions with equal free Cu2+, Zn2+ and Mn2+ activities, plant concentrations of these metals were generally greater when grown in the solutions with the greater total amount of Cu, Zn, or Mn. When the free Zn2+ activity was kept constant while the total amount of Zn was increased from 4.4 to 49 μM, leaf Zn concentration increased from 77 to 146 μg g-1. In order to predict metal availability to barley and other species in chelator-buffered nutrient solutions, both free and total metal concentrations in solution must be considered. The critical Fe3+ activities required by barley in this study are much higher than those from tomato and soybean, 10-28M, which strongly supports the Strategy 2 model of Fe uptake for Poaceae. This is related to the importance of the Fe3+ (barley) and the Fe2+ (tomato and soybean) ions in Fe uptake. Fe-stressed barley is known to release phytosiderophores which compete for Fe3+ in the nutrient solution, while tomato and soybean reduce Fe3+ to Fe2+ at the epidermal cell membranes to allow uptake of Fe2+ from Fe3+ chelates in solution.

No NIST (National Institutes Standards Technology) standards for the Si concentration of biological materials are available, although Si has been determined for one NIST material by non-NIST personnel. We determined the Si concentrations of NIST materials and a proposed rice-straw (Oryza saliva L.) standard using an autoclave-induced digestion, colorimetric method. We measured 1410 mg Si kg -1 for NIST material no. 1575, which was not significantly different from five of seven analyses reported in the literature (P > 0.05). Silicon concentrations of NIST and other materials were 2160 mg kg -1 (no. 1547), 1500 mg kg -1 (no. 1515), 1920 mg kg -1 (no. 8412), and 69300 mg kg -1 (rice straw).

Plant availability of soil K is controlled by dynamic interactions among its different pools. Misunderstanding of these dynamics leads to mismanagement of soil fertility. This study was conducted to evaluate buffering characteristics of low exchangeable-K soils that showed different sugarcane (Saccharum spp. L.) responses to K amendment. Three silt loams, Crowley (fine, smectitic, hyperthermic Typic Albaqualfs), Dundee (fine-silty, mixed, active, thermic Typic Endoaqualfs), and Norwood (fine-silty, mixed, superactive, hyperthermic Fluventic Eutrudepts), were evaluated by using a modified quantity/intensity (Q/I) approach, which allows partitioning of K changes in the soil-solution system into exchangeable and nonexchangeable pools. Total potential buffering capacity (PBC,) was found to correlate significantly (r = 0.97, P < 0.01) with the buffering capacity due to nonexchangeable K (PBC n ) rather with that due to exchangeable K (PBC e ). Impact factor (β), a measure of effect of added K on nonexchangeable K, was inversely correlated with a soil's conversion magnitude (a) of converting added K to exchangeable K (r = 0.95, P < 0.01). Of the three soils, Dundee exhibited much smaller β values than Crowley and Norwood but the soil converted much of added K to exchangeable K (60-65%) throughout its surface and subsurface soils. Both Crowley and Norwood possessed higher PBC, as well as higher PBC, and PBC e than Dundee, but Crowley required relatively lower critical exchangeable K (EK,) and solution K (CK,) levels below which release of nonexchangeable K was initiated. The overall results indicated that the partitioned Q/I approach could be used to explicitly evaluate short-term K dynamics in soil-solution systems. The nonexchangeable K buffering characteristics along with the differences between critical levels (EK, or CK, and EK 0 or CK 0 ) have important implications in assessing the likelihood of nonexchangeable K release and could be calibrated for soil fertility management.

Nicotiana tabacum L. was grown to maturity in 1984 at two research sites in Maryland which were amended with municipal sludge materials representing a variety of wastewater treatment technologies in 1972, 1976 and 1978. Four sludges from Washington, D.C. and Annapolis, MD were applied at rates equal to 0, 56, 112 and 224 Mg ha‐1. A high‐metal sludge from Chicago was applied at rates equal to 50 and 100 Mg ha‐1 in 1978. Composite leaf samples of cured tobacco and Ap horizon soil samples were analyzed for Zn, Cu, Mn, Fe, Pb, Ni and Cd. Available soil metals were estimated using three procedures: DTPA (pH 7.3), Double Acid and Mehlich 3. DTPA and Double Acid produced significant correlation coefficients (r) for Zn, Cu, Mn, Ni and Cd when compared with plant metal contents; however, none of the extractants produced significant r values for Fe or Pb. All sludge sources resulted in significant increases in DTPA soil Zn, Cu, Ni and Cd with increased application rates; however, plant levels were affected...

Tomato plants (cv. ‘Rutgers') were grown in nutrient solutions without and with FeEDDHA or at low phosphorus levels to evaluate the formation of prussian blue (Fe4[Fe(CN)6]3‐nH2O), a stain used in determining the site of ferric reduction on roots. The effect of Fe source, Fe concentration, solution pH, and time were evaluated. Prussian blue was compared with nitro‐BT, and agar systems with Fe‐chelates and ferrous color reagents. Ferric iron was supplied as a chelate, Fe‐EDDHA or Fe‐HEDTA; or as a salt, FeNH4(SO4)2 or Fe(NO3)3. The staining procedure producing the most distinct and localized stain on the roots was the combination of FeNH4(SO4)2 and ferricyanide both at 100 μM for approximately 1 hour. The initial pH was 3.0 to maintain ferric soluble. Greater salt and ferricyanide concentrations, lower solution pH's or lengthening staining times resulted in stains on most of the root with less differences in the extent of staining between Fe sufficient and Fe deficient plants. When roots were stai...

When plant nutrition problems are observed in the field, one is faced with the question “What is the best and most economical way to solve this problem?” Traditionally, workers in both agronomy and horticulture have used soil amendments to correct deficiencies of macro- and micronutrients, and to correct soil pH to avoid Al or Mn toxicity. Horticulturists have had few economic limitations in solving plant nutrition problems because they work with crops with higher production costs and potential profit. Philosophically, we must recognize that some nutrients are removed from soils by cropping, and these must be replaced eventually. We can remove stored nutrients from the soil, but this reduces soil fertility. For elements such as Zn, Cu, Mn, B, and Co, addition of elemental fertilizers is both effective and inexpensive in nearly all cases. Boron, Cu, and Zn fertilization are normal horticultural management practices. Soil testing or plant analysis can identify potential microelement fertility problems and deficiencies can be avoided by timely fertilizer application. Similarly, the pH of the surface soil can be economically raised by limestone to reduce the availability of some toxic ions such as Al and Mn. This approach has been called “Change the soil”.

The objectives of this investigation were to examine the long-term residual effects of metal loading through sewage sludge applications on the total vs. diethylene triamine pentacetic acid (DTPA) extractable metal concentrations in soil and leaf accumulations in tobacco. Maryland tobacco ( Nicotiana tabacum L.), cv. ‘MD 609’, was grown in 1983 and 1984 at two sites in Maryland that had been amended in 1972 with dewatered, digested sewage sludge from washington, DC, at rates equal to 0, 56, 112 and 224 mg ha −1 . The metal concentrations in the sludge, in mg kg −1 dry weight, were: 1300 Zn, 570 Cu, 280 Pb, 45 Ni and 13 Cd. Soil samples collected from the surface horizon and composite leaf samples of cured tobacco were analyzed for total Zn, Cu, Mn, Fe, Pb, Ni and Cd concentrations. The soil samples were also examined for soil pH and DTPA extractable metals. Equations were generated using polynomic and stepwise regression analyses which described the relationships between total vs. DTPA extractable soil metals, and between DTPA soil and soil pH vs. plant metal concentrations, respectively. Significant increases were observed for both total and DTPA extractable metal concentrations for all metals, with all but total Mn and Ni being significant for linear and quadratic effects regarding sludge rates. However, linear relationships were found between DTPA extractable vs. total soil concentrations for all elements except Pb and Ni which were quadratic. Significant increases in plant Zn, Cu, Mn, Ni and Cd and decreases in Fe were observed with increased sludge rates. Plant Pb levels were unaffected by sludge applied Pb. Linear relationships were observed between plant Zn and Cd and DTPA soil metal levels: however, Mn and Cu levels were described by quadratic and cubic relationship, respectively. Relationships between plant Fe and Pb and DTPA extractable concentrations were nonsignificant. Additional safeguards to protect crop contamination from heavy metals such as Cd were discussed.

Tomato plants (Lycopersicum esculentum Mill.) were grown for 21-days in a complete hydroponic nutrient solution including Fe(3+)-ethylenediamine-di(o-hydroxyphenylacetate) and subsequently switched to nutrient solution withholding Fe for 8 days to induce Fe stress. The roots of Fe-stressed plants reduced chelated Fe at rates sevenfold higher than roots of plants grown under Fe-sufficient conditions. The response in intact Fe-deficient roots was localized to root hairs, which developed on secondary roots during the period of Fe stress. Plasma membranes (PM) isolated by aqueous two-phase partitioning from tomato roots grown under Fe stress exhibited a 94% increase in rates of NADH-dependent Fe(3+)-citrate reduction compared to PM isolated from roots of Fe-sufficient plants. Optimal detection of the reductase activity required the presence of detergent indicating structural latency. In contrast, NADPH-dependent Fe(3+)-citrate reduction was not significantly different in root PM isolated from Fe-deficient versus Fe-sufficient plants and proceeded at substantially lower rates than NADH-dependent reduction. Mg(2+)-ATPase activity was increased 22% in PM from roots of Fe-deficient plants compared to PM isolated from roots of Fe-sufficient plants. The results localized the increase in Fe reductase activity in roots grown under Fe stress to the PM.

The application of municipal sewage sludge to agricultural land has become an established practice in the United States, especially in areas adjacent to major metropolitan centers.1 The U.S. Environmental Protection Agency (EPA) established guidelines for regulating the application of sludge materials on farmlands in the 1970s.2 However, several agricultural experiment stations in the highly urbanized northeastern states, including Maryland, have established their own guidelines for the disposal of sewage sludge on crop lands.1–3 The primary factors which limit the quantities of sludge that may be applied to an area are the amounts of heavy metals present in a given sludge and the nutrient requirements of the crops being grown.1,2 The N and P requirements of the crop generally limit the quantity of sludge that can be applied in a given year and the amount of heavy metals applied to soils are commonly used to establish lifetime loading limits.1–8,10,13,14

In dicotyledons, Fe3+ must be reduced to Fe2+ before uptake and transport of this essential macronutrient can occur. Ambler et al demonstrated that reduction along the root could be observed by the formation of a stain, Prussian blue (PB), Fe4 [Fe(CN)6]3 n H2O (where n = 14-16). This stain, which is an insoluble precipitate, forms at the reduction site when the nutrient solution contains Fe3+ and ferricyanide. In 1972, Chaney et al proposed a model which suggested that the Fe3+ reduction site occurred outside the cell membrane; however, no physical evidence to support the model was presented at that time. A more recent study using the PB stain indicates that rapid reduction of Fe3+ occurs in a region of the root containing young root hairs. Furthermore the most pronounced activity occurs in plants that are deficient in Fe. To more precisely localize the site of Fe3+ reduction, scanning electron microscopy (SEM), x-ray analysis, and transmission electron microscopy (TEM) were utilized to examine the distribution of the PB precipitate that was induced to form in roots.