@article{dall'orsoletta_gatiboni_mumbach_schmitt_boitt_smyth_2021, title={Soil slope and texture as factors of phosphorus exportation from pasture areas receiving pig slurry}, volume={761}, ISSN={["1879-1026"]}, DOI={10.1016/j.scitotenv.2020.144004}, abstractNote={Phosphorus (P) loss from agricultural areas to waterbodies is a worldwide concern. However, the effect of soil source and transport factors, such as clay (C) content and slope (S), on the magnitude of the P transport in Brazilian subtropical soils is still understudied. The objectives of this study were i) to quantify the loss of P fractions by runoff in areas receiving pig slurry application and with variations in S and C content; ii) propose an environmental critical limit model of P (P-threshold) for Brazilian subtropical soils. Thus, two series of experiments were conducted from 2016 to 2018, one under a Nitisol with 642 g kg−1 of C and another under a Cambisol with 225 g kg−1 of C. The treatments were four P rates (0, 56, 112 and 224 kg P ha−1 year−1) superficially applied as pig slurry, on Tifton (Cynodon sp) pasture, and three S (10, 20 and 30% in the Nitisol and 15, 25 and 35% in Cambisol). P losses increased in both soils as the S and P rates rose. The Nitisol showed P losses three times higher than the Cambisol. Soil S above 25% promotes P losses at a rate three times higher than in soil below this limit. Therefore, we propose a P-threshold model for Mehlich-1 extractable P levels for Brazilian subtropical soils as: “P-threshold = (42.287 + C) − (0.230 S + 0.0123 C S)” in soils with a S ≤ 25% and “P-threshold = (42.287 + C) − (−0.437 S + 0.039 C S)” in soils with a S >25%, where both C and S are shown in percentage. The soil clay content and slope are aggravating factors to the P transfer process, thus must be considered in suitable models to predict the P losses risk.}, journal={SCIENCE OF THE TOTAL ENVIRONMENT}, author={Dall'Orsoletta, D. J. and Gatiboni, L. C. and Mumbach, G. L. and Schmitt, D. E. and Boitt, G. and Smyth, T. J.}, year={2021}, month={Mar} }
 @article{stephenson_carvalho_castillo_crozier_smyth_heitman_2021, title={Water use and biomass yield of bioenergy crops in the North Carolina Piedmont}, volume={113}, ISSN={["1435-0645"]}, DOI={10.1002/agj2.20646}, abstractNote={Abstract}, number={3}, journal={AGRONOMY JOURNAL}, author={Stephenson, Thomas D. and Carvalho, Henrique D. R. and Castillo, Miguel S. and Crozier, Carl R. and Smyth, Thomas J. and Heitman, Joshua L.}, year={2021}, month={May}, pages={2463–2473} }
 @article{heitman_castillo_smyth_crozier_2018, title={Stem, Leaf, and Panicle Yield and Nutrient Content of Biomass and Sweet Sorghum}, volume={110}, ISSN={["1435-0645"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85052711959&partnerID=MN8TOARS}, DOI={10.2134/agronj2018.03.0178}, abstractNote={Core Ideas
Sorghum is a potential dedicated bioenergy crop both from biomass and sugar yields.
Increasing rates of N fertilizer affected biomass yield and nutrient removal for sorghum cultivar ES5200 by partitioning resources primarily toward the stem component.
For sorghum M81‐E, the seed head component accounted for a greater proportion of biomass, compared with sorghum ES5200, and biomass yield and nutrients were more evenly distributed among the three components.
Returning the leaf and seed head components back to the field to enhance soil fertility has the potential to provide at least 45, 7, and, 26 kg ha−1 of N, P, and K, respectively.
}, number={5}, journal={AGRONOMY JOURNAL}, author={Heitman, A. J. and Castillo, M. S. and Smyth, T. J. and Crozier, C. R.}, year={2018}, pages={1659–1665} }
 @article{wang_jot smyth_crozier_gehl_heitman_2018, title={Yield and Nitrogen Removal of Bioenergy Grasses as Influenced by Nitrogen Rate and Harvest Management in the Coastal Plain Region of North Carolina}, volume={11}, ISSN={1939-1234 1939-1242}, url={http://dx.doi.org/10.1007/S12155-017-9876-X}, DOI={10.1007/s12155-017-9876-x}, number={1}, journal={BioEnergy Research}, publisher={Springer Science and Business Media LLC}, author={Wang, Zan and Jot Smyth, T. and Crozier, Carl R. and Gehl, Ronald J. and Heitman, Adam J.}, year={2018}, month={Mar}, pages={44–53} }
 @article{heitman_castillo_smyth_crozier_wang_heiniger_gehl_2017, title={Nitrogen Fertilization Effects on Yield and Nutrient Removal of Biomass and Sweet Sorghum}, volume={109}, ISSN={["1435-0645"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85023770813&partnerID=MN8TOARS}, DOI={10.2134/agronj2016.12.0710}, abstractNote={Core Ideas
During the 4‐yr period of this trial, N fertilization increased dry matter yield in 2 out of 4 yr for biomass sorghum and there was no effect on dry matter yield of sweet sorghum.
High DM yield supports sorghum as a bioenergy crop, however, the relatively low nutrient removal rate may limit its utilization in nutrient‐rich environments such as spray fields.
Greatest dry matter yields achieved were ∼18.5 Mg ha−1 at a N fertilization rate of 67 kg N ha−1 yr−1 for biomass sorghum.
}, number={4}, journal={AGRONOMY JOURNAL}, author={Heitman, Adam J. and Castillo, Miguel S. and Smyth, T. Jot and Crozier, Carl R. and Wang, Zan and Heiniger, Ron W. and Gehl, Ronald J.}, year={2017}, pages={1352–1358} }
 @article{wang_heitman_smyth_crozier_franzluebbers_lee_gehl_2017, title={Soil Responses to Bioenergy Crop Production in the North Carolina Piedmont}, volume={109}, ISSN={["1435-0645"]}, DOI={10.2134/agronj2017.02.0068}, abstractNote={Core Ideas
Three bioenergy and two traditional cropping systems were compared in the North Carolina Piedmont.
Bioenergy crops sorghum, switchgrass, and giant mischanthus produced large yields.
Removal of N, P, and K was least for perennial bioenergy crops.
Perennial bioenergy crops had slightly poorer soil physical conditions after 3 yr.
Organic C pools were greatest with giant miscanthus and fescue.
}, number={4}, journal={AGRONOMY JOURNAL}, author={Wang, Zan and Heitman, Joshua L. and Smyth, T. Jot and Crozier, Carl R. and Franzluebbers, Alan and Lee, Sage and Gehl, Ronald J.}, year={2017}, pages={1368–1378} }
 @article{wang_smyth_crozier_gehl_heitman_2017, title={Yield and Nutrient Removal by Bioenergy Grasses on Swine Effluent Spray Fields in the Coastal Plain Region of North Carolina}, volume={10}, ISSN={1939-1234 1939-1242}, url={http://dx.doi.org/10.1007/S12155-017-9856-1}, DOI={10.1007/s12155-017-9856-1}, number={4}, journal={BioEnergy Research}, publisher={Springer Nature}, author={Wang, Zan and Smyth, T. Jot and Crozier, Carl R. and Gehl, Ronald J. and Heitman, Adam J.}, year={2017}, month={Jul}, pages={979–991} }
 @article{savala_crozier_smyth_2016, title={Poultry Manure Nitrogen Availability Influences Winter Wheat Yield and Yield Components}, volume={108}, ISSN={["1435-0645"]}, DOI={10.2134/agronj2015.0355}, abstractNote={Standard poultry manure use recommendations in North Carolina consider waste analysis but not differences among manure types, cropping seasons, or application timing. This study evaluated poultry manure source, N rate strategy, and application time effects on soft red winter wheat (Triticum aestivum L.) tiller density, yield components, grain yield, and N availability coefficients. Coefficients included fertilizer N equivalence based on grain yield and plant‐available N based on aboveground plant N content. Four field experiments used broiler litter (BL) and composted layer manure (CLM), two rates (67 and 134 kg total‐N ha−1), and three different application times (incorporated in October preplant, Feekes’ 3 in December/January, or Feekes’ 4 in February). Dual‐source treatments received 67 kg N ha−1 of manure plus 67 kg N ha−1 as urea ammonium nitrate (UAN) solution at Feekes’ 5. Fertilizer‐N (UAN) rate treatments (0, 39, 78, 117, and 156 kg N ha−1) were also included. Yields responded to N inputs but were lowest when BL and CLM were applied at 67 kg N ha−1 either preplant or at Feekes’ 3. Grain yield and N availability were greater with CLM than with BL (3.0 vs. 2.8 t ha−1 grain and 58 vs. 52 kg ha−1 N uptake, respectively). Availability coefficients ranged from 12 to 32%, lower than the standard assumed values of 50 to 60%. The feasible poultry manure application window includes preplant until Feekes’ 4, but fertilizing winter wheat crops solely with poultry manure may supply less N than intended.}, number={2}, journal={AGRONOMY JOURNAL}, author={Savala, Canon E. N. and Crozier, Carl R. and Smyth, T. Jot}, year={2016}, pages={864–872} }
 @article{jani_grossman_smyth_hu_2016, title={Winter legume cover-crop root decomposition and N release dynamics under disking and roller-crimping termination approaches}, volume={31}, ISSN={1742-1705 1742-1713}, url={http://dx.doi.org/10.1017/S1742170515000113}, DOI={10.1017/s1742170515000113}, abstractNote={Abstract}, number={3}, journal={Renewable Agriculture and Food Systems}, publisher={Cambridge University Press (CUP)}, author={Jani, Arun D. and Grossman, Julie and Smyth, Thomas J. and Hu, Shuijin}, year={2016}, pages={214–229} }
 @article{israel_smyth_2015, title={Crop Utilization of Nitrogen in Swine Lagoon Sludge}, volume={46}, ISSN={["1532-2416"]}, DOI={10.1080/00103624.2015.1043459}, abstractNote={Swine lagoon sludge is commonly applied to soil as a source of nitrogen (N) for crop production but the fate of applied N not recovered from the soil by the receiver crop has received little attention. The objectives of this study were to (1) assess the yield and N accumulation responses of corn (Zea mays L.) and wheat (Triticum aestivum) to different levels of N applied as swine lagoon sludge, (2) quantify recovery of residual N accumulation by the second and third crops after sludge application, and (3) evaluate the effect of different sludge N rates on nitrate (NO3-N) concentrations in the soil. Sludge N trials were conducted with wheat on two swine farms and with corn on one swine farm in the coastal plain of North Carolina. Agronomic optimum N rates for wheat grown at two locations was 360 kg total sludge N ha−1 and the optimum N rate for corn at one location was 327 kg total sludge N ha−1. Residual N recovered by subsequent wheat and corn crops following the corn crop that received lagoon sludge was 3 and 12 kg N ha−1, respectively, on a whole-plant basis and 2 and 10 kg N ha−1, respectively, on a grain basis at the agronomic optimum N rate for corn (327 kg sludge N ha−1). From the 327 kg ha−1 of sludge N applied to corn, 249 kg N ha−1 were not recovered after harvest of three crops for grain. Accumulation in recalcitrant soil organic N pools, ammonia (NH3) volatilization during sludge application, return of N in stover/straw to the soil, and leaching of NO3 from the root zone probably account for much of the nonutilized N. At the agronomic sludge N rate for corn (327 kg N ha−1), downward movement of NO3-N through the soil was similar to that for the 168 kg N ha−1 urea ammonium nitrate (UAN) treatment. Thus, potential N pollution of groundwater by land application of lagoon sludge would not exceed that caused by UAN application.}, number={12}, journal={COMMUNICATIONS IN SOIL SCIENCE AND PLANT ANALYSIS}, author={Israel, Daniel W. and Smyth, T. Jot}, year={2015}, month={Jul}, pages={1525–1539} }
 @article{jani_grossman_smyth_hu_2015, title={Influence of soil inorganic nitrogen and root diameter size on legume cover crop root decomposition and nitrogen release}, volume={393}, ISSN={["1573-5036"]}, DOI={10.1007/s11104-015-2473-x}, number={1-2}, journal={PLANT AND SOIL}, author={Jani, Arun D. and Grossman, Julie M. and Smyth, Thomas J. and Hu, Shuijin}, year={2015}, month={Aug}, pages={57–68} }
 @article{gatiboni_smyth_schmitt_cassol_oliveira_2015, title={SOIL PHOSPHORUS THRESHOLDS IN EVALUATING RISK OF ENVIRONMENTAL TRANSFER TO SURFACE WATERS IN SANTA CATARINA, BRAZIL}, volume={39}, ISSN={["0100-0683"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84943328551&partnerID=MN8TOARS}, DOI={10.1590/01000683rbcs20140461}, abstractNote={The State of Santa Catarina, Brazil, has agricultural and livestock activities, such as pig farming, that are responsible for adding large amounts of phosphorus (P) to soils. However, a method is required to evaluate the environmental risk of these high soil P levels. One possible method for evaluating the environmental risk of P fertilization, whether organic or mineral, is to establish threshold levels of soil available P, measured by Mehlich-1 extractions, below which there is not a high risk of P transfer from the soil to surface waters. However, the Mehlich-1 extractant is sensitive to soil clay content, and that factor should be considered when establishing such P-thresholds. The objective of this study was to determine P-thresholds using the Mehlich-1 extractant for soils with different clay contents in the State of Santa Catarina, Brazil. Soil from the B-horizon of an Oxisol with 800 g kg-1 clay was mixed with different amounts of sand to prepare artificial soils with 200, 400, 600, and 800 g kg-1 clay. The artificial soils were incubated for 30 days with moisture content at 80 % of field capacity to stabilize their physicochemical properties, followed by additional incubation for 30 days after liming to raise the pH(H2O) to 6.0. Soil P sorption curves were produced, and the maximum sorption (Pmax) was determined using the Langmuir model for each soil texture evaluated. Based on the Pmax values, seven rates of P were added to four replicates of each soil, and incubated for 20 days more. Following incubation, available P contents (P-Mehlich-1) and P dissolved in the soil solution (P-water) were determined. A change-point value (the P-Mehlich-1 value above which P-water starts increasing sharply) was calculated through the use of segmented equations. The maximum level of P that a soil might safely adsorb (P-threshold) was defined as 80 % of the change-point value to maintain a margin for environmental safety. The P-threshold value, in mg dm-3, was dependent on the soil clay content according to the model P-threshold = 40 + Clay, where the soil clay content is expressed as a percentage. The model was tested in 82 diverse soil samples from the State of Santa Catarina and was able to distinguish samples with high and low environmental risk.}, number={4}, journal={REVISTA BRASILEIRA DE CIENCIA DO SOLO}, author={Gatiboni, Luciano Colpo and Smyth, Thomas Jot and Schmitt, Djalma Eugenio and Cassol, Paulo Cezar and Oliveira, Clovisson Menotti}, year={2015}, pages={1225–1234} }
 @article{oliveira_gatiboni_miquelluti_smyth_almeida_2014, title={MAXIMUM PHOSPHORUS ADSORPTION CAPACITY AND BINDING ENERGY CONSTANT OF AN OXISOL FITTING DIFFERENT LANGMUIR MODELS}, volume={38}, ISSN={["0100-0683"]}, DOI={10.1590/s0100-06832014000600015}, abstractNote={A capacidade máxima de adsorção de fósforo (CMAP) é um parâmetro bastante útil para caracterizar a capacidade de adsorção de fósforo (P) do solo e, por isso, o modelo de Langmuir, que possibilita essa estimativa, é bastante difundido. Porém, se o ajuste da equação for realizado por modelos não lineares ou linearizados, ou se forem escolhidos modelos de região única ou múltiplas, nem sempre os valores estimados da CMAP e da constante de energia de ligação (k) são semelhantes. O objetivo deste trabalho foi avaliar o efeito do uso de diferentes métodos de ajuste do modelo de Langmuir sobre os valores estimados de CMAP e k. Para isso, utilizouse um único solo de alta capacidade de adsorção de P, o qual foi misturado a quantidades crescentes de areia lavada, construindo-se sistemas com capacidades de sorção crescentes, mas com a fase sólida constituída da mesma mineralogia. Foi utilizado solo do horizonte B de um Latossolo Bruno com 800 g kg-1 de argila, o qual foi misturado com areia em quantidades para obterem-se solos artificiais com 0, 200, 400, 600 e 800 g kg-1 de argila. Esses solos artificiais foram incubados por 30 dias com calcário para elevar o pH(H2O) até 6,0 e, após, foram secos em estufa e peneirados. Foram realizadas as isotermas de adsorção e os dados ajustados pelo modelo de Langmuir, usando os seguintes métodos: NLin - não linear com região única; L-1R - linearização com região única; L-2RG - linearização com duas regiões, ajuste gráfico; L-3RG - linearização com três regiões, ajuste gráfico; L-2RE linerização com duas regiões, ajuste estatístico. Os resultados evidenciaram que todos os métodos utilizados estimaram valores de CMAP proporcionais ao teor de argila dos solos e poderiam ser usados para caracterizar os solos. Contudo, quando utilizados ajustes com mais de uma região de adsorção, os valores da CMAP para a última região foram sensivelmente superiores àqueles observados após a incubação do solo com doses de P em um teste adicional. Isso indica que a CMAP da última região deve ser evitada como caracterizadora da capacidade de adsorção do solo. Conforme era esperado, os valores de k foram proporcionais aos teores de argila do solo na primeira (ou única) região dos modelos linearizados; contudo, não seguiram essa tendência no modelo não linear, recomendando-se cautela na interpretação da constante k ajustada por modelos não lineares.}, number={6}, journal={REVISTA BRASILEIRA DE CIENCIA DO SOLO}, author={Oliveira, Clovisson Menotti and Gatiboni, Luciano Colpo and Miquelluti, David Jose and Smyth, Thomas Jot and Almeida, Jaime Antonio}, year={2014}, pages={1805–1815} }
 @article{sobral_smyth_fageria_stone_2013, title={Comparison of Copper, Manganese, and Zinc Extraction with Mehlich 1, Mehlich 3, and DTPA Solutions for Soils of the Brazilian Coastal Tablelands}, volume={44}, ISSN={["1532-2416"]}, DOI={10.1080/00103624.2013.812731}, abstractNote={Deficiency of micronutrients is increasing in crop plants in recent years in Oxisols and Ultisols in the tropics. The predominant soils in the coastal tablelands of Brazil are Ultisols and Oxisols, with low cation exchange capacity and kaolinitic clay mineralogy. Soil copper (Cu), manganese (Mn), and zinc (Zn) extracted by the Mehlich 1 solution, currently used in the regional soil-testing laboratories, were compared with those extracted by the Mehlich 3 and diethylenetriaminepentaacetic acid (DTPA) solutions in a greenhouse experiment with 10 soil samples (0–20 cm deep) collected from representative Ultisols and Oxisols from various locations in the region. Corn was grown as a test crop, and its dry matter and micronutrient uptake was measured at 30 days of growth. Soil Cu, Mn, and Zn extracted with the three solutions were significantly correlated (0.65–0.95 range for r values), with the Mehlich 3 solution extracting greater quantities than the Mehlich 1 and DTPA solutions. Zinc and Cu taken up by corn plants were significantly related to their soil-extractable levels measured at harvest with all three of the solutions, except for Zn DTPA. However, similar relations between plant uptake and soil extractable Mn were poor, except for DTPA extracting solution.}, number={17}, journal={COMMUNICATIONS IN SOIL SCIENCE AND PLANT ANALYSIS}, author={Sobral, L. F. and Smyth, J. T. and Fageria, N. K. and Stone, L. F.}, year={2013}, month={Sep}, pages={2507–2513} }
 @article{shuai_yost_smyth_2011, title={Predicting Soil Phosphorus Fertilizer Rate Using Hierarchical Segmented Regression Models}, volume={176}, ISSN={["0038-075X"]}, DOI={10.1097/ss.0b013e318219db24}, abstractNote={Predicting soil phosphorus (P) needs and P fertilizer requirements is important for plant nutrition and reducing environmental risk. The P requirement (PR) can be calculated from three components: the current status of soil P (P0), soil P buffer coefficient (PBC), and the soil P critical level (PCL). The PBC and PCL can be predicted from soil clay content using linear-plateau models. The PR, PBC, and PCL form a hierarchical model because PR depends on PBC and PCL, which, in turn, depend on soil clay content. The objective of this study is to estimate the parameters in this hierarchical model to ensure reasonable performance and behavior of PR in a large range of soil clay contents. Results showed that the linear-plateau model described the change of PBC with soil clay content in the range of 39 to 760 g kg−1. This model also described the change of PCL with soil clay content in the range of 80 to 760 g kg−1 for six crops, including cotton, cowpea, maize, peanut, soybean, and wheat. The obtained PR showed irregular behavior of PR within soil clay content range from 288 to 357 g kg−1 when PBC and PCL were independently predicted from soil clay. When the join points in the linear-plateau models of PBC and PCL were set to be equal, the irregular change of PR with soil clay content disappeared. The hierarchically modeled system predicts a decrease in PR with increasing current status of soil P and a curve-plateau trend with soil clay content.}, number={6}, journal={SOIL SCIENCE}, author={Shuai, Xiufu and Yost, Russell S. and Smyth, T. Jot}, year={2011}, month={Jun}, pages={303–306} }
 @article{hashimoto_smyth_israel_hesterberg_2010, title={LACK OF SOYBEAN ROOT ELONGATION RESPONSES TO MICROMOLAR MAGNESIUM ADDITIONS AND FATE OF ROOT-EXUDED CITRATE IN ACID SUBSOILS}, volume={33}, ISSN={["1532-4087"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-73149088156&partnerID=MN8TOARS}, DOI={10.1080/01904160903434279}, abstractNote={Additions of micromolar concentrations of magnesium (Mg) to hydroponics enhance aluminum (Al) tolerance of soybean by increasing citrate secretion from roots and external complexation of toxic Al species. The objective of this study was to assess the ameliorative effect of Mg additions on soybean root elongation into mineralogically different acid soils. Roots of soybean seedlings grew for 28 days into acid soils treated with three Mg levels in their soil solution (Control, 150 and 300 μM) and lime. Root growth in the acid soils and aboveground dry matter responses to the Mg treatments were less than for the lime treatments. Citrate fate in the acid soils revealed that 66–99% of added citrate was either adsorbed or biodegraded, suggesting that root secreting citrate in the soil abundant with Al and iron (Fe) hydroxides potentially reduces the availability to complex rhizotoxic Al. A calcium (Ca) deficiency may have constrained root growth response to the Mg-treated soils.}, number={2}, journal={JOURNAL OF PLANT NUTRITION}, author={Hashimoto, Yohey and Smyth, T. Jot and Israel, Daniel W. and Hesterberg, Dean}, year={2010}, pages={219–239} }
 @article{grijalva_crozier_smyth_hardy_2010, title={Nitrogen, Phosphorus, and Liming Effects of Poultry Layer Manures in Coastal Plain and Piedmont Soils}, volume={102}, ISSN={["1435-0645"]}, DOI={10.2134/agronj2009.0283}, abstractNote={Since soil type and manure processing can affect nutrient release, laboratory and greenhouse experiments determined N and P availability, and liming value under representative layer manure application scenarios. Fresh, composted, and pelleted manures were applied to surface samples of three North Carolina soils (Belhaven, loamy, mixed, dysic, thermic Terric Haplosaprists; Cecil, fine, kaolinitic, thermic Typic Kanhapludults; and Lynchburg, fine‐loamy, siliceous, semiactive, thermic Aeric Paleaquults). A 90 d N mineralization incubation found greater N mineralization (83, 73, and 61% of total N applied in fresh, composted, and pelleted manures, respectively), in the Lynchburg than in the Cecil soil (41, 33, and 25% for the same manures); while mean N availability of urea was 80% for all soils. All manures exhibited effects on soil pH and Mehlich‐3 extractable soil P during separate 21 d incubations that were consistent with their calcium carbonate equivalence and total P content. In a 30 d greenhouse experiment with millet [Urochloa ramosa (L.) T. Q. Nguyen] in the same soils, plant available N from the manures followed the decreasing order of fresh > composted > pelleted, similar to the rank order obtained in the N incubation study. Application of either inorganic or manure P sources to the Belhaven muck resulted in more water soluble soil P and greater plant P uptake than when P was applied to the mineral soils. Both soil and manure source influenced manure nutrient availability, but the availability coefficients from these laboratory and greenhouse experiments should be verified under field conditions.}, number={5}, journal={AGRONOMY JOURNAL}, author={Grijalva, D. F. Montalvo and Crozier, C. R. and Smyth, T. J. and Hardy, D. H.}, year={2010}, pages={1329–1339} }
 @article{sao jose_silva_barros_novais_silva_smyth_leite_nunes_gebrim_2009, title={BORON MOBILITY IN EUCALYPTUS CLONES}, volume={33}, ISSN={["0100-0683"]}, DOI={10.1590/s0100-06832009000600022}, abstractNote={Understanding the magnitude of B mobility in eucalyptus may help to select clones that are more efficient for B use and to design new practices of B fertilization. This study consisted of five experiments with three eucalyptus clones (129, 57 and 58) where the response to and mobility of B were evaluated. Results indicated that clone 129 was less sensitive to B deficiency than clones 68 and 57, apparently due to its ability to translocate B previously absorbed via root systems to younger tissues when B in solution became limiting. Translocation also occurred when B was applied as boric acid only once to a single mature leaf, resulting in higher B concentration in roots, stems and younger leaves. The growth of B-deficient plants was also recovere by a single foliar application of B to a mature leaf. This mobility was greater, when foliar-applied B was supplied in complexed (boric acid + manitol) than in non-complexed form (boric acid alone). When the root system of clone 129 was split in two solution compartments, B supplied to one root compartment was translocated to the shoot and back to the roots in the other compartment, improving the B status and growth. Thus, it appears that B is relatively mobile in eucalyptus, especially in clone 129, and its higher mobility could be due to the presence of an organic compound such as manitol, able to complex B.}, number={6}, journal={REVISTA BRASILEIRA DE CIENCIA DO SOLO}, author={Sao Jose, Jackson Freitas and Silva, Ivo Ribeiro and Barros, Nairam Felix and Novais, Roberto Ferreira and Silva, Eulene Francisco and Smyth, Thomas Jot and Leite, Fernando Palha and Nunes, Flancer Novais and Gebrim, Fabricio Oliveira}, year={2009}, pages={1733–1744} }
 @article{silva_cortes correa_novais_smyth_rufty_silva_gebrim_nunes_2009, title={TIMING, LOCATION AND CROP SPECIES INFLUENCE THE MAGNITUDE OF AMELIORATION OF ALUMINUM TOXICITY BY MAGNESIUM}, volume={33}, ISSN={["0100-0683"]}, DOI={10.1590/s0100-06832009000100007}, abstractNote={The protective effect of cations, especially Ca and Mg, against aluminum (Al) rhizotoxicity has been extensively investigated in the last decades. The mechanisms by which the process occurs are however only beginning to be elucidated. Six experiments were carried out here to characterize the protective effect of Mg application in relation to timing, location and crop specificity: Experiment 1 - Protective effect of Mg compared to Ca; Experiment 2 - Protective effect of Mg on distinct root classes of 15 soybean genotypes; Experiment 3 - Effect of timing of Mg supply on the response of soybean cvs. to Al; Experiment 4 - Investigating whether the Mg protective effect is apoplastic or simplastic using a split-root system; Experiment 5 - Protective effect of Mg supplied in solution or foliar spraying, and Experiment 6 - Protective effect of Mg on Al rhizotoxicity in other crops. It was found that the addition of 50 mmol L-1 Mg to solutions containing toxic Al increased Al tolerance in 15 soybean cultivars. This caused soybean cultivars known as Al-sensitive to behave as if they were tolerant. The protective action of Mg seems to require constant Mg supply in the external medium. Supplying Mg up to 6 h after root exposition to Al was sufficient to maintain normal soybean root growth, but root growth was not recovered by Mg addition 12 h after Al treatments. Mg application to half of the root system not exposed to Al was not sufficient to prevent Al toxicity on the other half exposed to Al without Mg in rooting medium, indicating the existence of an external protection mechanism of Mg. Foliar spraying with Mg also failed to decrease Al toxicity, indicating a possible apoplastic role of Mg. The protective effect of Mg appeared to be soybean-specific since Mg supply did not substantially improve root elongation in sorghum, wheat, corn, cotton, rice, or snap bean when grown in the presence of toxic Al concentrations.}, number={1}, journal={REVISTA BRASILEIRA DE CIENCIA DO SOLO}, author={Silva, Ivo Ribeiro and Cortes Correa, Tarcisio Fernando and Novais, Roberto Ferreira and Smyth, T. Jot and Rufty, Thomas and Silva, Eulene Francisco and Gebrim, Fabricio Oliveira and Nunes, Flancer Novais}, year={2009}, pages={65–76} }
 @article{silva_cortes correa_novais_gebrim_nunes_salva_smyth_2008, title={PROTECTIVE EFFECT OF DIVALENT CATIONS AGAINST ALUMINUM TOXICITY IN SOYBEAN}, volume={32}, ISSN={["0100-0683"]}, DOI={10.1590/s0100-06832008000500027}, abstractNote={A large proportion of soybean fields in Brazil are currently cultivated in the Cerrado region, where the area planted with this crop is growing considerably every year. Soybean cultivation in acid soils is also increasing worldwide. Since the levels of toxic aluminum (Al) in these acid soils is usually high it is important to understand how cations can reduce Al rhizotoxicity in soybean. In the present study we evaluated the ameliorative effect of nine divalent cations (Ca, Mg, Mn, Sr, Sn, Cu, Zn, Co and Ba) in solution culture on Al rhizotoxicity in soybean. The growth benefit of Ca and Mg to plants in an acid Inceptisol was also evaluated. In this experiment soil exchangeable Ca:Mg ratios were adjusted to reach 10 and 60 % base saturation, controlled by different amounts of CaCl2 or MgCl2 (at proportions from 100:0 up to 0:100), without altering the soil pH level. The low (10 %) and adequate (60 %) base saturation were used to examine how plant roots respond to Al at distinct (Ca + Mg)/Al ratios, as if they were growing in soils with distinct acidity levels. Negative and positive control treatments consisted of absence (under native soil or undisturbed conditions) or presence of lime (CaCO3) to reach 10 and 60 % base saturation, respectively. It was observed that in the absence of Aluminum, Cu, Zn, Co and Sn were toxic even at a low concentration (25 µmol L-1), while the effect of Mn, Ba, Sr and Mg was positive or absent on soybean root elongation when used in concentrations up to 100 µmol L-1. At a level of 10 µmol L-1 Al, root growth was only reverted to the level of control plants by the Mg treatment. Higher Tin doses led to a small alleviation of Al rhizotoxicity, while the other cations reduced root growth or had no effect. This is an indication that the Mg effect is ion-specific and not associated to an electrostatic protection mechanism only, since all ions were divalent and used at low concentrations. An increased exchangeable Ca:Mg ratio (at constant soil pH) in the acid soil almost doubled the soybean shoot and root dry matter even though treatments did not modify soil pH and exchangeable Al3+. This indicates a more efficient alleviation of Al toxicity by Mg2+ than by Ca2+. The reason for the positive response to Mg2+ was not the supply of a deficient nutrient because CaCO3 increased soybean growth by increasing soil pH without inducing Mg2+ deficiency. Both in hydroponics and acid soil, the reduction in Al toxicity was accompanied by a lower Al accumulation in plant tissue, suggesting a competitive cation absorption and/or exclusion of Al from plant tissue stimulated by an Mg-induced physiological mechanism.}, number={5}, journal={REVISTA BRASILEIRA DE CIENCIA DO SOLO}, author={Silva, Ivo Ribeiro and Cortes Correa, Tarcisio Fernando and Novais, Roberto Ferreira and Gebrim, Fabricio de Oliveira and Nunes, Flancer Novais and Salva, Eulene Francisco and Smyth, Thomas Jot}, year={2008}, pages={2061–2071} }
 @article{perez_smyth_israel_2007, title={Comparative effects of two forage species on rhizosphere acidification and solubilization of phosphate rocks of different reactivity}, volume={30}, DOI={10.1080/01904160701556778}, abstractNote={ABSTRACT Dissolution of phosphate rocks (PR) in soils requires an adequate supply of acid (H+) and the removal of the dissolved products [calcium (Ca2 +) and dihydrogen phosphate (H2PO4 −)]. Plant roots may excrete H+ or OH− in quantities that are stoichiometrically equal to excess cation or anion uptake in order to maintain internal electroneutrality. Extrusion of H+ or OH− may affect rhizosphere pH and PR dissolution. Differences in rhizosphere acidity and solubilization of three PRs were compared with triple superphosphate between a grass (Brachiaria decumbens) and a legume (Stylosanthes guianensis) forage species at two pH levels (4.9 and 5.8) in a phosphorus (P)-deficient Ultisol with low Ca content. The experiment was performed in a growth chamber with pots designed to isolate rhizosphere and non-rhizosphere soil. Assessment of P solubility with chemical extractants led to ranking the PRs investigated as either low (Monte Fresco) or high solubility (Riecito and North Carolina). Solubilization of the PRs was influenced by both forage species and mineral composition of the PR. The low solubility PR had a higher content of calcite than the high solubility PRs, which led to increased soil pH values (> 7.0) and exchangeable Ca, and relatively little change in bicarbonate-extractable soil P. Rhizosphere soil pH decreased under Stylosanthes but increased under Brachiaria. The greater ability of Stylosanthes to acidify rhizosphere soil and solubilize PR relative to Brachiaria is attributed to differences between species in net ion uptake. Stylosanthes had an excess cation uptake, defined by a large Ca uptake and its dependence on N2 fixation, which induced a significant H+ extrusion from roots to maintain cell electroneutrality. Brachiaria had an excess of anion uptake, with nitrate (NO3 −) comprising 92% of total anion uptake. Nitrate and sulfate (SO4 2 −) reduction in Brachiaria root cells may have generated a significant amount of cytoplasmic hydroxide (OH−), which could have increased cytoplasmic pH and induced synthesis of organic acids and OH− extrusion from roots.}, number={7-9}, journal={Journal of Plant Nutrition}, author={Perez, M. J. and Smyth, T. J. and Israel, D. W.}, year={2007}, pages={1421–1439} }
 @article{hashimoto_smyth_hesterberg_israel_2007, title={Soybean root growth in relation to ionic composition in magnesium-amended acid subsoils: Implications on root citrate ameliorating aluminum constraints}, volume={53}, ISSN={["1747-0765"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-36249018938&partnerID=MN8TOARS}, DOI={10.1111/j.1747-0765.2007.00191.x}, abstractNote={Abstract Hydroponic studies with soybean (Glycine max [L.] Merr.) have shown that µmol L−1 additions of Mg2+ were as effective in ameliorating Al rhizotoxicity as additions of Ca2+in the mmol L−1 concentration range. The objectives of this study were to assess the ameliorative effects of Mg on soybean root growth in acidic subsoils and to relate the soil solution ionic compositions to soybean root growth. Roots of soybean cultivar Plant Introduction 416937 extending from a limed surface soil compartment grew for 28 days into a subsurface compartment containing acid subsoils from the Cecil (oxidic and kaolinitic), Creedmoor (montmorillonitic) and Norfolk (kaolinitic) series. The three Mg treatments consisted of native equilibrium soil solution concentrations in each soil (50 or 100 µmol L−1) and MgCl2 additions to achieve 150 and 300 µmol L−1 Mg (Mg150 and Mg300, respectively) in the soil solutions. Root elongations into Mg-treated subsoils were compared with a CaCO3 treatment limed to achieve a soil pH value of 6. Subsoil root growth responses to the Mg treatments were less than for the lime treatments. Root length relative to the limed treatments for all subsoils (RRL) was poorly related to the activity of the soil solution Al species (Al3+ and Al-hydroxyl species) and Mg2+. However, the RRL values were more closely related to the parameters associated with soil solution Ca activity, including (Ca2+), (Al3+)/(Ca2+) and (Al3+)/([Ca2+] + [Mg2+]), suggesting that Ca could be a primary factor ameliorating Al and H+ rhizotoxicity in these subsoils. Increased tolerance to Al rhizotoxicity of soybean by micromolar Mg additions to hydroponic solutions, inducing citrate secretion from roots to externally complex toxic Al, may be less important in acid subsoils with low native Ca levels.}, number={6}, journal={SOIL SCIENCE AND PLANT NUTRITION}, author={Hashimoto, Yohey and Smyth, T. Jot and Hesterberg, Dean and Israel, Daniel W.}, year={2007}, month={Dec}, pages={753–763} }
 @article{fichtner_hesterberg_smyth_shew_2006, title={Differential sensitivity of Phytophthora parasitica var. nicotianae and Thielaviopsis basicola to monomeric aluminum species}, volume={96}, ISBN={0031-949X}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-33644892775&partnerID=MN8TOARS}, DOI={10.1094/phyto-96-0212}, abstractNote={ Aluminum (Al) is toxic to many plant pathogens, including Thielaviopsis basicola and Phytophthora parasitica var. nicotianae. Because fungi-toxicity of Al has been described in soils over a wide pH range, multiple species of Al may be responsible for pathogen suppression. The goals of this work were to determine the sensitivity of T. basicola and P. para-sitica var. nicotianae to Al over a range of pH values, quantify the toxicity of monomeric Al species to production of sporangia of P. parasitica var. nicotianae and chlamydospores of T. basicola, and detect the accumulation of Al in pathogen structures. A complete factorial treatment design was used with Al levels ranging from 0 to 100 μM and pH levels ranging from 4 to 6 in a minimal salts medium. The chemistry of test solutions was modeled using GEOCHEM-PC. Colonies were grown in 5% carrot broth, and after 1 or 2 days, the nutrient solution was removed, colonies were rinsed with water, and Al test solutions were added to each of four replicate plates. After 2 days, propagules were counted and colonies were stained with the Al-specific, fluorescent stain lumogallion. The oomycete P. parasitica var. nicotianae was sensitive to multiple monomeric Al species, whereas sensitivity of T. basicola to Al was pH-dependent, suggesting that only Al3+ is responsible for suppression of this fungal pathogen. Chlamydospore production by T. basicola was inhibited at pH values <5.0 and Al levels >20 μM, whereas sporangia production by P. parasitica was inhibited at Al levels as low as 2 μM across all pH values tested. The lumogallion stain was an effective technique for detection of Al in fungal tissues. Aluminum accumulated in sporangia and zoospores of P. parasitica var. nicotianae and in nonmelanized chlamy-dospores of T. basicola, but not in cell walls of either organism. The differential sensitivity of the two organisms may indicate that true fungi respond differently to Al than members of the oomycota, which are more closely related to plants. }, number={3}, journal={Phytopathology}, author={Fichtner, E. J. and Hesterberg, Dean and Smyth, T. J. and Shew, H. D.}, year={2006}, pages={212} }
 @article{lima_silva_neves_novais_barros_mendonca_smyth_moreira_leite_2006, title={Soil organic carbon dynamics following afforestation of degraded pastures with eucalyptus in southeastern Brazil}, volume={235}, ISSN={["1872-7042"]}, DOI={10.1016/j.foreco.2006.08.331}, abstractNote={Afforestation of degraded pastures can potentially enhance carbon sequestration, but little is known about the effects of eucalyptus plantations on soil organic matter (SOM) fractions. We used density and particle size SOM fractionations to evaluate changes in SOM for a chronosequence of eucalyptus plantations established on degraded pastures in two contrasting regions in southeastern Brazil. Declines in the content of soil C derived from the pasture (C4 photosynthetic pathway) and the accumulation of that derived from the eucalyptus (C3 photosynthetic pathway) were followed through 13C natural abundance of the SOM. The two study areas were in the Rio Doce River Valley, Minas Gerais State, namely: 1, Belo Oriente (BO, a region with lower elevation, higher mean annual temperature, lower forest productivities and dominated by clayey Typic Haplustoxs); 2, Virginópolis (VG, a region of higher elevation, higher forest productivities and dominated by clayey Rhodic Ustoxs). In the BO region the chronosequence included 0, 4.2, 13.2, 22.2, 32.0 and 34.2 years of eucalyptus cultivation and in the VG region soils were cultivated with eucalyptus for 0, 8.2, 19.2, 29.2 and 33.2 years. The accumulated cultivation time corresponds to about five rotations. In both regions the initial soil condition was represented by a site that was still under pasture. Soil samples collected at 0–10 and 10–20 cm depths were analyzed for: total organic carbon (TOC); C in the fulvic (FAF), humic (HAF) and humin (HF) fractions; C in the free (FLF) and occluded (OLF) light fractions; C associated with the heavy fractions, namely, the sand (SF), silt plus clay (S + CF) and clay (CF) fractions; and C in the microbial biomass (MB). Carbon stocks of virtually all SOM fractions were about twice as high in the VG region than in the BO region. Eucalyptus cultivation in the BO region increased C stocks in all SOM fractions, except for the MB fraction that was not altered and the SF fraction that declined with time of eucalyptus cultivation. Increases in TOC, FAF and HF organic C fractions were observed in the VG region. Mean annual accumulations across the entire cultivation period in the 0–10 cm soil layer showed virtually no difference averaging 0.22 Mg C ha−1 year−1 for the BO region and 0.23 Mg C ha−1 year−1 for the VG region. However, gains of TOC peaked by the end of the third rotation in the BO region and the second rotation in the VG region, so the TOC accumulation rate during the respective aggrading periods would correspond to 0.35 and 0.57 Mg C ha−1 year−1. There was no clear evidence that the more labile, fast cycling SOM fractions were more sensitive indicators of the impact of eucalyptus cultivation in the BO region, whereas in the VG region the FLF and OLF were more sensitive to the land use change than TOC.}, number={1-3}, journal={FOREST ECOLOGY AND MANAGEMENT}, author={Lima, Augusto M. N. and Silva, Ivo R. and Neves, Julio C. L. and Novais, Roberto F. and Barros, Nairam F. and Mendonca, Eduardo S. and Smyth, Thomas J. and Moreira, Michelle S. and Leite, Fernando P.}, year={2006}, month={Nov}, pages={219–231} }
 @article{pegoraro_silva_novais_mendonca_alvarez_nunes_fonseca_smyth_2005, title={Diffusive flux of cationic micronutrients in two oxisols as affected by low-molecular-weight organic acids and cover-crop residue}, volume={168}, ISSN={["1522-2624"]}, DOI={10.1002/jpln.200421455}, abstractNote={Abstract}, number={3}, journal={JOURNAL OF PLANT NUTRITION AND SOIL SCIENCE}, author={Pegoraro, RF and Silva, IR and Novais, RF and Mendonca, ES and Alvarez, VHV and Nunes, FN and Fonseca, FM and Smyth, TJ}, year={2005}, month={Apr}, pages={334–340} }
 @article{soto_luna-orea_wagger_smyth_alvarado_2005, title={Foliage residue decomposition and nutrient release in peach palm (Bactris gasipaes Kunth) plantations for heart-of-palm production in Costa Rica}, volume={97}, ISSN={["1435-0645"]}, DOI={10.2134/agronj2004.0250}, abstractNote={Peach palm (Bactris gasipaes Kunth) for heart‐of‐palm production exports relatively low amounts of nutrients from the field and leaves considerable amounts of residue and nutrients on the ground as mulch. The primary objective of this study was to gain an understanding of residue decomposition and nutrient release patterns of peach palm foliage in a mature plantation in Costa Rica. The study was conducted within a 16‐yr commercial peach palm stand during two typically seasonal wet periods and one typically dry period. The third leaf of the five leaves cut during harvest of the stem portion were placed in 1‐mm mesh nylon bags. Bags were placed on the soil surface and retrieved at 1, 2, 4, 8, 16, 24, 32, 40, and 48 wk. Initial residue N concentrations over the three placement periods ranged from 24.2 to 28.1 g kg−1, C to N ratios between 16:1 and 17:1, cellulose from 251 to 325 g kg−1, and lignin from 80 to 104 g kg−1. There was no effect of seasonal periods on residue decomposition and N, P, and K release. Residue decomposition and nutrient release were best fitted by single‐exponential, three‐parameter models. The residue decomposition rate was 0.1472 wk−1 while nutrient release rates ranged from 0.0297 to 0.2998 wk−1. The potentially available nutrient pools in 4‐ and 8‐yr peach palm stands from a companion experiment ranged on an annual basis from 93 to 107 kg N ha−1, 14 to 15 kg P ha−1, 90 to 116 kg K ha−1, 19 to 23 kg Ca ha−1, and 13 to 14 kg Mg ha−1. The relatively rapid decomposition and nutrient release rates would seem to be ideal for this perennial cropping system where plants are continuously absorbing nutrients during the year to support the growth of offshoots that eventually become harvestable stems.}, number={5}, journal={AGRONOMY JOURNAL}, author={Soto, G and Luna-Orea, P and Wagger, MG and Smyth, TJ and Alvarado, A}, year={2005}, pages={1396–1402} }
 @article{silva_ferrufino_sanzonowicz_smyth_israel_junior_2005, title={Interactions between magnesium, calcium, and aluminum on soybean root elongation}, volume={29}, ISSN={["0100-0683"]}, DOI={10.1590/s0100-06832005000500010}, abstractNote={Alleviation of Al rhizotoxicity by Ca and Mg can differ among species and genotypes. Root elongation of soybean [Glycine max (L.) Merr.] line N93-S-179 and cvs. Young and Ransom exposed to varying concentrations of Al, Ca and Mg were compared in two experiments using a vertically split root system. Roots extending from a surface compartment with limed soil grew for 12 days into a subsurface compartment with nutrient solution treatments maintained at pH 4.6 with either 0 or 15 µmol L-1 Al. Calcium and Mg concentrations in treatments ranging from 0 to 20 mmol L-1. Although an adequate supply of Mg was provided in the surface soil compartment for soybean top growth, an inclusion of Mg was necessary in the subsurface solutions to promote root elongation in both the presence and absence of Al. In the absence of Al in the subsurface solution, tap root length increased by 74 % and lateral root length tripled when Mg in the solutions was increased from 0 to either 2 or 10 mmol L-1. In the presence of 15 µmol L-1 Al, additions of 2 or 10 mmol L-1 Mg increased tap root length fourfold and lateral root length by a factor of 65. This high efficacy of Mg may have masked differences in Al tolerance between genotypes N93 and Young. Magnesium was more effective than Ca in alleviating Al rhizotoxicity, and its ameliorative properties could not be accounted for by estimated electrostatic changes in root membrane potential and Al3+ activity at the root surface. The physiological mechanisms of Mg alleviation of Al injury in roots, however, are not known.}, number={5}, journal={REVISTA BRASILEIRA DE CIENCIA DO SOLO}, author={Silva, IR and Ferrufino, A and Sanzonowicz, C and Smyth, TJ and Israel, DW and Junior, TEC}, year={2005}, pages={747–754} }
 @article{stewart_dibb_johnston_smyth_2005, title={The contribution of commercial fertilizer nutrients to food production}, volume={97}, ISSN={["0002-1962"]}, DOI={10.2134/agronj2005.0001}, abstractNote={Nutrient inputs in crop production systems have come under increased scrutiny in recent years because of the potential for environmental impact from inputs such as N and P. The benefits of nutrient inputs are often minimized in discussions of potential risk. The purpose of this article is to examine existing data and approximate the effects of nutrient inputs, specifically from commercial fertilizers, on crop yield. Several long‐term studies in the USA, England, and the tropics, along with the results from an agricultural chemical use study and nutrient budget information, were evaluated. A total of 362 seasons of crop production were included in the long‐term study evaluations. Crops utilized in these studies included corn (Zea mays L.), wheat (Triticum aestivum L.), soybean [Glycine max (L.) Merr.], rice (Oryza sativa L.), and cowpea [Vigna unguiculata (L.) Walp.]. The average percentage of yield attributable to fertilizer generally ranged from about 40 to 60% in the USA and England and tended to be much higher in the tropics. Recently calculated budgets for N, P, and K indicate that commercial fertilizer makes up the majority of nutrient inputs necessary to sustain current crop yields in the USA. The results of this investigation indicate that the commonly cited generalization that at least 30 to 50% of crop yield is attributable to commercial fertilizer nutrient inputs is a reasonable, if not conservative estimate.}, number={1}, journal={AGRONOMY JOURNAL}, author={Stewart, WM and Dibb, DW and Johnston, AE and Smyth, TJ}, year={2005}, pages={1–6} }
 @article{ares_quesada_boniche_yost_molina_smyth_2002, title={Allometric relationships in Bactris gasipaes for heart-of-palm production agroecosystems in Costa Rica}, volume={138}, ISSN={["0021-8596"]}, DOI={10.1017/S0021859602002009}, abstractNote={Peach palm (Bactris gasipaes Kunth) agroecosystems for hearts-of-palm constitute a productive and sustainable land use for the humid tropics. Allometric models allow to predict biomass non-destructively at any time, and subsequently, to determine the span of growth phases, biomass and nutrient pools, and economic yields. The overall goals of this study were to obtain and validate predictive functions of above-ground dry biomass of peach palm shoots, and to relate standing biomass with heart-of-palm yields as well. Towards this purpose, peach palm shoots were harvested and separated into components (foliage, petiole and stem) in the Atlantic region of Costa Rica. Basal diameter (BD) was a more effective predictor of biomass than height to the fork between the spear leaf and the first fully expanded leaf, total height and number of leaves. Regression models explained 70–89% of the variance in component (foliage, petiole and stem) or total shoot biomass. Nonlinear regression, which independently calculates equation coefficients for biomass components and total shoot biomass, was compared with a nonlinear seemingly unrelated regression (NSUR) procedure, which simultaneously fits the component equations that predict leaf, petiole and stem in order to assure biomass additivity. Equation coefficients for NSUR fitted-regressions that also model unequal variances, were substantially different from those for individual regressions; e.g. Biomassleaf = 11·4739 BD1·8042, Residual mean square (RMS) = 69·9 for the individual equation, versus Biomassleaf = 6·841 BD2·086, RMS = 72·4 for the NSUR fitted-equation. NSUR equations had slightly less precision in estimating biomass than individual equations but consistently less bias. In separate harvests of peach palm plants within four stands ranging in age from 1·9 to 21 years, estimates of component and total above-ground shoot biomass were similar to observed values except for the youngest stand in which biomass was overestimated. In another harvest, yield of heart-of-palm per plant was linearly related to total above-ground biomass in two peach palm stands of age 5 and 9 years. The non-destructive estimation of above-ground biomass from easily measured plant dimensions will permit any-time, less expensive and reasonable precise biomass estimates in peach palm. Biomass data can be incorporated to decision support aids for nutrient management in heart-of-palm agroecosystems and serve other purposes such as for carbon sequestration calculations.}, journal={JOURNAL OF AGRICULTURAL SCIENCE}, author={Ares, A and Quesada, JP and Boniche, J and Yost, RS and Molina, E and Smyth, J}, year={2002}, month={May}, pages={285–292} }
 @article{silva_smyth_israel_rufty_2001, title={Altered aluminum inhibition of soybean root elongation in the presence of magnesium}, volume={230}, DOI={10.1023/A:1010384516517}, number={2}, journal={Plant and Soil}, author={Silva, I. R. and Smyth, T. J. and Israel, D. W. and Rufty, T. W.}, year={2001}, pages={223–230} }
 @article{silva_smyth_raper_carter_rufty_2001, title={Differential aluminum tolerance in soybean: An evaluation of the role of organic acids}, volume={112}, ISSN={["1399-3054"]}, DOI={10.1034/j.1399-3054.2001.1120208.x}, abstractNote={The role of organic acids in aluminum (Al) tolerance has been the object of intensive research. In the present work, we evaluated the roles of organic acid exudation and concentrations at the root tip on Al tolerance of soybean. Exposing soybean seedlings to Al3+ activities up to 4.7 μM in solution led to different degrees of restriction of primary root elongation. Al tolerance among genotypes was associated with citrate accumulation and excretion into the external media. Citrate and malate efflux increased in all genotypes during the first 6 h of Al exposure, but only citrate efflux in Al‐tolerant genotypes was sustained for an extended period. Tolerance to Al was correlated with the concentration of citrate in root tips of 8 genotypes with a range of Al sensitivities (r2=0.75). The fluorescent stain lumogallion indicated that more Al accumulated in root tips of the Al‐sensitive genotype Young than the Al‐tolerant genotype PI 416937, suggesting that the sustained release of citrate from roots of the tolerant genotype was involved in Al exclusion. The initial stimulation of citrate and malate excretion and accumulation in the tip of all genotypes suggested the involvement of additional tolerance mechanisms. The experiments included an examination of Al effects on lateral root elongation. Extension of lateral roots was more sensitive to Al than that of tap roots, and lateral root tips accumulated more Al and had lower levels of citrate.}, number={2}, journal={PHYSIOLOGIA PLANTARUM}, author={Silva, IR and Smyth, TJ and Raper, CD and Carter, TE and Rufty, TW}, year={2001}, month={Jun}, pages={200–210} }
 @article{silva_smyth_israel_raper_rufty_2001, title={Magnesium ameliorates aluminum rhizotoxicity in soybean by increasing citric acid production and exudation by roots}, volume={42}, ISSN={["1471-9053"]}, DOI={10.1093/pcp/pce067}, abstractNote={Superior effectiveness of Mg over Ca in alleviating Al rhizotoxicity cannot be accounted for by predicted changes in plasma membrane Al3+ activity. The influence of Ca and Mg on the production and secretion of citrate and malate, and on Al accumulation by roots was investigated with soybean genotypes Young and PI 416937 which differ in Al tolerance. In the presence of a solution Al3+ activity of 4.6 microM, citrate and malate concentrations of tap root tips of both genotypes increased with additions of either Ca up to 3 mM or Mg up to 50 microM. Citrate efflux rate from roots exposed to Al was only enhanced with Mg additions and exceeded malate efflux rates by as much as 50-fold. Maximum citrate release occurred within 12 h after adding Mg to solution treatments. Adding 50 microM Mg to 0.8 mM CaSO4 solutions containing Al3+ activities up to 4.6 microM increased citrate concentration of tap root tips by 3- to 5-fold and root exudation of citrate by 6- to 9-fold. Plants treated with either 50 microM Mg or 3 mM Ca had similar reductions in Al accumulation at tap root tips, which coincided with the respective ability of these ions to relieve Al rhizotoxicity. Amelioration of Al inhibition of soybean root elongation by low concentrations of Mg in solution involved Mg-stimulated production and efflux of citrate by roots.}, number={5}, journal={PLANT AND CELL PHYSIOLOGY}, author={Silva, IR and Smyth, TJ and Israel, DW and Raper, CD and Rufty, TW}, year={2001}, month={May}, pages={546–554} }
 @article{silva_smyth_israel_raper_rufty_2001, title={Magnesium is more efficient than calcium in alleviating aluminum rhizotoxicity in soybean and its ameliorative effect is not explained by the Gouy-Chapman-Stern model}, volume={42}, ISSN={["1471-9053"]}, DOI={10.1093/pcp/pce066}, abstractNote={The mechanistic basis for cation amelioration of Al rhizotoxicity in soybean was investigated through a series of studies comparing protective effects of Ca and Mg against Al inhibition of root elongation in a background 0.8 mM CaSO4 solution (pH 4.3). A modified Gouy-Chapman-Stern model was used to evaluate the effect of cations on electrical potential and Al3+ activity at root plasma membrane surfaces. Activities of Al3+ up to 4.6 microM in the background solution inhibited soybean tap root elongation by more than 80%. There was little or no response in root elongation when Ca and Mg were added to background solutions in the absence of AL: When added to Al-toxic solutions in the micromolar concentration range, Mg was 100-fold more effective than Ca in alleviating Al toxicity, whereas both cations were equally effective when added in the millimolar concentration range. The protective effect of micromolar additions of Mg on root elongation was specific for Al and it failed to alleviate La rhizotoxicity. In contrast to wheat, Mg amelioration of Al toxicity to soybean root elongation at low Mg concentration could not be explained by changes in potential and Al3+ activity at the root plasma membrane surfaces as predicted by a Gouy-Chapman-Stern model. These results suggest that Mg is not acting as an indifferent cation when present at low concentration and implies the involvement of a mechanism other than pure electrostatic effects at the root surface.}, number={5}, journal={PLANT AND CELL PHYSIOLOGY}, author={Silva, IR and Smyth, TJ and Israel, DW and Raper, CD and Rufty, TW}, year={2001}, month={May}, pages={538–545} }
 @article{silva_smyth_moxley_carter_allen_rufty_2000, title={Aluminum accumulation at nuclei of cells in the root tip. Fluorescence detection using lumogallion and confocal laser scanning microscopy}, volume={123}, ISSN={["1532-2548"]}, DOI={10.1104/pp.123.2.543}, abstractNote={Abstract}, number={2}, journal={PLANT PHYSIOLOGY}, author={Silva, IR and Smyth, TJ and Moxley, DF and Carter, TE and Allen, NS and Rufty, TW}, year={2000}, month={Jun}, pages={543–552} }
 @article{oliveira_novais_smyth_neves_2000, title={Aluminum diffusion in oxisols as influenced by soil water matric potential, pH, lime, gypsum, potassium chloride, and calcium phosphate}, volume={31}, ISSN={["0010-3624"]}, DOI={10.1080/00103620009370606}, abstractNote={Abstract Plant root exposure to soil aluminum (Al) depends on the soil solution Al concentration and transport to the root by diffusion. Changes in Al diffusive flux for two Oxisols was measured under laboratory conditions as a function of pH, water matric potential, and applications of gypsum, potassium chloride, and calcium phosphate. Double‐faced cation exchange resin sheets served as sinks for Al transported during 10‐day incubations through chambers containing 314 cm3 of soil. Across a range of soil pH values from 4.5 to 5.5, maximum diffusive flux of Al occurred at pH values of 4.7–4.8 in both soils and corresponded to increases of 2.2–3.0% relative to the unlimed treatment. Between pH values of 4.7–4.8 and 5.4, diffusive flux of Al decreased by 38 and 46% in the two Oxisols. Diffusive flux of Al decreased by 16–20% for the two Oxisols as soil water potentials decreased from ‐10 to ‐200 kPa. Magnitude of the reductions in diffusive flux of Al with decreasing soil water potential were less than those reported for diffusive flux of phosphorus (P) in prior investigations. Diffusive flux of Al increased by as much as 4‐fold with additions of CaSO4 and KCl, which increased the soil solution Al concentration. Additions of 400 mg P dm‐3 of soil had no effect on Al diffusion in either Oxisol.}, number={15-16}, journal={COMMUNICATIONS IN SOIL SCIENCE AND PLANT ANALYSIS}, author={Oliveira, FHT and Novais, RF and Smyth, TJ and Neves, CJL}, year={2000}, pages={2523–2533} }
 @article{oliveira_novais_smyth_neves_2000, title={Comparisons of phosphorus availability between anion exchange resin and Mehlich-1 extractions among oxisols with different capacity factors}, volume={31}, ISSN={["0010-3624"]}, DOI={10.1080/00103620009370464}, abstractNote={Abstract Acid and dilute‐salt chemical extractants are commonly used to assess and adjust phosphorus (P) availability in soils. Soybean was grown for 45 days under greenhouse conditions on samples of 10 Oxisols treated with variable levels of soluble P to compare critical soil P levels between an anion exchange resin (AER) and the Mehlich‐1 extractant, and to evaluate the influence of the soil P capacity factor (PCF) on the critical soil P levels. Variation among soils in the quantities of extracted P and critical P levels with the AER was less than that with Mehlich‐1. Low correlation values between soil characteristics related to PCF and measurements of AER soil P suggested that the AER method was not as sensitive to variations in soil PCF as Mehlich‐1. Interpretations of AER critical P levels, therefore, do not need auxiliary measures of PCF as with the Mehlich‐1 extractant. The reverse was true, however, for P uptake. Therefore, the criteria used to assess plant response to P (P uptake or dry matter production) in soils with variable PCF will influence the results obtained in correlations between methods used to extract soil P.}, number={5-6}, journal={COMMUNICATIONS IN SOIL SCIENCE AND PLANT ANALYSIS}, author={Oliveira, FHT and Novais, RF and Smyth, TJ and Neves, JCL}, year={2000}, pages={615–630} }
 @article{ferrufino_smyth_israel_carter_2000, title={Root elongation of soybean genotypes in response to acidity constraints in a subsurface solution compartment}, volume={40}, ISSN={["0011-183X"]}, DOI={10.2135/cropsci2000.402413x}, abstractNote={Aluminum‐tolerant germplasm is needed to overcome subsurface acidity constraints to root growth and plant access to water and nutrients. Root elongation of four soybean [Glycine max (L.) Merr.] genotypes exposed to varying concentrations of Al, H, and Ca were compared in two experiments using a vertically split root system. Roots extending from a limed surface soil compartment grew for 12 d into a subsurface compartment with nutrient solution treatments. In Exp. 1 root growth for cv. Ransom and Plant Introduction 416937 (PI) were compared in solutions with factorial combinations of pH (4.2, 5.2) and Al (0, 7.5, 15 μM) with Ca maintained at 10 mM In Exp. 2 soybean line N93‐S‐179 (N93), PI, and cultivars Ransom and Young were compared in solutions with factorial combinations of Ca (2 and 10 mM) and Al (7.5 and 15 μM) maintained at pH 4.6. Ransom and PI had similar responses in tap and lateral root elongation to solution pH and Al treatments in Exp. 1, but mean tap root length of Ransom in the subsurface compartment exceeded that of PI by 22%. Aluminum inhibited the length of lateral roots more than tap roots in both experiments. Molar activity ratios between Ca and Al3+ {Ca/Al3+} accounted for most of the differences in root elongation response among solution treatments in Exp. 2. A 50% reduction in relative length of tap roots for all genotypes occurred with a {Ca/Al3+} value of 891. Values of {Ca/Al3+} for 50% reductions in relative length of lateral roots differed among genotypes and were 1.6 to 3.5 times greater than for tap roots. On the basis of the {Ca/Al3+} indices for lateral root length, line N93 and Ransom exhibited greater tolerance to subsurface solution Al than PI and Young.}, number={2}, journal={CROP SCIENCE}, author={Ferrufino, A and Smyth, TJ and Israel, DW and Carter, TE}, year={2000}, pages={413–421} }
 @book{novais_smyth_1999, title={Fosforo em solo e planta em condicoes tropicais}, publisher={Vicosa, Brazil: Universidade Federal de Vicosa}, author={Novais, R. F. and Smyth, T. J.}, year={1999} }
 @article{jallah_smyth_1998, title={Assessment of rhizotoxic aluminum in soil solutions by computer and chromogenic speciation}, volume={29}, ISSN={["1532-2416"]}, DOI={10.1080/00103629809369927}, abstractNote={Abstract Numerous chemical species of aluminum (Al) occur in acid soils and simple but accurate methods are needed to characterize phytotoxicity. Kinetic reaction studies between Al and ferron were used to separate Al into instantaneously reactive (Ala), metastable (Alb), and non‐reactive (Alc) fractions in soil solutions of two North Carolina Ultisols. Relative root growth of field‐grown corn (Zea mays L.) was used to assess rhizotoxicity of kinetically measured Al forms. Reaction of Alb with ferron conformed to first order kinetics, with rate constant values ranging from 0.53 to 9.13 minute‐1. The Ala fraction correlated significantly with Al reacting in 30 seconds (r2=0.99), but the former averaged 10% less than the latter. Both Ala and Al reacting in 30 seconds correlated significantly with the Alb fraction (r2≥0.89), but not with the Alc fraction (r2<0.1). Correlation exercises between ferronreactive Al fractions and various Al species predicted by the GEOCHEM‐PC speciation program revealed a strong ...}, number={1-2}, journal={COMMUNICATIONS IN SOIL SCIENCE AND PLANT ANALYSIS}, author={Jallah, JK and Smyth, TJ}, year={1998}, pages={37–50} }
 @article{sanzonowicz_smyth_israel_1998, title={Calcium alleviation of hydrogen and aluminum inhibition of soybean root extension from limed soil into acid subsurface solutions}, volume={21}, ISSN={["0190-4167"]}, DOI={10.1080/01904169809365442}, abstractNote={Abstract Alleviation by calcium (Ca) of inhibition of soybean [Glycine max (L.) Merr. cv. ‘Ransom'] root elongation by hydrogen (H) and aluminum (Al) was evaluated in a vertical split‐root system. Roots extending from a limed and fertilized soil compartment grew for 12 days into a subsurface compartment containing nutrient solution with treatments consisting of factorial combinations of either pH (4.0, 4.6, and 5.5) and Ca (0.2, 2.0, 10, and 20 mM), Al (7.5, 15, and 30 μM) and Ca (2.0,10, and 20 mM) at pH 4.6, or Ca (2, 7, and 12 mM) levels and counter ions (SO4 and Cl) at pH 4.6 and 15 μM Al. Length of tap roots and their laterals increased with solution Ca concentration and pH value, but decreased with increasing Al level. Length of both tap and lateral roots were greater when Ca was supplied as CaSO4 than as CaCl2, but increasing Ca concentration from 2 to 12 mM had a greater effect on alleviating Al toxicity than Ca source. In the absence of Al, relative root length (RRL) of tap and lateral roots amon...}, number={4}, journal={JOURNAL OF PLANT NUTRITION}, author={Sanzonowicz, C and Smyth, TJ and Israel, DW}, year={1998}, pages={785–804} }
 @article{sanzonowicz_smyth_israel_1998, title={Hydrogen and aluminum inhibition of soybean root extension from limed soil into acid subsurface solutions}, volume={21}, ISSN={["0190-4167"]}, DOI={10.1080/01904169809365410}, abstractNote={Abstract Soybean [Glycine max (L.) Merr. cv. ‘Ransom'] root elongation under varying concentrations of solution hydrogen (H) and aluminum (Al) was investigated in a vertical split‐root system. Roots extending from a limed and fertilized soil compartment grew for 12 days into a subsurface compartment with solutions adjusted to either different pH values from 3.7 to 5.5 or a factorial combination of pH (4.0,4.6, and 5.2) and Al (0,7.5, 15, and 30 μM) levels. Ionic forms of Al were estimated with GEOCHEM and solution Al was determined with ferron. Boron (B) (18.5 μM) and zinc (Zn) (0.5 μM) were supplied to all solution treatments, in addition to 2000 μM Ca, after preliminary studies at pH 5.2 without Al indicated that their omission inhibited length of tap roots and their laterals in the subsurface compartment. Both H+ and Al inhibited the length of lateral roots more than tap roots. Lateral roots failed to develop on tap roots at pH<4.3 or in treatments with 30 μM Al. Relative tap root length (RRL) among tr...}, number={2}, journal={JOURNAL OF PLANT NUTRITION}, author={Sanzonowicz, C and Smyth, TJ and Israel, DW}, year={1998}, pages={387–403} }
 @article{cravo_smyth_1997, title={Manejo sustentado da fertilidade de um latossolo da Amazonia central sob cultivos sucessivos}, volume={21}, DOI={10.1590/s0100-06831997000400011}, abstractNote={Estimativas da área desmatada na Amazônia brasileira, principalmente para a pecuária e agricultura itinerante, já ultrapassam o equivalente à superfície do Estado de Rondônia. Com objetivo de estabelecer o modelo de exaustão de nutrientes do solo e determinar as necessidades de fertilizantes e de calcário para o cultivo sucessivo, após desmatamento e queima da vegetação, foi instalado um experimento em um latossolo amarelo próximo de Manaus (AM). Foram avaliadas respostas às aplicações de N, P, K, Mg, S, B, Cu, Mn, Zn e calcário, durante oito anos de cultivo. No período de 1981 a 1990, foram feitos 17 cultivos, observando-se respostas ao P, K, calcário e Mg, a partir do primeiro, segundo, terceiro e décimo primeiro cultivos, respectivamente. Para N, só houve resposta nos cultivos de milho, sendo necessário aumentar as aplicações a cada cultivo. Na ausência de adubação e de calagem, houve redução dos teores de N, P, K, Ca, Mg, C e do pH e aumento da saturação de Al, com o tempo de cultivo. O uso de fertilizantes e de calcário, com base na análise do solo, permitiu o cultivo contínuo da mesma área, com uma produtividade média de 4,1 t ha-1 ano-1 de grãos, contra 0,2 t ha-1 ano-1 na testemunha. Seria necessário cultivar, aproximadamente, 24 ha no sistema itinerante, para se conseguir o total de grãos produzidos em 1 ha, durante oito anos, com manejo adequado de fertilizantes e de calcário.}, number={1997}, journal={Revista Brasileira De Ciencia Do Solo}, author={Cravo, M. S. and Smyth, T. J.}, year={1997}, pages={607–616} }
 @article{smyth_cravo_1992, title={ALUMINUM AND CALCIUM CONSTRAINTS TO CONTINUOUS CROP PRODUCTION IN A BRAZILIAN AMAZON OXISOL}, volume={84}, ISSN={["1435-0645"]}, DOI={10.2134/agronj1992.00021962008400050016x}, abstractNote={Abstract}, number={5}, journal={AGRONOMY JOURNAL}, author={SMYTH, TJ and CRAVO, MS}, year={1992}, pages={843–850} }
 @article{smyth_cravo_melgar_1991, title={Nitrogen supplied to corn by legumes in a central Amazon Oxisol}, volume={68}, number={4}, journal={Tropical Agriculture}, author={Smyth, T. J. and Cravo, M. S. and Melgar, R. J.}, year={1991}, pages={366} }
 @article{smyth_cravo_1990, title={CRITICAL PHOSPHORUS LEVELS FOR CORN AND COWPEA IN A BRAZILIAN AMAZON OXISOL}, volume={82}, ISSN={["1435-0645"]}, DOI={10.2134/agronj1990.00021962008200020027x}, abstractNote={Abstract}, number={2}, journal={AGRONOMY JOURNAL}, author={SMYTH, TJ and CRAVO, MS}, year={1990}, pages={309–312} }
 @article{smyth_cravo_1990, title={PHOSPHORUS MANAGEMENT FOR CONTINUOUS CORN-COWPEA PRODUCTION IN A BRAZILIAN AMAZON OXISOL}, volume={82}, ISSN={["1435-0645"]}, DOI={10.2134/agronj1990.00021962008200020026x}, abstractNote={Abstract}, number={2}, journal={AGRONOMY JOURNAL}, author={SMYTH, TJ and CRAVO, MS}, year={1990}, pages={305–309} }