Abstract In many cases, traditional analysis of breeding trials based on analysis of variance (ANOVA) do not allow a suitable genetic evaluation. Alternatively, mixed model-based approaches create the possibility of dealing with unbalanced data and modeling spatial trends. The aims of this study were to compare the goodness-of-fit of the model and the genotype ranking through different residual modeling approaches and to select the best performing tropical wheat genotypes based on the best-fitting model. A panel of tropical wheat genotypes was evaluated in three field trials conducted between 2020 and 2021 for grain yield. Linear mixed model analyses were used on the data to estimate the genetic parameters and to predict the genotypic values in analyses of single- and multi-environment trials. Accounting for spatial trends in the analyses of single- and multi-environment trials provides better outcomes than the compound symmetry model does. cases ANOVA (ANOVA evaluation Alternatively modelbased goodnessoffit goodness fit bestfitting fitting 202 yield single multienvironment multi environment does 20 2

ABSTRACT The immediate need for the increase in wheat production to meet the future world demand, associated with the occurrence of drastic climatic events, such as drought, makes it necessary to develop drought-resilient genotypes. The aims of this work were to evaluate the use of drought-tolerance indices for the selection of wheat genotypes, to compare the genetic gains in grain yield using different selection strategies by means of a multi-trait index, and to select superior drought-tolerant wheat genotypes. The total of 31 tropical wheat lines was evaluated in two experiments. Five agronomic traits were accessed. The grain yield data from the stress and nonstress experiments were used to obtain five drought-tolerance indices. The data were subjected to mixed model analysis, and four selection scenarios were designed. There was a significant effect of genotype for all traits. The inclusion of drought-tolerance indices in the selection index provided superior genetic gains in drought condition. Seven lines were selected due the high frequency of favorable alleles for drought-tolerance and other important agronomic traits. Drought-tolerance indices are appropriate for characterizing the response of wheat genotypes to drought-stress. The inclusion of drought-tolerance indices along with agronomic traits in multi-trait selection strategies provides for superior gains in grain yield compared to the non-inclusion of the indices. demand events droughtresilient resilient droughttolerance tolerance multitrait multi trait droughttolerant tolerant 3 accessed analysis designed condition Droughttolerance Drought droughtstress. droughtstress stress. drought-stress noninclusion non

RESUMO: O processo de desenvolvimento de uma nova cultivar de trigo requer tempo entre a obtenção da população base e a seleção da linhagem mais promissora. Estimar parâmetros genéticos com mais precisão nas primeiras gerações com vistas a antecipar a seleção significa avanços importantes para os programas de melhoramento de trigo. Assim, o presente estudo estima os parâmetros genéticos de populações F2 de trigo tropical e o ganho genético da seleção via abordagem Bayesiana. Para tanto, os autores avaliaram a produtividade de grãos por parcela de 34 populações F2 de trigo tropical. A abordagem Bayesiana proporcionou um ajuste adequado ao modelo, estimando parâmetros genéticos dentro do espaço paramétrico. A herdabilidade (h2) foi de 0,51. Dentre as selecionadas, 11 populações F2 obtiveram desempenho superior às cultivares controle, com ganho genético de seleção de 7,80%. As seguintes populações foram as mais promissoras: Tbio Sossego/CD 1303, CD 1303/Tbio Ponteiro, BRS 254/CD 1303, Tbio Duque/Tbio Aton e Tbio Aton/CD 1303. A inferência Bayesiana pode ser usada para melhorar significativamente programas de melhoramento de trigo tropical.

ABSTRACT: The development process of a new wheat cultivar requires time between obtaining the base population and selecting the most promising line. Estimating genetic parameters more accurately in early generations with a view to anticipating selection means important advances for wheat breeding programs. Thus, the present study estimated the genetic parameters of F2 populations of tropical wheat and the genetic gain from selection via the Bayesian approach. To this end, the authors assessed the grain yield per plot of 34 F2 populations of tropical wheat. The Bayesian approach provided an adequate fit to the model, estimating genetic parameters within the parametric space. Heritability (h2) was 0.51. Among those selected, 11 F2 populations performed better than the control cultivars, with genetic gain of 7.80%. The following populations were the most promising: TbioSossego/CD 1303, CD 1303/TbioPonteiro, BRS 254/CD 1303, Tbio Duque/Tbio Aton, and Tbio Aton/CD 1303. Bayesian inference can be used to significantly improve tropical wheat breeding programs.

ABSTRACT A large set of variables is assessed for progeny selection in a plant-breeding program and other agronomic fields. The meta-analysis of the coefficient of variation (CVe) produces information for researchers and breeders on the experimental quality of trials. This analysis can also be applied in the decision-making process of the experimental plan regarding the experimental design, the number of repetitions, and the treatments and plants/progenies to be measured. In this study, we evaluated the dataset distribution and the descriptive statistics of CVe through the Frequentist and Bayesian approaches, aiming to establish the credibility and confidence intervals. We submitted CVe data of ten wheat (Triticum aestivum L.) traits reported in 1,068 articles published to the Bayesian and Frequentist analyses. Sample data were analyzed via Gamma and normal models. We selected the model with the lowest Akaike Information Criterion (AIC) value, and then we tested three link functions. In the Bayesian analysis, uniform distributions were used as non-informative priors for the Gamma distribution parameters with three ranges of q~U (a,b,). Thus, the prior probability density function was given by: p θ = 1 β - α , θ ∈ α , β . The Bayesian and Frequentist approaches with the Gamma model presented similar results for CVe; however, the range Bayesian credible intervals was narrower than the Frequentist confidence intervals. Gamma distribution fitted the CVe data better than the normal distribution. The credible and confidence intervals of CVe were successfully applied to wheat traits and could be used as experimental accuracy measurements in other experiments.

RESUMO: As análises de correlações canônicas baseadas nas correlações genotípicas, permitem determinar associações entre grupos de caracteres e realizar a seleção direta ou indireta de genótipos superiores. Objetivou-se com este trabalho investigar a existência de relações lineares e multivariadas entre caracteres de alta e baixa herdabilidade via análise de correlações canônicas com base nas correlações genotípicas. O experimento foi conduzido no Campo Experimental Professor Diogo Alves de Melo da Universidade Federal de Viçosa, em Viçosa, Minas Gerais. 90 cultivares de trigo foram avaliadas sob o delineamento alpha-lattice 9 × 10, com três repetições e parcelas constituídas por quatro linhas de três metros espaçadas a 0.20 metros. Os grupos canônicos foram estabelecidos entre altura de espiga e planta, dias para o espigamento, número de espiguetas por espiga e número de grãos por espiga (Grupo I) e, peso de espiga, massa de grãos da espiga, massa de 100 grãos, peso hectolitro e produtividade de grãos (Grupo II). Houve dependência entre os grupos estabelecidos, o que permitiu a investigação das relações entre os caracteres com base em seus valores genotípicos. Os caracteres ciclo e altura de plantas podem ser utilizados para a seleção indireta de genótipos superiores em peso hectolitro e produtividade, fatores estes importantes para indústrias e produtores.

ABSTRACT: Canonical correlation analysis based on genotypic correlations allows determining the associations between groups of traits and carrying out the direct or indirect selection of superior genotypes. This study investigated the existence of linear and multivariate relationships between high and low heritability traits via canonical correlation analysis based on genotypic correlations. The experiment was conducted at the Professor Diogo Alves de Melo Experimental Field at the Universidade Federal de Viçosa, in Viçosa, MG. 90 wheat cultivars were evaluated under a 9 × 10 alpha-lattice design, with three replications and plots consisting of four rows of three meters spaced at 0.20 meters. Canonical groups were established between spike height and plant height, days for heading, number of spikelets per spike, and number of grains per spike (Group I) and, spike weight, spike grain mass, 100-grain mass, hectoliter weight, and grain yield (Group II). There was dependence between the established groups, which allowed the investigation of the relationships between traits based on their genotypic values. The traits cycle and plant height can be used for indirect selection of genotypes superior in hectoliter weight and grain yield, which are important factors for industries and farmers.

RESUMEN La selección de poblaciones segregantes con potencial para derivar líneas es esencial para los programas de mejoramiento. El presente trabajo presenta el potencial de las poblaciones tropicales de trigo F2 (Triticum aestivum L.) generadas a partir de combinaciones de cruces dialélicos completos. Para ello, se combinaron ocho cultivares de trigo tropical en un diseño dialélico completo en 2019 después de multiplicar semillas Fj en invernadero y se evaluaron en campo las semillas de 56 poblaciones F2, más los ocho progenitores, en la cosecha de invierno de 2020 en un diseño reticular simple (8x8) en Vicosa, MG, Brasil. Se evaluaron las variables: severidad de la mancha amarilla (Pyrenophora triticirepentis), severidad del tizón (WHB) (Magnaporthe oryzae pathotype Triticum), número de días hasta embuchamiento, altura de la espiga y peso total de grano en la parcela. El análisis dialélico se realizó utilizando modelos mixtos para obtener los efectos de capacidad combinatoria general (GCA), capacidad combinatoria específica (SCA) y estimación de valores genotípicos de la población. El efecto aditivo predominó para el control de todas las variables, excepto para la altura de la espiga. Hubo mayores efectos de GCA para el conjunto de plantas madres progenitoras. La he-redabilidad, en sentido estricto, osciló entre 0.20 (tizón) y 0.66 (embuchamiento). Hubo efecto de la CGA materna para todas las variables, mientras que para la CGA paterna solo para número de días hasta embuchamiento y peso total de grano en la parcela. Las poblaciones derivadas de los cultivares TBIO Aton, TBIO Ponteiro y TBIO Sossego presentaron menor severidad de la enfermedad, mientras que las combinaciones de BRS 254, BRS 264 y BRS 394 presentaron un tiempo de maduración más temprano. Las combinaciones más promisorias para derivar líneas para el conjunto de variables evaluadas fueron BRS 254 x CD 1303, BRS 394 x TBIO Aton, TBIO Aton x BRS 254, CD 1303 x BRS 254 y CD 1303 x BRS 264.

ABSTRACT The selection of segregating populations with the potential for derived lines is essential for breeding programs. The present work analyzes the potential of tropical F2 wheat (Triticum aestivum L.) populations originated from complete diallel cross combinations. For this purpose, eight tropical wheat cultivars were combined in a complete diallel design in 2019 after Fj seeds were multiplied in a greenhouse and the seeds of 56 F2 populations, plus the eight parents, were evaluated in the field in Vicosa, MG, Brazil in the winter harvest of 2020 using a simple lattice design (8x8). The trait scores of (1) severity of tan spot (Pyrenophora triticirepentis), (2) severity of wheat head blast (WHB) (Magnaporthe oryzae pathotype Triticum), (3) days to heading, (4) spike height, (5) and total grain weight of the plot were evaluated. We performed a diallel analysis using mixed models to obtain the effects of general combining ability (GCA), specific combining ability (SCA), and estimation of population genotypic values. The additive effect predominated for the control of all traits, except for spike height. There were greater GCA effects for the set of parental maternal plants. Heritability, in the narrow sense, ranged from 0.20 (blast) to 0.66 (heading). There was an effect of maternal GCA for all variables, while for paternal GCA the effect was only for days passed for head and total grain weight. Populations derived from the cultivars TBIO Aton, TBIO Ponteiro, and TBIO Sossego had lower disease severity, while the combinations from BRS 254, BRS 264, and BRS 394 had earlier maturation time. The most promising combinations to derive lines for the set of traits were BRS 254 x CD 1303, BRS 394 x TBIO Aton, TBIO Aton x BRS 254, CD 1303 x BRS 254, and CD 1303 x BRS 264.

RESUMO Os grãos de feijão apresentam grande variabilidade genética para os caracteres da qualidade tecnológica, concentração de minerais e compostos bioativos. Por isso, o estudo das correlações entre esses caracteres em linhagens de feijão de diferentes grupos gênicos proporciona avanços no programa de biofortificação. Para tanto, duas populações homozigotas recombinantes de feijão Mesoamericano e Andino foram avaliadas em geração F5:7. A qualidade tecnológica foi analisada pela massa de 100 grãos e pela coloração dos grãos determinada em um colorímetro pelos valores de L* (branco ao preto), a* (verde a vermelho) e b* (azul a amarelo). A concentração de seis minerais e de compostos bioativos (fitatos e compostos fenólicos) foi avaliada e usada para caracterizar a composição nutricional das linhagens. As linhagens de feijão avaliadas diferiram para todos os caracteres da qualidade tecnológica e para a concentração de minerais e de compostos bioativos, exceto para a concentração de zinco nas linhagens de feijão Andino. A coloração dos grãos (valores de L*, a* e b*) apresentou alta correlação com a maioria dos minerais avaliados e com os fitatos em feijão Mesoamericano. Em feijão Andino, a coloração dos grãos (valores de L*, a* e b*) foi correlacionada com as concentrações de potássio, magnésio, ferro e compostos fenólicos. A composição nutricional das linhagens de feijão de diferentes classes de grãos é variável: feijão preto apresenta as maiores concentrações de potássio, fósforo, cálcio, zinco e fitatos; feijão carioca se destaca pela alta concentração de magnésio; feijão rajado tem maior concentração de potássio, magnésio e ferro.

ABSTRACT The common bean exhibits wide genetic variability for technological quality traits, mineral concentrations, and bioactive compounds. For this reason, investigating the correlations between those traits in common bean lines of different gene pools contributes to the progress of biofortification programs. In the present study, two recombinant inbred line populations of Mesoamerican and Andean common bean were evaluated at the F5:7 generation. Technological quality was evaluated based on mass of 100 grains and seed coat color, which was determined using a colorimeter that analyzed the L* (white to black), a* (green to red) and b* (blue to yellow) values. The concentration of six minerals and bioactive compounds (phytates and phenolic compounds) was evaluated and used to characterize the nutritional composition of the lines. The evaluated common bean lines differed (p ≤ 0.05) for all technological quality traits, mineral concentrations, and bioactive compounds, except for the zinc concentration in Andean beans. Seed coat color (L*, a*, and b* values) was highly correlated with most of the evaluated minerals and with the phytates in Mesoamerican beans. In Andean beans, seed coat color (L*, a*, and b* values) was correlated with the concentrations of potassium, magnesium, iron, and phenolic compounds. The nutritional composition of common bean lines of different classes is variable: black beans have higher concentrations of potassium, phosphorus, calcium, zinc, and phytates; carioca beans stand out with high magnesium concentration; and cranberry beans have higher concentrations of potassium, magnesium, and iron.

Abstract The improvement of superior wheat cultivars depends on the identification of promising segregating populations to derive superior lines. A lattice model (8×8) involving 56 F2 populations and eight parents was conducted in the 2020 cropping season, and grain yield per plant was evaluated for every F2 population, with further analysis of the population potential by Jinks and Pooni method via REML/BLUP. A total of 5,410 F2 plants were evaluated in this study. The results showed that the use of genetic variance associated with the individual genotypic value (BLUP) was superior compared with the use of variance and traditional phenotypic values. The F2 populations, CD 1303/BRS 254, CD 1303/Tbio Duque, CD 1303/Tbio Ponteiro, BRS 264/Tbio Aton, Tbio Ponteiro/Tbio Aton, and Tbio Sossego/CD 1303 had the highest likelihood of deriving superior lines.

RESUMO O desenvolvimento de linhagens de feijão Andino com alta concentração de macrominerais e com concentração de compostos fenólicos que atenda às necessidades da dieta do consumidor é inédito na literatura. Os objetivos desse trabalho foram obter estimativas de parâmetros fenotípicos para a concentração de macrominerais e compostos fenólicos em uma população de linhagens recombinantes (LR) de feijão Andino e selecionar linhagens com propriedades nutricionais e funcionais. As LR foram obtidas a partir do cruzamento entre as cultivares Hooter e Cal 96. As linhagens em geração F5:6 e F5:7 e as cultivares foram avaliadas em dois experimentos consecutivos na mesma área experimental. A concentração de K, P, Mg and Ca foi determinada por digestão ácida e a concentração de compostos fenólicos foi obtida pelo método de Follin-Ciocalteu. Efeito significativo para genótipo foi observado para todos os caracteres avaliados nas gerações F5:6 e F5:7. Herdabilidade de intermediaria a alta magnitude (h2: 43,15 a 98,85%) foi verificada para a concentração de K, P, Mg, Ca e compostos fenólicos. Esses caracteres apresentaram segregação transgressiva e herança quantitativa na população de LR de feijão Andino. As linhagens DFA 34-18 e DFA 46-18 possuem alta concentração de K e P e baixa concentração de compostos fenólicos e serão selecionadas para a nutrição humana. As linhagens DFA 04-18 e DFA 05-18 e as cultivares Pérola, IPR Siriri, IAC Imperador e IPR Tangará apresentam alta concentração de dois ou mais macrominerais e de compostos fenólicos, portanto têm propriedades nutricionais e funcionais e serão selecionadas pelo programa de melhoramento.

ABSTRACT The development of Andean common bean lines that contain high macromineral concentration and a phenolic compound concentration that meets the consumer’s dietary requirements is unprecedented in the literature. The objectives of this study were to obtain estimates of phenotypic parameters for the macromineral and phenolic compound concentrations in a recombinant inbred line (RIL) population of Andean beans and to select lines with nutritional and functional properties. The RIL was obtained from a cross between cultivars Hooter and Cal 96. The lines in the F5:6 and F5:7 generations and the cultivars were evaluated in two consecutive experiments in the same experimental area. The concentrations of potassium (K), phosphorus (P), magnesium (Mg), and calcium (Ca) were determined by acid digestion, whereas the phenolic compound concentration was obtained by the Follin-Ciocalteu method. A significant genotype effect was observed for all traits evaluated in the F5:6 and F5:7 generations. Intermediate-to-high heritability estimates (h2: 43.15 to 98.85%) were obtained for the concentrations of K, P, Mg, Ca and phenolic compounds. These traits exhibited transgressive segregation and quantitative inheritance in the RIL population of Andean beans. Lines DFA 34-18 and DFA 46-18 have high K and P concentrations and low phenolic compound concentration and will be selected by the human nutrition. Lines DFA 04-18 and DFA 05-18 and cultivars Pérola, IPR Siriri, IAC Imperador, and IPR Tangará showed high concentrations of two or more macrominerals and phenolic compounds; therefore, they have nutritional and functional properties and will be selected by the breeding program.

Abstract Parent selection is a crucial step in breeding programs. In the present study, we evaluated the genetic diversity in tropical wheat genotypes using best linear unbiased predictions (BLUPs) by different grouping methods. We identified potential parents to compose a crossing block with the aim of improving wheat for the Brazilian Cerrado. A total of 41 tropical wheat genotypes were evaluated in a field experiment. The evaluated traits included days to flowering; disease symptoms of fusarium head blight, blast, and leaf rust; flag leaf height; plant height; spike mass; hectoliter weight; and grain yield. The BLUPs were predicted and, from these, the standardized average Euclidean distance was calculated. Then, UPGMA, Tocher, and principal component clusters were generated from this genotypic distance matrix. Evaluating genetic diversity based on BLUP allowed the identification of two groups of highly dissimilar genotypes with high estimated genotypic values with which to compose a partial diallel.

RESUMO O desenvolvimento de cultivares de feijão com concentração de minerais e de fitatos que atendam aos diferentes requerimentos nutricionais dos consumidores é uma nova estratégia dos programas de melhoramento. Os objetivos desse trabalho foram obter estimativas de parâmetros genéticos para a concentração de fósforo, fitatos, ferro e zinco em uma população de linhagens homozigotas recombinantes (LHR) de feijão Mesoamericano, estudar as correlações entre esses caracteres e selecionar linhagens de feijão para o programa de biofortificação e para dietas que necessitam diminuir a ingestão desses minerais. A LHR foi obtida pelo cruzamento entre BRS Esteio e SCS 205 Riqueza. Variabilidade genética e segregação transgressiva foram observados para todos os caracteres avaliados. Estimativas de herdabilidade para a concentração de fósforo, fitatos, ferro e zinco foram de intermediária (h2: 30,31%) a alta magnitude (h2: 98,68%) e herança quantitativa foi observada. A concentração de fósforo mostrou intermediária correlação com as concentrações de ferro (r= 0,4157) e zinco (r= 0,5693). A cultivar BRS Expedito e a linhagem L 56-17 apresentam baixa concentração de fitatos (≤ 1,29%) e alta concentração de ferro (≥ 95 mg kg-1 de matéria seca - MS) e serão selecionadas pelo programa de biofortificação do feijão. As linhagens L 59-17, L 31-17 e L 26-17 e as cultivares IPR Siriri e BRS Valente possuem alta concentração de fitatos (≥ 2,57%) e baixa concentração de zinco (≤ 26 mg kg-1 de MS) e serão selecionadas para uso em dietas que visam as propriedades benéficas dos fitatos e a redução da ingestão de zinco.

ABSTRACT The development of common bean cultivars that contain satisfactory minerals and phytate concentrations for the different nutritional requirements of consumers is a new strategy of breeding programs. This work aimed to obtain estimates of genetic parameters for the concentrations of phosphorus, phytate, iron, and zinc in a recombinant inbred line (RIL) population of Mesoamerican common bean, to study the correlations between these traits, and to select common bean lines for the biofortification program and for diets that require the decrease in the intake of these minerals. The RIL were obtained from the cross between BRS Esteio and SCS 205 Riqueza. Genetic variability and transgressive segregation were detected for all traits evaluated. Heritability estimates for the concentrations of phosphorus, phytate, iron, and zinc ranged from intermediate (h2: 30.31%) to high (h2: 98.68%) magnitude, and quantitative inheritance was observed. The phosphorus concentration showed an intermediate correlation estimate with iron (r = 0.4157) and zinc (r = 0.5693) concentrations. Cultivar BRS Expedito and line L 56-17 have a low phytate concentration (≤ 1.29%) and a high iron concentration (≥ 95 mg kg-1 of dry matter - DM), and will be selected by the common bean biofortification program. Lines L 59-17, L 31-17, and L 26-17 and cultivars IPR Siriri and BRS Valente have a high phytate concentration (≥ 2.57%) and a low zinc concentration (≤ 26 mg kg-1 DM) and will be selected for diets that aim at using the beneficial properties of phytate and reducing the zinc intake.

A compactação do solo é uma consequência indesejável do uso agrícola do solo, sobretudo em sistemas de cultivo com mínimo revolvimento do solo, como é o caso do plantio direto (PD). Contudo, a compactação que o tráfego de máquinas causa no solo sob PD não inviabiliza a produção das culturas, indicando que mecanismos intrínsecos a ele promovem reversão da compactação. Neste estudo, avaliou-se a influência de ciclos de contração e expansão sobre a densidade do solo (ρ) de um Latossolo Vermelho argiloso (0,57 kg kg-1 de argila e 0,12 kg kg-1 de areia) e a mudança temporal da ρ no campo. Amostras de solo foram compactadas no laboratório até atingirem ρ de 1464 kg m-3 e submetidas a cinco ciclos de contração (secagem ao ar) e expansão (saturação). Durante a contração, foi monitorado o conteúdo gravimétrico de água e a ρ. A ρ foi medida também no campo, nos anos de 2010, 2011 e 2013. O decréscimo do conteúdo de água nas amostras provocou aumento da ρ conforme uma função sigmoide com duas assíntotas, e o aumento da ρ foi expressivo em conteúdos de água menores que o do ponto de murcha permanente (1,5 MPa). Embora tenha havido aumento da ρ durante a contração, os sucessivos eventos de contração e expansão reduziram gradativamente a ρ de 1713 para 1570 kg m-3 (final da contração), e de 1464 para 1385 kg m-3 (próximo à saturação). Em solo compactado no campo também foi verificado a variação decrescente de ρ (de 1406 para 1327 kg m-3) a uma taxa de -26 kg m-3 ano-1. Concluiu-se que a diminuição do grau de compactação no campo está ligada em grande parte ao mesmo mecanismo que diminuiu o grau de compactação das amostras no laboratório. Assim, no solo usado neste estudo, a contração e expansão conseguiram reverter grande parte da compactação que o tráfego de máquinas causa nele.

Soil compaction is an undesirable consequence of land use for crop production, especially under cultivation with minimum soil turnover as in the no-tillage system (NTS). However, the compaction caused by machine traffic on soils under NTS does not make crop production unviable, indicating that some intrinsic mechanisms promote the reversion of soil compaction. In this study, the influence of alternate contraction and expansion cycles was evaluated with regard to the bulk density (ρ) of a Latossolo Vermelho argiloso (clayey Oxisol) (0.57 kg kg-1 clay, and 0.12 kg kg-1 sand) and the temporal change in ρ in the field. Soil samples were compacted in the laboratory to reach a ρ of 1,464 kg m-3 and subjected to five cycles of contraction (air drying) and expansion (saturation). During the contraction process, soil gravimetric water content and ρ were monitored. Soil ρ was also measured in the field in the years 2010, 2011, and 2013. A decrease in soil water content in the samples increased the ρ according to a sigmoid function with two asymptotes, and the increase in ρ was significant at water contents lower than that of the permanent wilting point (1.5 MPa). Although there was an increase in ρ during contraction, successive contraction and expansion events steadily reduced ρ from 1,713 to 1,570 kg m-3 (end of contraction), and from 1,464 to 1,385 kg m-3 (near saturation). In the field, a decline in ρ was observed in compacted soil (from 1,406 to 1,327 kg m-3) at a rate of -26 kg m-3 yr-1. We conclude that the decrease in the state of field compaction is largely linked to the same mechanisms that cause the decrease in compaction in the samples in the laboratory. We conclude that for the soil used in this study, contraction and expansion cycles may reverse most of the compaction that machine traffic causes to the soil.