ABSTRACT Soil chemical and physical analyses are the major sources of data for agriculture. However, traditional soil analyses are time-consuming, not cost-efficient, and not environmentally friendly. An alternative to traditional soil analyses is soil spectroscopy. This technique is a low-cost and quick analytical method, which can be implemented in a laboratory and/or in-situ. Nevertheless, some spectrometers are expensive and do not contemplate the entire spectrum. Despite this limitation, the main objective of the study was to create a soil spectral library of the Piauí State using only the 1000–2500 nm range. In this sense, it was evaluated and standardized the soil spectral library by accessing the combination of smoothing, standard normal variate, continuum removal, and Savitzky-Golay derivative spectral preprocessing procedures with partial least squares, random forest, and cubist machine learning algorithms. It was collected 262 geo-referenced soil samples at the layer of 0.00–0.20 m across the entire Piauí State, representing most of its soil variability. The soil properties evaluated were pH(H2O), sand, clay, and soil organic carbon (SOC) contents. This study demonstrated that the Standard Normal Variate was one of the most promising preprocessing procedures to improve model predictions for pH(H2O), sand, and clay. For SOC and pH, the best overall results were without preprocessing the soil spectra. Moreover, the cubist model was the most accurate in predicting soil properties. Finally, our study showed evidence of the potential and feasibility of using this soil spectral library to estimate soil properties such as pH(H2O), sand, clay, and SOC.

ABSTRACT: Environmental impacts caused by the addition of rare earth elements (REEs) to agricultural soils are a growing concern. The sedimentary basin of the Gurguéia River is located in one of the last agricultural frontiers in Brazil; nevertheless, data regarding quality reference values (QRVs) for REEs in soils are still scarce. The objective of this study was therefore to determine the natural concentration and establish the QRVs of REEs in soils of Gurguéia watershed, Brazil. Fifty-five composite soil samples were collected at sites under no or minimal anthropic interference. The average REE natural concentrations in soils from the Gurguéia watershed were lower than those found in other regions of Brazil and worldwide, following the order (mg kg−1): Ce (14.01) > Nd (6.19) > La (5.52) > Pr (2.51) > Sm (1.45) > Gd (0.93) > Dy (0.63) > Er (0.42) > Yb (0.39) > Tb (0.28) > Eu (0.26) > Lu (0.20). The parent material was the main factor that controlled the distribution of REEs in soils. The QRVs in soils followed the order (mg kg−1): Ce (18.8) > Nd (7.92) > La (6.32) > Pr (3.3) > Sm (1.97) > Gd (1.35) > Dy (0.85) > Er (0.55) > Yb (0.47) > Tb (0.37) > Lu (0.25). These values serve as a basis to assist the development of legislation, including REE thresholds for Brazilian soils.

ABSTRACT The conservation tillage systems is based on the surface protection by crop residue and reduced soil disturbance. These two principles can favor the soil quality and promote sustainable agricultural systems. The study was developed with the objective of measure soil microbial biomass, soil basal respiration, enzymatic activity and soybean yield in conservation systems cultivated with cover crops species in the Northeastern Cerrado. The experiment was carried out in 2016/2017 and 2017/2018 cropping seasons, performed in a randomized blocks design. The treatments were soil tillage systems allocated in the main plots: no-tillage (NT) and minimum tillage (MT) and the cover crops were allocated in the subplots: Pennisetum glaucum (millet), Urochloa ruziziensis (brachiaria), Crotalaria spectabilis (C. spectabilis), Crotalaria ochroleuca (C. ochroleuca), Pennisetum glaucum + Crotalaria spectabilis (millet + C. spectabilis) and spontaneous plants with three replicates. The evaluated variables were dry mass (DM) production and nutrient accumulation in cover crops; soil biological properties, namely microbial biomass carbon and nitrogen (MBC and MBN, respectively), respiration, metabolic quotient (qCO2), dehydrogenase enzymatic activity (DH), fluorescein diacetate (FDA); and soybean yield. The higher production of dry mass and nutrient cycling occurs with the intercropping millet + C. spectabilis and single millet. The highest soybean yield occurs in succession to C. ochroleuca and intercropping of the millet + C. spectabilis. Cover crops in conservation systems improve soil microbial quality and increase soybean yield.

ABSTRACT Parkia platycephala Benth. (Fava-de-bolota) found in areas of Cerrado-Caatinga transition, is a species with potential for feeding ruminants in arid regions. The objective of this study was to evaluate the effect of inoculation of arbuscular mycorrhizal fungi (AMF) on the initial growth and nutrition of P. platycephala Benth. seedlings under water stress. The experimental design was a randomized block design in a 2 × 6 factorial scheme with five replications, consisting of two water regime conditions (with and without stress), four AMF strains (Gigaspora rosea, Gigaspora margarita, Acaulospora koskei, and Acaulospora morrowiae), one treatment with associated inoculum (Mix), and one control. At 120 days after sowing, the morphological variables height (H), stem diameter (SD), number of leaves (NL), root length (RL), total root volume (TRV), shoot dry mass (SDM), root dry mass (SDM) and total dry mass (TDM) were evaluated. Nutrient contents and mycorrhizal colonization rate were also evaluated. The variables NL, SDM and TDM presented significant interaction between inoculation with the fungi and the studied water conditions. For the contents of P, Mg and Mn there was also interaction, being the best results with the strains A. koskei, Mix, A. morrowiae and control, respectively, in the condition without water stress. Mycorrhizal fungi favored plant growth as well as the absorption of P, Mg, Mn and Zn.

ABSTRACT One of the great challenges in the post-nursery phase is to plant seedlings in the field. It is, therefore, important to produce them to a high standard of quality aiming to achieve an economically feasible and environmentally sustainable process. For this purpose, the use of organic residues in the composition of substrates, associated with biotechnologies available on the market, is a feasible alternative, which, however, requires further research for process optimization. Thus, the objective was to evaluate the morphophysiological characteristics, nutrition and quality of Copaifera langsdorffii seedlings in substrates formulated with organic residues and Fertbokashi premium®. The treatments were distributed in a randomized block design, with four repetitions, in a 5 x 2 factorial scheme, with four substrates (carnauba residue, goat manure, unprocessed and carbonized rice husks) and one control (soil) with or without applying bokashi. A part of the results, the highest values observed in the morphophysiological and nutritional variables, were for plants grown in the substrate with carnauba residue, followed by goat manure, both in association with bokashi. Among the residues studied, carnauba residue had the highest N and P contents and the lowest C:N ratio, raising the quality variables. The use of bokashi associated with the residues promotes the best results for most of the morphophysiological and nutritional parameters of the Copaiba seedlings. The substrates formulated with carnauba residue and goat manure are the most appropriate for seedling production. The regional residues can be used as a substrate to produce Copaiba seedlings to a high standard of quality.

RESUMO A presença de palhada de plantas de cobertura pode causar mudanças significativas na atividade e população microbiana com efeitos ambientais e na dinâmica de C e N no solo, fornecendo informações importantes para o planejamento do uso adequado da terra no Cerrado brasileiro. O objetivo deste trabalho foi avaliar o efeito da palhada de plantas de cobertura sobre os atributos microbianos do solo, e na qualidade da matéria orgânica. As unidades experimentais consistiram de potes plásticos acondicionados com 100 g de solo misturados com palhada de plantas de cobertura. Os tratamentos foram distribuídos em um DIC, em esquema fatorial 7 x 7 + 1, com sete tipos de palhadas, avaliados aos 7, 14, 21, 28, 42, 63 e 105 dias após a incubação, e controle sem palhada, com três repetições. O qCO2 variou de 0,1 (Crotalaria spectabilis aos 14 dias) a 5,1% (Cajanus cajan 'IAPAR 43' aos 42 dias). Os reservatórios de carbono e nitrogênio orgânicos são afetados de diferentes formas pelas palhadas de leguminosas e gramíneas em cada data de avaliação. A incorporação de Brachiaria brizantha e Mucuna aterrima tiveram impactos positivos nos atributos microbianos até o 21º dia de incubação (qCO2, Cmic and Nmic), com baixa liberação de CO2 e aumento da população microbiana. Todas as espécies avaliadas apresentaram potencial para serem usadas em sistema de rotação, tornando viável para o plantio direto na região do Cerrado piauiense. Contudo, é recomendado a seleção de espécies de acordo com o propósito específico.

ABSTRACT The cover crop straw may cause changes in the microbial activity and population, with repercussions on environmental changes and on the C and N dynamics, providing important information for the planning of adequate land use in the Cerrado. The objective of this study was to evaluate the effect of straw of cover crops on the soil microbial attributes and quality of organic matter. Experimental units consisted of 100 g of sieved soil placed in small plastic cups mixed with straw from cover plants. Treatments were distributed in a CRD, in a factorial scheme of 7 x 7 + 1, with seven types of straw, evaluated at 7, 14, 21, 28, 42, 63 and 105 days after incubation, and control without straw, with three replicates. The qCO2 ranged from 0.1 (Crotalaria spectabilis at 14 days) to 5.1% (Cajanus cajan ‘IAPAR 43’ at 42 days). The organic carbon and nitrogen reservoir are differently affected by straw of legumes and grasses on the dates. The incorporation of Brachiaria brizantha and Mucuna aterrima had a positive impact on the microbial attributes until the 21st incubation (qCO2, Cmic and Nmic), with little loss of carbon dioxide and growth of the microbial population. All the evaluated species presented a potential to be used in crop rotation systems, enabling no-tillage systems in the Cerrado of Piauí. However, it is recommended to select species according to specific purposes. Thus, the use of cover crops is an important tool for increasing the biological quality of Brazilian northeastern cerrado soils.

ABSTRACT Sugarcane is one of the first activities of economic importance in Brazil. The understanding of the nutritional dynamics at different phenological stages of the sugarcane crop with the use of nitrogen-fixing bacteria has been one of the alternatives to decrease fertilizer consumption and increasing plant production. This study aimed to assess the morphophysiological attributes in the initial growth and nutrition of two sugarcane varieties inoculated with strains of diazotrophic bacteria, individually and in an association, in a greenhouse. The experimental design was a randomized block design in a 2 × 8 factorial arrangement with two cultivars (Co 1341-76 and RB 867515) and eight treatments consisting of bacteria inoculated individually with BR 11140T (Azospirillum amazonense), BR 11175T (Herbaspirillum seropedicae), BR 11192T (Herbaspirillum rubrisubalbicans), BR 11281T (Gluconacetobacter diazotrophicus), and BR 11366T (Burkholderia tropica), inoculation associated with the studied bacteria, N fertilization with 120 kg ha-1 of N, and absolute control without inoculation and nitrogen fertilization. Plants were conducted for 75 days after germination, and biometric variables and nutrient accumulation were measured. The sprouting rate index and root fresh matter were significant for inoculation (p<0.01). Inoculation with the strains BR 11192T (H. rubrisubalbicans), BR 11281T (G. diazotrophicus), and RB 11366T (B. tropica) showed the best results for root fresh matter regardless of the cultivar. The strains RB 11366T (B. tropica), BR 11192T (H. rubrisubalbicans), and BR 11175T (H. seropedicae) stood out regarding the sprouting rate index. Inoculation showed a significant effect for stem diameter (p<0.01), especially the strains BR 11140T (A. amazonense) and RB 11366T (B. tropica). All inoculations were efficient for the biometric variable related to leaf length. Nitrogen, Fe, and Zn contents showed a significant effect of the interaction between cultivars and inoculation. The inoculation with the strain RB 11366T (B. tropica), total N fertilization, followed by the other inoculations and the control stood out compared to the cultivar Co 1341-76 within the factor inoculation, indicating that the association of this strain with the cultivar Co 1341-76 is more efficient regarding the recommended commercial N dose for sugarcane. The cultivars Co 1341-76 and RB 867515 responded positively to the individual inoculation of strains of diazotrophic bacteria. The strains promoted improvements in some morphological and/or nutritional attributes of sugarcane plants. The strain B. tropica showed the best interaction with the tested cultivars for the biological N fixation, resulting in gains of biomass productivity and nutrient contents when not inoculated.

Resumo A utilização de materiais renováveis como fonte de nutrientes, além de ser uma interessante solução para destinação dos resíduos, pode também ser uma saída efetiva para a redução dos altos custos de insumos necessários para produção de mudas florestais. Este trabalho objetivou avaliar o crescimento de Anadenanthera colubrina (Vell. Brenan) (angico branco) cultivado em substratos orgânicos. Foi adotado delineamento em blocos casualizados e os tratamentos distribuídos em esquema fatorial 3 × 5, sendo três resíduos orgânicos: caule decomposto de buriti, bagana de carnaúba e composto orgânico misturados ao solo em quatro percentuais, 20% ,40%, 60% e 80% da composição do substrato e um tratamento testemunha apenas com solo sem incorporação de resíduo orgânico, com seis repetições. Aos noventa dias após a emergência, as mudas foram coletadas para determinação dos parâmetros de crescimento: diâmetro do coleto (DC), altura (H), dos índices: H/D, número de folhas (NF), clorofila total (CT), área foliar (AF), massa seca da parte aérea (MSPA), massa seca das raízes (MSR) e massa seca total (MST), H/MSPA; MSPA/MSR e de qualidade de Dickson (IQD). Os tratamentos que continham 60% e 80% de composto orgânico apresentaram as melhores respostas. Conclui-se que a produção de mudas de angico branco cultivadas com substratos acrescidos de 80:20 (composto orgânico: solo) apresentam os melhores resultados e tecnicamente viável de acordo com as características e os índices analisados.

Abstract The use of renewable materials as a source of nutrients, besides being a solution of interest for waste disposal, may also be an effective way to reduce the high costs of inputs needed for the production of forestry seedlings. The purpose of this study was to evaluate the growth of Anadenanthera colubrina (Vell. Brenan) (angico branco) cultivated in organic substrates. A randomized block design was adopted and the treatments were distributed in a 3 × 5 factorial scheme, with three organic residues: decomposed burity (moriche palm) stem, carnaúba straw and organic compost mixed with the soil in four percentages: 20%, 40%, 60% and 80% of the composition of substrate and a control treatment with soil only, without incorporating the organic residue, with six repetitions. Ninety days after emergence, the seedlings were collected to determine the growth parameters: stem diameter (SD), height (H), of the following indexes: H/D, leaf number (LN), total chlorophyll (T), leaf area (LA), dry mass of the aerial part (DMAP), dry mass of roots (DMR), total dry mass (TDM) H/DMAP: DMAP/DMR, and Dickson Quality Index (DQI). The treatments that contained 60% and 80% of organic compost presented the best responses. It is concluded that the production of angico branco seedlings cultivated with substrate with the addition of 80:20 (organic compost: soil) presented the best results and was technically feasible according to the characteristics and indexes analyzed.

ABSTRACT The two main bottlenecks for a successful phytoremediation program are the metal availability in soil and the metal uptake and transfer to shoots of high biomass plants. Several agronomical practices have been tested to boost the bioavailability of metals in soils and accumulation in plants. Here we assessed the feasibility of plant-growth-promoting bacteria (PGPB) isolated from a site contaminated by gold ore processing activities to assist the phytoremediation of As, Cd, and Pb by Sorghum bicolor and mitigate the metal toxicity in plants. The bacteria Kluyvera intermedia, Klebsiella oxytoca, and Citrobacter murliniae were evaluated in single, double, and triple inoculations. They are regarded as metal resistant and were isolated from the rhizosphere of species naturally growing on the metal contaminated site. The treatments comprised two soils (contaminated and non-contaminated) and single (K. intermedia, K. oxytoca, or C. murliniae) or multiple inoculations (K. intermedia + K. oxytoca; K. intermedia + C. murliniae; K. oxytoca + C. murliniae; K. intermedia + K. oxytoca + C. murliniae). Plants were grown for 42 days after inoculation. The results showed that the PGPB K. oxytoca and the combination of K. intermedia + K. oxytoca and K. intermedia + C. murliniae were able to mitigate the metal toxicity in the contaminated soil and hence increase the shoot biomass, with implications to the effectiveness of phytoextraction. The sorghum ability to translocate Cd to shoots in the contaminated soil was enhanced through the single inoculation with K. oxytoca, C. murliniae, and K. oxytoca, as well as by the joint-inoculation with K. oxytoca + C. murliniae, and K. intermedia + K. oxytoca + C. murliniae. Higher accumulation of metals in shoots is a crucial factor in successful phytoextraction. Arsenic and Pb, on the other hand, had their uptake and concentration in roots stimulated by the inoculation. Therefore, regarding these two metals, phytostabilization programs could benefit from the use of the bacteria studied here.

ABSTRACT Rock powder and boiler ash are residues with a high potential for the fertilization of substrates to produce forestry seedlings. They are the source of macro and micronutrients, besides having an effect on soil pH. Therefore, this study aimed to evaluate the effect of the isolated application of rock power, boiler ash, dolomitic limestone and calcium carbonate on the reaction of soils with a sandy and clayey texture in the Cerrado Piauiense and on the growth and quality of ipê-amarelo seedlings. For this purpose, the pH values of soil in water and CaCl2 solution and the following morphophysiological parameters as indicators of the quality of forest seedlings were analyzed: length of the aerial part (LAP), and root (RL), stem diameter (SD), number of leaves (NL), total chlorophyll (TC), fresh mass of the aerial part (FMAP), fresh mass of the root (FMR), dry mass of the aerial part (DMAP), of the root (DMR) and total (TRM), and the DMAP/DMR and LAP/SD ratios and Dickson quality index (DQI). It was found that the rock powder and boiler ash residues change the pH values in clayey and sandy soils, and promote the growth and quality of ipê-amarelo seedlings.

ABSTRACT Besides being used in the wood industry, copaiba has medicinal properties. However, continuous and excessive extraction both of wood and of oil may impair the regeneration and make the product scarce. It is very important to produce quality seedlings, both for sustainable exploitation and for the recovery of degraded and disturbed areas. The purpose of the present study was to evaluate the initial growth and nutrition of Copaiba seedlings, incorporating organic residues into different classes of soils. The treatments were disposed in a design of entirely randomized blocks using the 5x4 factorial scheme, with four organic residues (rice husks in natura, carbonized rice husks, goat manure, carnauba residue), plus a treatment with soil only and four classes of soil (Latossolo Vermelho-Amarelo, Neossolo Quartzarênio, Gleissolo Háplico e Argissolo Vermelho-Amarelo), with four repetitions. At 90 days, the morpho-physiological variables of the seedling and macronutrient contents of the aerial part were evaluated. As to the morpho-physiological variables, the carnauba residue was outstanding among the residues tested in the present study. There was an increase in the quantities of P, K, Ca and Mg in the aerial part of copaiba seedlings resulting in the combination between the organic residues and the soil classes.

ABSTRACT In semi-arid regions of developing countries worldwide it is necessary to develop low cost technology methods to acquire new water supplies. The objective was to evaluate the changes in the attributes of soil quality irrigated with treated sewage effluent. The treatments consisted of applying treated sewage effluent (TSE) and underground well water (UWW) in the following proportions: E0% (chemical fertilization and UWW), E25% (25% TSE and 75% UWW), E50% (50% of TSE and UWW), E75% (75% TSE and 25% UWW) and E100% (100% TSE). The sodium content did not differ significantly among the treatments, but the sodium input diminished as the percentage of residuary water in the irrigation grew. There was a greater increment of microbial biomass carbon in the E25% treatment. On the other hand, although treatments E50% to E100% have a greater nutrient input, they were no different from control treatments performed with well water. Treated domestic sewage effluent at a proportion of 25% is a feasible alternative for castor bean irrigation, however it is necessary to monitor the possible changes in the soil attributes over successive crops. Microbial attributes can be used as a quick, good indicator of changes in soil quality.

RESUMEN Las plantas de pimiento dulce se cultivaron utilizando un sistema hidropónico Nutrient Film Technique (NFT). Su objetivo fue evaluar el efecto del uso de agua salobre en la producción de fruta. El experimento se llevó a cabo en un diseño de bloques al azar con siete tratamientos y cinco repeticiones. La conductividad eléctrica del agua fue 0,29; 1,39; 2,75; 4,49; 5,90; 6,76 y 7,09 dS m-1 en los tratamientos; también, esta agua se usó tanto para la preparación de la solución de nutrientes como para la reposición de la evapotranspiración del cultivo. Los parámetros de la planta: longitud del fruto, número de frutos por planta, peso medio del fruto, peso total de las frutas por planta y la relación longitud/diámetro del fruto se evaluaron 69 días después del trasplante. El uso de agua salobre con altos valores de conductividad eléctrica no interfiere directamente en la producción de chile dulce en los sistemas hidropónicos NFT, siempre que estos valores no excedan la tolerancia a la sal de pimienta dulce de 1,5 a 1,8 dS m-1.

ABSTRACT Sweet pepper plants were grown using a Nutrient Film Technique (NFT) hydroponic system. This study aimed to evaluate the effect of using brackish water on fruit production. The experiment was carried out in a randomized block design with seven treatments and five replications. The electrical conductivity of the water was 0.29, 1.39, 2.75, 4.49, 5.90, 6.76, and 7.09 dS m-1 in the treatments; this water was used for both the nutrient solution preparation and replenishment of crop evapotranspiration. The plant parameters: fruit diameter, fruit length, number of fruits per plant, mean fruit weight, total fruit weight per plant and fruit length/diameter ratio were evaluated 69 days after the transplanting. The use of brackish water with high electric conductivity values did not directly interfere with the sweet pepper production in NFT hydroponic systems, as long as these values did not exceed the sweet pepper salt tolerance of 1.5 to 1.8 dS m-1.

ABSTRACT There is a complex interaction between various components of the soil ecosystem, including microbial biomass and soil chemical contaminants such as heavy metals and radionuclides, which may greatly affect the efficiency of bioremediation techniques. The aim of this study was to investigate microbial capacity to change pH, changes in the metal soluble-exchangeable fraction, and effects of initial heavy metal contents on soil samples in microbial solubilization/immobilization capacity. The soil samples used in this study were collected at a known metal-contaminated site. Three highly metal-resistant bacteria were isolated from rhizosphere soil samples collected on weed species identified as Senecio brasiliensis, Senecio leptolobus, and Baccharis trimera. A completely randomized experimental design in a factorial arrangement was used, with three replicates. In general, with an acid pH, the isolates neutralized the contaminated growth media. In a neutral or basic initial pH, increases in pH were observed in the media, so these bacteria have an alkalizing effect on the growth media. Soluble metal contents were quite different and depend on the microbial species and heavy metal contents in the soil samples. The soluble-exchangeable fraction of metal such as Cu, Zn, Ni, Cr, Cd, Pb, and Ba may be unavailable after inoculation with heavy metalresistant rhizobacteria. A promising approach seems to be the application of inoculants with metal-resistant bacteria in bioremediation of multi-metal-polluted environments to improve the efficiency of this environmentally friendly technology.

ABSTRACT Bioavailability of heavy metals at contaminated sites is largely controlled by the physicochemical properties of the environmental media such as dissolved organic matter, hydroxides and clay colloids, pH, soil cation exchange capacity and oxidation-reduction potential. The aim of this study was to investigate soil pH and heavy metal solubility effect by levels of humic and fulvic acids applied in soil samples with different levels of contamination by heavy metals. The soil samples used in this study were collected in a known metal-contaminated site. Humic acid (HA) and fulvic acid (FA) were purchased as a commercially available liquid material extracted from Leonardite. The experiment was carried out in a factorial scheme of 4 × (4 + 1), with four contaminated soil samples and four treatments, comprised of two levels of HA, two levels of FA and a control. The HA treatments increased the solubility of Cu, Zn, Ni, Cr, Cd, Pb, As and Ba from soils, while FA treatments decreased, thus raising or not their availability and mobility in soil. Humic acid concentration did not influence soil pH and FA decreased soil pH until 0.7 units. The initial heavy metal concentration in soil affects the magnitude of the processes involving humic substances. The lower releases of heavy metals by FA verified the importance of the complexation properties of organic compounds. These results appear to encourage the use of HA for increased plant-availability of heavy metals in remediation projects and the use of FA for decreased plant-availability of heavy metals at contaminated sites with a risk of introducing metals into the food chain.