ABSTRACT Despite the importance given to Silicon in the relief of stress in cultivated plants, there are no experimental studies on abiotic stresses that address this function of Si in plants under natural environments, aiming to identify responses that would indicate acclimatisation to the conditions at their place of origin. The goal of this study was to answer the following questions: 1) Does abiotic stress increase Si absorption? 2) Does the presence of Si stimulate biomass production in natural environments? and 3) Do plants from different environments display differences in Si absorption? To do so, Eugenia punicifolia was selected as a study species since it has a wide distribution, occurring in three different physiognomies: Coastal Savanna, Dense Deciduous Shrubland and Seasonal Deciduous Forest. The Si absorption varied depending on the temperature and this was directly related to increases in dry matter production in E. punicifolia plants, suggesting that this may be a relief mechanism for temperature and water stresses. Differences in the response to stress conditions may be a result of the phenotypic plasticity which occurs in E. punicifolia and suggests that plasticity could be a useful asset in the use of Si fertilizer for crops. origin questions 1 2 3 so distribution physiognomies Savanna Forest E crops

ABSTRACT Soil fertility evaluation is important for adopting conservation management and adequate nutrient supply. The objective of this study was to identify critical levels and soil fertility classes using the boundary line method for rainfed crops (corn, cowpea and sabiá [Mimosa caesalpiniifolia]) in the Brazilian semi-arid region. A database of 226 soil fertility analyses of samples from the 0.00-0.20 m soil layer, and corn, cowpea and sabiá yields from Ceará State was used to generate interpretation classes (at 80 and 95 % of maximum yield). In a scatter plot, soil nutrient concentrations (x-axis) and relative crop yields (y-axis) were correlated, and the border points fitted to a quadratic model. Proposed interpretation classes were classified as very low, low, adequate, high and very high, except for Na+, whose adequate class was considered tolerable. Generated models showed coefficients of determination (R2) for the chemical properties ranging from 0.54 to 0.92. Based on the interpretation classes, the critical level was determined as 6.3 for pH, 10.8 g dm-3 for OM, 20.9 mg dm-3 for P, 81 mg dm-3 for K, 55 mmolc dm-3 for Ca2+, 24 mmolc dm-3 for Mg2+ and 8 mg dm-3 for S-SO42-. Interpretation classes for soils with high-activity clay in the Brazilian semi-arid region were superior to those in the reference literature. Boundary line method established fertility classes and critical levels for soil chemical properties in more than one crop, using the concept of relative yield. supply corn (corn Mimosa caesalpiniifolia caesalpiniifolia] semiarid semi arid 22 0.000.20 000020 0.00 0.20 0 00 20 0.00-0.2 layer at 9 yield . yield) plot xaxis x axis (x-axis yaxis y (y-axis correlated model low Na Na+ tolerable R2 R (R2 054 54 0.5 092 92 0.92 63 6 3 6. pH 108 10 10. dm3 dm dm- OM 209 20. P K 5 Ca2 Ca Ca2+ 2 Mg2 Mg SSO42. SSO42 SSO S SO42 SO S-SO42- highactivity activity literature 000 0.000.2 00002 0.0 020 0.2 0.00-0. (R 05 0. 09 0.9 1 SSO4 SO4 S-SO42 0.000. 0000 02 0.00-0 S-SO4 0.000 0.00- S-SO

ABSTRACT The long-term use of agrichemicals might add some heavy metals to soils and, there is little information about the dynamics of these elements in soils under saline conditions in semiarid regions. This study aimed to investigate the dynamics of heavy metals in the different fractions of Fluvic Entisols with saline conditions under long term of coconut cultivation in a semiarid region. Composite soil samples were collected in five agricultural areas and three areas under native vegetation. Physical, chemical, and heavy metal analyses were carried out in soil (semi total and fractionated contents). Quality of irrigation water and drainage water was also evaluated. Analytical results were normalized and subjected to analysis of variance, and means were compared by Scott-Knott test (P < 0.05). Pearson correlation analysis was also used to assure a minimum correlation of variables justifying its use in the matrix of a factorial analysis. Semi-total contents of Cr, Ni, Pb and Zn (except Cu in some areas) were lower than previous local assessment and national guiding values, indicating that they do not cause harmful alterations in soil quality. Analyses of waters showed high levels of HCO3, indicating moderate restriction to use (due to the high levels of EC, SAR, Na and Cl). Fractionation of heavy metals revealed low risk of environmental pollution since most metal contents were bound to the oxidic, organic and residual fractions. The water used in irrigation contributes to the contents of heavy metals and to the salinity condition of the evaluated soils. longterm regions region vegetation Physical chemical semi contents. . contents) variance ScottKnott Scott Knott P 0.05. 005 0.05 0 05 0.05) Semitotal Semi Cr Ni except values quality HCO3 HCO due EC SAR Cl. Cl Cl) oxidic 00 0.0 0.

RESUMO Considerando a importância do Silício (Si) para as plantas, nas últimas décadas muitos estudos avaliaram a capacidade do elemento em aliviar o estresse abiótico em diferentes espécies, a maioria delas de interesse agrícola. Para todas as espécies, o Si oferece uma gama de benefícios às plantas na redução dos efeitos do estresse biótico e abiótico, estando especialmente associado a aumentos na biomassa das plantas. No entanto, quando realizamos uma revisão quantitativa sistemática de estudos que relacionam o Si ao alívio do estresse abiótico em plantas, demonstramos que há uma redução dos efeitos do Si ao longo do tempo e que os efeitos do silício foram menores nos estudos mais recentes. Além disso, descobrimos que plantas sob diferentes tipos de estresse tiveram respostas semelhantes ao Si, sugerindo que os mecanismos de alívio do estresse abiótico nas plantas podem ser comuns entre as condições de estresse hídrico, salinidade e metais pesados – os principais estresses ambientais estudados na literatura. Nosso estudo pode direcionar estudos futuros, que não devem se limitar a simplesmente avaliar a existência de quaisquer efeitos de alívio de estresse do Si, mas também compreender a variação que existe nesses mecanismos e que depende do tipo de estresse e dos fatores envolvidos na redução desses efeitos.

ABSTRACT Considering the importance of Silicon (Si) for plants, many studies have focused to evaluate the ability of the element to alleviate abiotic stress in different species, mainly of agricultural interest. For all species, Si offers a range of benefits in reducing the effects of biotic and abiotic stress, being especially associated with increases in plant biomass. However, after performed a systematic quantitative review of studies linking Si to the relief of abiotic stress in plants, it was demonstrated that there is a reduction in the effects of Si over time and that the effects of Si were smaller in recent studies. Furthermore, was found that plants under different types of stress had similar responses to Si, suggesting that abiotic stress relief mechanisms in plants may be common among conditions of water stress, salinity, and heavy metals – the main environmental stresses studied in the literature. This study can guide future research, which should not be limited to simply evaluating the existence of any Si stress-relieving effects, but also to understand the variation that exists in these mechanisms and considered that they depend on the type of stress and the factors involved in reducing these effects.

RESUMO: Irrigação com água produzida, que é gerada durante a extração de petróleo bruto e gás pode ser uma opção para agricultura irrigada em regiões semi-áridas mas o efeito desta água tratada no estado nutricional das plantas e no crescimento e desenvolvimento das culturas deve ser avaliado. Com esse propósito, determinamos alterações nos aspectos nutricionais da cultura de girassol irrigado com água produzida e os efeitos na produção de biomassa e de grãos de girassol. O girassol cv. BRS 321 foi cultivado durante três ciclos em áreas irrigadas com água produzida filtrada (FPW) e tratada por osmose (OPW) e água subterrânea (GW). Ao final de cada ciclo, raízes, parte aérea e grãos foram coletados para determinar as concentrações de nutrientes. Irrigação com água produzida afetou o acúmulo de nutrientes em plantas de girassol. Irrigação com OPW promoveu acúmulo de Ca, Na, N, P e Mg. Plantas irrigadas com FPW acumularam maiores teores de Na em raízes e parte aérea, e afetou negativamente a produção de biomassa e de grãos de girassol. Os níveis de Na na parte aérea de plantas irrigadas com FPW aumentaram ao longo dos três ciclos de cultivo. Sob condições controladas, é possível reutilizar a água produzida tratada por osmose inversa na agricultura, mas necessita de mais estudos a longo prazo para compreender o efeito cumulativo, nas propriedades químicas e biológicas do solo e na produção das culturas. Estes resultados sugerem que a irrigação com água produzida tratada adequadamente, é uma boa estratégia para a sustentabilidade dos recursos hídricos.

ABSTRACT: Irrigation using produced water, which is generated during crude oil and gas recovery and treated by the exploration industry, could be an option for irrigated agriculture in semiarid regions. To determine the viability of this option, the effects of this treated water on the nutritional status of plants should be assessed. For this purpose, we examined the nutritional changes in sunflowers after they were irrigated with oil-produced water and the effects of this water on plant biomass and seed production. The sunflower cultivar BRS 321 was grown for three crop cycles in areas irrigated with filtered produced water (FPW), reverse osmosis-treated produced water (OPW), or ground water (GW). At the end of each cycle, roots, shoots, and seeds were collected to examine their nutrient concentrations. Produced water irrigation affected nutrient accumulation in the sunflower plants. OPW irrigation promoted the accumulation of Ca, Na, N, P, and Mg. FPW irrigation favored the accumulation of Na in both roots and shoots, and biomass and seed production were negatively affected. The Na in the shoots of plants irrigated with FPW increased throughout the three crop cycles. Under controlled conditions, it is possible to reuse reverse osmosis-treated produced water in agriculture. However, more long-term research is needed to understand its cumulative effects on the chemical and biological properties of the soil and crop production.

Na região semiárida, o manejo inadequado dos sistemas de cultivo, aliado à baixa produção de fitomassa, pode contribuir para reduzir os estoques de carbono (C) e nitrogênio (N) do solo; portanto, a adoção de sistemas de manejo para a preservação desses elementos é necessária. Objetivou-se avaliar as alterações promovidas nos estoques de C e N do solo por sistemas agrícolas agroflorestais (agrossilvipastoril e silvipastoril) e tradicional (com derrubada da vegetação, queima e cultivo por dois-três anos), confrontando-os à vegetação natural de Caatinga, após 13 anos, em experimento instalado em um Luvissolo Crômico órtico típico, no município de Sobral, Ceará. Amostras de solo foram coletadas nas profundidades de 0-6, 6-12, 12-20, 20-40 e 40-60 cm, em quatro repetições, considerando os relevos plano, convexo e côncavo em cada situação de estudo, sendo determinados o C orgânico total, o N total e as densidades do solo. Entre os sistemas agroflorestais estudados, o silvipastoril, em longo prazo, promoveu as maiores reduções nos estoques de C e N, enquanto o agrossilvipastoril as menores perdas, representando alternativa sustentável para o sequestro de C e N do solo nessas condições semiáridas. O sistema de cultivo tradicional apresentou reduções de 58,87 e 9,57 Mg ha-1 dos estoques de C orgânico e N total, respectivamente, indicando sua não adequação para as condições semiáridas brasileiras. Os relevos côncavo, no sistema agrossilvipastoril, e plano, no silvipastoril, apresentaram os maiores estoques de C orgânico, enquanto para o N total, a forma côncava apresentou os maiores valores na vegetação nativa, agrossilvipastoril e silvipastoril.

In the semiarid region of Brazil, inadequate management of cropping systems and low plant biomass production can contribute to reduce soil carbon (C) and nitrogen (N) stocks; therefore, management systems that preserve C and N must be adopted. This study aimed to evaluate the changes in soil C and N stocks that were promoted by agroforestry (agrosilvopastoral and silvopastoral) and traditional agricultural systems (slash-and-burn clearing and cultivation for two and three years) and to compare these systems with the natural Caatinga vegetation after 13 years of cultivation. The experiment was carried out on a typical Ortic Chromic Luvisol in the municipality of Sobral, Ceará, Brazil. Soil samples were collected (layers 0-6, 6-12, 12-20, 20-40 and 40-60 cm) with four replications. The plain, convex and concave landforms in each study situation were analyzed, and the total organic C, total N and densities of the soil samples were assessed. The silvopastoral system promoted the greatest long-term reductions in C and N stocks, while the agrosilvopastoral system promoted the smallest losses and therefore represents a sustainable alternative for soil C and N sequestration in these semiarid conditions. The traditional agricultural system produced reductions of 58.87 and 9.57 Mg ha-1 in the organic C and total N stocks, respectively, which suggests that this system is inadequate for these semiarid conditions. The organic C stocks were largest in the concave landform in the agrosilvopastoral system and in the plain landform in the silvopastoral system, while the total N values were highest in the concave landform in the native, agrosilvopastoral and silvopastoral systems.