Brizantha Plants Research Articles

Endophytic Capacity of Entomopathogenic Fungi in a Pasture Grass and Their Potential to Control the Spittlebug Mahanarva spectabilis (Hemiptera: Cercopidae)

Pests in pastures have compromised the production of biomass for feeding livestock herds. Many strategies have been applied to sustainably solve this problem. One viable and innovative technique is the delivery of entomopathogenic fungi through endophytes. Therefore, this study aimed to (i) evaluate the endophytic capacity of two entomopathogenic fungi, Fusarium multiceps UFMGCB 11443 and Metarhizium anisopliae UFMGCB 11444, in Urochloa brizantha [(Hochst. ex A. Rich.) Stapf] (Poaceae) cultivar ‘Marundu’) via foliar inoculation or seed treatment, and (ii) measure their efficiency in controlling Mahanarva spectabilis Distant, 1909 (Hemiptera: Cercopidae) in U. brizantha. In the greenhouse, the fungi colonized the tissues of U. brizantha plants when inoculated via foliar spraying or seed treatment. The fungi F. multiceps and M. anisopliae caused 88% and 97.1% epizootic effects via seed inoculation, respectively, and 100% epizootic effects via foliar inoculation. In the field, the lowest fungal dose of 0.5 kg/ha had the same effect as a fourfold greater dose, with a >86% decrease in insect pest infestation observed. In summary, the fungi F. multiceps and M. anisopliae have endophytic effects and can effectively control M. spectabilis in U. brizantha pastures.

Luminous restriction and chemical control with glyphosate in integrated management of Urochloa brizantha L.

The objective was to evaluate the effect of different light conditions in the cultivation environment on the control of U. brizantha by glyphosate. The experimental design was in a plot scheme divided into randomized blocks with five replications. In the plots, environments with light conditions were allocated: full sun, intermittent shading with 3 hours of sun/day, and continuous shading. In the subplots, the herbicide doses: 0, 480, 960, and 1440 g. a. e. glyphosate ha-1 applied to U. brizantha plants. The control of U. brizantha by the herbicide glyphosate was more efficient in shaded environments, either with continuous or intermittent shading, in relation to full sun, indicating that the conditions of light influenced the action of the herbicide. At 35 DAA, control values of U. brizantha above 80% were observed from the 765 g. a. e ha-1 dose of glyphosate for treatments with shading. Already in conditions of full sun, 65% of control values were reached in the highest dose, which is considered unsatisfactory for the management of this species. U. brizantha submitted to light restriction had the content of epicuticular wax, starch, soluble and total sugar reduced; however, the leaf area was larger in these environments compared to full sun. The reserve content, epicuticular wax, and leaf area variables are affected by shading with a direct relationship with the greater control of U. brizantha by glyphosate in this cultivation condition.

Development of a taxon-discriminating molecular marker to trace and quantify a mycorrhizal inoculum in roots and soils of agroecosystems.

Crop inoculation with Glomus cubense isolate (INCAM-4, DAOM-241198) promotes yield in banana, cassava, forages, and others. Yield improvements range from 20 to 80% depending on crops, nutrient supply, and edaphoclimatic conditions. However, it is difficult to connect yield effects with G. cubense abundance in roots due to the lack of an adequate methodology to trace this taxon in the field. It is necessary to establish an accurate evaluation framework of its contribution to root colonization separated from native arbuscular mycorrhizal fungi (AMF). A taxon-discriminating primer set was designed based on the ITS nrDNA marker and two molecular approaches were optimized and validated (endpoint PCR and quantitative real-time PCR) to trace and quantify the G. cubense isolate in root and soil samples under greenhouse and environmental conditions. The detection limit and specificity assays were performed by both approaches. Different 18 AMF taxa were used for endpoint PCR specificity assay, showing that primers specifically amplified the INCAM-4 isolate yielding a 370bp-PCR product. In the greenhouse, Urochloa brizantha plants inoculated with three isolates (Rhizophagus irregularis, R. clarus, and G. cubense) and environmental root and soil samples were successfully traced and quantified by qPCR. The AMF root colonization reached 41-70% and the spore number 4-128 per g of soil. This study demonstrates for the first time the feasibility to trace and quantify the G. cubense isolate using a taxon-discriminating ITS marker in roots and soils. The validated approaches reveal their potential to be used for the quality control of other mycorrhizal inoculants and their relative quantification in agroecosystems.

Kamafugite From the Alto Paranaíba Province as a Multi-nutrient Fertilizer

The study evaluated the potential agricultural use of kamafugite as a multi-nutrient fertilizer in the cultivation of Urochloa brizantha. Two experiments were carried out under greenhouse conditions, one using a Ferralsol and the other an Arenosol. The experimental design was a randomized block with four replicates, in a factorial scheme 4 × 2 + 2, comprising four doses of kamafugite (1667, 3334, 6668, and 13336 mg dm-3), two product forms (filler and powder), and two additional treatments, TSF + KCl and a control treatment without K2O and P2O5 application. The sources were incubated for 60 days on two soil types and, after the incubation period, Urochloa brizantha plants were grown and two consecutive cuts were performed. The kamafugite was efficient in increasing plant dry mass and the levels of P, K, Ca, and Mg accumulated in plants, mainly in the 2nd Urochloa brizantha crop. The granulometry filler was more efficient in the sandy soil and the form powder in the clayey soil. Kamafugite can be used as an alternative source of nutrients for the Urochloa brizantha crop, being a low-cost and a potential source to improve tropical soil fertility over time.

Light availability interferes with absorption and translocation of 14C-glyphosate in Urochloa brizantha cv. Marandu plants

This research aimed to evaluate the absorption and translocation of 14C-glyphosate in Urochloa brizantha cv. Marandu subjected to different light availabilities. Six light conditions were studied: application followed by 24, 48 or 72 h of dark, 72 h of light, 24 h of dark + 48 h of light and daytime in different evaluation times: 0, 3, 6, 12, 24, 48, and 72 h after application of 14C-glyphosate (1.67 kBq/plant). The herbicide absorption was higher in plants with less light availability at 72 HAA (48 and 21% for 72 h of darkness and 72 h of light, respectively); however, there was a greater translocation of 14C-glyphosate to roots in the high availability of light (23 and 5% for 72 h of light and 72 h of dark, respectively). Thus, in U. brizantha plants, under conditions of greater light availability, 14C-glyphosate was less absorbed, but the product was more translocated. It is recommended that farmers to apply glyphosate at daytime since the light positively favored translocation, which is essential to the herbicidal activity.

Glauconitic siltstone as a multi-nutrient fertilizer for Urochloa brizantha cv. Marandú

Potassium (K) is one of the most absorbed nutrients by forage plants and it is found at low levels in tropical soils, requiring large amounts of fertilizers. The use of glauconitic siltstone as multi-nutrient fertilizers is an economic alternative to improve pasture-based production systems due to their low-cost production and long-term nutrient release. This study evaluated the effect of the glauconitic siltstone (GS) powder on three successive crops of Urochloa brizantha cv. Marandú (Syn. Brachiaria brizantha). Two experiments were carried out under greenhouse conditions, one using a Typic Dystrustox and the other a Typic Quartzipsamment. Both experiments were arranged in a completely randomized design with one factor, i.e., five glauconitic siltstone doses (0, 5, 20, 40, and 80 mg dm-3 of K2O) and four replications. In addition, three additional treatments were used, as potassium chloride, wollastonite and manganese sulfate at doses of 80 mg dm-3 of K2O, 270 mg dm-3 of silicon (Si) and 2 mg dm-3 of manganese (Mn), respectively. The sources were incubated for 60 days on the two soil types and, after the incubation period, Urochloa brizantha plants were grown. Three consecutive cuts were performed at 68, 104 and 168 days after sowing. The application of the GS in tropical soils promoted increases in plant dry matter, as well as K, Si and Mn levels in soil samples and accumulated in plants. In general, greater effects were obtained following the application of GS after consecutive cropping cycles due to its long-term release. Results described in this study provide an important understanding of the use of glauconitic siltstone as multi-nutrient fertilizers in tropical soils, being an efficient alternative to improve soil fertility and increase tropical pasture productivity.

Competitive Capacity of Native Species From the Carajás National Forest, Brazil

The present research had the objective to use the factor analysis in the evaluation of the competitive capacity of three native species from the Carajás National Forest in competition with different plant densities of the Urochloa brizantha grass. The experiment was conducted in a greenhouse and consisted in planting pots with the native species Bauhinia longipedicellata, Mimosa acutistipula and Solanum crinitum in competition with the exotic grass Urochloa brizantha. The exotic grass was established at densities ranging from 1 to 5 plants per pot, composing a 3 × 5 factorial arrangement with four replications that were delineated completely at random. Data were submitted to factor analysis for further analysis of variance and Tukey’s test at a 0.05 level of significance with the extracted factors. The effects of U. brizantha densities were evaluated by regression analysis. Out of the four extracted factors, three could be interpreted and were defined as vegetative growth index, infestation density index and physiological quality index. The Solanum crinitum species was slightly greater than the others in terms of vegetative growth rate and physiological quality. Generally speaking, native species maintain their vegetative growth in competitive conditions with up to two Urochloa brizantha plants; above that, the vegetative growth index tends to zero, while the infestation density index becomes positive.

Physiological and Biochemical Alterations of Urocholoa brizantha Submitted to Water Deficit and Silicate Fertilization

The correction of soil acidity and the evaluation of the effects of correctives used are not frequent practices in pasture areas. The benefits of silicon on the physiology and biochemistry of pastures is a subject that has not been explored in great detail. The objective of this study was to evaluate the performance of Urochloa brizantha plants (cultivar Xaraés) submited to condictions of water deficity and silicate fertilization through physiological and biochemical parameters. The experiment was carried out in pots under greenhouse conditions..The experimental design was randomized blocks, in a 2 × 2 factorial arrangement, with eight replications. The treatments consisted of a combination of the presence and absence of silicon (by means of soil correction using agrosilicon and dolomitic limestone, to raise the base saturation to 50%) with 2 soil water conditions (40 and 80% of field capacity). The analyzes were performed to determine: net CO2 assimilation rate, stomatal conductance, transpiration rate, water use efficiency, superoxide dismutase and catalase enzyme activities, shoot dry matter ,neutral detergent fiber and acid detergent fiber determinations and leave protein. The application of silicon in Urochloa brizantha cultivar Xaraés has the potential of attenuate the water deficity, increasing the photosynthesis, plant dry matter and antioxidant enzymes activity.

Effect of <i>Pseudomonas fluorescens</i> and <i>Burkholderia pyrrocinia</i> on the Growth Improvement and Physiological Responses in <i>Brachiaria brizantha</i>

The use of beneficial microorganisms in forage grasses is a potentially advantageous technique for a more sustainable pasture management by decreasing the need for chemical fertilization. Our aims were to determine the best method of microorganism inoculation on Brachiaria (Syn. Urochloa) brizantha cv. BRS Piata, compare the responses of inoculated plants of this forage grass with fertilized and unfertilized controls and examine its effect on some morphological, physiological and biochemical responses. On the first experiment, three inoculation methods were tested: in the seed, seed and soil, and soil, with Pseudomonas fluorescens (BRM-32111) and Burkholderia pyrrocinia (BRM-32113). In the second experiment, fertilized and unfertilized plants were either inoculated with BRM-32111, BRM-32113 and co-inoculated (BRM-32111 + BRM-32113). In a final experiment, B. brizantha was inoculated by soil drenching with BRM-32111, BRM-32113 and co-inoculated (BRM-32111 + BRM-32113), and compared to fertilized- and unfertilized-controls. The inoculation by soil drenching, at seedling stage, was more effective than inoculation only in the seed or both in the seed and by soil drenching. The fertilizer may have suppressed the beneficial bacterial effects on the growth of B. brizantha. P. fluorescens and B. pyrrocinia co-inoculated increased nitrate, protein, nitrogen concentration, Spad index (chlorophyll content), leaf area, number of tillers, net photosynthesis and total biomass production of B. brizantha plants. Our results point out to a potentially valuable source of practical information in the search of an eco-friendlier approach to increase pasture productivity.

Brachiaria brizantha GROWTH IN AMENDED SOIL BY EFFLUENTS FROM THE MILK INDUSTRY

he present work had as objective the verification of the effects of the incorporation of organic residues originating from ETE of the milk factory products in the soil and the effects in the development of the Brachiaria brizantha plants. The organic material was collected in the discard area of the factory, and been evaporated, triturated and separated in three granule size: powder, medium particles (with 2.0 mm diameter) and grains (medium particles with 6.0 mm diameter) and incorporate in soil by quantity of 0, 5, 10, 15 and 20 t. ha-1 followed by the planting of the forage. During the development of the plants, three cuts were appraised the dry weight and number of tillers. At the end, analysis of the fertility of soil was executing. The used experimental design was representing by randomized blocks with four repetitions. The application of organic material originating from ETE residual of dairies was have shown highly promising results vin the development of the forage plants, mainly when they are used in the powder form or attached and in higher amounts. Also considering some absorption by the plants during the experiment, the level of the nutrients and available minerals in the soil increas ed, except for the magnesium.

BbrizAGL6 Is Differentially Expressed During Embryo Sac Formation of Apomictic and Sexual Brachiaria brizantha Plants

Species of the genus Brachiaria comprise plants with different modes of reproduction, sexual and apomictic. In apomixis, the embryo sac differentiates from an unreduced cell, and the embryo develops in the absence of egg cell fertilisation. In this work, the characterisation and expression analyses of a MADS-box gene from Brachiaria brizantha, named BbrizAGL6, was described in sexual and apomictic plants. Phylogenetic analyses indicated that BbrizAGL6 belongs to the AGL6-like subfamily of proteins and clusters together with the AGL6-like protein of other monocots. BbrizAGL6 and AGL6 show conservation of the protein complex. Furthermore, BbrizAGL6 expressed preferentially in reproductive tissues and corresponding transcripts were detected in anthers and ovules. In ovules of B. brizantha, where the main differences among sexual and apomictic reproduction occur, BbrizAGL6 was differentially modulated. Transcripts of BbrizAGL6 were localised in the megaspore mother cell of ovaries from apomictic and sexual plants and, additionally, in the region where aposporic initial cells differentiate, in the nucellus of apomictic plants. For the first time, a role of an AGL6-like gene in megasporogenesis of apomictic and sexual plants is suggested.

Expression analyses of Brachiaria brizantha genes encoding ribosomal proteins BbrizRPS8, BbrizRPS15a, and BbrizRPL41 during development of ovaries and anthers

Brachiaria brizantha is a forage grass of the Poaceae family. Introduced from Africa, it is largely used for beef cattle production in Brazil. Brachiaria reproduces sexually or asexually by apomixis, and development of biotechnological tools for gene transfer is being researched to support the breeding programs. The molecular bases of reproduction have not yet been fully elucidated; it is known that gametophyte formation and main reproductive events occur inside the anthers and ovaries. There is therefore much interest in identifying genes expressed in these organs and their corresponding upstream regulatory sequences. In this work we characterized three cDNA from ovaries of B. brizantha plants (CL 09, CL10, and CL21) which show similarity in databases with genes encoding ribosomal proteins S8, S15a, and L41 and were named BbrizRPS8, BbrizRPS15a, and BbrizRPL41, respectively. These clones show higher expression in ovaries, anthers and roots, mitotically active tissues, when compared to leaves of B. brizantha. Localization of transcripts of BbrizRPS8, BbrizRPS15a, and BbrizRPL41 was investigated in the reproductive organs, ovaries, and anthers, from the beginning of development up to maturity. Their activity was higher in early stages of anther development, while expression was detected in all developmental stages in the ovaries, except for BbrizS15a, which was detected only in synergids of apomictic plants.

Brachiaria brizantha control by using fluazifop-p-butil on Tifton 85 pasture formation

This study was carried out with the aim of assessing the efficacy of the fluazifop-p-butyl herbicide to control Brachiaria brizantha, cultivar Marandu, in the formation of Tifton 85 grazing. Treatments consisted of five doses of fluazifop-p-butyl herbicide (0.0, 62.5, 125.0, 187.5 and 250.0 g ha-1) plus controls with no herbicide, in a completely randomized layout, with four replications. Each plot consisted of a 10-L capacity pot, with two B. brizantha plants and two Tifton 85 plants. The herbicide application was conducted before the tillage of B. brizantha, when they were about 15 cm high. Visual assessments of control of B. brizantha and intoxication of Tifton 85 plants, at 07, 21 and 45 days after application were carried out. Sixty days after application, plants were harvested at ground level and oven-dried. Regrowth was assessed in the same manner, 60 days after cutting, to determine their dry weight. Control of B. brizantha was noted to be above 50%, from doses of 218.75 g ha-1 at 45 days after application. The fluazifop-p-butylherbicide did not show to be efficient in the control of B. brizantha in the doses assessed and caused intoxication to Tifton 85 plants.

Supressão imposta pelo mesotrione a Brachiaria brizantha em sistema de integração lavoura-pecuária

Mesotrione é um importante herbicida registrado para uso na cultura do milho, porém pouco tem sido feito para estudar a suscetibilidade de espécies como Brachiaria brizantha a esse herbicida. O presente trabalho teve por objetivo avaliar a supressão imposta pelo mesotrione em plantas de Brachiaria brizantha, visando à viabilização de um cultivo integrado com a cultura do milho. Os tratamentos foram distribuídos em blocos casualizados, com quatro repetições, sendo estes constituídos por sete doses de mesotrione (0, 12, 24, 48, 96, 144 e 192 g ha-1), um tratamento com o cultivo de milho solteiro e capinado, além de um tratamento com capim-braquiária cultivado de forma solteira e capinada, totalizando assim nove tratamentos. As espécies milho e B. brizantha (cv. Marandu) foram semeadas concomitantemente. Os tratamentos herbicidas foram aplicados aos 20 dias após a emergência das espécies. O mesotrione mostrou maior potencial de fitointoxicação em plantas de B. brizantha ao ser aplicado na dose de 192 g ha-1. Entretanto, a espécie forrageira apresentou tolerância satisfatória ao herbicida, demonstrando potencial de utilização no sistema de integração lavoura-pecuária. A competição interespecífica proporcionou reduções no rendimento do milho, e a melhor relação dose-benefício para esse sistema foi obtida com a utilização de 96 g ha-1 de mesotrione.

Efeitos da aplicação de manganês no crescimento, na nutrição e na produção de matéria seca de plantas de Brachiaria brizantha (cv. MG4) em condições de casa de vegetação

A adubação com micronutrientes, como o manganês em gramíneas forrageiras tropicais, contribui para o atendimento das exigências nutricionais tanto das plantas quanto dos animais. Objetivou-se, neste trabalho, estudar os efeitos da aplicação de manganês no crescimento, na nutrição e na produção de matéria seca de plantas de Brachiaria brizantha, em condições de casa de vegetação. Para isto, realizou-se um experimento em casa de vegetação da FCAV/UNESP, Campus de Jaboticabal, com Brachiaria brizantha (cv. MG4), em vasos com 3,5 dm³ preenchidos com amostras de um Latossolo Vermelho distrófico (Mn = 0,6 mg dm-3). O delineamento experimental foi inteiramente casualizado, com cinco tratamentos, que corresponderam às doses de manganês (0, 15, 30, 60 e 120 mg dm-3), e quatro repetições. Avaliaram-se, nos dois cortes da forrageira (primeiro corte, 35 dias após o transplantio e, segundo, 30 dias após o primeiro), as variáveis de crescimento, produção de massa de forragem, teor e acúmulo de Mn na parte aérea. As doses de manganês aplicadas aumentaram a concentração deste micronutriente no solo e nas plantas e a produção de massa de forragem no primeiro corte. A Brachiaria brizantha cv. MG4 apresenta alta tolerância ao manganês, atingindo elevados teores de Mn na parte aérea, mesmo sem provocar sintomas visuais de toxicidade.

Seletividade de herbicidas aplicados em pré-emergência em gramíneas forrageiras

O presente trabalho teve o objetivo de avaliar a seletividade de herbicidas aplicados em pré-emergência sobre a produção e a qualidade de sementes de Brachiaria brizantha cv. Marandu e Brachiaria decumbens cv. Basilisk. Os herbicidas avaliados foram: diuron (800 e 1.600 g ha-1), ametryn (625 e 1.250 g ha-1), imazaquin (75 e 150 g ha-1), imazethapyr (50 e 100 g ha-1) e flumetsulam (70 e 140 g ha-1), além de uma testemunha sem aplicação de herbicidas. As espécies foram avaliadas separadamente no campo. Os experimentos foram instalados no delineamento em blocos casualizados com quatro repetições. Os herbicidas ametryn (625 g ha-1), imazaquin (75 e 150 g ha-1), imazethapyr (50 e 100 g ha-1) e flumetsulam (70 e 140 g ha-1) foram os que proporcionaram maior seletividade às plantas de B. brizantha, enquanto para B. decumbens o diuron (800 e 1.600 g ha-1), o ametryn (625 e 1.250 g ha-1) e o imazethapyr (50 e 100 g ha-1) foram mais seletivos, destacando-se o diuron na menor dose. Contudo, os herbicidas avaliados não alteram a produção e a qualidade das sementes das forrageiras estudadas.

Efeito de pontas de pulverização na deposição e na dessecação em plantas de Brachiaria brizantha

Objetivou-se com este trabalho avaliar a eficiência de pontas de pulverização com diferentes vazões e tamanhos de gotas na deposição e na dessecação de plantas de Brachiaria brizantha cv. Marandu, além da quantificação das perdas da calda de pulverização para o solo. O delineamento experimental adotado foi o de blocos casualizados, com quatro repetições. Cada unidade experimental constituiu-se de três linhas de 5 m de comprimento, espaçadas de 1 m. A aplicação dos tratamentos foi realizada 16 meses após a semeadura da braquiária; 40 dias antes da aplicação foi realizada uma roçagem para uniformização da área. Foram avaliadas as pontas de pulverização de jato plano XR 11001 VS (100 L ha-1) e XR 11002 VS (200 L ha-1), jato cônico TX-4VS (100 L ha-1) e TX-8 VK (200 L ha-1), ponta com indução de ar AI 11002 VS (200 L ha-1) e jato plano duplo TJ60 11002 VS (200 L ha-1). A calda foi aplicada com o herbicida glyphosate na dose de 1.800 g ha-1, mais um traçador (FD&C nº1 2.000 ppm). Foram coletados imediatamente após a aplicação da calda 25 perfilhos por repetição, sendo lavadas separadamente as folhas e caules de cada perfilho em 150 ml de água destilada, para posterior quantificação do traçador em espectrofotômetro. Os dados foram ajustados à curva de regressão pelo modelo de Gompertz. Todas as pontas utilizadas foram eficientes na dessecação das plantas de B. brizantha, independentemente do volume utilizado, o que evidencia a possibilidade de redução do volume de aplicação e da dosagem do herbicida na dessecação de pastagens, considerando-se a utilização de herbicidas sistêmicos. Ressalta-se que houve diferença na quantidade e na uniformidade de distribuição da calda pulverizada nos alvos avaliados em função da ponta testada e, conseqüentemente, do volume utilizado.

Controle de Brachiaria brizantha com uso do glyphosate após o estabelecimento de Tifton 85 (Cynodon spp.)

A eficiência do glyphosate no controle de Brachiaria brizantha cv. Marandu em áreas de cultivo do Tifton 85 foi avaliada utilizando o delineamento experimental em blocos casualizados, com oito doses de glyphosate (0, 90, 180, 360, 720, 1.080, 1.440 e 1.800 g ha-1), e quatro repetições. Cada parcela foi constituída de um vaso com duas plantas de B. brizantha cv. Marandu e duas plantas de Tifton-85. A aplicação do herbicida foi feita quando as plantas de B. brizantha apresentavam cerca de 40 cm de altura. O nível de intoxicação nas plantas de Tifton 85 e a eficiência do herbicida no controle de B. brizantha foram avaliados aos 15, 30 e 60 dias após aplicação (DAA). Aos 60 DAA, as plantas foram colhidas ao nível do solo e secas em estufa. A rebrota foi avaliada, do mesmo modo, aos 60 dias após o corte (DAC). Obeservou-se controle superior a 90% de B. brizantha, a partir da dose de 738,28 g ha-1 de glyphosate, enquanto a intoxicação para as plantas de Tifton 85 foi de apenas 12,05. Aos 60 DAA, houve redução na produção de massa seca de braquiária a partir da dose de 90 g ha-1. Doses superiores a 720 g ha-1 diminuíram o crescimento e desenvolvimento do Tifton 85, afetando sua produção, sem, no entanto, ocasionar a morte das plantas. Os resultados evidenciam boa tolerância do Tifton 85 até a dose de 720 g ha-1 de glyphosate.

Crescimento da parte aérea de plantas cultivadas em vaso, submetidas à irrigação subsuperficial e a diferentes graus de compactação de um Latossolo Vermelho-Escuro distrófico

A compactação é um processo que pode ocorrer em solos manejados inadequadamente, afetando, direta ou indiretamente, o crescimento e a produção das culturas. Com o objetivo de avaliar o crescimento da parte aérea de plantas, considerando os diferentes graus de compactação subsuperficial, plantas de soja, milho, algodão e Brachiaria brizantha foram cultivadas em vasos com material de um Latossolo Vermelho-Escuro distrófico, sob condição de fornecimento subsuperficial de água. O experimento foi realizado, sob telado, na Faculdade de Agronomia e Medicina Veterinária da UFMT, em vasos de PVC rígido de 195 mm de diâmetro interno, adotando-se delineamento inteiramente casualizado em esquema fatorial 4 x 4 x 5 (quatro espécies, densidades do solo de 1,0; 1,2; 1,4 e 1,5 Mg m-3 e cinco repetições). O conteúdo de água no sistema solo/vaso foi mantido acima de 60 % da capacidade de campo. Ao fim do experimento, mediu-se a altura das plantas, cortaram-se as plantas rente ao solo e foram determinadas a área foliar, a massa seca de frutificações (algodão, soja e milho) e a massa seca total da parte aérea. A compactação do solo provocou reduções significativas no crescimento da parte aérea do algodoeiro, milho e soja a partir de 1,4 Mg m-3 e na densidade do solo de 1,5 Mg m-3, para Brachiaria brizantha. A soja apresentou os maiores incrementos das características avaliadas na densidade do solo de 1,2 Mg m-3. A Brachiaria brizantha mostrou-se como a espécie de maior tolerância, enquanto o algodoeiro revelou maior susceptibilidade aos efeitos da compactação. Em geral, o modelo quadrático explicou adequadamente o crescimento das plantas de acordo com a compactação.

Níveis críticos de fósforo para Brachiaria brizantha e suas relações com características físicas e químicas em solos de Pernambuco

A influência de características físicas e químicas relacionadas com o fator capacidade de P (FCP) na determinação dos níveis críticos de P pelos extratores Mehlich-1, Mehlich-3 e Bray-1 e na parte aérea de plantas foram estudadas em amostras superficiais de seis solos de Pernambuco cultivadas com Brachiaria brizantha (Hochst ex A. Rich.) Stapf. cv Marandu. O estudo foi realizado em casa de vegetação, com amostras de solos de diferentes teores de argila, nas quais foram aplicadas doses de P definidas pelos valores do P remanescente (P-rem). O experimento consistiu de um fatorial 6 x 6 (seis solos e seis doses de P), com os tratamentos distribuídos em blocos ao acaso, com três repetições. O teor de argila não foi tão estreitamente correlacionado com o FCP, com o nível crítico de P no solo, nem com os níveis críticos de P em B. brizantha. As características que melhor refletiram o FCP foram a capacidade máxima de adsorção de P (CMAP) e o P-rem. Como a CMAP é uma análise de difícil operacionalização, a determinação do P-rem é indicada para estimar o FCP do solo em laboratório de rotina. Dentre os extratores utilizados para quantificar o P disponível, o Bray-1 apresentou a maior recuperação do P aplicado e o Mehlich-1 a menor. Os extratores que melhor se correlacionaram com o P absorvido pelas plantas foram o Mehlich-1 e o Mehlich-3. Os valores dos níveis críticos nos solos variaram de 15,2 a 138,5 mg dm-3, no primeiro corte, e de 2,1 a 62,3 mg dm-3, no segundo corte. Características químicas como CMAP e P-rem influenciaram os níveis críticos de P nos solos e planta. Os níveis críticos de P no solo e em plantas de B. brizantha foram menores em solos com maior CMAP e com menor P-rem.