Sérgio Ricardo Silva

Atributos físicos de dois Latossolos afetados pela compactação do solo

An experiment was carried out in order to evaluate the effects of soil compaction on the physical characteristics of two soils: a oxidic-gibbsitic Red Yellow Oxisol (LVA) and a caulinitic Yellow Oxisol (LA). The experiment consisted of eight levels of pressure applied to compact the soil (0, 60, 120, 240, 360, 540, 720 e 900 kPa). The experimental unit was composed of a PVC pipe with 6 cm in height and 4.55 cm of internal diameter to evaluate: hydraulic conductivity, microporosity, macroporosity, total porosity, soil penetration resistence and water-stable aggregates. Soil water retention at 0.01 and 1.5 MPa was evaluated using the samples compacted in the PVC pipe with 1.9 cm in height and 4.55 cm of internal diameter. The caulinitic soil was more sensitive to soil compaction than the to oxidic-gibbsitic soil. The increase of microporosity with soil compaction increased the soil water retention at 0.01 and 1.5 MPa, however it did not affect available water holding capacity. The properties of soil which have higher sensibility to effects of soil compaction were hydraulic conductivity and penetration resistence.

Soil compaction and eucalyptus growth in response to forwarder traffic intensity and load

Em povoamentos florestais, durante a retirada de madeira, as maquinas trafegam numa mesma linha varias vezes, o que pode causar a compactacao do solo e, como consequencia, facilitar o processo erosivo e dificultar o crescimento de raizes. O grau de compactacao, alem do numero de passadas da maquina, pode tambem ser afetado pelo peso de madeira transportado. Este trabalho teve como objetivo avaliar a compactacao do solo e o crescimento de eucalipto de acordo com a intensidade de trânsito e a carga de madeira de um forwarder. O estudo foi realizado no municipio de Santa Maria de Itabira, MG, em um Latossolo Vermelho-Amarelo (LVA) oxidico-gibbsitico. Um povoamento de eucalipto com sete anos de idade foi abatido por motosserra, sendo a madeira retirada da area manualmente. Em seguida, demarcaram-se parcelas de quatro entrelinhas de arvores com 12 m de comprimento (espacamento 3 x 2 m), com area de 144 m2 cada. Dois ensaios foram feitos. No primeiro, testou-se o efeito da intensidade de trânsito, no qual um forwarder, com tara de 11.900 kg, foi carregado com 12 m3 de madeira (densidade de 480 kg m-3) e dirigido sobre a mesma entrelinha por 0, 2, 4 e 8 vezes. No segundo, o forwarder recebeu cargas correspondentes a 4, 8 e 12 m3 de madeira e dirigido quatro vezes sobre a mesma entrelinha. Em cada parcela, quatro entrelinhas foram compactadas pelas rodas. Foi realizado o plantio de eucalipto em covas de 30 x 30 x 30 cm, abertas sobre as trilhas compactadas. O teor de carbono orgânico total (COT) era de 406 e 272 g kg-1 e a umidade atual do solo era de 248 e 249 g kg-1 nas camadas de 0-5 e 5-10 cm de profundidade, respectivamente. O teor de argila era de 470 e de areia 440 g kg-1. As avaliacoes realizadas apos a aplicacao dos tratamentos, nas camadas de 0-5 e 5-10 cm de profundidade, foram: densidade do solo e agregados estaveis em agua. Determinou-se, ainda, a velocidade de infiltracao basica (VIB) pelo metodo do infiltrometro de cilindro. Apos 441 dias, estas mensuracoes foram realizadas novamente, sendo acrescidas de outras analises: COT, N total, N-NH4+, N-NO3-, porosidade e resistencia a penetracao. Nas plantas, foram mensurados altura, diâmetro a altura do peito e materia seca de tronco. Verificou-se que o trânsito do forwarder aumentou a densidade, microporosidade e a resistencia do solo a penetracao e reduziu o diâmetro medio geometrico, a porosidade total, a macroporosidade e a infiltracao de agua no solo. Nao houve efeito da compactacao sobre a producao de materia seca de tronco e altura das plantas. A maior parte dos efeitos da compactacao foi manifestada por apenas duas passadas do forwarder. Os efeitos da compactacao ainda permaneciam no solo apos 441 dias do trânsito do forwarder.

Effect of compaction on microbial activity and carbon and nitrogen transformations in two oxisols with different mineralogy

The use of machinery in agricultural and forest management activities frequently increases soil compaction, resulting in greater soil density and microporosity, which in turn reduces hydraulic conductivity and O2 and CO2 diffusion rates, among other negative effects. Thus, soil compaction has the potential to affect soil microbial activity and the processes involved in organic matter decomposition and nutrient cycling. This study was carried out under controlled conditions to evaluate the effect of soil compaction on microbial activity and carbon (C) and nitrogen (N) mineralization. Two Oxisols with different mineralogy were utilized: a clayey oxidic-gibbsitic Typic Acrustox and a clayey kaolinitic Xantic Haplustox (Latossolo Vermelho-Amarelo acrico - LVA, and Latossolo Amarelo distrofico - LA, respectively, in the Brazil Soil Classification System). Eight treatments (compaction levels) were assessed for each soil type in a complete block design, with six repetitions. The experimental unit consisted of PVC rings (height 6 cm, internal diameter 4.55 cm, volume 97.6 cm3). The PVC rings were filled with enough soil mass to reach a final density of 1.05 and 1.10 kg dm-3, respectively, in the LVA and LA. Then the soil samples were wetted (0.20 kg kg-1 = 80 % of field capacity) and compacted by a hydraulic press at pressures of 0, 60, 120, 240, 360, 540, 720 and 900 kPa. After soil compression the new bulk density was calculated according to the new volume occupied by the soil. Subsequently each PVC ring was placed within a 1 L plastic pot which was then tightly closed. The soils were incubated under aerobic conditions for 35 days and the basal respiration rate (CO2-C production) was estimated in the last two weeks. After the incubation period, the following soil chemical and microbiological properties were detremined: soil microbial biomass C (CMIC), total soil organic C (TOC), total N, and mineral N (NH4+-N and NO3--N). After that, mineral N, organic N and the rate of net N mineralization was calculated. Soil compaction increased NH4+-N and net N mineralization in both, LVA and LA, and NO3--N in the LVA; diminished the rate of TOC loss in both soils and the concentration of NO3--N in the LA and CO2-C in the LVA. It also decreased the CMIC at higher compaction levels in the LA. Thus, soil compaction decreases the TOC turnover probably due to increased physical protection of soil organic matter and lower aerobic microbial activity. Therefore, it is possible to conclude that under controlled conditions, the oxidic-gibbsitic Oxisol (LVA) was more susceptible to the effects of high compaction than the kaolinitic (LA) as far as organic matter cycling is concerned; and compaction pressures above 540 kPa reduced the total and organic nitrogen in the kaolinitic soil (LA), which was attributed to gaseous N losses.

Fotossíntese, condutância estomática e produtividade de clones de Eucalyptus sob diferentes condições edafoclimáticas

The objective of this study was to evaluate photosynthesis rate, stomatal conductance and productivity of Eucalyptus clones in two different sites; one in Eunapolis, southern Bahia with well distributed rainfall throughout the year (wet area) and another on Salto da Divisa, east of Minas Gerais, with rainfall concentrated over the hot months of the year (dry area). Four different clones were examined, measurements of plants growth were performed by means of inventory and the photosynthetic parameters were measured with IRGA (Infrared Gas Analyser). Within each area, there is difference between clones only in the wet area for the variable volume. The average productivity of the clones in the wet area was 3.3 times higher comparing to the dry area. All clones in wet area decreased stomatal conductance in response to increase in vapor pressure deficit, decreasing 0.16 mol m2 s-1 to each 1kPa increase in VPD and the maximum photosynthetic rate ranging from 12.5 to 16.4 µmol m2 s-1 in this area. The comparison between clones within each area resulted in a significant difference in the wet area, with the clone A reaching maximum photosynthesis higher than others. In the dry area, there was no correlation between stomatal conductance and VPD, and there was no difference in photosynthesis between the clones, ranging from 1.2 to 3.4 µmol m2 s-1. A linear relationship was observed between the maximum photosynthesis and clones productivity, suggesting that photosynthetic rate was one of the factors responsible for the increased Eucalyptus productivity of the wet area.

Diffusive fluxes of phosphorus, potassium and metallic microelements as affected by soil compaction

ABSTRACT The objective was to evaluate the effects of soil compaction on phosphorus (P), potassium (K), zinc (Zn), copper (Cu), iron (Fe) and manganese (Mn) diffusive fluxes. The experiment consisted of two Oxisols and eight compaction pressures. The soil samples were placed in diffusion chambers, simultaneously with two ion-exchange membranes (anionic and cationic), compressed and incubated for 20 days. The P, K, Zn, Cu, Fe, and Mn diffusive fluxes (PDF, KDF, ZnDF, CuDF, FeDF, and MnDF) were determined. The compaction decreased the PDF in the oxidic-gibbsitic soil, and increased KDF, ZnDF, CuDF, and MnDF, in both soils. There was a higher diffusion of Zn, Cu, and Mn in the kaolinitic than the oxidic-gibbsitic soil. The descending order of cationic-microelement diffusive flux was MnDF > ZnDF ⋙ FeDF > CuDF. Presumably, Fe was mainly diffused as organic complexes with net negative charges, whereas Zn and Mn as free ions and, or, inorganic and organic complexes with positive charges. Abbreviations: CuDF, cupper diffusive flux; FeDF, iron diffusive flux; KDF, potassium diffusive flux; MnDF, manganese diffusive flux; PDF, phosphorus diffusive flux; ZnDF, zinc diffusive flux; AEM, anion-exchange membrane; CEM, cation-exchange membrane

Resposta do trigo BRS Guamirim à aplicação de Azospirillum, nitrogênio e substâncias promotoras do crescimento

Substâncias e microrganismos promotores do crescimento vegetal tem sido disponibilizados aos produtores rurais visando aumentar o rendimento das culturas. Este trabalho objetivou avaliar doses de nitrogenio e produtos contendo microrganismos e/ou substâncias promotoras do crescimento sobre os componentes de rendimento e produtividade da cultivar de trigo BRS Guamirim; bem como avaliar se a adicao complementar de N, com ureia, e eficaz na manutencao de maior rendimento de trigo inoculado com Azospirillum brasilense e se esta inoculacao pode substituir total ou parcialmente a adubacao nitrogenada do trigo. O experimento foi conduzido em Coxilha/RS, na safra de 2014. O delineamento experimental foi de blocos casualizados, com quatro repeticoes. Nove tratamentos compuseram o estudo: uma testemunha; quatro produtos (Azospirillum brasilense, hormonio vegetal sintetico, estimulador vegetal mineral e biofertilizante); um tratamento com uso simultâneo dos quatro produtos; e tres doses adicionais de nitrogenio (0, 40 e 120 kg ha-1) associadas com Azospirillum. A cultivar de trigo foi avaliada quanto ao rendimento de graos, componentes do rendimento, indice de colheita aparente, peso hectolitrico, materia seca e conteudo de N na parte aerea, e indice de vegetacao. Os produtos avaliados, contendo microrganismos e/ou substâncias promotoras do crescimento, nao alteram o rendimento de graos de trigo na ausencia de deficiencias hidrica e nutricional. O Azospirillum brasilense nao substitui total ou parcialmente a adubacao nitrogenada da cultivar de trigo BRS Guamirim.

Validation of an efficient visual method for estimating leaf area index in clonal Eucalyptus plantations

Leaf area index (LAI) is a key ecophysiological parameter in forest stands because it characterises the interface between atmospheric processes and plant physiology. Several indirect methods for estimating LAI have been developed. However, these methods have limitations that can affect the estimates. This study aimed to evaluate the accuracy and applicability of a visual method for estimating LAI in clonal Eucalyptus grandis × E. urophylla plantations and to compare it with hemispherical photography, ceptometer and LAI-2000® estimates. Destructive sampling for direct determination of the actual LAI was performed in 22 plots at two geographical locations in Brazil. Actual LAI values were then used to develop a field guide with photographic images representing an LAI range of 1.0–5.0 m2 m−2 (leaf area/ground area). The visual LAI estimation guide was evaluated with 17 observers in the field. The average difference between actual LAI and visual LAI estimation was 12% and the absolute difference between the two methods was less than or equal to 0.5 m2 m−2 in 77% of plots. Pearson’s correlation coefficients were high between actual LAI and hemispherical photographs (0.8), visual estimation (0.93) and LAI-2000® (0.99) and low for the ceptometer (0.18). However, absolute values differed among methods, with the average difference between the actual and estimated LAI of [12]% for visual estimation, 28% for the LAI-2000®, 37% for the ceptometer and −43% for hemispherical photographs. The LAI-2000® and ceptometer overestimated LAI in all plots, whereas hemispherical photographs underestimated the values in all measurements, showing that these methods need calibration to be used. No differences were observed between actual LAI and visual estimates across stand ages of 2–8 years and LAI of 1.5–5.3 m2 m−2 (P > 0.05). The results show that visual estimation of LAI in Eucalyptus stands is a practical method that is unaffected by atmospheric characteristics and can be used on an operational scale.