Roberto Ferreira Novais

Global resorption efficiencies and concentrations of carbon and nutrients in leaves of terrestrial plants

Nutrient resorption in plants influences nutrient availability and cycling and is a key process in biogeochemical models. Improved estimates of resorption parameters are needed for predicting long-term primary productivity and for improving such models. Currently, most models assume a value of 50% resorption for nitrogen (N) and phosphorus (P) and lack resorption data for other nutrients and for specific vegetation types. We provide global estimates of resorption efficiencies and nutrient concentrations for carbon (C), N, and P and the first global-scale estimates for essential nutrients such as potassium (K), calcium (Ca), and magnesium (Mg). We also examine leaf mass loss during senescence (LML) globally and for different plant types, thus defining a mass loss correction factor (MLCF) needed to quantify unbiased resorption values. We used a global meta-analysis of 86 studies and ∼1000 data points across climates for green and senesced leaves in six plant types: ferns, forbs, graminoids, conifers, and ev...

Frações da matéria orgânica do solo após três décadas de cultivo de eucalipto no Vale do Rio Doce-MG

SUMMARY : SOIL ORGANIC MATTER FRACTIONS AFTER THREE DECADESOF EUCALYPT CULTIVATION IN THE RIO DOCE VALLEY,BRAZIL Little is known about the changes in different soil organic matter (SOM) fractionsunder short-rotation eucalypt plantations. This study aimed to evaluate the impact ofeucalypt cultivation on C stocks of several organic matter fractions in soils previouslycovered with degraded pasture, as well as to identify which SOM fractions are more sensitiveindicators of land use change impacts. The study was conducted at two sites (Belo Orienteand Virginopolis) with commercial short-rotation eucalypt plantations in the Rio DoceValley region, Minas Gerais state, Brazil. The soil samples were analyzed for: total organicC (TOC), light fraction C (free light – FLL and occluded light- FLO), C associated to heavyfractions (sand – AR, silt + clay – S+A and clay - ARG), microbial biomass C (BM) andhumic fractions C (fulvic acids– FAF; humic acid– FAH and humin– FH). Results indicatethat overall organic C stockst in all SOM fractions were higher in soils of Virginopolis thanthose of Belo Oriente due to the lower annual mean temperature and higher clay content.Thus, soil C sequestration by eucalypt plantations was higher in Virginopolis (14.2 t ha

POTASSIUM AND MAGNESIUM IN CLAY MINERALS OF SOME BRAZILIAN SOILS AS INDICATED BY A SEQUENTIAL EXTRACTION PROCEDURE

The total contents of potassium (K) and magnesium (Mg) in selected Brazilian soils (Oxisols, Ultisols, Inceptsols, and Alfisols) developed from different parent materials were investigated to estimate the contribution of clay minerals to K and Mg reserves. Total K and Mg contents in the Na-saturated clay were determined by HF total digestion. The contribution of each mineral species to the total contents of K and Mg, was estimated by a sequential mineral extraction procedure, following the order: Na-saturated clay—1) amorphous aluminum and iron oxides (ammonium oxalate); 2) crystalline iron oxides (dithionite–citrate–bicarbonate); 3) amorphous aluminosilicate and gibbsite (0.5 M NaOH); 4) kaolinite (5 M NaOH); 5) mica (NaHSO4), and 6) feldspar (HF total digestion). In order to monitor mineralogical changes, after each extraction, the samples were studied by x-ray diffraction (XRD), analytical transmission electron microscopy (ATEM), differential thermal analysis and thermo-gravimetric analysis. Total amounts of K and Mg in the clay of the strongly weathered soils were very low, indicating a low reserve of these nutrients. Due to the high proportion of kaolinite in the clay fraction of these strongly weathered soils, this mineral accounts for more than 50% of the total K and Mg. The relative proportion of kaolinite and its contribution to the K and Mg reserves increased with weathering. In strongly weathered soils, the contribution of micaceous minerals to the total K and Mg ranged from 17 to 75% and from 8 to 59%, respectively, whereas in the younger soils the range was between 51 and 83%, and 35 and 82%, respectively. Only after the removal of the iron oxides and of the kaolinite was the mica concentration in the clay fraction high enough to be detected by XRD in some of the strongly weathered soils. Dioctahedral illite was the dominant micaceous mineral due to its high resistance to weathering. Microanalysis of individual mica particles by EDAX–ATEM revealed K2O and MgO concentrations between 62 and 121 g kg−1, and between 5 and 10 g kg−1, respectively.

ESTOQUES DE CARBONO E NITROGÊNIO EM FRAÇÕES LÁBEIS E ESTÁVEIS DA MATÉRIA ORGÂNICA DE SOLOS SOB EUCALIPTO, PASTAGEM E CERRADO NO VALE DOJEQUITINHONHA - MG

The substitution of the native Cerrado (Brazilian savanna) vegetation by planted eucalyptus forests can influence the C and N pools in the different soil organic matter (SOM) fractions. However, the intensity and direction of this change depend on the soil type, climate, and management techniques in the planted area. The objective of this study was to determine the effect of eucalypt plantations on the C and N pool of labile and stable SOM fractions in an area previously occupied with savanna-like vegetation in the Vale do Jequitinhonha, MG, Brazil. Soil samples were collected from Eucalyptus urophylla plantations and adjacent areas with natural savanna vegetation, and managed pasture. The eucalypt plantation was 20-year old, and had succeeded the savanna vegetation, which was cut, the firewood removed and the residues burned. The pasture had been planted about 15 years earlier using the same site preparation procedures. There were no differences in total organic carbon (TOC) among soil samples of the three vegetation types. In the humic acid (HA) and fulvic acid (FA) fractions, the C contents were about 16.6 and 17.5 % higher for the eucalypt soil in comparison with the soils from the pasture and, 17.5 and 36.9 % higher than in soils from the savanna, respectively. Replacing the savanna vegetation by eucalypt did not reduce the C and N pools of the soil microbial biomass of the soil, but increased the amounts of C and N in the light organic matter (LOM), contributing to an increase in SOM. The estimated contribution of C derived from eucalypt to SOM based on 13C natural abundance was 5 %. This indicates a low substitution rate of native C by C derived from eucalypt, with an mean annual rate of 0.25 %. It can be concluded that substituting the native savanna vegetation by eucalypt did not reduce the C pools in the different SOM fractions.

Alocação de nutrientes em plantios de eucalipto no Brasil

Forest management practices can alter nutrient exportation from the site. The purpose of this study was to estimate nutrient contents in the aboveground biomass of eucalyptus plantations in Brazil. The influence of key climatic variables on eucalypt productivity and nutrient content was evaluated, using the database from the Reserch Programa on Soil and Eucalyptus Nutrition of the Soil Science, Departament - Federal University of Vicosa, Minas Gerais State, Brazil. Climatic characteristics were an important component of the models. In regions with low water availability the nutrient accumulation in aboveground biomass as well as biomass production were lower. The highest proportion of all nutrients (68 % N, 69 % P, 67 % K, 63 % Ca, and 68 % Mg) was accumulated in the biomass within 4.5 years after planting for harvesting after approximately 6.5 years. After 4.5 years, the potential of fertilizer response was lower. Canopy and stem bark together accounted for 65 % N, 70 % P, 64 % K, 79 % Ca, and 79 % Mg in the aboveground biomass. Debarking in the field can therefore substantially reduce nutrient exportation and contribute to a more sustainable production in eucalyptus plantations.

Valores de referência para macronutrientes em eucalipto obtidos pelos métodos DRIS e chance matemática

Data from 1.213 trees of Eucalyptus grandis x E. urophylla hybrids were collected between 1988 and 1994 from the Aracruz Celulose S.A. commercial plantation in the State of Espirito Santo, Brazil. Data on stand productivity and macronutrient concentration in four tree components (leaf, branch, stembark and stemwood) were used to determine the reference values of nutrient concentration by the methods of Mathematical Chance and DRIS. The formula of Jones and the population distribution based on age and selection of the relation between elemental concentrations by the F test were used in the calculation of DRIS indices. Critical levels were obtained using the DRIS method, by the following processes: determining the mean nutrient concentration in the nutritionally balanced and productive (optimum critical level) eucalypt stands; and by graphs (critical-level graph). The mean concentration proved to be a promising method, even when compared to the Mathematical Chance method. This latter method was appropriate mainly for the determination of the optimum range, which could be used as minimum and maximum limits for the range of nutrient sufficiency in productive trees.

Modelagem da recomendação de corretivos e fertilizantes para a cultura da soja

A recomendacao de adubacao para as culturas agricolas, no Brasil, e feita com base em tabelas que relacionam a classe de disponibilidade do nutriente no solo com a dose a ser aplicada. Este trabalho apresenta uma alternativa para recomendar corretivos e fertilizantes para a cultura da soja, o SIRSo (sistema de recomendacao de corretivos e fertilizantes para a cultura da soja). O principio desse sistema e o balanco nutricional, ou seja, a recomendacao se faz a partir da diferenca entre o requerimento de nutrientes pela planta e o suprimento de nutrientes pelo solo, por residuos orgânicos, por fertilizantes e pela calagem. O sistema considera ainda o fator sustentabilidade, visando manter uma quantidade de nutriente no solo capaz de garantir produtividade minima em cultivos subsequentes. Para recomendar calagem, o sistema considera dois metodos: a neutralizacao do Al3+ e a elevacao dos teores de Ca2+ + Mg2+, ou a saturacao por bases. O requerimento de nutrientes varia com a produtividade esperada de graos, com as caracteristicas do solo e com a taxa de recuperacao pela planta do nutriente aplicado ao solo. O suprimento pelo solo depende da disponibilidade do nutriente, estimada a partir da analise de solo e da taxa de recuperacao pelo extrator do nutriente aplicado. As comparacoes entre as recomendacoes geradas pelo SIRSo e aquelas oriundas das tabelas em uso no Pais mostram, em geral, que o SIRSo recomenda maior quantidade de nutrientes, principalmente de P e K quando consideradas as maiores produtividades, fato confirmado pela analise de sensibilidade, que mostrou grande variacao da dose a ser recomendada desses nutrientes com a produtividade de graos. Esse fato pode ser considerado como vantagem do SIRSo em relacao as tabelas, muitas das quais apresentam pouca ou nenhuma variabilidade das doses em relacao a produtividade.

Eucalyptus urophylla root growth, stem sprouting and nutrient supply from the roots and soil☆

Lack of information concerning root growth of trees limits our knowledge of plant development and fertilizer response. The objective of this work was to study root growth dynamics of an E. urophylla forest after harvesting and the supply of nutrients from the roots and the soil to the new sprouts originating from the stumps. About 7-year-old eucalypt trees were felled and the sprouts and roots were sampled at 0, 60, 120, 180, 240, 330 days after harvesting. The roots were separated into fine roots ( 3 mm), and taproot. Nutrient supply to sprouts from the old roots and the soil was calculated based on the change in nutrient content of the roots with time and accumulation of nutrients in the sprouts. Fine, medium and coarse root biomass increased with time after harvesting. However, the increase was more pronounced with fine roots. Between harvesting and day 60 of the new growth, all nutrients allocated to the sprouts, excluding potassium, were supplied by the soil. K was the nutrient most dependent on root reserves for the initial growth of sprouts. The contribution of the old roots to N, P, Ca, and Mg accumulation in the sprouts increased between day 60 and 120. At 330 days after harvesting, about 9.2, 23.9, and 12.6% of the N, K, and Mg, respectively, that had accumulated in the sprouts were supplied by the roots, while all P and Ca were supplied by the soil.

Relação entre o zinco "disponível", por diferentes extratores, e as frações de zinco em amostras de solos

Many extracting procedures for the plant-available zinc have been developed. Total soil Zn fractionation has been used as an attempt to understand the reactions of this nutrient in soils and the behaviour of the extracting procedures. This work evaluated the influence of soil characteristics on the concentration of Zn extracted by different procedures and on soil Zn fractions. Samples were collected from the 0-20 cm surface layer of twelve soils, representing the great soil groups of Dark-Red Latosol (LE), Red-Yellow Latosol (LV), Yellow Latosol (LA), Red-Yellow Podzolic (PV), and Quartzi Psaments (AQ). The soil samples received 0 and 20 mg dm-3 of Zn and were incubated for 30 days. Soil Zn concentration was determined after extraction with DTPA-TEA-CaCL2, 0.1 mol L-1 HCl, Mehlich-1 (M-1) and Mehlich-3 (M-3). Zinc fractionation was also carried out to determine exchangeable Zn (ExZn), Zn tied up to organic matter (OmZn), to manganese oxide (MnZn), to amorphous iron oxide (AFeZn), and to crystalline iron oxide (CFeZn). DTPA and M-3 were the extractants with larger sensitivity to the soil characteristics related to the capacity factor (buffering power). The M-1 and HCl extractants presented lower sensitivity and lower correlation with these characteristics due to their larger extraction power. The ratio Zn recovered by the extractant/Zn applied to the soil showed the best correlation with soil characteristics related to the Zn capacity factor. Exchangeable Zn fraction was the largest source of this nutrient to the tested extractants. The fractions of ExZn, OmZn, MnZn AFeZn and CFeZn did not account for the zinc recovered by the extractants, in all cases.

Mineralogia das frações areia, silte e argila de sedimentos do grupo barreiras no município de Aracruz, estado do Espírito Santo

To investigate the mineralogical variations with depth, 11samples were collected down to 14m, in an exposed sediment packet of the Barreiras Group in Aracruz, Espirito Santo, Brazil.The sand, silt and clay fractions were studied by X-ray diffraction, differential thermal analysis, thermogravimetry and electron microscopy.The total contents of Fe in the clay and silt fractions and Ti and Zr in the silt fraction were determined by ICP after fluoridric acid extraction.Clay and silt fractions were submitted to selective and sequential mineral extractions, to characterize and quantify their constituents.The sand fraction showed a uniform mineralogical composition, almost solely quartz, with small amounts of mica, anatase, kaolinite and iron aggregates.In the 2.1; 4.2 and 7.7m depths, the occurrence of iron mottles with dark-red colour was observed.Silt fraction, as well, is constituted mainly by quartz, with stable kaolinite aggregates and hematite.The clay fraction showed a high proportion of kaolinite, reaching 950gkg-1 at 14m depth.The low contents of Fe in the sediments and the humid conditions of the Coastal Tablelands favored kaolinite concentration and removal of minerals, mainly Fe oxides. Contents of Goethite (main Fe oxide in the sediment) decreased with depth.The amount of low cristalinity material in the clay fraction is small, varying from 3.2 to 24.0gkg-1 for ammonium oxalate extraction and from 0.6 to 3.5gkg-1 for extraction with 0.5molL-1 NaOH, due to the high degree of development of the sediments.For the same reason, the mica contents in the clay and silt fractions were lower than 5.0gkg-1.As observed for kaolinite, the mica content in the clay fraction increased with depth.