Cimélio Bayer

HUMIFICATION DEGREE OF SOIL HUMIC ACIDS DETERMINED BY FLUORESCENCE SPECTROSCOPY

The humification process increases semiquinone-type free radical concentrations (SFRC) in humus. Their quantification by electron spin resonance spectroscopy (ESR) has been a good indicator of the degree of humification of soil organic matter. As an alternative to relatively complex and expensive ESR spectroscopy, fluorescence spectroscopy was used in this study to evaluate the humification degree of 18 humic acids (HA) extracted from four Brazilian soils under different land use, tillage, or cropping systems. Two fluorescence humification indexes of HA were calculated based on work done by Zsolnay et al. and Kalbitz et al. in 1999, and a third new fluorescence index was proposed. Our proposal is to use the blue wavelength (465 nm) as the HA fluorescence excitation source. As this wavelength is more resonant with the humificated groups present in soil HA samples, our hypothesis is that the resultant fluorescence will provide information about these structures and, therefore, on the degree of humification of the HA. The SFRC varied from 1.90 × 1017 to 14.75 × 1017 spins/g HA, characterizing a wide range of the degree of humification of soil HA. The lowest SFRC occurred in native forests (1.90 × 1017 to 7.50 × 1017 spins/g HA) and pasture soils (2.30 × 1017 to 4.64 × 1017 spins/g HA). In cultivated sites, soil HAs from no-tillage soil were less humified (2.41 × 1017 to 13.30 × 1017 spins/g HA) than those in conventionally tilled soil (5.68 to 14.75 × 1017 spins/g HA). The three fluorescence indexes show the same tendency as SFRC. Our fluorescence method was closely related to procedures found in the works of Zsolnay et al. and Kalbitz et al. (R∼0.9, P < 0.0001) and with SFRC (R∼0.85, P < 0.02), showing their potential as a simple and sensitive technique for evaluating the effect of land use and soil management systems on the humification degree of soil humic acids.

Armazenamento de carbono em frações lábeis da matéria orgânica de um Latossolo Vermelho sob plantio direto

Carbon storage in the soil organic matter (SOM) is an important strategy to mitigate carbon dioxide concentration in the atmosphere. The objective of this study was to evaluate the effect of the no-tillage (NT) use for six years, under four autumn (dry-season) cover crops based maize and soybean crop rotations (pigeon pea- pearl millet, bengan hemp-sorghum, sunflower-black oat, and wild radish-maize), on C storage in the particulate (>53 µm) and mineral-associated (<53 µm) SOM fractions of a clayey Oxisol from Brazilian Cerrado region. In comparison to conventional tillage (CT) under summer cash-crops, NT increased the total organic carbon (TOC) stocks in the surface soil layer (0-5 cm). In the top 20 cm layer, NT soil under wild radish-maize had 9% (4.66 Mg ha -1 ) more TOC than the conventionally tilled soil. On the other hand, C storage in NT soil under other cropping systems was statiscally similar to the CT soil. The C stocks in the particulate SOM fraction increased by 37 to 52% in NT soil (0-20 cm) in comparison to CT. The higher sensitivity to soil management changes made the particulate organic matter a more adequate soil quality index compared to the TOC stocks. The C stock in the mineral-associated SOM fraction was not affected by soil management systems, which can be related to the short-term under NT and or to the highly stable soil microaggregates in this clayey Oxisol. The preferential C storage in the labile SOM fraction is an environmental benefit, which is expected to occur only under continuous no-tillage and crop residues addition.

Managing grazing animals to achieve nutrient cycling and soil improvement in no-till integrated systems

Crop-livestock systems are regaining their importance as an alternative to unsustainable intensive farming systems. Loss of biodiversity, nutrient pollution and habitat fragmentation are a few of many concerns recently reported with modern agriculture. Integrating crops and pastures in no-till systems can result in better environmental services, since conservation agriculture is improved by system diversity, paths of nutrient flux, and other processes common in nature. The presence of large herbivores can positively modify nutrient pathways and soil aggregation, increasing soil quality. Despite the low diversity involved, the integration of crops and pastures enhances nature’s biomimicry and allows attainment of a higher system organization level. This paper illustrates these benefits focusing on the use of grazing animals integrated with crops under no-tillage systems characteristic of southern Brazil.

Adição de carbono e nitrogênio e sua relação com os estoques no solo e com o rendimento do milho em sistemas de manejo

Long-term experiments are essential for research about organic matter dynamics of soils. This paper reports results of an experiment installed in September 1985 on a Paleudult soil degraded under inadequate management for 16 years. The experiment was conducted at the Experimental Station of the Federal University of Rio Grande do Sul (Brazil) in Eldorado do Sul county. Three soil tillage methods (conventional tillage-CT, reduced tillage-RT and no-tillage-NT), three crop systems (oat/corn-O/C, vetch/corn-V/C and oat + vetch/corn + cowpea-O + V/C + Cp), and two N rates applied to corn as urea (0 and 139 kg ha-1) were tested. A split-plot design arranged in randomized blocks with three replications was used with soil tillage as main plot, the cropping systems as sub-plots and nitrogen rates as sub-blocks. Carbon and nitrogen addition by crops was estimated for the experimental period of 13 years. In September 1998, the soil was sampled in six layers down to 0.30 m depth, and total organic carbon (TOC) and total nitrogen (TN) contents were determined in each layer and then calculated for the 0-0.175 m and 0.175-0.30 m layers. Legumes were responsible for the greatest annual soil C and N increase by crops (4.17 to 8.39 Mg ha-1 and -21 to 178 kg ha-1, respectively). The highest C and N additions were positively related to these elements stocks in the soil under NT (0-0.175 m layer), and promoted gradual corn yield increase in all soil tillage treatments. The annual rate of C addition (A) necessary to maintain de initial condition (dC/dt = zero) was estimated at 4.2 Mg ha-1 for NT, 7.3 Mg ha-1 for RT and 8.9 Mg ha-1 for CT. Similarly, the annual rate of N addition required to maintain the initial condition (dN/dt = zero) was 5 kg ha-1 for NT, 31 kg ha-1 for RT, and 94 kg ha-1 for CT. An estimation by the angular coefficient of the linear regression, which relates the annual C addition rates and annual TOC stock variation in the surface layer, calculated that 12.9 % for NT, 8.1 % for RT, and 11.5 % for CT of the C added to the soil was retained in the soil organic matter, representing approximately the humification coefficient (k1). Likewise, it was estimated that 49.7 % of the net annual N addition under NT, 21.0 % under RT, and 33.1 % under CT was retained as TN in the soil. The TOC loss coefficient from the soil (k2), calculated for the condition dC/dt = zero, was 0.0166 yr-1 under NT, 0.0182 yr-1 under RT, and 0.0314 yr-1 under CT. No-tillage systems with the reduction of TOC loss (k2), and legume based crop systems with the high C and N additions are good alternatives to recover the soil TOC and TN stocks and increase corn yield in the subtropical region of southern Brazil.

Acidificação de um Latossolo sob plantio direto

Soil tillage affects soil acidification and nutrient cycling and possibly causes effects on crop development and yields. In this study, the long-term (21 yr) effect of the no-tillage system (NT) on soil chemical characteristics (solid phase and solution) was evaluated in a south Brazilian Oxisol (Guarapuava, Parana State), focussing on acidity components. NT caused an acidification process in the top soil layer, demonstrated by lower pH values (2-10 cm) and higher concentration and saturation values of Al (6-20 cm), in comparison to soil with conventional tillage (CT). However, the highest values of exchangeable and soil solution Ca, Mg and K, bases saturation, available P (Mehlich-1 and Resin), and total and soluble organic carbon in no-tilled soil off-set the negative effect of the soil acidification and contribute to a 22 % higher accumulated crop yield (39 harvests) than under conventionally tilled soil.

Tillage and cropping system effects on soil humic acid characteristics as determined by electron spin resonance and fluorescence spectroscopies

Abstract Long-term (5- and 9-year) effects were evaluated of two tillage regimes (conventional tillage: CT; and no-tillage: NT) and two cropping systems (oat/maize: O/M; and oat+vetch/maize+cowpea: O+V/M+C) on characteristics of humic acids (HAs) from surface layer (0 to 25 mm) of a subtropical Brazilian Paleudult soil. Generally, soil HA samples from conservation management systems with no soil disturbance (NT) and high crop residue addition (O+V/M+C) showed lowest humification degree, as demonstrated by lowest concentration of semiquinone-type free radicals, determined by electron spin resonance (ESR), and lowest total fluorescence (TF), which is proportional to area under fluorescence spectrum; however, cropping systems had less effect than tillage regimes on two spectroscopic parameters. Since all HA samples presented a maximum fluorescence emission peak around 518 nm, when excited with blue light, we believe that differences in the fluorescence intensity could be attributed to concentration of similar condensed aromatic moiety. This assumption was consistent with strong correlation with stable semiquinone-type free radicals (r=0.84, P

Comportamento de atributos relacionados com a forma da estrutura de Latossolo Vermelho sob sistemas de preparo e plantas de cobertura

Soil tillage and crop systems have significant influence on the soil structure, affecting water and air flow. The objective of this study was to evaluate the effects the management has on the soil properties of a Hapludox cultivated with maize intercropped with summer cover crops. Two experiments were carried out in Chapeco, State of Santa Catarina, Brazil under reduced tillage (RT) from 1993 to 1998 and conventional tillage (CT) from 1994 to 1998. Three cropping systems were evaluated under each tillage system: maize + Cajanus cajan (pigeon pea), maize + Stilozobiun niveun (mucuna) and maize in monoculture. For comparison purposes the soil of a adjacent native forest was also sampled. In comparison to the native forest, the tillage systems modified the soil structure by increasing the bulk density and penetration resistance and reducing macroporosity and total porosity. After five years of soil use, the reduced tillage with maize in monoculture had not recovered the properties of soil related to its structure while the use of intercropped maize-Stilozobiun niveun increased the soil macropores, total porosity and saturated hydraulic conductivity and reduced the bulk density. These improvements through the use of summer cover crops were not observed under conventional tillage. The use of intercropped systems improved the soil physical quality of this clayey Hapludox, especially due to the increase in crop residue inputs.

Chemical Modifications Caused by Liming Below the Limed Layer in a Predominantly Variable Charge Acid Soil

Abstract Despite the low mobility in soil, surface liming has increased plant growth and yield. Since only the topsoil is affected by this technique, the benefits may be caused by improvements in soil solution. This experiment aimed to assess chemical changes in the solid phase and leached solutions after addition of calcitic limes to a Humic Hapludox. Calcium carbonate or calcium hydroxide was throughly mixed with soil samples at rates of 0, 0.25, 0.50, 1.0, and 1.50-times that required to raise soil pH to 6.0 (equivalent to 0, 3.5, 7.0, 14, and 21 t ha−1). After 60 days, treated samples were transferred to the top (30 cm) of leaching columns, filled with unlimed soil in the bottom (23 cm). Water was percolated weekly through the columns during 12 weeks. Chemical determinations were performed on all leached solutions, and at different soil depths below the limed layer at the end of the experiment. Calcium (Ca), magnesium (Mg), and aluminum (Al) increased linearly in the percolated solution with increases on lime sources; the opposite occurred for leachate pH, probably due to hydrolysis of Al that was replaced from the negative charges on unlimed soil by added calcium. Calcitic limes increased pH and Ca, and decreased Al and Mg in the solid phase below the limed layer up to a maximum of 3 cm. Lime, thus, positively affected only the top of the unlimed solid phase; its effect on leached solution, however, was similar to that caused by neutral salts on acid soils, with increases in cations and decreases in pH.

Mobilidade vertical de cátions influenciada pelo método de aplicação de cloreto de potássio em solos com carga variável

The magnitude of the vertical movement of nutrients in the soil profile determines their contact with plant roots and leaching, thus affecting the timing and method of fertilizer application. This study aimed to assess the K mobility in the soil as influenced by rate and method of potassium chloride addition. The experiment was carried out in 1998, using 7.5 cm wide and 35 cm long PVC leaching columns. Potassium was applied at rates of 0, 150 and 300 mg kg-1 on the soil surface or incorporated 15 cm deep into two acid soils. Distilled water (300 mL per column) was percolated every seven days, for eight weeks. The volume of percolated water, and its Ca, Mg and K concentrations were determined. KCl addition on the soil surface caused a downward movement of K to a depth beyond 10 cm. Nevertheless, K leaching was small, and was evident in the initial percolations, was proportional to the applied rate, and was higher in the soil-incorporated treatments. KCl addition increased Ca and Mg leaching in the first five percolations, which may temporarily raise the availability of these nutrients because it coincides with the period of crop establishment when the plant nutrient demand is high. Even in these highly buffered soils, K spread on the soil surface moved downward to reasonable depths, without promoting significant leaching.

Propriedades físicas e teor de carbono orgânico de um Argissolo Vermelho sob distintos sistemas de uso e manejo

A conservacao do solo e a produtividade das culturas podem ser negativamente afetadas por mudancas causadas a composicao e arranjos dos constituintes do solo por diferentes sistemas de manejo. O objetivo deste estudo foi avaliar a influencia da intensidade de revolvimento sobre atributos fisicos e teor de carbono orgânico (CO) do solo. O experimento foi realizado por 17 anos em Eldorado do Sul (RS), num Argissolo Vermelho de textura media sob diferentes sistemas de manejo: preparo convencional (PC), preparo reduzido (PR) e semeadura direta (SD), utilizando a sucessao de culturas ervilhaca-milho. Uma area de campo nativo (CN), adjacente as parcelas agricolas, foi utilizada como testemunha. As amostras de solo foram coletadas antes do estabelecimento da cultura de verao, nas camadas de 0-2,5, 2,5-7,5, 7,5-12,5 e 12,5-17,5 cm de profundidade. As propriedades avaliadas foram: teor de carbono orgânico, densidade do solo e de particulas, macro, micro e porosidade total, grau de floculacao e estabilidade de agregados. Os sistemas de preparo nao influenciaram a densidade e a porosidade total do solo, mas a distribuicao do tamanho de poros variou conforme a profundidade de amostragem. A macroporosidade foi maior no preparo convencional em relacao ao preparo reduzido e semeadura direta somente na camada de 7,5-12,5 cm, e os microporos foram mais abundantes de 0-2,5 cm na semeadura direta em relacao aos demais sistemas. A adocao da semeadura direta aumentou a estabilidade de agregados da camada superficial do solo em relacao ao preparo convencional, mediante a elevacao no teor de carbono orgânico.