Danilo dos Santos Rheinheimer

Biodisponibilidade de formas de fósforo acumuladas em solo sob sistema plantio direto

The addition of fertilizers to the soil increases P contents in many forms of different bond energies with soil colloids. This has been observed in the soil surface layer under no tillage system, however there is little information about the availability of these P forms to plants. The study aimed to evaluate the bioavailability of P forms of a soil under no tillage with P applications. Samples were collected (0-10 cm) in a Rhodic Hapludox that had been fertilized with 0, 180, 360, 540, and 720 kg ha-1 of P2O5 over six years of cultivation prior to this study. The samples were dried, ground, filled in 2 kg pots and subjected to 15 successive crops without replacement of absorbed P. After every three successive crops, soil samples were collected for analysis. Phosphorus fractionation was analyzed by Hedleys method. Results showed that inorganic P extracted by NaHCO3 0.5 mol L-1 has a buffering capacity similar to P available by anion exchange resin, and can be considered labile P as well. In the long term, all soil P forms act in the soil solution buffer. In fertilized soils, the inorganic and organic P forms act in a similar way buffering the absorbed P by plants. In soils with little or no fertilization, the organic forms are the main P source of plants.

Distribuição do fósforo inorgânico em sistemas de manejo de solo

The intensity of the reactions of the phosphate fertilizer in the soil should vary in function of the different management systems. The study had the objective of evaluating the modifications in the inorganic fractions of P as affected by soil tillage and crop sequence. In May 1997, three soil layers of four long-term field experiments, involving no-tillage and conventional tillage with different crop sequences, were sampled. The total P and six fractions of inorganic P were evaluated. The medium content of total P was much higher than the native P. Total P increased in the upper soil layer under no-tillage. Available (resin and NaHCO3 0.5 mol L-1) and nonlabile inorganic P (HCl 1.0 mol L-1) were higher in the surface layer under no-tillage than in conventional tillage. The highest concentrations of inorganic P were moderately labile (NaOH 0.1 mol L-1). The crop sequences did not influence the fractions of inorganic P.

ALTERAÇÕES DE ATRIBUTOS DO SOLO PELA CALAGEM SUPERFICIAL E INCORPORADA A PARTIR DE PASTAGEM NATURAL

Superficial liming is an alternative way to correct soil acidity in no till system. The objective of this study was to evaluate the effects of superficial and incorporated liming on native pasture. The experiment was carried out at the experimental field of the Soil Science Department, at the Universidade Federal de Santa Maria (Brazil), on a Plinthaquult medium texture and with high potential acidity under native pasture. Lime rates of 0.0, 2.0, 8.5 and 17.0 Mg ha-1 were used. On half of the plots lime was mixed with the topsoil by disk plow and left on the surface on the other half of the plot. The experimental design was arranged in completely randomized blocks with four replications. After 6, 18, 36, and 48 months, soil was sampled at four depths, 0.0-2.5, 2.5-5.0, 5.0-10.0 and 10.0-15.0 cm and the attributes related to soil acidity evaluated. The surface applied lime was effective in neutralizing soil acidity, at a depth proportional to the rate and time. With 2.0 + 2.0 t ha-1, aluminum saturation reached near zero (0.0-2.5 cm layer) at 36 months; with 8.5 t ha-1, it reached near zero (2.5-5.0 cm) at 36 months; with 17.0 t ha-1 it reached near zero (5.0-10.0 cm) at 48 months.

Formas de fósforo no solo após sucessivas adições de dejeto líquido de suínos em pastagem natural

The swine industry generates large amounts of pig slurry (PS), which is reused as agricultural fertilizer. However, if applied at excessive rates, pig slurry becomes a severe environmental pollutant. The objective of this study was to evaluate forms of soil phosphorus accumulation after successive swine manure applications. The experiment was installed in 1995, in an area of native pasture. Rates of 0, 20 and 40 m3 ha-1 of PS were applied periodically (at 45 to 60 days intervals) during five years. In 1999, after 28 PS applications totaling 0, 560 and 1.120 m3 ha-1 of PS, soil samples were collected from the layers 0-2.5, 2.5-5.0, 5-10, 10-15, and 15-20 cm. Soil phosphorus in the samples was fractionated using Hedleys fractionation scheme (Hedley et al., 1982). The maximum phosphorus adsorption capacity (MPAC) was determined in soil samples without PS application using the Langmuir model. Results showed that phosphorus added as PS is accumulated essentially in inorganic forms, mainly those extractable by anion exchange resin, NaHCO3 0.5 mol L-1, NaOH 0.1 mol L-1 and HCl 1.0 mol L-1.

Modificações em atributos químicos de solo arenoso sob sistema plantio direto

No-tillage soil management does not permit incorporation of crop residues and requires surface application of fertilizers and corrective agents, thereby affecting nutrient availability and distribution. This study was carried out to evaluate the chemical changes in no-tillage system compared to conventional tillage and native grass field. Samples from a sandy/clay Red-Yellow Podzolic (Typic Hapludalf), taken at 0-5, 5-10, 10-20 and 20-40 cm depth, were used to determine zero point of salt effect (ZPSE), humic substances, permanent charge, soil pH, exchangeable Al, Ca + Mg and H + Al, total and mineral N, available, total and organic P and available, exchangeable and soil solution K. Effective CTC and pH 7.0, aluminum and base saturations and the percentage of organic P were determined. The soil management did not affect the ZPSE. The no-tillage system increased the fulvic and humic acids, nutrient availability, negative charges, and soil acidity.

APLICAÇÃO SUPERFICIAL DE CALCÁRIO NO SISTEMA PLANTIO DIRETO CONSOLIDADO EM SOLO ARENOSO

1 Engenheiro Agrônomo, MSc., Professor Assistente, Departamento de Solos, Centro de Ciências Rurais (CCR), Universidade Federal de Santa Maria (UFSM), 97105–900, Santa Maria, RS. Danilo@creta.ccr.ufsm.br. Autor para correspondência. 2 Engenheiro Agrônomo, MSc., Professor Substituto, Departamento de Solos, CCR, UFSM. 3 Engenheiro Agrônomo, Doutor, Professor Titular aposentado, Departamento de Solos, CCR, UFSM. 4 Engenheiro Agrônomo, Especialista, Professor Titular aposentado, Departamento de Solos, CCR, UFSM. RESUMOSurface liming is an alternative way to correct soil acidity. The objective of this study was to evaluate the effects of surface liming on soil properties and crop yield under no-tillage. The experiment was carried out at Federal University of Santa Maria, Southern Brazil, on a Typic Hapludult, under no-tillage, for five years, with pH 5.0, 13, 140 and 610g kg-1 OM, clay and sand, respectively. The lime rates used were 0, 1.2, 1.8 and 3.6Mg ha-1, applied on the soil surface without incorporation. The crops used were corn (94/95), black oat (95 and 96) and soybean (95/96 and 96/97). Grain yield was evaluated for corn and soybeans; dry matter production was evaluated for black oats. Six, 12, and 18 moths after liming, soil was sampled at four depths, 0-2.5, 2.5-5, 5-10 and 10-15cm to measure some attributes related to soil acidity. Treatments were set up in a complete block design with four replications. Superficial applied lime did not induce crop yield differences, but modified acidity and increased pH, calcium and magnesium contents in the 0-5cm layer.

Investigation of the occurrence of pesticide residues in rural wells and surface water following application to tobacco

In this work the exposure of wells and surface water to pesticides, commonly used for tobacco cropping, was assessed. Water consumption wells and surface water flows were sampled at different times. After a preconcentration step with solid phase extraction (SPE), the selected pesticides were determined by gas chromatography with electron capture detection (GC-ECD) or high performance liquid chromatography with diode array detection (HPLC-DAD). No pesticides were detected in the well water samples and surface water flow in the winter season. However, in the spring and summer higher concentrations of chlorpyrifos and imidacloprid were found in the water source samples. Atrazine, simazine and clomazone were also found. The occurrence of pesticides in collected water samples was related with the application to tobacco.

Contaminação de águas superficiais por agrotóxicos em função do uso do solo numa microbacia hidrográfica de Agudo, RS

This work was accomplished with the intention of quantifying the presence of pesticide molecules in surface waters of three landscape units (LU) with different usage configurations in the Agudo watershed of the State of Rio Grande do Sul, Brazil. Two semiautomatic water collectors were installed at the stream of each LU, from which samples were collected during rain over three stages of the tobacco growing season: seedling transplant, tobacco plants with 6-10 expanded leaves, and at harvest. Imidacloprid, atrazine, simazine, and clomazone compounds were quantified by High Performance Liquid Chromatography with Ultraviolet Detector (HPLC-UV). Chlorpyrifos, flumetralin and iprodione were analyzed by Gas Chromatography with Electron Capture Detector (GC-ECD), but these compounds were not detected in the samples. The sampling points where the LU was configured with both the presence of tobacco crops and reduced gallery forest, showed at least one pesticide compound in a sampling time. No pesticide was detected in the LU, which is completely covered with permanent vegetation or with gallery forest protecting the water courses.

Organic and inorganic phosphorus as characterized by phosphorus-31 nuclear magnetic resonance in subtropical soils under management systems

The area under no tillage system largely increased in the last decade in southern Brazil. The increase in total phosphorus (P), mainly in the topsoil layer in no-tillage management, is distributed in different inorganic and organic forms. The 31P nuclear magnetic resonance (NMR) technique can improve the understanding of the dynamics of phosphorus by identifying the structure of the major groups of this element in soils. This research determined the organic and inorganic phosphorus groups, identified by NMR and by chemical analysis in three subtropical soils under conventional and no-tillage systems. Samples of two soil layers from three long-term experiments located in the state of Rio Grande do Sul, southern Brazil, were used. The first experiment was set up in 1979, in a very clayey Rhodic Hapludox; the second, in 1983, in a clayey Rhodic Hapludox, and the third, in 1985, in a sandy clay loam Rhodic Paleudult. Total, inorganic, and organic P, biomass-associated and NaHCO3 extracted P were determined by chemical analysis and the NaOH+EDTA extract was submitted to 31P NMR for organic and inorganic determination. There was an overestimation of the organic phosphate content by the ignition method when compared with the NMR in surface-active soils (Hapludoxes). The NMR method allowed a good characterization of organic and inorganic phosphate groups in soils. Inorganic orthophosphate was the dominant P form; the organic P portion was higher in the low surface-active (Paleudult) soil, with a dominance of monoester over diester P, independently of soil type, tillage, or depth. A significant positive correlation was found between diester and microbial biomass P content.

Depleção do fósforo inorgânico de diferentes frações provocada pela extração sucessiva com resina em diferentes solos e manejos

Available soil phosphorus is maintained by less labile form that, in the long term, can become available to the plants. The aim of this research was to determine the depletion of various inorganic phosphorus fractions after successive extraction with resin. Soil samples were collected in four long-term experiments under no tillage or conventional tillage systems with different crop sequence. The soils (heavy clay Rhodic Hapludox, clay Rhodic Hapludox and clay loam Rhodic Paleudult) were collected from three depths, 0-2.5, 2.5-7.5 and 7.5-17.5 cm. Inorganic phosphorus was fractioned by a modified Hedley technique before and after successive phosphorus extraction by membrane resin. The fraction of phosphorus extracted with 1.0 mol L-1 HCl is not labile. Those extracted with 0.5 mol L-1 NaHCO3 and 0.1 mol L-1 NaOH can be considered labile, regardless the soil type, method of cultivation and crop sequence. In the Oxisols, the inorganic phosphorus fraction extracted by 0.5 mol L-1 NaOH is also labile.