Egon José Meurer

Carbono orgânico e fósforo microbiano em sistema de integração agricultura-pecuária submetido a diferentes intensidades de pastejo em plantio direto

Integrated crop-livestock systems have attracted more interest in the last few years due to their capacity of improving stability and sustainability of agricultural systems as compared to more specialized production systems. Soil organic carbon content has been used as an indicator of soil sustainability and stability. In this sense, this study aimed to measure the stocks of total organic carbon fractions and phosphorus in the microbial biomass in a Rhodic Hapludox (Oxisol) under integrated crop-livestock system with different grazing intensities in the winter. Soil samples were collected in November 2006 in Sao Miguel das Missoes, state of Rio Grande do Sul, Brazil. The experimental area had been cultivated under no-tillage for 10 years before implementing the integrated system in 2001. The experimental design was completely randomized blocks with three replicates. The treatments consisted of grazing intensities represented by sward heights of 10, 20 and 40 cm during the pasture cycle in winter. This pasture was composed of a black oat (Avena strigosa Schreb) and Italian ryegrass (Lolium multiflorum Lam.) mix, and a control area with no grazing. Total and particulate organic matter (POM) carbon stocks, phosphorus and carbon content in the microbial biomass, as well as microbial biomass activity were evaluated. The total organic stocks carbon were not affected by grazing intensities; however, the stocks of POM carbon were smaller in soils under the highest grazing intensity. The microbial biomass was stimulated at the highest grazing intensity, in which greater root growth was observed. The phosphorus content in the microbial biomass increased linearly with the decrease of the grazing intensity, while an inverse pattern was observed for the microbial biomass. Particulate organic matter carbon was more sensitive to changes in soil organic carbon under the experimental pasture management.

Empirical models to predict soil nitrogen mineralization

Modelos empiricos sao equacoes matematicas que podem ser ajustadas a resultados experimentais. Esses modelos podem ser utilizados para avaliar ou predizer fenomenos observados ou dados experimentais e auxiliar no desenvolvimento de praticas adequadas de manejo do solo. Desse modo, o presente trabalho teve por objetivo comparar oito modelos matematicos descritos na literatura, utilizando como dados experimentais o N mineralizado de dez solos do Rio Grande do Sul, acumulado durante 32 semanas de incubacao. O N mineralizado foi obtido experimentalmente em um experimento de incubacao, seguido de lixiviacao com CaCl2 0,01mol L-1. O N mineral foi determinado no comeco do periodo de incubacao e ao final da 2a, 4a, 8a, 16a e 32a semanas. Entre os modelos testados, o melhor ajuste do N mineralizado foi obtido com os modelos exponenciais simples, ao passo que a obtencao desses ajustes nos modelos exponenciais duplos esteve condicionado ao aumento de parâmetros na equacao. Em funcao dos resultados observados e das condicoes experimentais, conclui-se que a hipotese em que os modelos exponenciais duplos estao baseados, isto e, na presenca de dois compartimentos de nitrogenio suscetiveis a mineralizacao, foi rejeitada.

Resposta do arroz irrigado ao suprimento de amônio e nitrato

In rice cultivated under flooded conditions, the anaerobic condition favors the formation of NH4+ in the soil, and is therefore considered the main available N source for this crop. However, the process of O2 transport through the aerenchyma and its release by roots, create a favorable environment for nitrification in the plant rizosphere. Nitrification intensity determines the proportions between available NH4+ and NO3- . In this case, it is believed that the presence of NO3- can favor rice growth and simultaneously avoid NH4+ toxicity. This experiment was carried out to evaluate the effect of different proportions between NH4+ and NO3- in nutrient solution on rice growth. The experiment was performed in a greenhouse, from September to November 2007, in a nutrient solution with the following NH4+ and NO3- proportions: 100:0, 75:25 and 25:75, in a 10.0 mmol L-1 N concentration. The plots were fulfilled with a inert substrate to create conditions to root growth. The genotypes IRGA 417 and Sasanishiki were compared and the biomass production, root length, root distribution and the N, Ca, Mg and K uptake were evaluated. The presence of NH4+ in the 100:0, 75:25 proportions resulted in plant toxicity, however, as the NO3- proportion increased, toxicity was reduced. The combined supply of NH4+ and NO3- increased biomass production compared to solely NH4+ supply. The rice root system of the two cultivars developed mainly in the 0-10 cm layer and the - greatest root length was observed in the treatment NH4+ 75:25 NO3- for IRGA 417. The presence of NH4+ in soil solution affected negatively calcium absorption, whereas no affect was observed on N, Mg or K absorption. The total absorbed N, K, and Ca indicated a higher absorption efficiency with the combined supply for IRGA 417, but for cultivar Sasanishiki no differences were verified. It was concluded that NH4+ is toxic to rice plants, and is not the main available source of nitrogen. Nitrate is indispensable to increase the N uptake, normal plant growth and total cation absorption.

Suprimento de potássio de solos do Rio Grande do Sul para arroz irrigado por alagamento

Pot experiments are being used to study the potassium supplying capacity of soils. A greenhouse experiment with this objective evaluated samples of two Planosols, a Chernosol and a Gleisol, where flooded rice did not respond to potassium fertilization. The soils were cropped during 50 days with rice (Oriza sativa - BR-IRGA 409). Potassium uptake by the plant shoot, the exchangeable and non-exchangeable soil K, extracted by NH4OAc 1 mol L-1 and boiling HNO3 1 mol L-1, respectively, were evaluated, before and after cropping. Potassium accumulated by the rice plants differed between the soils and decreased in the order: Gleisol > Chernosol > Planosol 1 > Planosol 2. Exchangeable K was not the only element form in the soil that supplied the nutrient to the rice plants, since non-exchangeable K forms contributed as well.

Teor de cádmio em fertilizantes fosfatados comercializados no Brasil

O Cd e toxico ao homem, aos animais e as plantas. Os fertilizantes fosfatados contem Cd, em concentracoes variaveis, dependendo da rocha fosfatica da qual foram obtidos. Adubacoes fosfatadas sucessivas podem acarretar acumulo de Cd no solo, causando impactos ao ambiente devido a sua alta toxicidade. Os objetivos deste trabalho foram quantificar o teor de Cd em amostras de 19 fertilizantes fosfatados comercializados no Brasil e comparar dois metodos de extracao: nitroperclorico (HNO3 - HClO4) e USEPA 3050B (HNO3 - H2O2). O teor de Cd nas amostras foi determinado por espectrometria de emissao atomica por plasma acoplado indutivamente (ICP-AES). Seis amostras apresentaram teor de Cd maior do que 12mg kg-1 (nitroperclorico) e uma maior do que 43mg kg-1. As demais continham menos do que 3mg de Cd kg-1 de fertilizante. A correlacao entre as quantidades de Cd extraidas pelo metodo nitroperclorico e o USEPA 3050B foi significativa (r=0,985**) porem, nas amostras em que o teor de Cd foi maior do que 6,0mg kg-1, a extracao nitroperclorica extraiu mais Cd das amostras.

Short chain organic acid dynamics in solution of flooded soil treated with ryegrass residues

Short chain organic acids (C2 to C5), toxic for paddy rice, can be produced in flooded soils treated with organic residues. In order to study the liberation of organic acids into the solution of a flooded soil treated with residues of a ryegrass crop, an experiment was carried out in the greenhouse. The trial was planned in random blocks with three replicates using the following treatments: (a) without ryegrass residues, (b) ryegrass residues kept on the soil surface, and (c) ryegrass residues incorporated into the soil. The organic acids acetic, propionic, butyric, isobutyric, valeric, and isovaleric, were evaluated during eight weeks by gas chromatography. Results showed that the use of ryegrass residues increases the organic acids concentration in the soil solution. The highest concentrations were obtained at 10 cm deep with incorporated ryegrass. However, the organic acid concentration at 2 cm deep with ryegrass kept on the surface was equally high, probably at toxic levels for paddy rice. Acetic acid was the one presented at the highest concentration in the soil solution for all treatments.

Diversidade metabólica e atividade microbiana no solo em sistema de integração lavoura-pecuária sob intensidades de pastejo

The objective of this work was to evaluate the metabolic diversity and the microbial activity in an integrated crop-livestock system under no-tillage, and at different grazing intensities and soybean production. The experiment was carried out in Sao Miguel das Missoes county, in Rio Grande do Sul state, Brazil, in a clayey Rhodic Hapludox (Oxisol), subjected to grazing intensities at 10, 20, 30 and 40 cm-height of pasture with black oat + italian ryegrass, and a nongrazing treatment, in the winter. The metabolic diversity was evaluated with the Biolog EcoPlate technique, by the Shannon diversity index, and the microbial activity by the fluorescein diacetate hydrolysis method. There was higher functional diversity at the moderate grazing intensities (20 to 40 cm). The highest microbial activity, in the soil, occurred in the nongrazing treatment because of the high quantity of plant residues. Microbial functional diversity and activity had alterations caused by the grazing intensities, which can be used as soil quality indicators on integrated crop-livestock systems under no-tillage.

Fracionamento sequencial de cádmio e chumbo em solos

O impacto da contaminacao e/ou poluicao por metais pesados nao deve ser avaliado somente pelo seu teor total em solos, mas pela sua biodisponibilidade, que e uma propriedade relacionada com sua mobilidade no solo e absorcao pelas plantas. Este estudo teve por objetivo avaliar, mediante extracoes quimicas sequenciais, a biodisponibilidade do cadmio e do chumbo em seis solos do Estado do Rio Grande do Sul. Para isto, utilizaram-se amostras nas quais foram adicionadas tres doses de Cd (1,25, 2,50 e 5,0mg kg-1 de solo) e tres doses de Pb (250, 500 e 1.000mg kg-1 de solo) em experimento conduzido em vasos com drenagem livre para a agua, a ceu aberto, por 10 anos. As extracoes sequenciais detectaram diferencas entre as formas de adsorcao dos dois metais nos solos. O Cd foi detectado em todas as fracoes, principalmente na trocavel e na orgânica, enquanto que o Pb se concentrou nas fracoes orgânica e residual. O Cd apresentou maior mobilidade nos solos, notadamente naqueles com menor teor de argila; a mobilidade do chumbo foi muito baixa.

Fontes de potássio em solos distroférricos cauliníticos originados de basalto no Rio Grande do Sul

The objective of this study was to identify the K-bearing minerals as well as the granulometric fraction of the soil with potential to supply K to the plants from two basaltic Oxisols (Hapludox and Kandiudox). The mineralogical analyses of the granulometric fractions of the Hapludox soil revealed the probable occurrence of a mica mineral in the fine silt and coarse clay fractions, while feldspar minerals occurred in the sand, coarse silt, and fine silt fractions. In the Kandiudox soil, a probable mica mineral was observed in the coarse silt, fine silt, and coarse clay fractions, whereas feldspar minerals were observed in the sand and silt fractions. In both soils, the presence of a 2:1 clay mineral with hydroxy interlayer material (2:1 EHI) was also observed. This clay mineral has the basic structure of a smectite mineral. The coarse clay fraction of both soils presented the strongest evidences of the presence of K-bearing minerals, representing the most promising fraction for K supply to plants.

Adsorção de fósforo e sua relação com formas de ferro em dez solos do Uruguai

Iron oxihydroxides form strong chemical bonds with phosphate anions, reducing P availability to plants. The objective of this study, conducted in 1994/95, was to quantify forms of iron oxides in soils from Uruguay, and to study their relationships with phosphorus sorption. Iron oxides extracted with dithionite-citrate-bicarbonate (Fed) from ten soil samples (0-15 cm depth) ranged from 1598 to 8.592 mg kg-1 and were related with their parent material. Poorly ordered Fe-oxihydroxides, extracted by 0.2 mol L-1 ammonium oxalate at pH 3 (Fe03), ranged from 45.2 to 78.2% of the total iron oxides extracted by dithionite. The maximum P-sorption soil capacity (K2), estimated by the Langmuir equation, ranged from 104 to 704 mg kg-1 of soil. The P sorption was strongly correlated (r = 0.894, P < 0.01) with the poorly ordered iron oxides (Fe03). The percent of phosphorus sorbed by soils after equilibrium with 600 mg kg-1 P (P600), was significantly correlated (r = 0.975, P < 0.01) with the maximum P-sorption capacity and, with poorly crystalline Fe-minerals (r = 0.894, P < 0.01) extracted by the 0.2 mol L-1 oxalate ammonium pH 3. This index can be used to estimate the P-sorption capacity of these soils.