R. F. Vieira

Foliar application of molybdenum in common beans. I. Nitrogenase and reductase activities in a soil of high fertility

Abstract Although common bean (Phaseolus vulgaris L.) has a good potential for N2 fixation, poor nodulation following inoculation, principally under field conditions, has led to increased nitrogen (N) fertilizer use in this crop. In the face of the negative environmental effects of N fertilizer, alternative methods have been studied to minimize the amount to be applied. In this sense, foliar application of molybdenum (Mo) has been cited as a promising method. Several papers show that high bean yields (1,500–2,500 kg ha‐1), may be obtained in the southeasten region of Brazil, when there is an application of N as side dressing or Mo spray 25 days after plant emergence. A field experiment was carried out to verify the effect of Mo foliar application on nitrogenase and nitrate reductase activities and on bean yield. Treatments included Rhizobium inoculation (with and without), foliar application of Mo (0 and 40 g ha‐1), N at planting (0 and 20 kg ha‐1) and N applied as side dressing (0 and 30 kg ha‐1). Molybd...

White Mold Management in Common Bean by Increasing Within-Row Distance Between Plants

White mold of common bean (Phaseolus vulgaris), caused by Sclerotinia sclerotiorum, is a major yield-limiting disease during the fall-winter season in Brazil. This study was conducted to evaluate the efficacy of decreasing within-row densities for an indeterminate growth habit (type IIIa) cultivar, keeping constant the between-row spacing of 0.5 m, to manage the disease. A modification of within-row plant distributions was also attempted in order to reduce white mold intensity. The study was conducted with sprinkler irrigation in two growing seasons (2000 and 2001) in Viçosa, State of Minas Gerais, Brazil, in an area naturally infested with sclerotia. In 2000, treatments were arranged as 3 × 2 × 2 factorial combination of within-row densities (15, 7.5, or 5 plants/m), within-row plant distributions (single and equidistant plants or equidistant groups of three plants), and fluazinam treatments (with or without). In 2001, 16, 12, 8, or 4 plants/m were combined with fluazinam treatments. Fluazinam was applied at both flowering onset and 10 or 13 days later. Average incidence was 92.6% in 2000 and 77.8% in 2001; severity index was 69.8% in 2000 and 40.2% in 2001; and yield was 1,656 kg/ha in 2000 and 2,542 kg/ha in 2001. White mold decreased and yield increased as within-row densities were reduced, regardless of fluazinam treatments. A distribution of equidistant groups of three plants was ineffective in reducing disease. The use of 4 equidistant plants/m in infested irrigated areas was an effective strategy in white mold management.

Paclobutrazol effects on soil microorganisms

The side effects of paclobutrazol, a plant growth regulator, on soil microbial community and activity were assessed in soil samples from Petrolina (PE), Pernambuco State and from Lins (SP), Sao Paulo State, in Brazil. The first experiment was carried out with soils from mango orchards of Petrolina, subjected to frequent field applications of paclobutrazol. A second experiment was conducted with soils from Petrolina and Lins with application of paclobutrazol under greenhouse conditions. For orchard soils, plate counting of soil microorganisms was carried out, while for the greenhouse experiment the parameters evaluated were: microbial biomass C, living hyphal length, dehydrogenase activity, and paclobutrazol dissipation. The paclobutrazol addition to soils of mango orchards in Petrolina, affected negatively the soil microbial community. The average values for total number of bacteria, fungi and actinomycetes were reduced by 58, 28, and 28%, respectively, compared to the paclobutrazol unamended soil. For the greenhouse experiment, the paclobutrazol application in the soils from Petrolina influenced negatively the dehydrogenase activity and the living hyphal length, but not the microbial biomass C. The addition of this substance to the Lins soils had no effect on the microbial parameters evaluated.

Foliar application of molybdenum in common bean. II. Nitrogenase and nitrate reductase activities in a soil of low fertility

Abstract Foliar application of molybdenum (Mo) at 40 g ha‐1 25 days after plant emergence greatly enhanced nitrogenase and nitrate reductase activities of common bean (Phaseolus vulgaris L.), resulting in an increase in total nitrogen (N) accumulation in shoots. Application of 20 kg N ha‐1 as ammonium sulfate [(NH4)2SO4] at sowing decreased nodulation and nitrogenase activity. Rhizobium inoculation did not affect nitrogenase activity which demonstrated that Mo application increased the efficiency of native Rhizobia strains. Nitrogen amendment, either at planting (20 kg N ha‐1) or as a side dressing (30 kg N ha‐1) 25 days after plant emergence, did not affect the foliar nitrate reductase activity. Molybdenum foliar spray as ammonium molybdate [(NH4)6Mo7O242H2O] and N applied as a side dressing increased equally the total amount of N in the pods. A 10% increase in the seed N concentration was obtained with foliar application of Mo, while N applied as a side dressing had no effect on seed N concentration. An...

Disponibilidade de nutrientes no solo, qualidade de grãos e produtividade da soja em solo adubado com lodo de esgoto

O objetivo deste trabalho foi verificar o efeito direto e residual da adubacao com lodo de esgoto, como fonte de P, na produtividade da soja, na qualidade dos graos para consumo humano e no potencial de lixiviacao do nitrato. O experimento foi realizado no campo e constituiu-se dos seguintes tratamentos: ausencia de adubacao quimica e de lodo; adubacao quimica completa; soja com inoculacao mais dose zero de lodo; soja com inoculacao mais 1,5 t ha-1 de lodo; soja com inoculacao mais 3 t ha-1 de lodo; soja com inoculacao mais 6 t ha-1 de lodo; e soja com inoculacao mais adubacao quimica, exceto a nitrogenada. As maiores produtividades de soja, tanto no primeiro como no segundo ano agricola, foram obtidas nas duas maiores doses de lodo. Os teores de varios elementos nos graos de soja, nos tratamentos com lodo, nao diferiram, significativamente, daqueles obtidos nos tratamentos testemunha ou com adubacao mineral. Perdas de NO3- para o ambiente podem ocorrer, principalmente no periodo inicial do ciclo da cultura.

Variações nos teores de nitrogênio mineral em solo suplementado com iodo de esgoto

The knowledge of the organic materials mineralization dynamic added to soil is important to predict the effects of possible N losses to the environment. The objective of this work was to evaluated the variation of mineral N in the dry and rainy periods, in a soil cultivated with maize, after its amendement with increasing doses of sewage sludge. The treatments were plots not fertilized, plots with N fertilization (NM), plots with dose of sewage sludge, calculated to supply the same N content of the NM treatment (1N), and plots with two, four and eight times the sewage sludge dose of the 1N treatment. The quantities of biosolid to be added to the soil should be different in the dry and rainy periods, even when they are based on N of the crop requirement, because great N losses may occur in periods of high pluvial precipitation.

Performance of Common Bean Using Seeds Harvested from Plants Fertilized with High Rates of Molybdenum

Abstract Three field trials were conducted with common bean. In the first trial, the effects of molybdenum (Mo) rates as foliar application on yield and Mo content of seeds were studied. In the other trials, a factorial 4×2 was used to investigate the effects of seeds with four Mo contents either with or without foliar Mo application. In the first, trial, seeds of the cv. ‘Pérola’ with 0.027 μ g Mo seed−1 were used in the following Mo treatments: (a) untreated control, (b) 90 g ha−1 at 21 days after emergence (DAE), (c) 180 g ha− 1 at 21 DAE, (d) 360 g ha− 1 at 21 DAE, (e) 720 g ha− 1 at 21 DAE, (f) 360 g ha− 1 at 17 DAE + 360 g ha− 1 at 23 DAE, (g) 1440 g ha− 1 at 21 DAE, (h) 720 g ha−1 at 17 DAE + 720 g ha− 1 at 23 DAE, (i) 360 g ha− 1 at 17 DAE + 360 g ha− 1 at 21 DAE + 360 g ha− 1 at 27 DAE + 360 g ha− 1 at 32 DAE. All plots received a basal fertilization of 32 kg N ha− 1, 49 kg P ha− 1, and 53 kg K ha− 1, with urea (110 kg ha− 1) as side dressing 14 days later. For the other trials, the following seed Mo contents were selected from the first trial: 0.080 ± 0.044, 0.096 ± 0.058, 0.722 ± 0.290, and 1.272 ± 0.579 μ g of Mo seed− 1. All plots received a basal fertilization of 24 kg N ha− 1, 37 kg P ha− 1, and 40 kg K ha− 1. Bean yields were not affected by the Mo treatments, and Mo contents of seed were increased from 0.096 (untreated control) to 1.272 μ g Mo seed− 1 (treatment i). Mo contents of seed did not affect yield when a N-rich soil was used. However, on a N-poor soil plants raised from seeds with 1.272 μ g Mo seed− 1 yielded more than those from seeds with low Mo content, especially when the plants did not receive Mo by foliar application. This investigation shows that it is possible to produce enriched seeds by foliar application of high Mo rates without grain yield reduction, and that plants raised from these seeds have a higher yield potential.

Inorganic nitrogen in a tropical soil with frequent amendments of sewage sludge

Accurate prediction of plant-available N release from sewage sludge is necessary to optimize crop yields and minimize NO3− leaching to groundwater. We conducted a 1.5-year study with three maize crops to determine N mineralization from an urban sewage sludge from Barueri, State of São Paulo, Brazil, and its potential to contaminate groundwater with NO3−. The soil at the experimental site was a loamy/clayey-textured Dark Red Dystroferric Oxisol. The treatments consisted of: plots without chemical fertilization or sludge, plots with complete chemical fertilization, and plots receiving four different doses of sewage sludge. Dose 1 was calculated at the agronomic N rate, while doses 2, 3 and 4 were, respectively, two, four, and eight times dose 1. The inorganic N addition increased with the rate of biosolid application. The high NO3− concentrations in relation to NH4+ were associated with intense soil nitrification. High N losses occurred for the first 27 days after soil sludge incorporation, even at the lowest dose, suggesting that land application of sewage sludge based on the N requirement of the crop may be overestimating the amount of sewage sludge to be applied.

Residual and cumulative effects of soil application of sewage sludge on corn productivity

The objective of this study was to evaluate the effect of frequent and periodic applications of sewage sludge to the soil, on corn productivity. The experiment was carried out as part of an experiment that has been underway since 1999, using two types of sludge. One came from the Barueri Sewage Treatment Station (BS, which receives both household and industrial sludge) and the other came from the Franca Sewage Treatment Station (FS, which receives only household sludge). The Barueri sludge was applied from 1999 up to the agricultural year of 2003/2004. With the exception of the agricultural years of 2004/2005 and 2005/2006, the Franca sludge was applied up to 2008/2009. All the applications were made in November, with the exception of the first one which was made in April 1999. After harvesting the corn, the soil remained fallow until the next cultivation. The experiment was set up as a completely randomized block design with three replications and the following treatments: control without chemical fertilization or sludge application, mineral fertilization, and dose 1 and dose 2 of sludge (Franca and Barueri). The sludges were applied individually. Dose 1 was calculated by considering the recommended N application for corn. Dose 2 was twice dose 1. It was evident from this work that the successive application of sludge to the soil in doses sufficient to reach the productivity desired with the use of nitrogen fertilizers could cause environmental problems due to N losses to the environment and that the residual and cumulative effects should be considered when calculating the application of sludge to soil.

Microrganismos endofíticos de mandioca de áreas comerciais e etnovariedades em três estados brasileiros

The aim of this work was to perform a survey of the diversity of endophytic microorganisms in cassava (Manihot esculenta Crantz) collected from commercial plantings, in the State of Sao Paulo, and in ethnovarieties collected in the States of Amazonas and Bahia, and also, to evaluate its potential of biological nitrogen fixation, and to produce indolacetic acid. In those States, 47 species of 27 genera were identified. Bacillus spp. was the most frequently found in all sampled regions. In Amazonas State, it was found the higher diversity of endophytic microorganisms. PCR amplifications of the nifH gene were evaluated in species of γ-Proteobacteria subgroup. IAA production was found in microorganism s isolated in cassava grown in all sampled States and belonged to the following subgroups: γ-Proteobacteria, β-Proteobacteria, Bacilli and Actinobacteria. In cassava, the occurrence of endophytic bacteria, with N-fixing and in vitro IAA-producing abilities, indicates potential for plant growth promotion.