Nickel sources affect soil biological properties but do not affect sorghum growth

Nickel (Ni) is an essential element, but it can be phytotoxic in high concentration, which may be caused by high availability in soil solution. The objective of this study was to evaluate the effect of sources and doses of Ni applied to a dystrophic Red Latosol cultivated with sorghum on i) the availability of the metal in the soil; ii) the impact on biological and biochemical properties of the soil; iii) the absorption and distribution in sorghum plants; and iv) crop productivity. The experiment was carried out within a completely randomized design with two nickel sources [nickel(II) nitrate, Ni(NO3)2 and nickel(III) oxide, Ni2O3], three doses (35, 70, and 140 mg Ni kg-1 soil), plus controls without Ni, with 3 replications. The concentrations of Ni in the soil, soil microbial biomass (SMB), basal soil respiration (BSR), metabolic quotient (qCO2), fluorescein diacetate (FDA) hydrolysis, and urease activity were determined. The concentrations of Ni in the leaf diagnostic and in the plant (shoot, root, and grains) were also measured. In the soil, the concentrations of available Ni remained between 0.21 and 54.01 mg Ni kg-1. Ni2O3 contributed very little to the increase in available Ni. SMB and the FDA hydrolysis were not affected by the Ni source or Ni dose, but BSR and qCO2 had significant increase with Ni application rates, suggesting the soil microorganisms faced stress. Soil urease activity was affected by Ni dose but not by Ni source. The dose of Ni as Ni(NO3)2 decreased the metal concentration in the plant, while that of Ni2O3 increased it. Nickel source did not affect dry mass production of the plants, but grain yield was affected in a dose-dependent manner when Ni2O3 was the source of Ni.

Time-dependent effect of composted tannery sludge on the chemical and microbial properties of soil

Composting has been suggested as an efficient method for tannery sludge recycling before its application to the soil. However, the application of composted tannery sludge (CTS) should be monitored to evaluate its effect on the chemical and microbial properties of soil. This study evaluated the time-dependent effect of CTS on the chemical and microbial properties of soil. CTS was applied at 0, 2.5, 5, 10, and 20 Mg ha^-1 and the soil chemical and microbial properties were evaluated at 0, 45, 75, 150, and 180 days. Increased CTS rates increased the levels of Ca, Cr, and Mg. While Soil pH, organic C, and P increased with the CTS rates initially, this effect decreased over time. Soil microbial biomass, respiration, metabolic quotient, and dehydrogenase increased with the application of CTS, but decreased over time. Analysis of the Principal Response Curve showed a significant effect of CTS rate on the chemical and microbial properties of the soil over time. The weight of each variable indicated that all soil properties, except β-glucosidase, dehydrogenase and microbial quotient, increased due to the CTS application. However, the highest weights were found for Cr, pH, Ca, P, phosphatase and total organic C. The application of CTS in the soil changed the chemical and microbial properties over time, indicating Cr, pH, Ca, phosphatase, and soil respiration as the more responsive chemical and microbial variables by CTS application.

Diversity of plant growth-promoting bacteria associated with sugarcane

The sugarcane (Saccharum spp) presents economic importance, mainly for tropical regions, being an important Brazilian commodity. However, this crop is strongly dependent on fertilizers, mainly nitrogen (N). This study assessed the plant growth-promoting bacteria (PGPB) associated with sugarcane that could be used as a potential inoculant to the crop. We evaluated the genetic diversity of PGPB in the plant tissue of sugarcane varieties (RB 867515, RB 1011, and RB 92579). The primer BOX-A1R was used to differentiate the similar isolated and further sequencing 16S rRNA ribosomal gene. The 16S rRNA gene showed the presence of seven different genera distributed into four groups, the genus Bacillus, followed by Paenibacillus (20%), Burkholderia (14%), Herbaspirillum (6%), Pseudomonas (6%), Methylobacterium (6%), and Brevibacillus (3%). The molecular characterization of endophytic isolates from sugarcane revealed a diversity of bacteria colonizing this plant, with a possible biotechnological potential to be used as inoculant and biofertilizers.

Chloroplast diversity of Casearia grandiflora in the Cerrado of Piauí State

Casearia grandiflora (Salicaceae) is a typical Cerrado species adapted to disturbed environments, making it useful for restoration projects. Knowledge of genetic diversity is important for establishing conservation strategies for this species. This study aimed to compare chloroplast haplotype diversity and structure of C. grandiflora, under the assumption that protected areas hold greater genetic diversity than disturbed areas. The populations studied are from Parque Nacional de Sete Cidades Conservation Unit and from the surroundings of the city of Cocal de Telha, both located in the State of Piauí. Molecular analyses were performed with seven chloroplast microsatellite loci. The number of private haplotypes and haplotype diversity were higher in the conservation unit, which reinforces the importance of these areas in maintaining biodiversity. Analysis of molecular variance showed that most of the genetic variation is found within populations, with a moderate divergence between them (F_ST = 0.14). The Bayesian analysis and discriminant analysis of principal components suggested that populations are not structured, revealing that a set of individuals from Parque Nacional de Sete Cidades were more divergent within populations than between them. Since literature has little information on C. grandiflora, the results of this study provide important contribution to a better understanding of the specie's genetic diversity.

Repeated application of composted tannery sludge affects differently soil microbial biomass, enzymes activity, and ammonia-oxidizing organisms

Repeated application of composted tannery sludge (CTS) changes the soil chemical properties and, consequently, can affect the soil microbial properties. The aim of this study was to evaluate the responses of soil microbial biomass and ammonia-oxidizing organisms to repeated application of CTS. CTS was applied repeatedly during 6 years, and, at the sixth year, the soil microbial biomass, enzymes activity, and ammonia-oxidizing organisms were determined in the soil. The treatments consisted of 0 (without CTS application), 2.5, 5, 10, and 20 t ha(-1) of CTS (dry basis). Soil pH, EC, SOC, total N, and Cr concentration increased with the increase in CTS rate. Soil microbial biomass did not change significantly with the amendment of 2.5 Mg ha(-1), while it decreased at the higher rates. Total and specific enzymes activity responded differently after CTS application. The abundance of bacteria did not change with the 2.5-Mg ha(-1) CTS treatment and decreased after this rate, while the abundance of archaea increased significantly with the 2.5-Mg ha(-1) CTS treatment. Repeated application of different CTS rates for 6 years had different effects on the soil microbial biomass and ammonia-oxidizing organisms as a response to changes in soil chemical properties.

Effect of composted textile sludge on growth, nodulation and nitrogen fixation of soybean and cowpea

The effect of composted textile sludge on growth, nodulation and nitrogen fixation of soybean and cowpea was evaluated in a greenhouse experiment. The compost was incorporated into soil at 0, 9.5, 19 and 38 t ha(-1) (bases upon the N requirement of the crops, i.e., 0, 50, 100 and 200 kg available N ha(-1)). Growth, nodulation and shoot accumulation of nitrogen were evaluated 36 and 63 days after plant emergence. Nodule glutamine synthetase (GS) activity and leghemoglobin content were evaluated 63 days after emergence. Composted textile sludge did not show negative effects on nodule number and weight, nodule GS activity and leghemoglobin content. Nitrogen accumulation in shoot dry matter in soybean and cowpea was higher than other treatments with application of 19 t ha(-1) of compost. Composting can be an alternate technology for the management of solid textile mill sludge. This study verifies that the composted textile sludge was not harmful to growth, nodulation and nitrogen fixation of soybean and cowpea.

Microbial biomass and activity in a Brazilian soil amended with untreated and composted textile sludge

This laboratory study examines the effect of application of untreated and composted textile sludge on microbial biomass and activity in a Brazilian soil. The soil was amended with untreated and composted sludge at rates equivalent of 6.4t ha(-1) (0.64 g per 100g of soil) and 19t ha(-1) (1.90 g per 100g of soil), respectively, and were incubated at 28 degrees C for 60 days and daily sampled for microbial activity. An additional experiment, in the same condition, was conduced for evaluation of microbial biomass and enumeration of microorganisms at 15, 30 and 60 days after incubation. The application of composted sludge increased significantly the microbial biomass and activity, and bacteria number of soil. There were not differences in the microbial activity and bacteria number among the control and untreated sludge amended soils. In conclusion, after 2 months of incubation, the effects of the two amendments on soil microorganisms were: microbial biomass, soil respiration and bacteria number were increased only in composted sludge treated soil. qCO2 and fungi number were not affected by untreated and composted sludge.

Effect of glyphosate on the microbial activity of two Brazilian soils

Glyphosate [N-(phosphonomethyl)-glycine] is a broad-spectrum, non-selective, post-emergence herbicide that is widely used in agricultural. We studied, in vitro, changes in the microbial activity of typical Hapludult and Hapludox Brazilian soils, with and without applied glyphosate. Glyphosate was applied at a rate of 2.16 mg glyphosate kg(-1) of soil and microbial activity was measured by soil respiration (evolution of CO(2)) and fluorescein diacetate (FDA) hydrolysis over a period of 32 days. We found an increase of 10-15% in the CO(2) evolved and a 9-19% increase in FDA hydrolyses in the presence of glyphosate compared with the same type of soil which had never received glyphosate. Soil which had been exposed to glyphosate for several years had the strongest response in microbial activity. Most probable number (MPN) counts showed that after 32 days incubation the number of actinomycetes and fungi had increased while the number of bacteria showed a slight reduction. After the incubation period, high pressure liquid chromatography (HPLC) detected the glyphosate metabolite aminomethyl phosphonic acid (AMPA), indicating glyphosate degradation by soil microorganisms.