Alleles of organic acid transporter genes are highly correlated with wheat resistance to acidic soil in field conditions.

2016

Soil management systems for sustainable melon cropping in the Submedian of the São Francisco Valley.

Changes in soils management systems, including the application of green manure, are able to increase crop productivity. The aim of this study was to propose a soil management system with the use of green manure to improve the nutritional status and melon productivity in the submedian of the São Francisco Valley. The experiment was installed in Typic Plinthustalf and conducted in split plot. There were two soil tillage systems, tillage (T) and no tillage (NT), and three types of green manure (two vegetal cocktails: VC1- 75% legumes (L) + 25% non-legumes (NL); VC2- 25% L+ 75% NL and spontaneous vegetation (SV)). The experimental design was a randomised block with four replications. Fourteen species of legumes, grasses and oilseeds were used for the composition of the plant cocktails. We evaluated production of the dry shoot and root biomass and carbon and nutrient accumulation by green manures and melon plant. Data were subjected to analysis of variance and the treatment means were compared by Tukey´s test (P<0.05). Shoot biomass production and carbon and nutrient accumulation were higher in plant mixtures compared to spontaneous vegetation. The root system of the plant cocktails added larger quantities of biomass and nutrients to the soil to a depth of 0.60 m when compared to the spontaneous vegetation. The cultivation of plant cocktails with soil tillage, regardless of their composition, is a viable alternative for adding biomass and nutrients to the soil in melon crops in semi-arid conditions, providing productivity increases.

Development of alternative methods for determining soil organic matter.

Soil organic matter (SOM) is important to fertility, since it performs several functions such as cycling, water and nutrient retention and soil aggregation, in addition to being an energy requirement for biological activity. This study proposes new trends to the Embrapa, Walkley-Black, and Mebius methods that allowed the determination of SOM by spectrophotometry, increasing functionality. The mass of 500 mg was reduced to 200 mg, generating a mean of 60 % saving of reagents and a decrease of 91 % in the volume of residue generated for the three methods without compromising accuracy and precision. We were able to optimize conditions for the Mebius method and establish the digestion time of maximum recovery of SOM by factorial design and response surface. The methods were validated by the estimate of figures of merits. Between the methods investigated, the optimized Mebius method was best suited for determining SOM, showing near 100 % recovery.

Growth and symbiosis of plants with arbuscular mycorrhizal fungi in soil submitted to biochar application.

Arbuscular mycorrhizal fungi (AMF), which is intrinsically present or may be introduced in soils by inoculation, is an example of natural and renewable resource to increase plant nutrient uptake. This kind of fungi produces structures (hyphae, arbuscles and sometimes vesicles) inside the plant root cortex. This mutualistic relationship promotes plant gains in terms of water and nutrient absorption (mainly phosphorus). Biochar can benefit plant interaction with AMF, however, it can contain potentially toxic compounds such as heavy metals and organic compounds (e.g. dioxins, furans and polycyclic aromatic hydrocarbons), depending on the feedstock and pyrolysis conditions, which may damage organisms. For these reasons, the present work will approach the impacts of biochar application on soil attributes, AMF-plant symbiosis and its responses in plant growth and phosphorus uptake. Eucalyptus biochar produced at high temperatures increases sorghum growth; symbiosis with AMF; and enhances spore germination. Enhanced plant growth in the presence of high temperature biochar and AMF is a response of root branching stimulated by an additive effect between biochar characteristics and root colonization. Biochar obtained at low temperature reduces AMF spore germination; however it does not affect plant growth and symbiosis in soil.

Atrazine sorption in soil treated with biochar.

Biochar has been used worldwide as soil amendment. Due to the high sorption capacity of organic compounds by charcoal in general, the use of biochar can change the soil sorptive properties, that could result in a environmental protective strategy in one hand and/or in need of higher pesticides doses in another hand. However no data in the literature is available about the long term effect of biochar application in the sorptive properties of the soil, even studies about the sorptive properties of soil treated with biochar are scarce, the few available papers are with pure biochar. This unprecedented work, evaluating the sorption of atrazine in a clayed soil treated with biochar, under experimental field conditions, evaluated the sorption isotherms one and three years after the single biochar application (16 Mg ha-1 of biochar). One year after the biochar application the Kf was two times higher for the biochar amended soil than for the control one (without biochar). This effect decreases after three years from the application, but it is even significantly higher (50% higher) than the control treatment.

Assessment of sugarcane harvesting residue effects on soil spectral behavior

When the harvesting of sugarcane involves a mechanized process, plant residues remain on the soil surface, which makes proximal and remote sensing difficult to monitor. This study aimed to evaluate, under laboratory conditions, differences in the soil spectral behavior of surface layers Quartzipsamment and Hapludox soil classes due to increasing levels of sugarcane?s dry (DL) and green (GL) leaf cover on the soil. Soil cover was quantified by supervised classification of the digital images (photography) taken of the treatments. The spectral reflectance of the samples was obtained using the FieldSpec Pro (350 to 2500 nm). TM-Landsat bands were simulated and the Normalized Difference Vegetation Index (NDVI) and soil line were also determined. Soil cover ranged from 0 to 89 % for DL and 0 to 80 % for GL. Dry leaf covering affected the features of the following soil constituents: iron oxides (480, 530 and 900 nm) and kaolinite (2200 nm). Water absorption (1400 and 1900 nm) and chlorophyll (670 nm) were determinant in differentiating between bare soil and GL covering. Bands 3 and 4 and NDVI showed pronounced variations as regards differences in soil cover percentage for both DL and GL. The soil line allowed for discrimination of the bare soil from the covered soil (DL and GL). High resolution sensors from about 50 % of the DL or GL covering are expected to reveal differences in soil spectral behavior. Above this coverage percentage, soil assessment by remote sensing is impaired.

Burning of tropical brazilian rainforest of sandy soil: does it affect soil organic matter?

This study aimed to investigate the impact of vegetation burning on the content and chemical composition of soil organic matter (SOM) along a profile of a sandy Acrisol in Southwestern Amazon, Brazil, within 3 years after experiment beginning(YAB).The study was performed in Rio Branco, Acre State, and the forest burning was performed under controlled conditions. Samples from 6 depth(0-100cm depth)were collected under burned forest (BF) and primary forest (PF) at 1 YAB and 3 YAB. Besides Cand N contents, humic substances and biomarkers were determined. Under PF, the C content decreased with depth from 12 to 2 g kg-1.C/N ratio ranged from 7.6 at the surface to values around 3 at 1 m depth, indicating a predominance of microbial products. Humin fraction was not detected in the whole profile. Burning of vegetation promoted an increase of C and of humic acids only at 0-5 cm. The n-alkane distribution showed a shift towards smaller chains in the 0-5 cm of BF, indicating main contribution of microbial products. Also PAH?s of high molecular weight were detected in this site. Vegetation burning imparts alterations on the SOM composition, but these tend to disappear within 3 years.

Combined effects of soil biotic and abiotic factors, influenced by sewage sludge incorporation, on the incidence of corn stalk rot.

Abstract: The objectives of this study were to evaluate the combined effects of soil bioticand abiotic factors on the incidence of Fusarium corn stalk rot, during four annual incorporations of two typesofsewagesludge intosoil ina 5-years field assay under tropical conditions and topredict the effectsof these variables on the disease. For each type of sewage sludge, the following treatments were included: control with mineral fertilization recommended for corn; control without fertilization; sewage sludge based on the nitrogen concentration that provided the same amount of nitrogen as in the mineral fertilizer treatment; and sewage sludge that provided two, four and eight times the nitrogen concentration recommended for corn. Increasing dosages of both types of sewage sludge incorporated into soil resulted in increased corn stalk rot incidence, being negatively correlated with corn yield. A global analysis highlighted the effect of the year of the experiment, followed by the sewage sludge dosages. The type of sewage sludge did not affect the disease incidence. Amultiple logistic model using a stepwise procedure was fitted based on the selection of a model that included the three explanatory parameters for disease incidence: electrical conductivity, magnesium and Fusarium population. In the selected model, the probability of higher disease incidence increased with an increase of these three explanatory parameters. When the explanatory parameters were compared, electrical conductivity presented a dominant effect and was the main variable to predict the probability distribution curves of Fusarium corn stalk rot, after sewage sludge application into the soil.