Luiz Fernando Pires

Management effects on nitrogen recovery in a sugarcane crop grown in Brazil

The present studys objectives were to quantify the fertilizer-N and residue-N balances of a sugar cane crop under two trash management systems. The fate of nitrogen (N) derived from fertilizer (NdfF) and N derived from residue (NdfR) was studied comparing: (i) the traditional harvest system with trash burning before harvest (“trash burning”) and (ii) an alternative system without trash burning, in which crop residues are left on the soil surface (“trash mulching”). The experiment consisted of three treatments: (i) T1: at planting, the sugarcane crop was fertilized with 63 kg N ha−1 as 15N-labeled ammonium sulfate, and after the 1st harvest received unlabeled trash from T2; (ii) T2: at planting, the crop was fertilized with 63 kg N ha−1 as unlabeled ammonium sulfate. At the 1st harvest time, this treatment received the labeled trash from T1; (iii) T3: at planting, the crop was fertilized with 63 kg N ha−1 as 15N-labeled ammonium sulfate, and every year, immediately before cutting, the crop residues were burnt. After the first harvest fertilizer-N was applied over the total soil area at a rate of 80 kg N ha−1 as unlabeled ammonium sulfate. The results indicated that the trash remaining as a surface blanket resulted in an average N recycling of 105.0 kg ha−1 year−1, while the practice of burning the trash produced an average N loss from the system of 83.5 kg ha−1 year−1. At the first harvest, about 75% of the labeled N was recovered in the soil–plant system. The majority was found in the plant, indicating a high availability of the fertilizer-N for the crop. At the end of the third crop cycle (2nd ratoon crop harvest), the total output of fertilizer-N (export+burning) was 60% for the burnt-trash treatment, and only 42% (export) for the trash-blanket treatment. The N liberated from the residue is mainly immobilized in the soil, reflecting that sugarcane trash is an N source of slow availability to the crop. This study indicated that green cane harvesting followed by mulching leads to a more efficient recycling of the N applied to the system and therefore reducing fertilizer-N needs.

Field spatial and temporal patterns of soil water content and bulk density changes

Umidade (q) e densidade do solo (rs) influenciam importantes processos no solo e planta tais como: movimento de agua, compactacao do solo, aeracao do solo e desenvolvimento radicular. Baseado neste fato, questoes referentes a variabilidade espacial e temporal de q e rs para diferentes periodos do ano e diferentes fases de desenvolvimento da cultura do cafe tornam-se de extremo interesse. Este trabalho teve como objetivo caracterizar padroes espaciais e temporais de q e rs durante diferentes periodos do ano e verificar se existem mudancas temporais significativas de rs na superficie do solo quando submetida a ciclos de umedecimento/secagem. O experimento foi conduzido em campo cultivado com cafe em um solo classificado como Nitossolo Vermelho Eutrofico. O experimento iniciou-se em maio de 2001 com espacamento de 1,75 m entre linhas e 0,75 m entre plantas. Medidas de q e rs foram feitas metro a metro ao longo de 200 m usando uma sonda de superficie neutron/gama. Durante o periodo umido nao houve padroes de diferenca espacial para q, enquanto que para o periodo seco o contrario foi observado. Estes padroes podem ser associados a eventos de precipitacao alterando a estrutura de correlacao espacial para observacoes adjacentes de q. Para rs existem mudancas temporais na superficie do solo ao longo do periodo estudado como uma consequencia dos ciclos de umedecimento/secagem no campo.

Soil bulk density evaluation by conventional and nuclear methods

Among the methods used to measure soil bulk density, the following have been prominent: paraffin sealed clod (PS), volumetric ring (VR), and the modern methods like gamma ray computed tomography (GCT) and the neutron/gamma surface gauge (SG). The objective of this work was to compare soil bulk density values obtained through these methods, with the aim of assisting researchers on the choice of the more appropriate method. For this, a 200-m spatial transect was chosen in an experimental area cultivated with coffee, belonging to ESALQ/USP, Piracicaba, SP, Brazil. The SG readings were first taken in the field and thereafter soil samples were collected at 8 different points, spaced at 25 m, for the other methods. The lowest values of soil bulk density were obtained for the SG method (average 1.468 g/cm3) and the highest for the PS (average 1.685 g/cm3), which was similar to the GCT method (average 1.684 g/cm3). The average soil bulk density for the VR method, which has been used in soil science as a standard method, was 1.544 g/cm3. The Tukey test indicates that the PS and GCT methods do not differ significantly (P > 0.05). They do differ in comparison with VR and SG, which also do not differ among themselves.

Damage to soil physical properties caused by soil sampler devices as assessed by gamma ray computed tomography

Soil sample physical properties can be greatly affected during soil sampling procedures. Improper procedures can impose modifications on soil sample structure and consequently lead to wrong measurements of soil properties. The objective of this work was to evaluate the damage caused by soil samplers to soil structure through the analysis of computed tomography (CT) images. A first generation tomograph was used, having a 241Am source and a 7.62 × 7.62 cm NaI(Tl) scintillation crystal detector coupled to a photomultiplier tube. Results confirm the effect of soil sampler devices on the structure of soil samples, and that the compaction caused during sampling causes significant alterations to soil bulk density. Through the use of CT it was possible to determine the level of compaction and to make a detailed analysis of the soil bulk density distribution within the soil sample.

Computed Tomography to Estimate the Representative Elementary Area for Soil Porosity Measurements

Computed tomography (CT) is a technique that provides images of different solid and porous materials. CT could be an ideal tool to study representative sizes of soil samples because of the noninvasive characteristic of this technique. The scrutiny of such representative elementary sizes (RESs) has been the target of attention of many researchers related to soil physics field owing to the strong relationship between physical properties and size of the soil sample. In the current work, data from gamma-ray CT were used to assess RES in measurements of soil porosity (ϕ). For statistical analysis, a study on the full width at a half maximum (FWHM) of the adjustment of distribution of ϕ at different areas (1.2 to 1162.8 mm2) selected inside of tomographic images was proposed herein. The results obtained point out that samples with a section area corresponding to at least 882.1 mm2 were the ones that provided representative values of ϕ for the studied Brazilian tropical soil.

Gamma-ray-computed tomography to investigate compaction on sewage-sludge-treated soil.

Soil compaction is one of the fundamental parameters to evaluate the environmental impact of agricultural machinery traffic on soils. Compaction causes modifications on soil physical properties such as changes in porosity and structure that are related to soil water movement and gas exchange The objective of this work was to evaluate soil surface sealing after sewage-sludge application, and the influence of agricultural machinery traffic, through computed tomography. A first generation tomograph was used having a 137Cs source and a 3 in x 3 in NaI(Tl) scintillation crystal detector coupled to a photomultiplier tube. Image analysis and tomographic unit profiles could successfully be used for the detection of soil surface sealing and soil compaction due to machinery traffic associated to sewage-sludge application.

The Use of Gamma Ray Computed Tomography to Investigate Soil Compaction Due to Core Sampling Devices

Compaction processes can influence soil physical properties such as soil density, porosity, pore size distribution, and processes like soil water and nutrient movements, root system distribution, and others. Soil porosity modification has important consequences like alterations in results of soil water retention curves. These alterations may cause differences in soil water storage calculations and matric potential values, which are utilized in irrigation management systems. Because of this, soil-sampling techniques should avoid alterations of sample structure. In this work soil sample compaction caused by core sampling devices was investigated using the gamma ray computed tomography technique. A first generation tomograph with fixed source-detector arrangement and translation/rotational movements of the sample was utilized to obtain the images. The radioactive source is 241Am, with an activity of 3.7 GBq, and the detector consists of a 3 in. x 3in. NaI(Tl) scintillation crystal coupled to a photomultiplier tube. Soil samples were taken from an experimental field utilizing cylinders 4.0 cm high and 2.6 cm in diameter. Based on image analyses it was possible to detect compacted regions in all samples next to the cylinder wall due to the sampling system. Tomographic unit profiles of the sample permitted to identify higher values of soil density for deeper regions of the sample, and it was possible to determine the average densities and thickness of these layers. Tomographic analyses showed to be a very useful tool for soil compaction characterization and presented many advantages in relation to traditional methods.

Gamma-ray computed tomography to characterize soil surface sealing

The application of sewage sludge as a fertilizer on soils may cause compacted surface layers (surface sealing), which can promote changes on soil physical properties. The objective of this work was to study the use of gamma-ray computed tomography, as a diagnostic tool for the evaluation of this sealing process through the measurement of soil bulk density distribution of the soil surface layer of samples subjected to sewage sludge application. Tomographic images were taken with a first generation tomograph with a resolution of 1 mm. The image analysis opened the possibility to obtain soil bulk density profiles and average soil bulk densities of the surface layer and to detect the presence of soil surface sealing. The sealing crust thickness was estimated to be in the range of 2-4 mm.

Pore system changes of damaged Brazilian oxisols and nitosols induced by wet-dry cycles as seen in 2-D micromorphologic image analysis

Soil pore structure characterization using 2-D image analysis constitutes a simple method to obtain essential information related to soil porosity and pore size distribution (PSD). Such information is important to infer on soil quality, which is related to soil structure and transport processes inside the soil. Most of the time soils are submitted to wetting and drying cycles (W-D), which can cause important changes in soils with damaged structures. This report uses 2-D image analysis to evaluate possible modifications induced by W-D cycles on the structure of damaged soil samples. Samples of three tropical soils (Geric Ferralsol, GF; Eutric Nitosol, EN; and Rhodic Ferralsol, RF) were submitted to three treatments: 0WD, the control treatment in which samples were not submitted to any W-D cycle; 3WD and 9WD with samples submitted to 3 and 9 consecutive W-D cycles, respectively. It was observed that W-D cycles produced significant changes in large irregular pores of the GF and RF soils, and in rounded pores of the EN soil. Nevertheless, important changes in smaller pores (35, 75, and 150 μm) were also observed for all soils. As an overall consideration, it can be said that the use of image analysis helped to explain important changes in soil pore systems (shape, number, and size distribution) as consequence of W-D cycles.

Software Image J to study soil pore distribution

In the soil science, a direct method that allows the study of soil pore distribution is the bi-dimensional (2D) digital image analysis. Such technique provides quantitative results of soil pore shape, number and size. The use of specific softwares for the treatment and processing of images allows a fast and efficient method to quantify the soil porous system. However, due to the high cost of commercial softwares, public ones can be an interesting alternative for soil structure analysis. The objective of this work was to evaluate the quality of data provided by the Image J software (public domain) used to characterize the voids of two soils, characterized as Geric Ferralsol and Rhodic Ferralsol, from the southeast region of Brazil. The pore distribution analysis technique from impregnated soil blocks was utilized for this purpose. The 2D image acquisition was carried out by using a CCD camera coupled to a conventional optical microscope. After acquisition and treatment of images, they were processed and analyzed by the software Noesis Visilog 5.4® (chosen as the reference program) and ImageJ. The parameters chosen to characterize the soil voids were: shape, number and pore size distribution. For both soils, the results obtained for the image total porosity (%), the total number of pores and the pore size distribution showed that the Image J is a suitable software to be applied in the characterization of the soil sample voids impregnated with resin.