Isabella Clerici De Maria

Sewage sludge application to agricultural land as soil physical conditioner

SUMMARY Water resource quality is a concern of today’s society and, as a consequence, low pollutant wastewaters and sludges are being increasingly treated, resulting in continuous production of sewage sludge. Sewage sludge (SS) can be used as soil physical conditioner of agricultural or degraded lands, due to its organic C component. The objective of this research was to evaluate the long-term SS effects on soil physical quality of properties such as bulk density, porosity, permeability and water retention of degraded soils treated with annual SS applications. The SS rates were calculated according to the crop N demand. The field experiment consisted of three treatments: mineral fertilization, 10 and 20 Mg ha -1 of SS (once and twice the SS quantity to meet the maize N demand, respectively), in annual applications to the surface layer of a eutroferric Red Latosol. SS reduced bulk density, increased macroporosity and decreased microporosity after the third application, but did not significantly alter the soil permeability and physical quality as measured by the S index in the surface layer.

Carbon stock and humification index of organic matter affected by sugarcane straw and soil management

The maintenance of sugarcane (Saccharum spp.) straw on a soil surface increases the soil carbon (C) stocks, but at lower rates than expected. This fact is probably associated with the soil management adopted during sugarcane replanting. This study aimed to assess the impact on soil C stocks and the humification index of soil organic matter (SOM) of adopting no-tillage (NT) and conventional tillage (CT) for sugarcane replanting. A greater C content and stock was observed in the NT area, but only in the 0-5 cm soil layer (p < 0.05). Greater soil C stock (0-60 cm) was found in soil under NT, when compared to CT and the baseline. While C stock of 116 Mg ha-1 was found in the baseline area, in areas under CT and NT systems the values ranged from 120 to 127 Mg ha-1. Carbon retention rates of 0.67 and 1.63 Mg C ha-1 year-1 were obtained in areas under CT and NT, respectively. Laser-Induced Fluorescence Spectroscopy showed that CT makes the soil surface (0-20 cm) more homogeneous than the NT system due to the effect of soil disturbance, and that the SOM humification index (HLIF) is larger in CT compared to NT conditions. In contrast, NT had a gradient of increasing HLIF, showing that the entry of labile organic material such as straw is also responsible for the accumulation of C in this system. The maintenance of straw on the soil surface and the adoption of NT during sugarcane planting are strategies that can increase soil C sequestration in the Brazilian sugarcane sector.

Chemical and microbiological attributes of an oxisol treated with successive applications of sewage sludge

Studies on sewage sludge (SS) have confirmed the possibilities of using this waste as fertilizer and/or soil conditioner in crop production areas. Despite restrictions with regard to the levels of potentially toxic elements (PTE) and pathogens, it is believed that properly treated SS with low PTE levels, applied to soil at adequate rates, may improve the soil chemical and microbiological properties. This study consisted of a long-term field experiment conducted on a Typic Haplorthox (eutroferric Red Latosol) treated with SS for seven successive years for maize production, to evaluate changes in the soil chemical and microbiological properties. The treatments consisted of two SS rates (single and double dose of the crop N requirement) and a mineral fertilizer treatment. Soil was sampled in the 0-0.20 m layer and analyzed for chemical properties (organic C, pH, P, K, Ca, Mg, CEC, B, Cu, Fe, Mn, Zn, Cd, Ni, and Pb) and microbiological properties (basal respiration, microbial biomass activity, microbial biomass C, metabolic quotient, microbial quotient, and protease and dehydrogenase enzyme activities). Successive SS applications to soil increased the macro- and micronutrient availability, but the highest SS dose reduced the soil pH significantly, indicating a need for periodic corrections. The SS treatments also affected soil microbial activity and biomass negatively. There were no significant differences among treatments for maize grain yield. After seven annual applications of the recommended sludge rate, the heavy metal levels in the soil had not reached toxic levels.

Sewage sludge application on cultivated soils: effects on runoff and trace metal load

The use of sewage sludge in agricultural soils as a macro and micronutrient source and as a soil conditioner has been one of the alternatives for its disposal. However, sewage sludge contains trace metals, which are potential sources of pollution. The goal of this study was to evaluate the effect of sewage sludge application on surface water contamination through runoff when it was applied in a soil cultivated with corn. The effect of sludge application on the concentration and load of copper, nickel and zinc and the volume of runoff water and sediment were evaluated. The experiment was set up in plots used to study erosion losses in Campinas, Sao Paulo State, Brazil. The soil is a clayey Rhodic Hapludox. Three treatments were studied: no sewage sludge, sewage sludge to supply the N required by the crop and twice that amount, with four replications. The water and sediment lost by runoff were measured after each rainfall, and sampled for chemical analysis. The volumes of water and sediment lost by runoff decreased after sewage sludge application. The waste application increased trace metal concentration in the runoff water and sediment, especially zinc, which was present in high concentration in the sewage sludge used. Nevertheless, the load of trace metals transported from the plot was mostly dependent on the total runoff volume. Most of the Cu, Zn and Ni losses were via sediment, and occurred in a few highly erosive rainfall events in the period studied.

Multiperspective analysis of erosion tolerance

Erosion tolerance is the most multidisciplinary field of soil erosion research. Scientists have shown lack in ability to adequately analyze the huge list of variables that influence soil loss tolerance definitions. For these the perspectives of erosion made by farmers, environmentalists, society and politicians have to be considered simultaneously. Partial and biased definitions of erosion tolerance may explain not only the polemic nature of the currently suggested values but also, in part, the nonadoption of the desired levels of erosion control. To move towards a solution, considerable changes would have to occur on how this topic is investigated, especially among scientists, who would have to change methods and strategies and extend the perspective of research out of the boundaries of the physical processes and the frontiers of the academy. A more effective integration and communication with the society and farmers, to learn about their perspective of erosion and a multidisciplinary approach, integrating soil, social, economic and environmental sciences are essential for improved erosion tolerance definitions. In the opinion of the authors, soil erosion research is not moving in this direction and a better understanding of erosion tolerance is not to be expected in the near future.

Relations between soil surface roughness, tortuosity, tillage treatments, rainfall intensity and soil and water losses from a red yellow latosol

The soil surface roughness increases water retention and infiltration, reduces the runoff volume and speed and influences soil losses by water erosion. Similarly to other parameters, soil roughness is affected by the tillage system and rainfall volume. Based on these assumptions, the main purpose of this study was to evaluate the effect of tillage treatments on soil surface roughness (RR) and tortuosity (T) and to investigate the relationship with soil and water losses in a series of simulated rainfall events. The field study was carried out at the experimental station of EMBRAPA Southeastern Cattle Research Center in Sao Carlos (Fazenda Canchim), in Sao Paulo State, Brazil. Experimental plots of 33 m2 were treated with two tillage practices in three replications, consisting of: untilled (no-tillage) soil (NTS) and conventionally tilled (plowing plus double disking) soil (CTS). Three successive simulated rain tests were applied in 24 h intervals. The three tests consisted of a first rain of 30 mm/h, a second of 30 mm/h and a third rain of 70 mm/h. Immediately after tilling and each rain simulation test, the surface roughness was measured, using a laser profile meter. The tillage treatments induced significant changes in soil surface roughness and tortuosity, demonstrating the importance of the tillage system for the physical surface conditions, favoring water retention and infiltration in the soil. The increase in surface roughness by the tillage treatments was considerably greater than its reduction by rain action. The surface roughness and tortuosity had more influence on the soil volume lost by surface runoff than in the conventional treatment. Possibly, other variables influenced soil and water losses from the no-tillage treatments, e.g., soil type, declivity, slope length, among others not analyzed in this study.

Geostatistical analysis of microrelief of an oxisol as a function of tillage and cumulative rainfall

A rugosidade da superficie pode ser influenciada pelo tipo e pela intensidade do preparo do solo, entre outros fatores. Em solos preparados o microrrelevo e aplanado consideravelmente com o acumulo da chuva. A Geoestatistica promove algumas ferramentas que podem ser uteis no estudo da dinâmica da variabilidade da superficie do solo. O objetivo desse estudo foi verificar se e possivel aplicar geoestatistica na analise da variacao do microrrelevo do solo. Os resultados foram obtidos num Latossolo sob seis tratamentos de preparo do solo: grade de discos, arado de discos, escarificador, grade de discos + grade niveladora, arado de discos + grade niveladora e escarificador + grade niveladora. As medidas foram feitas logo apos o preparo do solo e subsequentemente apos cumulativos eventos de chuva natural. Medicoes duplicadas foram feitas em cada tratamento para cada data, produzindo um total de 48 superficies. Um rugosimetro de agulhas foi utilizado para as medidas da rugosidade da superficie. A area de cada parcela era 1,35 m por 1,35 m e as medidas espacadas de 25 mm, produzindo um total de 3025 pontos por parcela. Antes da analise geoestatistica, a tendencia foi removida dos dados experimentais por dois diferentes metodos. Foram ajustados modelos aos semivariogramas de cada superficie, e os parâmetros desses modelos foram analisados. O metodo usado para remover a tendencia influenciou os resultados geoestatisticos. O parâmetro geoestatistico razao de dependencia mostrou que a dependencia espacial aumentou para a maioria das superficies com o aumento da precipitacao pluvial acumulada.

Distribuição espacial de fósforo em Latossolo tratado com lodo de esgoto e adubação mineral

In agricultural soils receiving sewage sludge and subjected to water erosion, may occur intense transport of phosphorus (P) to the lower parts of the landscape and eventually to water bodies. The objective of this study was to evaluate the spatial distribution of P in an Oxisol cultivated with maize. The treatments were evaluated with application of mineral fertilization (MF) and sewage sludge (SS). Soil samples were collected following a sampling grid of 69 points in each treatment at the beginning and at the end of the crop cycle, in an experimental area with 10% slope. There was a moderate spatial dependence of P in the soil in the treatment of MF, resulting in higher concentrations of P in the deeper layers of the soil caused by erosion. The same standard was observed for the soil attributes sum of bases, cation exchange capacity and soil organic matter. Conversely, when SS was applied there was a randomized distribution of P in the plots because of the non-uniform manner of its application. Such random distribution of P showed correlation with soil organic matter.

Intervalo hídrico ótimo em um Latossolo vermelho cultivado em sistema semeadura direta por 25 anos

Least Limiting Water Range (LLWR) integrates soil physical properties related to crop growth and corresponds to the interval between the upper and lower limits of water content in the soil within which limitations to root growth are minimal. In agricultural areas, soil management can lead to changes in its structure, mainly due to compaction and, subsequently, bulk density can reach values outside the limits in which conditions are ideal for plant growth. Therefore, the aim of this study was to use the LLWR to evaluate soil physical quality and to identify areas that restrict plant growth, with a view toward localized management. This study was carried out using the LLWR to evaluate soil physical quality so as to identify areas in which bulk density is higher than critical bulk density in an Oxisol under no-tillage system since 1985, in Campinas, Sao Paulo, Brazil. Undisturbed samples were collected at the depths of 0.00-0.10, 0.10-0.20 and 0.20-0.30 m to obtain the following attributes: bulk density, penetration resistance curve, water retention curve and soil porosity. Data on spatial variability of bulk density and critical bulk density were analyzed by semivariograms to map these attributes. The LLWR decreased in depth and was limited at the top by the moisture at field capacity and at the bottom by resistance to penetration at the three depths studied. Critical soil density was 1.42 Mg m-3 for the 0.00-0.10 m layer and 1.39 and 1.41 Mg m-3, respectively, for the 0.10-0.20 and 0.20-0.30 m layers. It was observed that soil bulk density was higher than critical soil density in the 0.00-0.10 and 0.10-0.20 m layers in the lower portions of the field, indicating a critical condition for plant growth. The use of LLWR, associated to maps of spatial variability of soil bulk density to determine points at which it is higher than critical soil bulk density aids decision making for intervention or modification of soil tillage, while the selection criterion of the critical value of penetration resistance can contribute to the interpretation of field results.

Compactação de um latossolo vermelho distroférrico com diferentes quantidades e manejos de palha em superfície

Soil compaction in areas under no-tillage has been pointed as a problem faced by farmers, particularly in areas with clay soils. Compaction is mainly caused by machinery traffic when the adequate soil moisture is not respected. Straw on the soil surface, by creating a physical barrier between the wheel and the ground may be a factor to minimize compaction. Therefore, the objective of this study was to evaluate the effect of millet straw on soil surface in reducing compaction caused by the tractor wheels. The experiment consisted of four treatments of straw quantity on surface (without straw and 5, 10 and 15 Mg ha-1) and three straw managements (standing up, lying down and fragmented). After the tractor passage, penetration resistance, water content, density and total porosity of soil were evaluated on the area where the wheel passed over. Density and porosity were not affected by wheel traffic. Treatments with straw had higher water content and as a result less resistance. There was no significant difference on resistance and soil moisture among straw management treatments. For an equal soil water content, higher densities of straw resulted in lower penetration resistance, which indicates less compaction.